AN EVALUATION OF METHYLCELLULGSE AND PAPER SEED RIBBONS FOR THE PRECISiON SEEDENG 0F LETTUCE (LACTUCA SATWA L.) AND OTHER VEGETABLES Thesis {or “18 Degree 0‘ pk. D. MECHIGAN STATE UNIVERSWY Nicky Allan Smith 1960 This is to certify that the thesis entitled AN EVALUATION OF METHYLCELIULOSE AND PAPER SEED RIBBOI 3 FOR THE PRECISION SEEDING OF LETTUCE (LAC'IUCA SATIVA. ) AND OTHER VEGETABLES presented by Nicky Allan Smith has been accepted towards fulfillment of the requirements for _P&Do__ degree in Within re CHMMWM a 291/ Mg); 1' r professor HEREAN .1qu CAREW Date December 9, 1960 LIBRARY Michigan State University ABSTRACT AN EVALUATION OF METHYLCELLULOSE AND PAPER SEED RIBBONS FOR THE PRECISION SEEDING OF LETTUCE (LACTUCA SATIVA L.) AND OTHER VEGETABLES by Nicky Allan Smith Individual plants of numerous agricultural crops must be spaced fairly accurately in the field for maximum yield and duality. Although the distance between individual wheat, oat, and corn plants, within certain limits, has little influence on yield or quality, accurate plant spacing is almost essential for lettuce, celery, cauliflower, and many high-value vegetable crops. The thinning operation accounts for a sizeable portion of labor costs in the production of many small—seeded vegetable crops. Reducing the amount of seed used and uniformly spacing the quantity planted should result in a considerable saving in labor requirements. This study evaluates two forms of seed ribbon or tape developed to achieve a uniform spacing of seed; plastic ribbon and paper ribbon. The plastic seed ribbon, composed of readily dissolvable methylcellulose, was used to place lettuce seed at intervals of 14, 7, and 3 1/2 inches in organic and mineral soils on commercial farms and in other experimental plots. Placement of the ribbon in the soil was by means of specially built or adapted planters provided by two commercial firms. Nicky Allan Smith - 2 Precision spacing of the seed reduced drastically the time required for thinning, varying directly with the seed interval. However, if weeding and thinning were performed simultaneously, as they usually are, time-saving benefits of spaced seeding became insignificant as the weed population in- creased. At harvest, the lettuce stand from ribbon seedings was below that achieved by direct seeding; 90% of the ideal population was considered as ac— ceptable commercially. Spacing the same number of seeds to correspond with the desired final mature plant population resulted in an average stand of 47. 58%. In other words, more than 50% of the seed loci were not occupied with plants at harvest due to undetermined causes. The methylcellulose seed ribbon in contrast to a standard seed sowing procedure resulted in a higher percentage of lettuce heads harvested, heavier average weight per head, and sturdier growth. Other experiments were conducted with plastic and paper seed ribbons to evaluate associated physiological phenomena. Delayed thinning of lettuce resulted in reduced fresh weight of foliage and roots. The number of seedlings emerging increased as the number of seeds was increased per locus (l, 2, and 4) under conditions of soil crusting but not when the soil was covered with polyethylene. When the surface of the soil was Nicky Allan Smith - 3 compressed at 1/2, 2, 5, or 10 psi, seedling emergence was reduced by 5 and 10 psi but not significantly so under conditions of these experiments. Emergence from the paper ribbon for tomato, cauliflower, lettuce, and celery in the greenhouse was significantly lower than from check plant- ings but considerably higher than was experienced in the field trials with tomatoes. Laboratory control of moisture and careful placement of ribbon partially contributed to this better emergence. Varying the level of soil moisture from 11% to field capacity plus 8 mm. of water did not affect total emergence from methylcellulose seed ribbon. When individual seeds of radish were precision spaced one inch from adjacent seeds, 65. 79% of the harvested radishes measured 16-30 mm. , a median marketable range, whereas when seed was distributed at random in the row, the percentage was 49. 45. In other words, precision spacing mar- kedly increased root diameter uniformity. Methylcellulose and paper seed ribbons or tapes were used successfully to space vegetable seeds at fairly precise intervals in the soil. Under field conditions, however, emergence was generally no greater than 50% indicating that precision seeding to a final desired plant population with these ribbon materials would be impractical. Precision seeding to reduce the thinning-labor requirement, rather than to eliminate it, was practical only if in-the-row weed populations were low. AN EVALUATION OF METHYLCELLULOSE AND PAPER SEED RIBBONS FOR THE PRECISION SEEDING OF LETTUCE (LACTUCA SATIVA L.) AND OTHER VEGETABLES By Nicky Allan Smith A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Horticulture 1960 ACKNOWLEDGMENTS The author is deeply indebted to Dr. H. John'Carew for his counsel and assistance during the graduate program and preparation of this thesis. The author wishes to thank the other members of the guidance com- mittee, Drs. R. L. Carolus, A. L. Kenworthy, R. E. Lucas, and G. P. Steinbauer, for their assistance with the program and this manuscript. Sincere thanks is extended to each and everyone who has assisted with this investigation. Special appreciation is due to my wife, Mrs. Manette McKinney Smith for her unwavering support. The financial support of the Minnesota Mining and Manufacturing Company is gratefully acknowledged. ii C ONTE N TS ACKNOWLEDGMENTS . CONTENTS . LIST OF TABLES LIST OF ILLUSTRATIONS INTRODUCTION. . .. . . . . . . .. REVIEW OF LITERATURE . Control of Seeding Rate . Equipment Pelleting Seed population and spacing Seed germination Control by Post-emergence Plant Spacing . . Thinning Hand thinning Mechanical thinning Physiological effect of thinning Direct seeding and transplanting METHODS AND MATERIALS - GENERAL . . Seed Ribbon Seeds Location of Experimental Plots Planters Greenhouse Soil Soil Compression iii Page ii iii vii 19 22 CONTENTS CONT' D Page EXPERIMENTALRESULTS................. 34 Field Experimental Trials- 1959 . . . . . . . . . . . 34 Experiment at Schonfeld farm Experiment at Anderson farm Experiment at Michigan State University Muck farm Other field experiments Greenhouse Experiments - 1960. . . . . . . . . . . . 54 Plant spacing experiment Soil crust experiments Soil compaction experiments Soil moisture experiments Fluctuations in soil moisture experiment FieldExperiments-l960. . . . . . . . . . . . . . 74 DISCUSSION....................... 84 SUMMARY 90 LITERATURECITED................... 93 iv Table 10 11 LIST OF TABLES Distribution of Lettuce Seed in Methylcellulose Ribbon . Germination of Lettuce (cv. Cornell 456, Lot No. 1352) on Top of Blotters in Covered Petri Dish at 20°C. . . Additional Information on Vegetable Seed . Effect of Method of Seeding and/or Spacing on Thinning and Weeding Time for Head Lettuce at Schonfeld Farm. Effect of Method of Seeding and/or Spacing on Survival, Harvest, and Percentage Harvested of Head Lettuce at Schonfeld Farm (Average of Two Replicates). Effect of Method of Seeding and/or Spacing on Total Weight, Average Weight per Head, and Tipburn of Harvested Let- tuce at Schonfeld Farm (Average of Two Replicates). Effect of Method of Seeding and/or Spacing on Thinning and Weeding Time, Survival, Yield, Percentage Harvested, and Tipburn of Harvested Lettuce at Anderson Farm (Average of Two Replicates). Effect of Method of Seeding and/or Spacing on Total Weight and Average Weight per Head of Harvested Lettuce at Anderson Farm (Average of Two Replicates). Effect of Method of Seeding and/or Spacing on Thinning Time, Survival, Yield at First and Total Harvest, and Percent- age of First and Total Harvest of Head Lettuce at MSU Muck Farm . . Number of Lettuce Plants Established on September 27,1959, as Affected by Method of Seeding and/or Spacing at MSU MuckFarm. . Effect of Time of Spacing on Fresh Weight of Foliage and Roots of Head Lettuce. . . . . . . . . . . . Page 23 24 25 35 39 41 44 46 48 53 55 Table 12 13 14 15 I6 17 18 TABLES CONT' D Effect of Number of Seeds per Locus on Emergence of Lettuce Seedlings. Effect of Number of Seeds per Hill on Seedling Emergence . Effect of Method of Seeding on Emergence of Lettuce Seed- lings . ....... . . . . ........ Effect of Compression and Method of Seeding on Emergence of Lettuce Seedlings . ....... . . . . . . . Effect of Method of Seeding on Seedling Emergence of Celery........ ........ Effect of Method of Seeding and Moisture Levels on Seed- ling Emergence of Lettuce ............ Effect of Method of Seeding and Moisture Levels on Seed- ling Emergence ................. vi Page 58 58 60 60 67 68 70 LIST OF ILLUSTRATIONS Figure Page 1 Photograph of International Harvester experimental QAMC 424 seed ribbon planter in operation at Schon- feld farm, Imlay City, Michigan, April 30. 1959 Photograph of International Harvester experimental QFE 2012 and QFE 2013 seed ribbon planter being loaded with methylcellulose seed tape at Michigan State University Experimental Muck Farm, Laings- burg, Michigan, June 9, 1959. Photograph of Planet Jr. hand seeder modified by Minne- sota Mining and Manufacturing Company for paper seed ribbon planting, 1960. Photograph of methylcellulose seed ribbon after placement in the soil (uncovered to show comparison) . . . . . . 29 2 Apparatus used to apply pressure onto soil surface . . . 33 3 Photograph of thinning head lettuce at Schonfeld farm, Imlay City, Michigan, May 25, 1959. Photograph of thinning head lettuce at the Anderson farm, Imlay City, Michigan, June 18, 1959. Photograph of plots at Michigan State University Experi- mental Muck Farm, Laingsburg, Michigan before thin- ning of head lettuce but after weeding. Photograph of plots at Michigan State University Experi- mental Muck Farm, Laingsburg, Michigan, 1959, in close up showing irregular emergence of lettuce seed- lings. ............... 37 4 Effect of planting depth on yield of lettuce at Michigan State University Muck Farm. Effect of irrigation immediately after planting on yield of lettuce at Michigan State University Muck Farm . . . 51 5 Emergence of cauliflower seedlings as influenced by pres- ' sure applied to soil surface. Emergence of tomato seedlings as influenced by pressure appliedtosoilsurface. . . . . . . . . . . . . . . 63 vii Figure 10 ILLUSTRATIONS CONT' D Page Emergence of celery seedlings as influenced by pressure applied to soil surface. Emergence of lettuce seedlings as influenced by levels of soilmoisture...... ..... 66 Cumulative emergence of lettuce seedlings from methyl- cellulose seed ribbon and regular seeding after 17 hours desiccation of soil . ...... . . . . . . . . . . 73 Cumulative number of tomato plants, cv. C-52, with three blossoms expanded in first floral cluster on main stem when grown as 1, 2, or 3 plants per hill. Cumulative number of tomato plants, cv. Fireball, with three blossoms expanded in first floral cluster on main stem when grown as 1, 2, or 3 plants per hill . . . . 76 Percentage distribution into size categories of radishes grown from seed distributed precisely or distributed at randomintherow................. 79 Photograph of plots of head lettuce seeded with methyl- cellulose seed ribbon in upland mineral soil at Michigan State University Horticulture Farm, East Lansing, Mich- igan. 1959. Photograph of plots seeded with paper seed ribbon for tomato in Delaware. 