SEE) CORN PRODUCYION A5 AFFECTED BY’ SOIL FERTKUTY AND PLAN-T POPULATION Thad: fol flu Om of M. 8. MECMGAN STATE UNIVERSSTY Game E. Cmr E960 JH E518 LIBRARY * -— SEED CORN PRODUCTION AS AFFECTED BY SOIL FERTILITY AND PLANT POPULATION BY GEORGE E. CARTER AN ABSTRACT Submitted to the College of Agriculture of Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Farm Crops 1960 /7 {‘"K ’/ 1/11": 1 - -— .— . ApprOVEd 41/(- \ r/e‘ \ d l Okla-’4 /; A“ La L1 ABSTRACT Several fertilizer and plant population treatments were evaluated for effects on seed production with inbred lines and single-cross hybrids in 1957 and 1958 on a Conover loam soil, testing high in residual fertility, in Ingham County, Michigan. Corn did not reach full maturity in any of the experiments. Average increases in yields from fertilizer were not significant for inbreds in either year, nor significant for single-cross hybrids in 1957, but were significant for single-cross hybrids in 1958. Plant population was the most important factor affecting seed yields. Inbred lines Seed yields on WF9 and Oh51 inbreds in 1957 were not affected significantly by complete fertilizer treatments of either 200 or 850 pounds 12-12-12 per acre. Sidedressed nitrogen applications of 29 and 40 pounds per acre did increase yields significantly but there was no difference between the 20 and 40 pound rates. Average yields increased significantly from 17.8 to 38.4 bushels per acre as population was increased from 5,500 to 16,000. The highest seed yields were 43.1 and 46.9 bushels per acre for these two inbreds. Fertilizer effects on seed yields of 25 inbreds in 1958 were not significant. Average yields increased significantly from 26.8 to 50.3 bushels per acre as population increased from 7,500 to 18,300. Good agreement was obtained between actual yields and predicted yields using Duncan's method (2). Predicted yields continued to increase up to 30,000 plants per acre for most inbreds and a few predicted yields increased to 40,000 population. As population was increased from 14,600 to 18,300: (1) yields of Oh51, Oh51A, W64A, Oh43, W22, WF9, M3116, M3211, and M31334 increased significantly 9.2 to 12.1 bushels, (2) 38-11, W10, W70, B8, M3132, A73, M324A, M3131, and M3206 increased 4.7 to 8.2 bushels which were not significant at the 5% level, and (3) W23, WR3, Hy2, M3130, M14, R53, and 0103 showed little or no increase in yield. Single-cross hybrids In 1957 (Experiment 2), average yield and grading of seed from WF9 x Oh51A were not significantly affected by complete fertilizer and nitrogen sidedressing treatments. Yields averaged 43.2, 60.6, 69.4, 88.8, and 91.6 bushels at populations of 6,100, 9,200, 11,200, 15,100, and 17,200 plants per acre, respectively. Each increase except the last was significant. In 1958 (Experiments 11 and 12), five single-cross hybrids averaged 11.6 and 9.6 bushels more when fertilized with 550 pounds of 15-15-15 and 40 pounds sidedressed nitrogen per acre at the highest plant populations. As population increased from 7,300 to 17,100 in Experiment 11, average yields increased significantly from 58.1 to 89.1 bushels. When population increased from 7,000 to 14,000 in Experiment 12, average yields increased from 46.9 to 74.7 bushels. incre 3 In both years, kernel width and length were reduced as population increased. Percent large flats decreased and small flats increased about the same amount while medium flats remained unchanged as population increased. Production per acre of medium flats, small flats, and rounds increased and production