1960. Photograph of tomato seedlings and paper seed ribbon. Photograph of tomato seedlings with paper seed ribbon un- coveredinthesoil................. 82 viii INTRODUCTION The system of private enterprise in American agriculture is irrevo- cably committed to exploiting every opportunity to increase returns by reduc- ing costs. The research efforts of American industry and agricultural experiment stations are directed toward providing improved means of achieving such economic objectives. Because labor costs of production comprised the overwhelming por— tion of final costs, the history of modern advancements in agricultural production has been a recapitulation of successive onslaughts on labor costs. The precision spacing of seed evaluated in this thesis is a new method of seeding offered to reduce labor costs. Occasionally an innovation is introduced that does not reduce costs; it is justified because the buyer is willing to pay for the improvement. Without being presumptive or anticipatory, it appears that precision spacing of seed is inevitable; it is primarily a question of method. Any study of methods of spacing soon expands into an assessment of the perti- nent environmental phenomena. Thus the scope of this thesis is marked out. REVIEW OF LITERATURE Since the time man gave up nomadic existence and became an agri- culturist, he has exercised some control over placement of seed and the rate of its distribution. Whether man used his hand or mechanical equip- ment to distribute seeds, be adjusted the method to the times and current knowledge. Always the quantitative variation in seeding has been primary while the specific distribution pattern of the seed on the soil surface has been largely incidental or secondary. Control of Seeding Rate. Equipment. --Until recently, in a mechanical planter, control of dis- tribution of quantity of seed has been largely by regulation of the aperture through which the seed flowed. The seeding rate was heavy so that subse- quently an adequate stand emerged from the least dense portions of the row (Harvey, 1958). This resulted in an excessive density of seedlings else- where in the row which required special thinning for crops like sugar beets and lettuce. Recently, to reduce thinning to a minimum, more precision in seed- ing has been demanded. Harvey (1958) has designated the minimum for sugar beets as being the preservation of a pattern of distribution. Frakes (1959) suggested, for sugar beets, that seeds be distributed four inches apart. Harvey (1958) stated that up to 30% of the seed groupings could be doubles without affecting subsequent yield significantly. With such a clarification of requirements for seeding, precision seeders were developed and marketed. Robertson (1957) and Maddox (1958) have described these for turnip seeding in Scotland. It is, however, in the sugar beet industry that some of the most rapid developments have taken place in precision seeders (Bainer, 1947; Bjerkan, 1947). Marx (1959) used a commercial version of a precision seeder for planting canning peas. Sweetman (1957) designed a suction operated seeder to distribute clover seed uniformly. It was tried experimentally for lettuce, carrot, parsnip, and wheat. For precision seeders to operate at maximum efficiency, Maddox (1958) cited the need for correctly sized seed. Bainer (1947) and Bjerkan (1947) similarly used sized sugar beet seed. Pelleting. --A planter adapted for planting uniform sized sugar beet seed can readily be used for pelleted seed of tomato (Bainer, 1947). Carolus (1949) pointed out the possibilities of pelleting. In pelleting the seed has been artificially made more uniform in size (Carolus, 1954) by addition of clays or other substances. Wolf (1953) studied seedings made with pelleted seed of cabbage, endive, lettuce, and onion. Zink (1955, 1956) studied the use of pelletized lettuce seed. Pursley (1960) reported that pelleted seed was still being tried by commercial growers for lettuce and onion. When pelleted seed was used, emergence of seedlings was delayed (Carolus, 1949; Zink, 1956). Brendler, Zink, and Crane (1955) reported an average saving in thinning time of 33 1/3% for lettuce. Use of pelleted seed resulted in no consistent effect on yield of lettuce (Zink, 1955, 1956). Zink (1955) stated that there was no difference in head size of lettuce or its maturity. Carolus (1949) mentioned better stands, more rapid maturity, and more vigor. Zink (1956) hypothesized that if pelleted seed was planted less seed was required. Hence better seed could be used, such as mosaic-tested lettuce seed. Wolf (1953) and Harvey (1958) concluded that pelleting of seed adversely affected emergence. Bainer (1947) reported the use of a John Deere No. 66 drill for planting twenty acres with pelleted tomato seed. So favorable was the reception to this by growers that the following year several hundred acres were planted in this manner. Despite certain attractive features of pelleted seed, the practice is not widely used. Seed population and spacing. - -Plant populations on a unit of area as an acre have been the subject of numerous investigations (Dunyan it al. , 1958; Coons, 1948). Often the seed distribution was in predetermined row widths dictated largely by existing tillage or harvesting equipment. Surveying the reports on spacing for sugar beets, Coons (1948) stated that a final recommendation for optimum spacing allotments could not be made. Spacing depends on a host of factors (Paponov, 1959; Coons, 1948) of which a single factor cannot be detached from the complex and evaluated (Coons, 1948). Coons warned against drawing conclusions from any experi- ments in which the stands were poor. Warne (1951b) similarly stated that for crops dependent on plant population, varietal comparison is valid only if identical stands are compared either actual or computed from a regression of yield on plant density. While it is laudable and theoretically essential to study a plant in totality with all factors under control, modern methods of scientific investi- gation are based on the selection of one factor and varying that factor. Hence, variety and species can be selected as a valid variable. Corn has been the subject of considerable investigation on plant popu- lation due, in large part, to its great economic importance. Dunyan, Lang, and Pendleton (1958) have recently summarized many findings. Grain pro- duction increased with increasing population from 4, 000 to 20, 000 plants per acre while size and weight of individual ear decreased. This inverse rela— tionship is even more pertinent when yield per acre is compared with weight of total ears per plant. An increase in the number of plants is correlated with a retardation of plant development as measured, for example, by the time interval between tasseling and silking. Increasing the number of plants from one to five per hill decreased leaf area per plant by 30%. Dunyan Eta}: cited evidence that plants spaced singly out yielded those in hills with a greater difference under more favorable conditions. The corn plant compensates somewhat for ad- jacent gaps but never completely. That this ability to compensate is con- siderable is confirmed by the feasibility of wide-row corn recommendations . Many factors enter into corn development as they do for any other plant. Bailey (1941) observed a similar response in sweet corn as Dunyan _e_t_ £31. reported for field corn. Pickett (1944) favored spaced over a hill system but stated that yields were nearly the same. Sugar beets, like corn, has been the subject of considerable research regarding yield and plant population. Deming (1940) obtained significantly higher gross yields with a spac- ing of 20 x 10 inches (single plants) as compared to a spacing of 20 x 20 inches (double plants). In agreement with statements of other investigators (Larsen, 1943), Harvey (1958) stated that regularity of plants was of critical importance to yield. He warned that precision spacing by drills or otherwise must result in an adequate number of plants in the thinnest portions of rows. Frakes (1959) outlined recommendations for spacing plants with precision drills and monogerm sugar beet seed. Ultimate plant population was deemed to be eight inches apart with spacing of seed at four inches apart. He warned that within these limits, emergence must be at least 80 percent with no concentration of its failure in any one area. In a study by Hunter-Smith and Williams (1927) using "mangolds" and kale in addition to sugar beets, these investigators concluded that a decrease in distance between plants resulted in an increase in yield and a decrease in size of individual roots. Other investigators reported similarly for carrots (Ward, 1959), garlic (Couto, 1958), and onion (Das and Dhyani, 1956). Coons (1948) attempted to summarize the reports of various investi- gators and to place their conclusions in proper perspective. An equidistant or square area per plant appeared with seeming regularity when optimum yields were analyzed for exact plant spacing. Frequently row widths exceeded this due to the preference for wider rows permitting machines to operate more efficiently. Coons concluded that a good even stand was a prerequisite for maximum yield of acceptable roots. The presence of even one root or one gap affects yield, although it is compensated for or masked by variation. Various legumes of commercial importance have also been investi- gated. Wiggans (1939) observed that uniformity of plant arrangement in- creased yields of soybeans despite a compensating effect by the plants. Hardenburg (1942) worked with four field bean varieties and found but slight advantage in favor of spacing when there was a constant plant population per foot of row. Larson and Peng-Fi (1948) found for lima beans that the more regu- larly shaped area (i. e. square) was associated with higher yields. While there is mounting evidence that uniform spacing of plant popu- lation is highly important for maximum yields, there are results that appear to contradict or at least to cast doubt on this conclusion. Perhaps, this contradiction is more apparent than real, and hence its amplification and resolution is pertinent. While not always stated or specifically qualified, conclusions that arrangement was inconsequential were usually based on variations in plant population that were either not wide or could be obscured by inherent variables. This is logical from the practical point of view. Thus contradictory results in them selves do not negate the general hypothesis that spacing and yield are related. Warne (1951c) observed that for yield of globe beet there was no prac- tical arrangement that was more especially advantageous. The variances used were twelve spacings of which four were row widths and three were thinning distances in the row along with two manurial treatments. Somos (1957) obtained no difference in weight of individual fruits of tomato at time of ripening as a result of spacing under greenhouse conditions. Holland (1957) and Holland and Campbell (1958) reported no significant differ- ence in total yield per acre for cannery tomatoes whether plants were arranged singly or in "clumps". About three times as many plants were present in the "clump" plots as in plots with single plants. Sprague and Farris (1931) took issue with Engledon over his conclusion that yields per acre are determined largely by the uniformity with which the seed is spaced in the row and went so far as to say that for seeding tests of barley, variations of seed spacing up to 40% in consecutive sections of rows could be