of large flats remained unchanged as population increased. SEED CORN PRODUCTION AS AFFECTED BY SOIL FERTILITY AND PLANT POPULATION By GEORGE E. CARTER A THESIS Submitted to the College of Agriculture of Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Farm Crops 1960 5 /073 \h kw Q\ L/ IS; SEED CORN PRODUCTION AS AFFECTED BY SOIL FERTILITY AND PLANT POPULATION ACKNOWLEDGMENTS The author wishes to acknowledge the help and guidance of Dr. E. C. Rossman, Professor H. M. Brown and Dr. C. M. Harrison during the course of this study. INTRODUCTION . LITERATURE REVIEW. MATERIALS AND METHODS. RESULTS. DISCUSSION . SUMMARY. LITERATURE CITED . TABLE OF CONTENTS 12 44 51 54 INTRODUCTION An estimated 400,000 acres of double-cross hybrid seed corn are produced each year to plant the 85 million acres of commercial corn in the United States. Extensive production research has been conducted with double-cross plants on the effects of soil fertility and plant population. Relatively little cultural and production information is available for the inbreds and single crosses used in seed production. The relatively low vigor and yielding ability of corn inbred lines makes production of inbred and single-cross seed much more costly than that of double-cross seed on the more vigorous and productive single-cross plants. One purpose of this research was to investigate the effects of soil fertility and plant population on seed production of inbreds and single crosses. In the development and evaluation of most corn hybrids, yield trials are conducted at several locations for a number of years under various soil, cultural, and climatic conditions. Hybrids with the best average performance under these conditions are selected for production. All hybrids do not respond alike to increases in fertilizer and plant population. By conducting all phases of inbreeding, selection, and evaluation of inbred lines and yield testing of hybrids under conditions of high soil fertility and plant population, it may be possible to develop hybrids better adapted to take full advantage of these conditions. 2 In planning an effective and efficient breeding program it would be helpful if existing inbred lines could be classified for response to high level production practices and a similar evaluation made of the hybrids composed of various combinations of these lines. The second objective of this research attempted to classify a group of 25 inbred lines preliminary to evaluation in single- and double-cross hybrids. LITERATURE REVIEW Many studies of effects of fertilizer and plant population on grain production have been conducted with double-cross hybrids, but no published information was found relating to effects of fertilizer and population on single-cross and double-cross seed production. Airy (1) suggests that because of drouth hazards, 12,000 to 14,000 plants per acre in double-cross seed production fields should be adequate, with 16,000 plants recommended only at highest fertility levels. No seed yields were presented. A method for predicting yield at any plant population from yield at any two actual populations was described by Duncan (2). He proposed that the logarithm of yield per plant bears a linear relationship to plant population. He suggests using reasonable limits between 5,000 and 25,000 plants per acre to predict double-cross yields. However, yields of some drawf and semi-dwarf corn maintained a linear relationship with plant populations up to 78,000 plants per acre. As ear corn moisture reduced in the field from 50% to 40%, Rather and Marsten (3) observed yield increases of five to twelve bushels per acre in twelve to sixteen days. Results were consistent between early and late maturing hybrids. MATERIALS AND METHODS Field experiments were conducted on Conover Clay loam in 1957 and 1958 to study the effects of soil fertility and plant population on seed production of several inbred lines and single-cross hybrids. Prior to plowing and fitting, soil samples were taken and plow-down fertilizer for the high fertility treatment in Experiments 1 and 2 (Table 1) was broadcast on predetermined areas. The plots, each one row 32 feet long, were planted with a regular corn planter equipped with special cone seeders for small plots. Row fertilizer was placed one inch below and three inches to the side of the seed. Simazin was band-sprayed over the rows at planting in 1958. Weeds were further controlled by cultivation and hoeing. Additional nitrogen treatments were applied by sidedressing with ammonium nitrate at the last cultivation. The same field was used in 1957 and 1958. Experiment 1 was planted in 1957 in a split-plot design with four replications to determine the effects of various levels of complete fertilizer, nitrogen sidedressing, and plant population on seed production 0f EWO inbred lines. Oh51, a midseason line, and WF9, a late maturing line for Michigan, were used. Since the amount of pollen produced and the timing of flowering are important factors in seed production and must be considered when producing a particular hybrid, it was decided to attempt to reduce or eliminate these pollination difficulties by providing extra pollen to assure full pollination if possible. Therefore, two rows of WF9 x Oh51A single cross were planted between every six rows of inbred plots on two later dates to provide more adequate pollen for inbred plants. The first single-cross planting was made when inbred seedlings emerged, and the second when the first planting started to emerge. A border row of inbreds was planted on each side of the single-cross rows to reduce competition from the more vigorous single-cross plants. Experiment 2 was planted in the same field in 1957 as a split-plot design with two replications. The effect of various levels of complete fertilizer, nitrogen sidedressing, and plant population on the production of various grades of seed of single-cross WF9 x Oh51A plants was studied. In 1958, 25 inbred lines were classified for response to two fertility and four population treatments. All lines were planted in eight: separate triple-lattice experiments--Nos. 3, 4, 5, 6, 7, 8, 9, and 10——with a different fertilizer and plant population treatment for each experiment. The experiments were arranged so that when combined, they could be analyzed as a 2 x 4 x 25 split-plot experiment with three replications. Five single-cross hybrids were planted June 2 and June 10, 1958, in two separate split-plot experiments, 11 and 12 respectively, and replicated three times with the same treatments for each. In addition to providing data on the effect of fertilizer and plant population on double-cross seed production, the two rows of these five single crosses bet-Ween every five rows of inbred plots also provided additional pollen for the 1958 inbred experiments. Fertilizer treatments, plant population, pedigrees, experimental designs, and cultural agronomic information are presented in Table l. r0 .msowu nmowammu m .mwmmawsm Sofia-uufiam muqum you pocHnEoo muamfiwummxm usmum HH< .maouumuufi mam“ m .mofiuumaumamfiuu mxm mm3 unmawuomxm 20mm Hmamz mm: mm: ¢¢o3 omawz «H2 mmm comm: mks mm< Hmno 0H3 HHNmZ .MH .mN ammHmz .NH .qm Haumm .HH .mm moHo .oH .NN <¢Nmz .m .HN oaflmz .w .om mus .5 .ma «mam: .0 .ma msS A .NH o~3 .q .0H «mm .m .mH oaoo o umpouuo amoH xmfio HoH Ho c.o :uoo mH .82800 N mash mmmH HH Hm>oaoo o Honouoo amoH meu Hod as 0.0 auoo ma umnouuo «N sax mmma oH-m um>oaoo RN .uamm aaoH mafia “am no H.k mMHwMH< oH umnouoo N «can HmmH N uw>oaoo RN .ummm EmoH mmHo NmN mo H.m mmHmmH< oH Huncuoo N mash mmmH H um>ocoo umoum mmwu ONM .WQNM. mm}. mono mmumm>umn pmuamHm ummw amass: wcHHHHx HHom ummu HHom maoH>mum mung mumn uamEHumaxm :oHumEDOHCH oHanouwm HmusuHsu ¢Hz x mm3 .m oo04¢H oquNH umumH pmmmouoova HHNmZ x oHHmz .q CON.HH oom.NH cmNOHUHa moanoa Cd msHm .maofiuwoaH «mm: x m~3 .m ooa.m ooq.oH son as mH-mH-nH masses own -amu m .uoHa-usHam quxm Mme x Hmno .N oomna cowhk mmz unmaHummxo nomm 1>ulation means 2.5 bu. @ 5%, 3. 4 bu. @ 1% Antrogen means 13 bu @5 57, 1 7 bu @ 170 Meg g: gegtglitfi Epopulation x nitrogen x inbred means = 7.1 bu. 15 650 pounds plow-down and 200 pounds starter fertilizer, 20 pounds nitrogen sidedressing, and 16,000 plants per acre. With no plow-down or starter fertilizer, the best yield for WF9 was 37.0 bushels for 40 pounds nitrogen sidedressing, and 16,000 population. There was no significant difference in average effects between the two inbreds. In general, Oh51 yielded more at low fertility and WF9 yielded more at high fertility. The inbred x fertility, inbred x population, and inbred x fertility x population interactions were significant. At low population, the two inbreds yielded about the same but Oh51 yielded more than WF9 at the high populations. At the highest fertility level, however, WF9 outyielded Oh51. Average ear moisture contents at harvest were 43.2 percent and 53.2 percent for Oh51 and WF9, respectively. Neither inbred was fully mature, using 40 percent ear moisture to indicate maturity. Killing frost occurred September 27 and the plots were harvested October 10. Maturity as measured by ear corn moisture was not affected by soil fertility, nitrogen sidedressings, or plant population. Experiments 3-10 Tables 6 through 10 present average yield, average percent moisture, and analyses of variance for 25 inbred lines. The average increase of only nine-tenths bushel per acre when fertilizer was applied was not statistically significant. Average yields were 39.3 and 40.2 bushels per acre for 0 and 550 pounds per acre of 15-15-15, respectively. Yield increased significantly with each plant population increase. Averages were 26.8, 37.5, 44.3, and 50.3 bushels per acre for plant TABLE 6 . 16 ANALYSIS OF VARIANCE FOR YIELD OF 25 INBRED LINES WITH AND WITHOUT FERTILIZER AT FOUR PLANT POPULATIONS EXPERIMENTS 3-10 COMBINED, 1958 hi **Significant at the 1% level of probability Degrees Sum Components of of Mean of Source of variance _= freedom squares square F varian_c_§___ Total 599 105879.5 Replication 2 80.3 40.1 -0.1 Fertilizer (F) 1 112.2 112.2 1.0 -0.1 Error 81 2 228.3 114.2 0.7 Population (P) 3 45750.5 15250.2 354.4** 101.5 F x P 3 374.4 124. 2.9 -1. Error b 12 516.3 43. l. Inbred (I) 24 29320.4 1221. 27.9** 47. F x I 24 2590.1 107. 2.4** l. P x I 72 6958.3 96. 2.2** ~16. F x P x I 72 14118.9 196. 12.9** 60. Error c 384 5829.8 15. 15. Error c + F x P x I 456 19948.7 43. 