ignored. They seeded consecutive feet of row at 6, 9, 11, or 14 pecks per acre to compare with a seeding at a uniform 10 pecks per acre. The yields from the heavier seeded portions of a row could conceivably counterbalance the more lightly seeded portions. Also this was a compari- son at only one seeding rate; namely, at 10 pecks per acre. Pickett (1944), speaking of sweet corn, stated that when the number per linear foot of row was the same, the number per hill, whether 1, 2, 3, or 4, did not affect yield significantly. Maddox (1958) expressed the view that different plant populations, again within limits, did not affect yields of turnips. For soybeans, Wiggans (1939) believed that maximum yield occurred with uniform distribution but said that within wide ranges of plant population per square foot there was little effect on net increase because of compensating ability. Marx (1959) observed a similar compensating effect in canning peas. Others reaching similar conclusions were Hardenburg (1942) with field beans, Deming (1940) with sugar beets, and Peterson and Haber (1948) with Irish Cobbler potatoes. Such disparate inferences foreshadow operation of fundamental fac- tors exercising far-reaching influences. Separation and evaluation of each where possible is pertinent. Broadly speaking, many, if not all, investigators would concede that a multitude of factors operate to affect plant growth and yield. For corn, 10 Dunyan et al. (1958) have mentioned climate, season, soil, variety, availa- bility of nutrients, as well as population. Deming (1940) has singled out water and fertility as over-riding factors. Bailey (1941) listed soil and climate as variables. While these prevail as broad factors, it is in plant competition between individual plants that each factor affects plant growth and development. There- fore, a study of the reaction of the individual plant to environmental factors is necessary. Warne (1951a) lamented that precise information in literature on "inter-plant" competition was meager. He was interested particularly in maximum number and weight of intermediate sized below-ground portions of root vegetables; an objective with practical usefulness (Warne, 1951a, 1951b, 1951c, 1953). Coons (1948) concluded that the number of plants and unit length of row were related as cause and effect. A significant linear positive corre- lation exists between weight of sugar beets and stand. Each plant or gap makes a contribution. If a gap occurs, it is compensated for in growth by adjoining beets even to the extent of 96. 2 percent (Coons, 1948; Warne, 1951b). On the other hand, Deming (1940) compared one plant on 400 square inches with two plants on the same area and obtained no difference in yield. Thus it appears that Coons (1948) was justified in saying that it was the number of hills and their spacing that was important rather than the number 11 of plants. Yet Harvey (1958) cited Frakes as warning against more than 30% doubles so as not to affect yield. While these are the quantitative variations in gross morphology that are expressed in size and weight, internal changes (Somos, 1954) occur which may be termed qualitative but which are measured quantitatively. For sugar beets not only is tonnage required but percentage sugar per acre is a more pertinent economic criterion. High sugar percentage is correlated with increasing density of plants; conversely, sugar content de- creases as spacing is increased. Sugar content varies with maturity, nitro- gen, and water. Crowded plants remain physiologically young longer under conditions of low nitrogen and low moisture; growth is retarded, even if accompanied by warm sunny weather, when photosynthesis continues thereby building desired sugars. Apparently inhibition of growth accelerates qualita- tive changes rather than the same type of growth being resumed at some later date. In this inhibition, a new and different stage is hastened or initiated whereas in temporary cessation there is merely a time delay. While Coons (1948) has stated that the sugar beet plant responds to these environmental factors in this manner, other investigators with other plants have obtained different results and conclusions. Dunyan _e_t a_l_. (1958) stated that reduced space by increase in population retarded development. Bailey (1941) agreed with Dunyan _e_tal_. for sweet corn stating that wide spac- ing provided earlier harvest by l to 2 days. Warne (1951b) stated that the globe beet remained physiologically younger in a thick planting. From these 12 observations of Coons and Warne it is not without hazard to infer that spac- ingper _s_e_ affects development and consequently date of maturity. Spacing may vary the conditions under which a plant may deplete moisture and nutrients which in turn may cause the developmental changes. Thus an ex- periment based on spacing becomes an experiment with camouflaged levels of nutrition and moisture availability unless care is used to assure the same amount of nutrients and water to all plants under variable spacing. Paponov (1959) studied the influence of spacing on plant development and reported work with lettuce, radish, tomato, cucumber, dill, and borage conducted from 1951 to 1958. Increasing plant density of lettuce resulted in delay in onset of bolting and flowering. Action of fertile soil was similar to decreased density, 1. e. hastening of flowering. In cucumbers, denser planting resulted in larger percentage of male flowers. In tomatoes, restrict- ing the root system by pot culture resulted in higher placement of the first floral cluster in terms of leaves subtending that cluster. Paponov also observed that the "area of feeding" (plant density) did not affect the first two clusters as much as it did the third and fourth Cluster. Maturation of fruit occurred in reverse order, that is, ripening proceeded more rapidly on soil of lower fertility or restricted root systems. Paponov believed that under crowding the mechanism of action was the same as under low fertility i. e. essentially one of nutrition. Thus, at greater plant density, a lower nutrient supply would be available to each plant. 13 Paponov cited instances in Russian literature of earlier flowering and maturation in wheat due to lower moisture levels. But strangely, he concluded with no further evidence, that despite these data, it could not be said that lowering of moisture levels hastens development of annuals. Winter (1952) also stated that reduction in growth rate delays later stages of development and flowering of both cauliflower and lettuce. Increasing population of corn plants (Dunyan _e_t_ 2_1_l_. , 1958) increased suckering and barrenness while grouping corn plants reduced lodging per- haps due to the mutual physical support. Increasing the spacing of lettuce increased bolting as well as "hearting" according to Winter (1952). Kokuskina-Saveleva (1957) claimed that increasing the number of squash and cucumber plants per unit of area resulted in deeper rooting with conse- quent greater uptake of water and hence greater yield. Banga and DeBruyn (1956) thought plant population influenced root shape; at wider spacings older carrots were more pointed as they matured and enlarged. Seed germination. - ~No account of pre-emergence plant population control and spacing would be complete without consideration of the phenomena associated with the germination of the seed. Standard conditions have been outlined by the Association of Official Seed Analysts (Rules for Testing Seeds, 1954; U. S. D. A. , 1952) for ger- mination (jones, 1927) of lettuce seed. Numerous environmental factors firmly .. .4 .h l H ,_ 1.1:.141moflr... WEE». ewes A.» l4 affect germination of seeds chief among which are temperature, light, aeration, and moisture. Thompson (1938) and Heydecker (1959) classified the factors as temperature, "moisture supply/air supply", and mechanical ob- struction. Post-harvest dormancy of lettuce seed is due to immaturity at har- vest (Thompson, 1938; Harrington and Thompson, 1951) which will disappear with ordinary storage. This dormancy exists in the two layers below the outer two of the seed (Bohn and Whitaker, 1951). Light has a variable effect depending on the wave length (Shuck, 1934; Leggatt, 1948; Borthwick gt a_l_., 1954). The response of lettuce seed to light during germination can be altered by temperature (Borthwick and Robbins, 1928), by nitrates (Shuck, 1934), and by hormone-like substances. In fact, light was deemed so im- portant that Shuck (1936) thought failure of lettuce seed to germinate in muck was due primarily to the exclusion of light by the dark organic soil Temperatures over 25° C when combined with high moisture levels are inhibitory to the germination of lettuce seed varying to some extent with the particular variety and other factors (Borthwick and Robbins, 1928). How- ever, if the seed is not in a state of dormancy the lettuce seed germinates under a wide range of temperatures from about 4' to 20"C (Shuck, 1933; Borthwick and Robbins, 1928; Thompson, 1938).! Heydecker (1958) observed that lettuce seed swelled in 15% carbon dioxide but did not germinate. He stated that the maximum concentration 15 of carbon dioxide present in the soil at any one location would be 4 percent (Heydecker, 1958). Lettuce does have a high oxygen requirement (Thompson, 1934) which may not be satisfied due to puddling of the soil as follows dash- ing rains (Thompson, 1934). Stout (1959) reported a similar effect on the soil by the passage of equipment. Moisture can be critical in seed germination. At certain low mois- ture levels germination does not occur while at optimum levels maximum germination takes place. At intermediate levels germination depends on many factors, among them the interaction of species and variety with mois— ture levels. Doneen and MacGillivray (1943) divided vegetable seeds into four groups based upon the percentage of germination at or near the permanent wilting point of Y010 fine sandy loam (8. 6%). The seeds of most vegetables germinated well at levels of moisture close to the permanent wilting point of the soil. Hansen lettuce was one of the several classified in a group fairly sensitive to lower levels of soil moisture. It would appear that Heydecker (1954, 1956) agreed with this for he classified lettuce as more sensitive than cabbage, carrot, and onion seeds to soil moisture. Doneen and MacGillivray (1943) found celery to be the most sensitive to soil moisture of all vegetable seeds they germinated (Taylor, 1951). They subscribed to the generalization that seeds germinated faster at higher moisture levels than at lower levels of soil moisture. Ayers (1952) reported that for Spanish onion, total ger- 16 mination as well as speed of germination decreased with decreasing soil moisture. Heydecker (1954) found that optimum soil moisture for germination of cabbage, lettuce, carrot, and onion seed was slightly below field capacity. Suput (1953, 1954) preferred to express soil moisture in terms of soil mois- ture capacity or a certain percentage of this soil moisture capacity when the soil was not completely saturated. Thus Suput considered 19-25% as mini- mum soil moisture capacity for germination of soybeans, vetch, sunflower, flax, hemp, and turnip. Optimum level was 25 to 60% with 40 to 45% for turnip, vetch, and sunflower; and 35 to 45% for flax and hemp. Observations of Toole e111. (1947) are in agreement with this when for sugar beets they obtained poor germination at 60% soil moisture and much better germination at 40%. A common method of expressing soil moisture is percentage on an oven dry basis (0. D. B. ). This provides a uniform quantitative basis but does not reflect the action of physical forces. Stout et all. (1956) cited Hunter and Dexter to the effect that segmented sugar beet seed balls ger- minated only between 12 and 21% soil moisture (O. D. B. ). Stout (1955) ob- tained 90% germination for sugar beets at 12 to 21% soil moisture (O. D. B. ); below 12%, emergence was reduced; and at 6 to 9% there was no visible ger- mination. Hunter and Erikson (1952) reported that minimum soil moisture (O. D. B.) 17 for sugar beets was 4. 