17 TABLE 7. AVERAGE PERCENT MOISTURE AND YIELD RANKED FOR 25 INBREDS, EXPERIMENTS 3-10, 1958 Experiments 3-10 All fertilizer and populations Experiments 3-6 Fertilizer-550 lbs/a. A11 populations Experiments 7-10 NO fertilizer A11 populations Yielci Bu.per Percent Bu.per Percent Bu.per Percent rank Inbred acre moisture Inbred acre moisture Inbred acre moisture 1 W23 50.7 36.8 W23 53.2 36.3 W70 51.2 52.6 2 N64A 49.1 47.0 Oh51 48.8 46.0 W64A 49.6 47.7 3 N70 48.4 53.1 N64A 48.5 45.2 Oh43 48.5 52.6 4 Oh51A 47.6 47.0 Oh51A 47.9 48.0 W23 48.3 37.4 5 Oh51 46.5 44.9 N70 45.5 53.7 Oh51A 47.4 46.0 6 Oh43 45.0 53.4 WR3 44.0 46.0 NR3 45.6 48.2 7 NR3 44.8 48.1 B8 43.7 41.0 Oh51 44.2 43.9 8 B8 43.2 40.8 Hy2 42.8 52.3 N22 43.7 53.6 9 N22 42.6 53.6 M8132 42.1 47.9 M14 43.2 50.1 10 M3132 42.4 46.7 A73 42.0 50.5 B8 42.7 40.6 11 ”M14 40.8 50.0 N10 41.8 50.2 M3132 42.7 45.5 12 N10 40.6 51.0 0h43 41.4 54.1 M3116 40.4 47.3 13 WF9 40.3 56.3 N22 41.4 53.6 WF9 40.1 56.4 14 :MS116 39.8 52.5 M3130 41.1 45.9 M8211 39.9 47.0 15 .A73 39.8 51.6 WF9 40.4 56.1 N10 39.3 51.8 16 Hy2 39.4 53.4 M8116 39.1 46.4 A73 37.6 52.6 17 M8130 39.3 45.3 M14 38.4 50.0 M8130 37.5 44.6 18 2M8211 38.0 48.2 M324A 36.4 43.1 M824A 36.8 41.3 19 M824A 36.6 42.2 M3211 36.1 49.5 M81334 36.4 38.5 20 M81334 35.8 40.2 R53 35.3 38.4 Hy2 35.9 54.6 21 R53 34.0 37.7 M81334 35.2 41.8 R53 32.8 37.0 22 M8206 32. 7 33. 3 M8206 32 . 6 32. 7 M8206 32. 7 34.0 23 M8131 30.6 57.8 M8131 31.5 59.5 M8131 29.7 56.0 24 38-11 23.5 59.9 38-11 28.1 55.9 38-11 18.8 64.0 .2: (3103 22.7 58.3 0103 27.5 53.0 0103 17.9 63.6 Averages 39.8 48.1 40.2 47.9 39.3 48.3 Least significant differences(LSD) for average yields: (a) over all fertilizer and plant population treatments LSD = 2.2 bu. @ 5%, 2.9 bu. @ 1% (b) within fertilizer treatments LSD = 3.1 bu. @ 5%, 4.1 bu. @ 1% (fc) between fertilizer treatments for the same inbred LSD = 8.9 bu. @ 5%, 11.7 bu. @ 1% 18 TABLE 8. AVERAGE YIELD RANKED FOR 25 INBREDS AT FOUR PLANT POPULATIONS - EXPERIMENTS 3-10, 1958 ——' Experiments Experiments Experiments Experiments 3 and 7 4 and 8 5 and 9 6 and 10 7,500 plants 11,400 plants 14,600 plants 18,300 plants per acre per acre per acre per acre Bu.per Bu.per Bu.per Bu.per Rank Inbred acre Inbred acre Inbred acre Inbred acre 1 W64A 34.2 W23 50.1 W23 59.6 Oh51 61.7 2 W70 33.2 W64A 49.0 Oh51 52.9 Oh51A 61.3 3 M14 32.7 WR3 46.1 Oh51A 52.0 W64A 61.2 ‘4- W23 32.3 Oh51A 45.3 W64A 51.9 W23 60.9 .5 W22 32.2 W70 44.6 WR3 50.9 W10 60.5 £5 Oh51A 31.9 Oh43 43.1 B8 50.8 W70 60.3 ‘7 WR3 30.9 M14 42.7 Hy2 48.6 Oh43 59.3 23 Oh43 30.1 Oh51 41.6 M3132 48.4 B8 56.7 9 Oh51 29.6 M3132 40.2 Oh43 47.2 W22 56.2 '].(3 WF9 27.7 B8 37.9 M3130 47.2 M3132 54.3 1.21 38 27.4 M3116 37.7 W22 46.4 WF9 53.0 1.12 ‘MSl32 26.6 A73 37.6 W70 45.4 M3116 52.5 1.13 M3130 25.9 WF9 37.2 M14 44.9 A73 52.2 JLAQ- M324A 25.8 M3211 35.7 A73 44.4 M3211 51.5 '].:5 M3116 25.4 M3130 35.7 M3116 43.4 WR3 51.2 ‘].(5 Hy2 25.3 W22 35.5 WF9 43.2 Hy2 49.4 '].77 W10 25.1 R53 35.2 W10 41.7 M31334 48.5 1.23 A73 25.0 W10 35.0 M324A 41.0 M3130 48.4 1.9? M5211 24.2 Hy2 34.1 M3206 40.9 M324A 45.7 20 M31334 22.2 M324A 34.0 M3211 40.6 M14 43. l 1221, 0103 21.9 M31334 33.3 R53 40.3 R53 39.6 1212 38-11 21.5 M3206 31.1 M31334 39.3 M3131 39.6 2213 R53 21.0 M3131 30.7 M3131 34.0 M3206 37.9 2243 M3206 20.6 C103 22.9 C103 22.0 38-11 29.5 1355 M5131 18.0 38-11 21.6 38-11 21.3 C103 23.9 Averages 26.8 37.5 44.3 50.3 Ideaéisst: significant differences (LSD) for average yields: (a) within populations LSD = 4.4 bu. @ 5%, 5.8 bu. @ 1% (b) between populations, any inbred LSD = 8.5 bu. @ 5%, 11.1 bu. @ 1% l9 TABLE 9. AVERAGE YIELD RANKED FOR 25 INBREDS WITH AND WITHOUT FERTILIZER AT 7,500 AND 11,400 PLANTS PER ACRE — 75.500 plants per acre 1L400flants3er acre Experiment 3 Experiment 7 Experiment 4 Experiment 8 Fertilized Unfertilized Fertilized Unfertilized Y ield Bushels Bushels Bushels Bushels :- ank Inbred per acre Inbred per acre Inbred per acre Inbred per acre fl 1 W64A 35.6 W22 35.0 W23 48.4 W64A 53.7 2 Oh51A 34.7 W70 34.0 W64A 44.3 W23 51.9 3 M14 33.3 W64A 32.8 Oh51 43.7 W70 51.6 4 W23 32. 