4-5. 45 to 17. 7% depending on soil texture and soil type. They presented evidence to support their contention that soil moisture tension was a more reliable and appropriate indicator of soil moisture for seed germination. Soil tension compensates automatically for differences in soil texture and soil type. They observed that each species they tested at- tained its own specific seed moisture percentage before germination. This varied from 26. 5% for rice to 50% for soybeans. They found comparable seed germination at different levels of soil moisture for different soil types. When these levels of soil moisture were compared with soil moisture tension curves for the particular soils, it was observed that the levels of soil mois- ture were about the same. These could be expressed in atmospheres of soil tension which did not vary from soil to soil. This is a logical method of expression inasmuch as 1/3 atmosphere is equivalent to field capacity and the permanent wilting point is at 15 atmospheres of tension. This system agrees with some results reported by Satoo (1948) when seeds of three species of woody plants germinated at 50% soil moisture or eight atmospheres in terms of soil tension. Placement of vegetable seed into the ground usually is accompanied by compression of the seil surface by press wheels. This compression of the soil is a factor in seed germination as mentioned above when Thompson (1934) cited a reduction in oxygen movement due to puddling. Stout 3t -a_l. (1960) surveyed the literature on sugar beet germination as influenced by soil com- 18 pression and concluded that the reduced germination was due to either re- duced movement of gases or to the physical obstruction of the soil. Hanks and Thorp (1957) thought that the latter could limit seedling emergence. In a study of "moisture x pressure" and consequently crusting interaction, it was observed that pressures above five pounds per square inch (psi) reduced germination and this was accentuated by reductions in soil moisture. Con- versely, at high soil moisture, crusting from pressure did not inhibit seed- ling emergence. To circumvent the difficulties associated with compression and its consequence, crusting due to drying (Ray _e_t_ a_l_. , 1952; Stout and Snyder, 1957), several investigators favored the old practice of compressing the seed and covering this with loose soil (Hollis and Burkhardt, 1959; Heydecker, 1954; Hollis, 1960; Marx, 1959; and Stout 9:31., 1960). Heydecker (1954) stated that this method accelerates germination. Hollis (1960) stated that more uniformity of maturation results because of less in-row competition as more plants are of the same size. Hollis and Burkhardt (1959) cited other quanti- tative variations in favor of seed firming. Hollis (1960) stated that best results occurred in light sandy soil and that seed firming could not replace good seed beds, high organic matter, and low clay content. i_*v3—; - r 19 Control by Post-emergence Plant Spacing Thinning. -—Thinning emerged seedlings is one method of achieving desired spacing at maturity. Spacing at this time eliminates some of the hazards that occur during the interval between seeding and thinning so popu- lation after thinning becomes solely dependent upon subsequent incidents. l Hand thinning. --Hand thinning is the oldest of methods and is still being used to a great extent on some crops. Bainer (1947) estimated that i 20 to 30 man-hours were required per acre of sugar beets for hand thinning. b In discussing pelleted seed and precision planters, Nissley (1955) mentioned that it cost from $40 to $60 to thin an acre of carrots. Currently, carrots like radishes are not thinned but the effect of spacing is achieved by scatter- ing of the seed in a band at seeding. Zink (1956) stated that thinning of direct seeded head lettuce required 22. 5 hours or 43% of the labor of production. Many factors, political and economic, predicate an increasing short- age of capable field hands to perform the tedious thinning at competitive rates. Mechanical thinning. "Mechanical thinners have ranged from short- handled hoes to modern mechanical machines. The object in thinning is to remove the excess of plants which frequently amounts to 60 to 90% of the plant population (Carolus, 1949). Many thinning operations are, to a large extent, subject to the control and judgment of man. Man can be the source of 8 to 9% reduction in yield just in the variation in hand thinning efficiency (Warne, 194 9). 20 Mechanical thinners have been described for sugar beets by Harvey (1958), Bainer (1947), Maughan, Wood and Chittey (1959), Frakes (1959), and Coons (1948); for turnips by Maddox (1958) and Robertson (1957); and for lettuce by Brendler_e_t_al. (1955), and Zink (1956). Guzman (1957) ex- perimented with chemical thinning. Physiologi_cal effect of thinning. - -The thinning operation has a phy- siological effect on the plants that remain. In addition, this effect varies with the time at which the thinning is performed. Zink (1955) reported that delayed thinning injured the root system. Warne (1951a) thought be detected an influence on yield governed by the time of thinning. Weaver and Bruner (1927) thought that "blocking out" of plants in "middle areas" (space between plants) was not harmful to the plants that remained but the thinning of the remaining plants in the hill to single plants could be. Maddox observed that when turnips were not hoed, they were firmer in the ground at harvest and more upright in growth. Zink (1956) mentioned damage to root systems of lettuce if plants remained thick in the row. Direct seeding and transplanting. - -Some of the reactions of plants to spacing can be observed by a study of their behavior under conditions of direct seeding and transplanting (Vinnik, 1960). Numerous reports attest to the favorable effect of direct seeding. Zlatkowsky (1953) experienced best results with direct seeding of cauliflower. kohlrabi, lettuce, and celeriac. For Corrales-Macedo (1955a), Capsicum 21 directly seeded out-yielded transplants and matured three weeks earlier. Tomatoes responded in a like manner (1955b). Apparently this reaction of tomatoes is normal, for Holmberg and Minges (1952) reported that field seeding of tomatoes in Yolo county, California, was becoming common— place. Maddox (1958) compared spaced turnips with singled (thinned) tur- nips and stated that the former were sturdier and made more vigorous growth. Conversely, transplanting was unfavorable to lettuce as well as cauliflower, kohlrabi, and celeriac (Zlatkowsky, 1953). Winter (1952) reported a reduction in the number of plants reaching marketable size when transplanted. Dullforce (1954) examined the retarding effect of thinning in some detail and concluded that "pricking out" was not detrimental to lettuce if the seedling was not disturbed. If, however, it was damaged, then there was an effect. Furthermore, Dullforce concluded that transplanting need not be a shock which retards the plants if the plants are not injured and provided the external conditions are the same as for the check plants with which the transplants are being compared. METHODS AND MATERIALS - GENERAL Seed Ribbon The seeds of various vegetable crops were enveloped in two types of materials prepared in ribbon form. 1 These were subjected to tests and 5‘41 evaluated. 5 Plastic seed ribbon. --Lettuce seed was folded within three layers, 1 l each two mils in thickness, of Methocel, 2 designated as Experimental Plastic Q-830. 20 film (Dow Chemical Company, Midland, Michigan, 1957; Minnesota Mining and Manufacturing Company, (3M), Saint Paul, Minnesota, letter 5 October 1959). An eight percent solution of Methocel was extruded onto the ribbon to serve as an adhesive for both retaining the seed and main- taining closure of the ribbon fold (3M, letter 9 November 1959). Water solubility was 37 seconds/2 mil at 77'F. for this two mil thickness methyl- cellulose ribbon (Dow Chemical Company, 1957; BM, letter 5 October 1959). Lettuce seed was placed in the methylcellulose seed ribbon at inter- vals of 3 1/2, 7, and 14 inches. Each ribbon contained but one spacing of the lettuce seed. Precision of seed spacing was checked and in Table l is 1Process developed and performed by the Minnesota Mining and Manufacturing Company, St. Paul, Minnesota. 2Registered trademark of the Dow Chemical Company, Midland, Michigan. 22 23 TABLE 1. --Distribution of Lettuce Seed in Methylcellulose Ribbon. a Seed Average Averageb Interval Skips Multiples 14 inches 1. 2% 19. 6% 7 inches 1. 8% 21. 0% 3 1/2 inches 2. 25% r 21. 5% aFrom data sheet dated 4 April 1959 (Thermofax), enclosure to 3M letter dated 3 June 1959 from Dr. R. J. Klug. bMultiples were practically all doubles with remainder triples. presented the frequency of skips, doubles, and triples for the three spacings. It varied but slightly between tapes. Skips and multiples when taken together accounted for almost one-fourth (20. 8 to 23. 75%) of the seed locations. Paper seed ribbon. --For experiments in 1960, seeds of lettuce, cauliflower, tomato, and celery were placed1 between a backing of unbleached sulfite crepe with high wet-strength and a facing of 15 pound lightweight tissue with no wet-strength (3M, conversation 15 June 1960 with Mr. H. D. Roussopoulos). Seeds Lettuce. --Seed of lettuce (Lactuca sativa var. capitata cv. Cornell 4562) was purchased (catalogue No. 508, Lot No. 1352) from Joseph Harris lProcess developed and performed by the Minnesota Mining and Manufacturing Company, St. Paul, Minnesota. 2Nomenclature based on Thompson (1939); Standardized Plant Names (1942); International Code of Botanical Nomenclature (Stockholm code) (1952); Inter- national Code of Botanical Nomenclature (Paris code) (1954); and International Code of Nomenclature of Cultivated Plants (1958). 24 Company, Incorporated, Moreton Farm, Rochester, New York. The tag attached to the seed bag listed the 1959 germination by test as 96%. During the course of these experiments several tests for germination were con- ducted by the seed laboratory at Michigan State University, East Lansing, Michigan. In Table 2 is presented the percentage germination of this lettuce 1 seed. The naked seed, either natural or made thus by washing off the methylcellulose, showed high germination percentage (86 to 98%) in 1959 and 1960. If the methylcellulose was left in contact with the seed, then germin- g ation dropped to 38%. TABLE 2. --Germination of Lettuce (Cv. Cornell 456, Lot No. 1352) on Top of Blotters in Covered Petri Dish at 20’C. a Condition of Seed Date Percentage of Germination on Day After Started Start 2 3 4 6 7 8 9 Regular seed without any treatment 4/20/59 11 44 47 68 77 84 93 Seed with methylcellu- lose seed ribbon 4/20/59 1 4 8 23 30 35 38 Seed with methylcellu- lose ribbon washed off 4/20/59 70 75 84 90 90 91 92 Regular seed washed with water 4/22/59 97 - 99 Seed with methylcellulose ribbon washed off 4/22/59 70 - 86 Regular seed without any treatment 3 /27/ 60 - 98 aGrateful appreciation is expressed to Dr. George P. Steinbauer, Department of Botany and Plant Pathology under whose supervision these determinations were made. Illegfimlmufl. all i l. i. 25 Cauliflower, tomato, and celery. --Seeds of cauliflower (Brassica oleracea var. botrytis cv. Snowball Imperial), tomato (Lycopersicon esculen- tum var. commune cv. Fireball), and celery (Apium graveolens var. dulce cv. Utah 52-70) were purchased from Joseph Harris Company, Inc. , Rochester, New York in 1960. Additional information imprinted on the seed containers by the seedsman is given in Table 3. The celery seed was not hot water treated. TABLE 3. --Additional Information on Vegetable Seed. _— 1 Vegetable Cultivar Catalogue Lot Germination in Number Number Test 1960 Cauliflowera Snowball Im - perial 339 466 88% Celery Utah 52-70 384 531 92% Tomatoa Fireball 861 1466 96% a Hot water treated. Radish. --Seed of radish (Raphanus sativus cv. Early Scarlet Globe) was purchased at Sears Roebuck and Company store, Frandor Shopping Center, Lansing, Michigan. Packets contained information that in January, 1960 test, seed possessed germination of 75%. Also, seed had been treated with the fungicide chloranil (tetrachloroquinone). 26 Location of Experimental Plots Schonfeld farm. --The first field planting of lettuce was made in the spring of 1959 at the Schonfeld farm five miles north northeast of Imlay City, Michigan (about 50 miles north of Detroit). Anderson farm. --The second field planting of head lettuce was made at the Anderson farm five miles east of Imlay City or about 45 miles north of Detroit, Michigan. Michigan State University Experimental Muck Farm. - -Two plantings at the Michigan State University Muck Farm located eleven miles north northeast of Michigan State University, East Lansing, Michigan. The June planting was factorial in design for soil moisture, depth of planting, and method of seeding. The July planting was for method of seeding only. Greenhouse. --The greenhouse experiments were conducted in the Michigan State University Plant Science Greenhouse, Farm Lane, East Lansing, Michigan. Field experiments. - -Field experiments on tomato flowering and radish root development were conducted at the Michigan State University Horticulture Farm, East Lansing, Michigan. Other field trials. --The location of other experimental plots in 1959 and 1960 will be mentioned when the particular experiment is discussed. 27 Planters A specially designed ribbon planter (Model QAMC 424)l, Figure 1 (upper left) was used to place the seed ribbon into the ground on plots at the Schonfeld and Anderson farms. A subsequent modification (QFE 2012 and QFE 2013)2 mounted as paired units, Figure 1 (upper right) was used for lettuce and cucumber on plots planted during June, 1959 at the Michigan State University Muck Farm and the Michigan State University Horticulture Farm. The later July 27, 1959 seeding was made with a Planet Jr. 3 modifi- 4 for seed ribbon planting similar to the model4 portrayed in Figure 1 cation (lower left). Check seedings with regular equipment were performed at the various locations as follows: At the Schonfeld farm, a Cliff Wetzel seeder (made in St. Johns, Michigan) drawn by a D-2 Caterpillar crawler type tractor was used to roll the soil and seed the lettuce. The seeding mechanism on this custom-made seeder consisted of six modified Planet Jr. seeder units mounted behind the roller. 1Designed, developed, and provided by the Farm Equipment Research and Engineering Center, International Harvester Company, Hinsdale, Illinois. 2Developed and provided by the Farm Equipment Research and Engineering Center, International Harvester Company, Hinsdale, Illinois. 3Trademark of’S. L. Allen and Company, Inc. , 3419 North 5th Street, Philadelphia, Pennsylvania. 4Adapted and provided by the Minnesota Mining and Manufacturing Company, St. Paul, Minnesota. 28 .EOmCmQEoo Beam 8 tono>oocsv :8 m5 5 EoEoomE Hots cons? poem 32332385 Ho samhweonm 4:me .mmBOA .003 .wEEmE scant boom momma new zchEoU wfiuaoflscflz one m5 .52 382822 .3 noEUOE Hoooom new: 9:. 352m Ho namuwouonm £2 .mmBOA .32 .e one. .esmEosz .mhfimwfimd .Eumm x032 LeucoECoaxm 36.835“ 38m :meHE be one» boom om2=:oo§5oE 5:5 nont wagon Houama moan? boom mam Mac one man mmO EEoEanxo Symptom 3:239:35 mo snowmouocm Jaw? £933 $2 .8 :3... .5955 Stu >25“ .EHE Ufiowconom um :oflmuoao E .8283 :02an boom mum 030 #3552338 Sammie: Ecozmcuoufi mo namuwgonm 82 .mmmn—D H enema 30 At the Anderson farm, an Allis-Chalmers tractor mounted seeder was used. At the Michigan State University Muck Farm, check rows in all plantings were made with a standard Planet Jr. hand seeder. All other plantings, both ribbon and regular seedings, are described in the appropriate place. Greenhouse soil All greenhouse experiments were conducted by using a Lock sandy loam topsoil with the exception of the 1960 Greenhouse Plant Spacing Experi- ment. Snyder (1957) has given the textural analysis for this Lock sandy loam as 60. 4% sand, 26. 7% silt (less than 50 microns and more than 2 mi- crons), and 12. 9% clay (less than 2 microns). Snyder (1957) calculated and showed a soil moisture curve for this soil in terms of soil moisture per- centage on an oven dry basis. From this curve and other illustrations, it appears that 1/3 atmosphere (field capacity) was at 16. 2% and 15 atmospheres (permanent wilting point) was at slightly below 6% soil moisture. The air dry soil was passed through a screen with 5 mesh to the inch. Soil moisture of the air dry soil was determined to be 1. 16% on an oven dry basis as an average of 4 samples dried at lOS‘C. 1 Tap water was added to this soil to obtain the desired level of soil moisture on an oven dry basis. lGrateful acknowledgment is made for use of the facilities of the Soil Science Department, Michigan State University. 31 Moisture was evenly distributed to the soil and the soil was mixed further. The soil was then placed in a closed container to permit the soil to reach an equilibrium. At the beginning of each experiment, the soil was again passed through a 5 mesh screen and placed in plastic traysl which measured 7 x 11 x 2 1/2 inches inside dimensions. Soil compression The desired soil compression measured in pounds per square inch (psi) was obtained by use of the apparatus illustrated by Stout, Snyder, and Buchele (1960) (see Figure 2). 1 Courtesy of the Minnesota Mining and Manufacturing Company, St. Paul, Minnesota. 32 Figure 2 Apparatus used to apply pressure onto soil surface Michigan State University Photo 18076 - 4. Figure 2 EXPERIMENTAL RESULTS Field Experimental Trials - 1959 Experiment at Schonfeld Farm Planting. --The Carlisle muck (Davis and Lucas, 1959) at the Schon- feld farm was plowed; 500 pounds of 5-10-20 fertilizer was broadcast and disced in; and the surface was made uniform by " floating". On April 30, 1959, four check rows and two guard rows were seeded at an estimated rate of 1/2 to 3/4 pound of lettuce seed per acre. Each of the rows in this experiment extended 2360 feet in a north-south direction. The next two westerly rows were planted with the seed ribbon in which the seed was spaced at 14 inches (14 inch ribbon). Starting at the north end, one round trip was made with the planter. The next two rows were planted in the same way, but with a ribbon in Which the lettuce seed was spaced‘at 7 inches (7 inch ribbon). The next two rows were planted with a ribbon in which the seed was spaced at 3 1/2 inches (3 1/2 inch ribbon). Then the next six rows were planted as the six rows just completed, i. e. two rows with 14, 7, and 3 1/2 inch ribbons successively. Soil moisture appeared to be at an excellent level for germination. Soil temperature at 4 inches below the surface of the floated soil was 50°F. at 3 p. m. The seed ribbon was found at 3/8 to 5/8 inch below the pressed surface of the ground. 3 4 35 Thinning and weeding. --Thinning and weeding was done on all plots on May 25, 1959 by a pair of experienced Texas-Mexican, male adults who used short-handled hoes. The two adjacent rows of the same treatment were thinned and weeded at the same time (Figure 3, upper, left). Plants were thinned to 14 to 16 inches apart in the row. Each worker worked on every treatment in both replicates. Time'varied from 10 to 18 minutes. This time was adjusted for a uniform distance to permit comparison. In Table 4 is presented the mean time for two replicates and two workers for each treatment. The pertinent portion of statistical analysis is included for comparison of means. TABLE 4. - -Effect of Method of Seeding and/or Spacing on Thinning and Weeding Time for Head Lettuce at Schonfeld Farm. Method of Seeding Timea (Minutes) Check seeding 13. 05 14. inch ribbon 11.99 7 inch ribbon ' 12.23 3 1/2 inch ribbon 12. 33 L. S. D. 05 V 0. 93 3Average time for thinning and weeding two adjacent ISO-foot rows (total - 300 feet). Average of two replicates. 36 .mwczvmom 8:32 «o oocow858 Hafizwmnfi @3308 a: 888 5 5m? £89822 .wusnmmfimq .Eumm x022 :38E #8me 388>ED 33m 83:22 8 32a Ho camuwouocm 3sz .mmgoq .mfiomoa 8am :5 8:32 U8: mo McEEE mnemmn 6mm: £83222 .wbfimwfimq .Eumm x032 8885 $.8an 38H8>ED 888m 8.3222 8 303 go :thwouosm £2 .mmBOA .ami .mm 32 8883 $2 .2 as; 58222 56 5.5 .Eufl acm8nc< 85 8 802:2 cam: maize: «o snowmouonm .EwE .mmmmD dons? comm 803283.385 :05 ”4...: m :33 powwow 8.83 885 mo £2 85 8 958 025 38c 9.5.. dons: comm 82380738,: :05 N. 5:: @288 8.83 :REE ummm .85 E 85 Ho a2 9: OH mBOH OE GEL... .Hmflmmm fimNumg mUmEquumSU 5:3 Umtmmw QHQB maou 025 885 mo Em: on“ 9 958 :< dong? ummm 823807388 :05 3 53> cmcomm 83 ~08 t2 9.8.382 of .8 82m. .858 no 25H 2:. .35 .8 :8... 8883 $2 .3 32 53222 56 3.5 .988 Emmconom 8 80:32 98: wficfifi mo camumouonm 82 .mmnED m 933m 37 m 8.33m . . c . . . . fair)... ....\4, t .v .I. p)“ .04” I... . 38 Harvest. --Four harvest plots were selected, each one hundred feet in length and extending across all rows, treatments, and replicates. Thus, each harvest plot of each treatment in each replicate consisted of two ad- jacent lOO-foot rows. On July 8, 1959, two regular experienced Texas- Mexican cutting crews each consisting of one male cutter and one female packer did the cutting and packing for commercial shipment. Weights and counts were made of all lettuce harvested. One full case (24 heads) was selected at random from each treat- ment in each harvest plot and replicate for subsequent cutting open and rating for degree of tipburn (Grogan _e_t_ a_l;, 1955). Thus, 768 heads were examined for degree of tipburn, a physiological disease of head lettuce. Each plant not harvested in the harvest plots was counted and classified as to reason for not being harvested on the basis of visual observation. Results. --From the thinning and weeding times presented in Table 4, it appeared that the only significant difference in time was between the check seeding and the 14 inch ribbon. However, the difference was significant only at the 5 percent level. The total number of plants per treatment that survived until harvest is listed in Table 5. There was no significant difference between the number of plants at harvest when the check seeding was compared with either the 7 or 3 1/2 inch ribbon. However, in the 14 inch ribbon plots, there were signifi- cantly (1% level) fewer plants at harvest than in any one of the other treatment plots either ribbon or regular. I'm-av?“ "" “W 39 TABLE 5. --Effect of Method of Seeding and/or Spacing on Survival, Harvest, and Percentage Harvested of Head Lettuce at Schonfeld Farm (Average of Two Replicates). M6th0d 0f Seeding Numbera Number ofb PercentageC and/or Spacing of Plants Heads Harvested Harvested Check seeding 519 299. 5 S7. 71 14 inch ribbon 386 239. 5 62. 05 7 inch ribbon 491 314. O 63. 95 3 1/2 inch ribbon 526 377. 0 71. 67 L. S. D. 05 59 7S. 3 12. 45 L. S. D. 01 84 138.3 -- a Total number of plants present at harvest on eight lOO-foot rows. bTotal number of heads harvested from eight 100-foot rows. c:Percentage of lettuce stand harvested from eight lOO—foot rows. Out of this stand at harvest, the number of heads that were of market acceptability and thus were harvested is given in Table 5. The total yield from the 3 1/2 inch ribbon (377 heads) was significantly different only at the 5% level from the regular planting (299. 5 heads). The greatest difference was between the different spacings of seed in the ribbon plantings particularly the 14 inch ribbon when compared to the other two. The relationship between the number of heads harvested and the total number of plants present at harvest is given in Table 5 as percentage har- vested. There was a significant difference only between the 3 1/2 inch ribbon reac ./\ 40 and the check seeding. Nevertheless, the percentage harvested was greater for each ribbon planting than for the check. The total weight of lettuce harvested is presented in Table 6. In large part, the weights reflect the number of heads harvested. Calculation of average weight per harvested head from data presented in Tables 5 and 6 are given in Table 6. There was a significant difference (5% level) in weight per head of lettuce between the check seeding and any one of the ribbon plantings. Furthermore, there is no significant difference between any one of the ribbon plantings. Tipburn evaluation was performed by rating the internal appearance of a head as either acceptable or non-acceptable for sale. In the acceptable group were included those heads that contained no trace of internal browning or only light tan-colored traces at the margins of the innermost leaves. In- cluded in the non-acceptable group were those heads with darker leaf mar- gins or slimy decay. Treatment means for this latter non-acceptable group- ing are listed in the fourth column of Table 6 with conversion into percentage of inspected heads in the fifth column of Table 6. A class comparison between the check seeding vs. the three ribbon spacings at a single degree of freedom resulted in a significant difference (F value — 13. 64; F 05 - 10. 13). Thus there was significantly more tipburn in the ribbon plantings than in the check seeding. The reason for this is not readily apparent. .5283 8 8888 m8. >n 88838 88: 8 wwwucmoummc 59:85 H8 8388008805 888 EEG .888 88.85 82 x88 8 @5288 328: 5:: 88888 $98: «.3 88 .8a 88: 8 .8282: mmm8>8m 8 5283. cam .88: .8a 8&83 www.8>< £383 8qu :o wfiomam .8828 wfinmmm 8 80:82 8 88am: .0 mqmafi. 42 Experiment at Anderson Farm Planting. -—The Spalding peat (Davis and Lucas, 1959) on the Anderson farm was plowed; 800 pounds of 5-20-20 fertilizer was broadcast and disced into the soil. Just before seeding, the soil surface was "floated" to assure a level seedbed. On May 28, 1959, the previously used Model QAMC 424 ribbon planter mounted on a tractor drawbar was used in the same manner as at the Schonfeld farm. Rows extended 2, 510 feet in length in a north and south direction. The same three spacings of seed in the methylcellulose seed ribbon (14, 7, and 3 1/2 inches) were used. Depth of planting varied from 1/2 to 3/4 inch below the surface of the soil. The first two rows were planted by making a round trip with the tractor and ribbon planter burying the 14 inch ribbon. To the west, two more rows were planted with the 7 inch ribbon; and the next two with 3 1/2 inch ribbon. This same planting pattern was repeated for the next six rows to the west. The next or last six rows were seeded with the grower's regular seeding equipment which consisted of a tractor mounted Allis-Chalmers lettuce seeder. Thinning and weeding. --On June 18, 1959, the plots were thinned and weeded at this time mainly because the check rows were so dense that thin- ning could not be delayed. 'IWo Texas-Mexican female workers did the thinning and weeding when thinning labor requirements were determined (Figure 3; upper, right). As at the Schonfeld farm, each worker worked for 10 to 15 minutes on each treatment in both replicates. This time and distance 43 thinned and weeded was converted to a uniform 300 feet of double row and is presented in Table 7 for each treatment. Harvesting. - -Three harvest plots were selected at random, each one hundred feet in length and extending across all rows, treatments, and repli- cates. Two adjacent rows made up each treatment within each harvest plot in each of two replicates. On July 30, 1959, two harvest crews, each consisting of an experienced Texas-Mexican cutter and packer, harvested all plots. Weight and number of heads of all harvested lettuce was recorded for subsequent analyses. For internal examination of individual heads, one case (24 heads) was selected at random from each treatment in each harvest plot of both replicates taken together. Thus 384 heads were broken open and rated for tipburn as at the Schonfeld farm. All plants present in harvest plots were counted on July 23, 1959 On July 30th, each plant not harvested was counted. All these data are presented in Table 7. Results. --The time required to thin and weed the check plots was sig- nificantly greater than for any of the ribbon plantings. In addition, there was no significant difference between any one of the seed spacings in the ribbon plantings. There was at least significantly fewer (5% level) plants surviving in the 14 inch ribbon plots than in the other ribbon plantings or particularly the check Planting. 44 888 8:888 888 480 8 w888808 8.2588 :83 88888 A808: 83 8880 H88 8888: 8 H8888 8w8H8>< .8858: 8 88Hw88 85 >5 088888 0888808 8088: 8 8w888oH8m8 480888 H8 8388888805 .888 >838 .0 838 808-84 58 80H“ 088888: 888 80:82 8 8w888o8mo .5088 958 808-84 038 8 888 8888: 8888 H8 H8382: 88L. 2 .w88 88 com £088 830H 888888 025 8 $588808 30H 8 88 008 H8 088588 8858 m .84 8.: cm .8 4o .0 .m .4 .m .2 .m .2 .0- .mm 80 mo .m mo .0 .m .4 E. .N we .0 c4 .0» m .08 m8 om .84 8088 :08 N\4 m on 4 mm .0 mm .8 m 4cm mwm oo .3 80848 :08 - S .8 oo 4 84 .3- o .34 8cm 2. .2 80.88 :88 v4 8 .o oo .o oo .8 m .28 83. B 48 8588 8820 88289. 8 H8585- o8w888o8m 8888883 8883 8 8888:): @8083 H0888 88m888o8m 8:83 8088: A“8088: £83852 888E. w8088m 8 00:82 48888888 03h. 8 8M8H8>H8I 8&8888H8m .88; 48Z>Hsm .883. 988883 088 MEEHEF :0 @8088 H0888 mc888m 8 8028.2 8 888m} .8. M492. 45 The number of heads harvested from the 14 inch ribbon plots was significantly lower than other ribbon plots and particularly the check plant- ing. Also, there was no significant difference between the yield from the regular seeding as compared to either the 7 or 3 1/2 inch ribbon. As is apparent in the fifth column of Table 7, there was no significant difference between any of the percentages of lettuce stand harvested. How- ever, the percentages in the ribbon plots were greater than the check by almost 8% on the average. This was an interesting and seemingly consistent difference. There was no difference in amount of tipburn. The total weights of lettuce harvested are given in Table 8. Since in large part they represented the number of heads harvested, it was not sur- prising that significance is approximately that given for the number of heads harvested. The weight per harvested head was computed and is given in Table 8. Although there was no difference between any of the weights, the average weight per head in each of the ribbon plantings was greater than in the check planting. Wt oln‘I. mxtvmr 46 TABLE 8. --Effect of Method of Seeding and/or Spacing on Total Weight and Average Weight per Head of Harvested Lettuce at Anderson Farm (Aver- age of Two Replicates). Method of Seeding Total Weight3 Weight per Headb and/or Spacing (Pounds) (Pounds) Check seeding 564. 5 1. 803 14 inch ribbon 286. 3 1.848 7 inch ribbon 517. 5 l. 899 3 1/2 inch ribbon 508. 3 l. 829 L. S. D. 05 132. 6 N. S. L. S. D. 01 243. 6 - - aWeight of all lettuce harvested from six lOO-foot rows. Computed average weight per head. Experiments at Michigan State University Experimental Muck Farm 9231.55 --The 1/4 acre was divided into three replicates. A regular split plot design was used. The main plots were either irrigated or not irri— gated immediately after planting. The sub-plots were planted either shallow or deep within the limits of the planter. The sub-subplots consisted of the check seeding and the three spacings of seed in the methylcellulose seed ribbon. Planting. --The Houghton muck (Davis and Lucas, 1959) was plowed and disced a number of times to reduce soil moisture as much as possible to provide a drier than normally desired seed bed. Treatments were planted . _ m” “ ‘. “I ; 9. ' A 47 on June 9, 1959, with the use of twin units of a modification of the ribbon planter. The irrigated plots received approximately one-half inch of water by sprinkler irrigation. Thinning. --Weeds were removed from the plots prior to thinning. Therefore, the thinning labor requirement does not include weed removal. On July 7, 1959, this thinning was done by a semi-skilled local crew em- ployed for the summer (Table 9). Since all rows were a uniform 54 feet long arranged in adjacent pairs, no adjustment of time was necessary. Harvesting. --The lettuce that was ready to harvest was harvested on two dates; August 13 and 17, 1959. Results. --While there was a significant difference between the times for thinning for the various seed ribbons, this difference was considerably smaller when compared to the difference between the regular seeding and any one of the ribbon seedings. As for the number of plants surviving until harvest, the check plots contained significantly more plants (84. 33) than even the 3 1/2 inch ribbon (68. 33). The number of heads harvested from the 14 inch ribbon plots was significantly less (5%) than from any of the plots. Conversely there was no significant difference in the number of heads at first harvest between the check planting and 3 1/2 or 7 inch ribbon. For the first harvest, there was no significant difference between the 48 .Aoumozaou you $03.96 38 52> moumo -zaou mob: Ho @9328 $58 884m oz: 3a 0mg .5 new 2 umsmqi :o @8852 93% :88 Ho ammucoouomw .Aocmozaou you 923.95 .38 .283 moumo -Saou ooh: 80 owmuo>mv 958 808-3 93 won am? .2 83 m8 “mamas. co coumozmc 836:. 80 .3953 838.6 .33 .2 “mamas... :0 633.82 033m _38 mo ommacooummu $2 .2 “mama... so @828: 3a $03.86 .38 :33 33833 3.3... 80 owmuogv mach 38-8% 025 you woumozm: memo: Ho 853320 .amfi .: “mums/w :o @3852 Ho: 332a mo .3593: 33 $2 .: “mama... so 8328me memo: 80 3533 cam meme .2 Hm=w=< so @0523: 23m: 80 .5953 of 95:36 .3 uoES -no @3838 you $03.86 .38 :83 3.3833 83.: mo owmuo>mv mach 384m 93 won 333 mo $33322 .Aoumozaou you 38a .95 .38 5:5 $3832 83.: 8o owmugmv mach 384m 03» Awficooa 32:33 55 3 $353 5 mErrm BA: omd $.22 mod $.08 vwd . 3 .D.m.4 mo .w mo .N. mm .o oo 4. mo .3 No .0 mo .0 .m .4 3 .3 on .8 so .3 mm .3 2.8 mm .m :88: 55 m: m 3 .ms oo .mv 3 .3 oo 4m mo .3 mm .m song: :05 p 3. .2 mm .3. co .om no .NN mv .wm me 4 sons? :05 3 mm .3 mm .mm we .wm mo .3. mm. .vw oo .2 @553 x0050 noamotmm coumotmm Cmozmm um: 38th pm: 353m :38. memo: umumozmz c0333: 332m 80 33:55: 950QO .833.“ 880 368mm £38. nucoonom omnmoI anon—H32 moEC. wfinoom mo c0522 .Eumm x022 DmE um 8:80..— me2 Mo 66538 Each. new “warm mo owwucoonom new .umotm: :38. can Hmhm 3 Bo; .~w>w>.3m .oEC. 9:333. :0 3:0QO H388 wamcomm Ho @0522 «0 888m: d mqm< 2964 @3532 Fe m m 005 .2 dusted Ho oocowHoEm 9360me no 2954 33822 new meadow .8 @0522 Ho Hootmi .2 m4m

< «3:682 mo $54 .oocomuofim mcznoom :o 2264 33222 new wcwooom mo U332 mo uoowm: .3 m4m mwczummw 08an no 2998895 .Ewfl .mmBOq 2m .5 82$ .8926: E Em? co wazumom E858 Hoe REE: :33 UmEuom—ou 8.8 a2 so mmcszmm dons? comm .893 can mmaznmmm 89:8 Ho 296.8995 £2 $5304 .38 .3 99.5 .8588 88.8: of E umumom 350838 t2 of E ”cons? .898 53, omnmmw 950.888 Em? of E .83 882680 E 08:56 H8 :onnfl boom .8an 2:3 .628me 303 Mo nambwouonm 8an £933 .8555 88.8: of 5 @283 8.83 EmC of :o mag 95 of 8:952 cmom :65 N. :33 @8683 8.83 :2 85 co :5“ 95 250.838 of E .omg 4895622. @5984 “mam .Eumm ouszsoruom 36.3325 33m 83:32 am :8 3855 3:29: 5 confiu 088m 323803585 53 novmmm 803.2 .68: m0 303 Ho camnwooonm £2 imam: 2 8ng O H 0.) Be In 83 for the Purdue Dwarf was 17% and for the Heinz 1370 was 25%. Fornaserro farm. --At the Thomas Fornaserro farm, Tracy, Calif- ornia, on May 12, 1960, check seedings and paper ribbon seedings were made with tomato variety Pearson VF. The reported low percentage for emer- gence from the ribbon plots was thought to be due to shallow planting result- ing in seed drying during the intervals between irrigations (Underhill, per- sonal correspondence, 1960). DISCUSSION The labor saving value of precision seeding was not realized under conditions of high weed population. Thus at the Schonfeld farm (high weed population) there was no great difference in thinning and weeding time between the seed ribbon and the standard plots, whereas at the Anderson farm (low weed population) the difference was appreciable. The methylcellulose seed ribbon, thus, offers another method of plant spacing as does pelleting (Zink, 1955, 1956; Brendler_e_t a_1_l_.', 1955), mechanical seeding (Coons, 1948), as well as post-emergence thinning (Maddox, 1958; Guzman, 1957). The methylcellulose seed ribbon with lettuce seed spaced at 14 inch intervals provided an excellent criterion of plant mortality from all causes. Without adjustment for small number of skips and multiples, survival of lettuce until harvest on 4 plots at 3 farms varied from 40. 64 to 56. 29% (aver- age - 47. 58%). Presence of doubles was not considered serious for tomatoes (Holland, 1957; Holland and Campbell, 1958) but should be below 30% for sugar beets (Harvey, 1958). An emergence of 80% recommended by Frakes (1959) for sugar beets should be a minimum for lettuce with seed spacing if a satisfactory yield is to be realized based on about a 65% harvest percentage. A reduced seeding rate necessitates higher survival which investigators have attempted to secure with seed-level soil compression (Hollis and Burkhardt, 1959) and modern seeders (Marx, 1959). A 90% Stand would have been 84 85 preferred as this approximated the stand in the check seedings. The irregular occurrence of increased head size, total yield, and earlier maturity of lettuce obtained with precision seeding in these experi- ments has also been reported for pelleting (Carolus, 1954; Zink, 1955). Varying the depth of seeding produced no significant difference in yield. Heydecker (1956) obtained 90% or higher emergence with seed depths for lettuce varying from 1/2 to 1 1/8 inches. Increased weight per head in the ribbon plots could be related to the reduced population as has been found with sugar beets (Coons, 1948) or the larger "feeding area" as mentioned by Paponov (1959) for tomatoes. In the Anderson and Schonfeld experiments, type of planting equip- ment was confounded with method of seeding. Subsequent experiments, how- ever, demonstrated that type of equipment had no effect on the relative re- sponses to seeding method. While all lettuce plots were on organic soils, mineral soils particularly if low in organic matter and/or high in clay con- tent might respond with greater crusting (Stout, 1955, 1959; Hollis, 1960). Irrigation after planting increased lettuce yields much more for the seed ribbon (particularly the 3 1/2 inch ribbon) than for the check seeding resulting in a significant interaction of irrigation and method of seeding and/ or spacing. Since intimate association of methylcellulose with lettuce seed in a seed laboratory test resulted in reduced germination compared with no methylcellulose, the favorable response of seed in ribbon to irrigation was :4 I; 1.11.5” .im 86 thought to be due to washing away of physical inhibition to germination brought about by the methylcellulose. Consequently, greenhouse experiments were conducted to evaluate this conjecture and are discussed elsewhere. For seeds of lettuce, cauliflower, and tomato (ribbon and regular), when soil pressures of 1/2, 2, 5, or 10 psi were applied immediately after planting, the resultant seedling emergence was not reduced significantly. This response is particularly noteworthy at the higher soil compressions be- cause seed of sugar beet has been reported (Stout, 1955, 1959; Stout SE31; , 1956, 1960) as responding with lower germination at higher (5 and 10 psi) soil compressions than at lower (1/2 and 2 psi) soil compressions. For celery, however, a reduced seedling emergence occurred at the 10 psi soil compression. Doneen and MacGillivray (1943) placed celery in a class by it- self because it responded with the smallest percentage of germination under moisture levels approaching permanent wilting point than any other vegetable seed tested inclusive of Hanson lettuce and Essar tomato. Stout (1959) and Stout 3t _a_l_. (1960) stated that compaction of soil resulted in reduced move- ment of soil water and gases. When fresh weight of both foliage and "roots" of lettuce was used as a criterion there was no significant difference between spaced seeding (non- ribbon) and sowing thickly with subsequent thinning a short time after emer- gence (one week). If the thinning was delayed, fresh weight was reduced. Since lettuce is thinned commercially three weeks or longer after emergence, 8 7 a reduction in fresh weight could be anticipated. While it would appear that subsequent growth would compensate for this, there is reason to believe (Coons, 1948) that this is never complete under normal conditions. Heydecker's (1954) conclusion that germination in soil near field capacity was higher than at other levels of soil moisture was in agreement with these results with lettuce, tomato, and cauliflower. Nevertheless, the paper ribbon showed more fluctuations in emergence percentages than did the methylcellulose ribbon. When seeds of lettuce, in methylcellulose seed ribbon and natural, was planted in soil at field capacity and subjected to drying followed by re- wetting, the emergence of seedlings was more rapid from the seed ribbon than from check plots, although the total percentage of emergence was the same. Perhaps this response of the seed in the presence of the ribbon is related to the hydrophilic properties upon hydration of methylcellulose mentioned by Felber (1944) and Felber and Gardner (1944). The lower seedling emergence of lettuce, tomato, cauliflower, and celery from the paper ribbon in contrast to standard seeding under variable moisture and soil compression as well as field tests with tomatoes could be related to the observed non-disintegration of the high wet-strength sulfite crepe backing. Thinning of tomato plants to singles, doubles, and triples had little effect on time of flowering. This agrees with the findings of Dunyan $2531: (1958) 88 for corn and Bailey (1941) for sweet corn. While the work of Holland (1957) and Holland and Campbell (1958) would appear to substantiate these findings with tomato, they compared "clump s" with single plants at unequal rather than identical plant populations per area. A comparison of hand spacing of radish seed with equal numbers dis- tributed at random over the same linear distance in the row, resulted in higher yields for spacing. This effect of larger plant parts when spaced and smaller when plants are thicker should be comparable to the effect that prevails in consecutive portions of rows under normal seeding and its attendant variation in number of plants per unit of length. This variation in sections of a row escapes notice when an entire row is considered in obtaining an average yield. This hand spacing of radish, also, resulted in 65. 79% of the radishes measuring 16-30 millimeters in diameter, a median marketable size, com- pared to 49. 45% when not spaced. Thus, spacing resulted in more pronounced grouping about the mean. This has economic significance if this is within the size range of a commercial grade. The conclusion of Sprague and Farris (1931) that up to 40% variation in plant density is permissible in con- secutive sections of a row of barley is not necessarily in conflict as they were concerned with total yield rather than uniformity. Theoretically, precision seeding should eliminate the need for plan thinning following emergence. However, in these field experiments, survival at time of harvest seldom exceeded 50%. 89 Therefore, precision seeding to a higher population in order to compensate for this plant mortality and yet to reduce thinning labor require- ments by presenting the laborer with single plants rather than clumps would seem an acceptable compromise. This proves economically feasible, how- ever, only if hand weeding of the crop is not necessary. Otherwise the thinning operation can be performed simultaneously with the weeding oper- ation at only a slightly greater expenditure of time. Until the factors accounting for the relatively high mortiality of lettuce seedlings in these experiments and in commercial crop production are brought under control, precision seeding to the final desired population appears to be impractical. SUMMARY Seed of lettuce (cv. Cornell 456) was spaced at 14, 7, and 3 1/2 inches in methylcellulose ribbon (tape) and planted in replicated field plots in organic and mineral soil. Lettuce, tomato, cauliflower, and celery were also spaced in a paper seed ribbon. Specially designed tape planters or modifica- tions of existing seeders were used to place both types of ribbons in the soil. Precision spacing with a methylcellulose seed ribbon resulted in re- duced thinning and weeding time. Thinning time reductions were more sig- nificant as the weed population decreased. If 90% of the mathematically ideal population is accepted as a com- mercial minimum after thinning (attained at 3 of 4 locations in check seedings) the average of the 90% ideal stand for 3 1/2 inch ribbon was 85. 14%; for 7 inch ribbon - 76. 81%; and for 14 inch ribbon - 52. 73% of this acceptable minimum. When ribbon seeded lettuce (14 inch ribbon) was not thinned, 47. 58% of the seed planted was present as plants at harvest. Thus, about one-half of the seeds planted were not present at harvest as mature plants. In field experiments the highest yields, in general, were from the check or regular seedings followed by 3 1/2-, 7-, and 14-inch ribbon seedings in that order. However, of the plants present at harvest the lowest percentage was harvested from the check seedings. When two harvests of a single planting 90 91 were made, the percentage harvested from ribbon plots at first harvest was significantly higher indicating that plants matured more rapidly in ribbon plantings. The weight per harvested head was greater from the precision seeded plots than from the check plots. At one location, there was signifi- cantly more tipburn in the lettuce harvested from ribbon plots, but no ex- planation could be given. In greenhouse experiments, delayed thinning (2 and 3 weeks after emergence) of ordinary lettuce stands resulted in smaller plants as measured by fresh weight (46 days after seeding) than earlier thinning or precision spacing. When lettuce seeds were arranged in l, 2, or 4 per hill, the ger- mination percentage was not altered if surface soil moisture was satisfactory. When the soil surface after seeding was compressed at 1/2, 2, 5, or 10 psi, germination of lettuce, cauliflower, and tomato (seed ribbon and regular) was not affected but germination of celery was affected at higher soil compressions (5 and 10 psi). Levels of soil moisture did not affect germination of lettuce, cauli- flower, and tomato seed in ribbon and regular seedings. Subjecting methyl- cellulose seed ribbon to wetting, drying, and rewetting resulted in more rapid germination of lettuce but not percentage germination. When direct-seeded tomato plants (cv. Fireball and C-52) were thinned to singles, doubles, and triples with six plants per six linear feet of row, the date of opening of the first three blossoms in the first cluster was approximately 92 the same in the doubles and triples as in the singles. Precision spacing of radish seed resulted in greater uniformity in size of edible portion. Thus, precision spacing of individual tomato plants appeared not to be necessary for highest yields. With lettuce, celery, radish, and cauliflower, however, where uniformity of plant shape is as important as total yield, in- dividual plant spacing is desirable for greater marketable yields. Methylcellulose and paper seed ribbons or tapes were used success- fully to space vegetable seeds at fairly precise intervals in the soil. Under the conditions of these experiments, however, emergence was generally no greater than 50% indicating that precision seeding to a final desired plant population with these ribbon materials would be impractical. Precision seed- ing to reduce the thinning-labor requirement, rather than to eliminate it, would be practical only if in-the-row weed populations were low. LITERATURE CITED Ayers, A. D. 1952. Seed germination as affected by soil moisture and alkalinity. Agronomy Jour. 44: 82-84. Bailey, R. M. 1941. The effect of plant spacing on yield, ear size, and other characters in sweet corn. Proc. Amer. Soc. Hort. Sci. 38: 546-553. Bainer, Roy. 1947. Precision planting equipment. Agricultural Engineering 28 (2): 49-54. Banga, O. , and J. W. DeBruyn. 1956. Selection of carrots for carotene content. III. Planting distances and ripening equilibrium of the roots. Euphytica 5: 87-93. From abstract in Hort. Abs. 26(3): 415 (#2823). 1956. Bjerkan, A. J. 1947. Precision planting. Agricultural Engineering 28 (2): 54, 57. Bohn, G W. , and T. W. Whitaker. 1951. Recently introduced varieties of head lettuce and methods used in their development. U. S. Dept. Agr. Cir. 881. Borthwick, H. A., S. B. Henricks, E. H. Toole, and V. K. Toole. 1954. Action of light on lettuce seed germination. Bot. Gaz. 115: 205-228. Borthwick, H. A., and W. W. Robbins. 1928. Lettuce seed and its germina- tion. Hilgardia 3 (11): 275-305. Brendler, R. A., F. W. Zink, and R. 1. Crane. 1955. Labor saving in the thinning of lettuce. Vegetable Crops Series 76. Dept. Veg. Crops, University of California, Davis, Cal. (mimeograph). Carolus, R. L. 1949. Possibilities with the use of pelleted seed. Ohio Veg. and Potato Growers Assoc. Annual Proc. 34: 56-62. 1952. Pelleted seed for precision planting. Amer. Veg. Grower 2 (I): 5, 16-17. 93 94 Coons, G. H. 1948. Space relationships as affecting yield and quality of sugar beets. Proc. Amer. Soc. Sugar Beet Technologists 1948: 252- 268. Corrales-Macedo, A. 1955a. Methods of sowing Capsicum. Boletin Tri- mestral de Experimentacion Agropeguaria, P. C. E.A. , Lima, Peru 4 (1): 7-11. From abstract in Hort. Abs. 26: 268 (#1834). 1957. 1955b. Method of sowing and spacing in tomato grow- ing. Informe Mensuql Estracion Experimental Agricola de " La Molina", Lima, Peru 29 (333): 6-12. From abstract in Hort. Abs. 26: 105 (#709). 1957. Couto, F. A. A. 1958. Effect of spacing on yield of garlic. Rev. Ceres. 10: 288-299. From abstract in Hort. Abs. 28 (4): 591 (#3705). 1958. Das, B. C., and K. C. Dhyani. 1956. Influence of differential spacing and nitrogen fertilization on growth and yield of onion. Phyton. 6: 47-56. From abstract in Hort. Abs. 26 (3): 414. 1956. Davis, J. F., and R. E. Lucas. 1959. Organic soils, their formation, distri- bution, utilization, and management. Michigan State Univ. Agr. Exp. Sta. Spec. Bul. 425. 156 pp. Deming, G. W. 1940. Comparative yields of equal plant populations of sugar beets with different spacing relations. Proc. Amer. Soc. Sugar Beet Technologists 3: 32-36. Doneen, L. D., and J. H. MacGillivray. 1943. Germination (emergence) of vegetable seed as affected by different soil moisture conditions. Plant Physiol. 18: 524-529. Dow Chemical Company, Midland, Michigan. 1957. Properties of experi- mental plastic Q-830-20, one mil thickness, Methocel film. Dullforce, W. M. 1954. Recovery from the check of transplanting. Research Report, Univ. Nottingham, Dept. Hort., Sch. Agr., Sutton Bonington, Loughborough, England. pp 10-12. Dunyan, G. H., A. L. Lang, and J. W. Pendleton. 1958. Corn plant popula- tion in relation to soil productivity. Advances in Agronomy 10: 435-473. Academic Press Inc. , New York. A. G. Norman, Editor. 95 Edmond, J. B. 1933. The influence of planting depth on the shape of the Scarlet Globe radish. Proc. Amer. Soc. Hort. Sci. 30: 554-562. Felber, I. M. 1944. Persistence of the moisture conserving effect of methyl- cellulose in soil. Proc. Amer. Soc. Hort. Sci. 45: 331-337. , and V. R. Gardner. 1944. Effect of a hydrophilic colloid of high viscosity on water loss from soils and plants. Michigan State College, East Lansing, Mich. Tech. Bul. 189. 30 pp. Frakes, M. G. 1959. Space planting a success. Sugar Beet Journal 24 (5): 1-3, 4. Grogan, R. G., W. C. Snyder, and R. Bardin. 1955. Diseases of lettuce. Calif. Agr. Exp. Sta. Ext. Serv. Cir. 448. 28 pp. Guzman, V. L. 1957. Chemical weeding and thinning when using pelletized vegetable seeds. Weeds 5 (3); 227-236. Hanks, R. J., and F. C. Thorp. 1957. Seedling emergence of wheat, grain sorghum, soybeans as influenced by soil crust strength and moisture content. Soil Sci. Soc. Amer. Proc. 21: 357-359. Hardenburg, E. V. 1942. Experiments with field beans. Cornell Univ. Agr. Exp. Sta. Bul. 776. 28 pp. Harrington, J. F., and R. C. Thompson. 1951. Effect of variety and area of production on subsequent germination of lettuce seed at high tem- peratures. Truck Crop Mimeo. 51, Univ. Calif. From abstract in Hort. Abs. 22: 366 (#2631). 1952. Harvey, P. N. 1958. Sowing and thinning the sugar beet crop. Field Crop Abstracts 11 (3): 151-160. Heinz Company, H. J., Salem, N. J. 1960. Report on Delaware direct seed- ing experiment. Letter 27 June 1960 by C. S. Landis and R. W. Scheuerman to Dr. H. John Carew. Hort. Dept. , Michigan State University, East Lansing, Michigan. Heydecker, W. 1954. The germination of vegetable seeds. Univ. Nottingham, Dept. Hort. , School Agriculture, Sutton Bonington, Loughborough, England. Res. Rept. 1954. pp 7-9. 96 Heydecker, W. 1956. Establishment of seedlings in the field. I. Influence of sowing depth on seedling emergence. Jour. Hort. Sci. 31 (2): 76- 88. 1958. Effect of anaerobic conditions on imbibed lettuce seeds. Nature 181: 1140-1141. 1959. Can we measure seedling vigour? XII International Seed Testing Convention, Oslo. (Preprint). 15 pp. Holland, A. L. 1957. Progress report on tomato improvement (plant spacing) State No. 3044. Agr. Ext. Serv., Univ. Calif. 4pp. , and I. B. Campbell. 1958. Progress report on tomato im- provement (plant spacing). State No. 3044. Agr. Ext. Serv., Univ. Calif. 4pp. Hollis, W. E. 1960. Personal communication, 5August1960. Univ. Maryland, Dept. Hort., College Park, Maryland. , and G. J. Burkhardt. 1959. Preliminary studies of seed firming as applied to snap beans. Maryland Agr. Exp. Sta. Misc. Article No. 378, Contribution No. 3114. Holmberg, D. M., and P. A. Minges. 1952. Field seeding of tomatoes survey in Yolo County investigates performance and problems encountered under commercial conditions. Calif. Agr. 6(3): 4. Hunter, J. R., and A. E. Erickson. 1952. Relation of seed germination to soil moisture tension. Agron. Jour. 44 (3): 107-109. Hunter-Smith, J. , and H. Rhys Williams. 1927. A census of an acre of roots. The relation of regularity and density of plants to yield per acre. Jour. Ministry Agric. 34(5): 448-455. From abstract in Biol. Abs. 2: 1145 (#12198). 1928. International Code of Botanical Nomenclature. 1952. Adopted by 7th Inter- national Botanical Congress, Stockholm. July, 1950. The Chronica Botanica Co. , Waltham, Mass. 228 pp. 1956. Adopted by 8th Inter- national Botanical Congress, Paris. July, 1954. Utrecht, Netherlands. 338 pp. 97 International Code of Nomenclature for Cultivated Plants. 1958. Formulated and adopted by the International Commission for the nomenclature of cultivated plants of The International Union of Biological Sciences (1. U. B. 8.). Jones, H. A. 1927. Pollination and life history studies of lettuce (Lactuca sativa L.). Hilgardia 2(13): 425-479. Kokushina-Saveleva, R. P. 1957. The development of aerial and underground organs of squash planted in groups. Uc. Zap. Saratovsk. Gos. Ped. In-T. No. 27. pp 173-201. From abstract in Hort. Abs. 30(2): 287 (#2196). 1960. Kotowski, F. 1926. Temperature relations to germination of vegetable seed. Proc. Amer. Soc. Hort. Sci. 23: 176-184. Larson, R. E. 1943. Interrelation of varieties and spacing on early and total yield of market peas. Proc. Amer. Soc. Hort. Sci. 42: 565-568. , and Li Peng-Fi. 1948. The influence of various row and plant spacings on yields of lima beans. Proc. Amer. Soc. Hort. Sci. 51: 479- 485. Leggatt, C. W. 1948. A contribution to the study of dormancy in seeds Lactuca sativa L. Canadian Jour. Res. 26: 194-217. Maddox, J. M. 1958. Precision seeding the turnip crop. Scottish Agriculture. 37(4): 181-184. Marx, G. A. 1959. Agronomic responses of canning peas to a new seeding implement. Univ. Wis. From author's abstract in Dissertation Abs. 20(2): 449-450. Maughan, G. L., G. M. Wood, and E. T. Chittey. 1959. Down-the-row thinning of sugar beets; harvesting of irregularly-spaced crops 1954-1957. Jour. Agr. Eng. Res. 4(1): 30-36. Minnesota Mining and Manufacturing Company, St. Paul, Minn. April 3, 1959 Data Sheet (Thermofax). Enclusure to letter 3 June 1959 from Dr. R. J. Klug. 1959. Letter dated October 5 from Dr. G. R. 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Sta. 1415: 1-2. From abstract in Biol. Abs. 26: 2850 (#32079), 1952. Robertson, 1. M. 1957. Mechanisation and the turnip crop. Scottish Agriculture. 1956-1957. 36(3): 162-164. Rules for testing seeds adopted by Association of Official Seed Analysts. 1954. 44:31-78. Proc. Assoc. of Official Seed Analysts. Reprint July, 1958. Satoo, T. 1948. Effect of wind and soil moisture on growth of seedlings of Robinia pseudacacia. Bul. Tokyo Univ. Forests. 36:36-40. From abstract in Biol. Abs. 24: 1034 (#10534). 1950. Shuck, A. L. 1933. Some suggestions for the prevention of erratic germina- tion of lettuce seed. Assoc. of Official Seed Analysts, Proc. 26: 284—285. 1934. Some factors influencing the germination of lettuce seed in seed laboratory practice. New York State Agr. Exp. Sta. Tech. Bul. 222. 21 pp. 1936. The germination of lettuce seed in the laboratory and in the field. Assoc. Official Seed Analysts Proc. 28: 80-83. 99 Snyder, F. W. 1957. 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