9 M14 32. 1 WR3 42. 2 Oh51A 50. 1 5 W70 32. 5 Oh43 32. l Oh43 41.6 WR3 50.0 6 WR3 32.2 W23 31.7 M3130 39. 1 M14 46.9 7 A73 31.3 WR3 29.7 WF9 38.6 Oh43 44.7 8 Oh51 31.0 WF9 29.1 M14 38.5 M3132 43.1 9 Hy2 30.1 Oh51A 29.1 W70 37.6 M3116 43.0 10 W22 29.4 Oh51 28.2 M3132 37.3 Oh51 39.5 1 1 Oh43 28.2 M324A 27.9 A73 37.2 B8 39.5 12 BS 27.8 B8 27.0 C103 36.6 M3211 39.3 1 3 M3132 27.2 M3130 26.3 M324A 35.5 A73 38.0 14 M3116 26.3 M3132 26.1 W22 34.8 R53 37.3 1 5 WF9 26.2 M3211 25.5 W10 34.7 W22 36.2 1 6 W10 25.8 M3116 24.5 Oh51A 34. 7 M31334 36.1 1 7 M3130 25.4 W10 24.3 R53 33.0 Hy2 35.9 18 M3206 24.1 38—11 23.3 38-11 32.6 WF9 35.8 1 9 M324A 23.7 C103 22.0 M3116 32.3 M3206 35.6 20 M31334 23.6 M31334 20.9 Hy2 32.3 W10 35.3 2 1 R53 23.4 Hy2 20.6 M3211 32.2 M324A 32.6 22 M3211 22.9 M3131 19.8 M3131 30.9 M3130 32.4 2 3 C103 21.8 R53 18.7 M31334 30.5 M3131 30.5 24 38-11 19.8 A73 18.6 B8 27.8 38-11 10.6 2 5 M3131 16.1 M3206 17.2 M3206 26.7 0103 9.3 Averages 27.4 26.3 36. 7 38.4 p Analyses of variance Degrees of 1 Source freed Mean squares Rep]. 1- I cation 2 101.8 22.0 269.6 2.5 [Db reds 24 71. 8** 80. 7** 74.4** 352.4** Bror 48 26.0 18.1 21.1 32.9 2 Least significant differences LSD 5% 8.4 7.0 7.5 9.4 .14§D 17. 11.1 9.3 10.0 12.5 **Significant at 1% level of probability TABLE 10 . 20 AVERAGE YIELD RANKED FOR 25 INBREDS WITH AND WITHOUT FERTILIZER AT 14,600 AND 18,300 PLANTS PER ACRE 14,600 plants per acre 18,300 plants per acre Experiment 5 Experiment 9 Experiment 6 Experiment 10 Fertilized Unfertilized Fertilized Unfertilized Sifii.eld Bushels Bushels Bushels Bushels rank Inbred per acre Inbred er acre Inbred per acre Inbred per acre 1 W23 61.8 W70 60.7 W23 69.6 Oh43 63.7 2 Oh51 57.3 W23 57.4 Oh51 63.0 W64A 61.4 3 Hy2 54.1 Oh43 53.5 Oh51A 62.9 Oh51 60.4 4- Oh51A 53.5 B8 52.2 W70 62.0 Oh51A 59.7 5 W64A 53.3 WR3 51.3 W10 61.5 W10 59.5 6 WR3 50.6 Oh51A 50.6 B8 61.1 W70 58.6 7 W70 50.0 W64A 50.4 W64A 60.9 WF9 55.7 8 M3130 49.8 W22 49.4 W22 58.1 W22 54.3 9 B8 49 .4 Oh51 48. 6 M3132 55. 1 M3132 53. 5 10 M3132 48.8 M3132 48.1 Oh43 55.0 A73 53.3 IL.]. A73 48.4 M14 47.8 Hy2 54.7 M3116 53.2 1.22 WF9 46.5 M3211 45.5 M3211 53.5 B8 52.3 1.13 'MSll6 45.9 M3130 44.5 M3116 51.9 W23 52.1 1.43 W10 45.2 Hy2 43.2 A73 51.1 WR3 51.4 11.15 W22 43.4 M324A 41.8 WR3 51.0 M31334 50.0 16 M3206 42.7 M3116 40.9 WF9 50.3 M3211 49.7 21.37 R53 42.0 A73 40.5 M3130 50.1 M3130 46.7 T].£3 M14 42.0 WF9 39.9 M31334 47.1 M14 46.2 1.59 Oh43 40.9 M3206 39.1 M324A 46.4 M324A 45.0 2 O M324A 40 . 2 M31334 38 . 8 R53 42 . 7 Hy2 44 . 2 22 I. M31334 39.9 R53 38.5 M3131 42.7 M3206 39.1 22 M3131 36.2 W10 38.3 M14 39.9 R53 36.6 23 M3211 35.7 M3131 31.8 38-11 38.7 M3131 36.5 2243- 0103 25.5 38-11 21.2 M3206 36.8 C103 21.8 25 38-11 21.3 0103 18.6 C103 26.0 38-11 20.3 Avegges 45.0 43.7 51.7 49.0 Analyses of variance Degrees of gource freed Mean squares Ei£3;)]_j,. cation 2 255.0 1.0 54.6 13.0 :[111>]:£ads 24 261.9** 288.5** 304.2** 374.6** Eror 48 57.1 45.6 73.4 34.3 ___ Least significant differences LSD 5% 12.4 10.8 14.1 9.6 £3 17. 16.5 14._4 18.8 12.8 **Significant at 1% level of probability 21 IDCDPUIatiOHS of 7,500, 11,400, 14,600, and 18,300 plants per acre, respectively. Differences among inbred yields were highly significant in each experiment and in the combined analysis. Average yields ranged from 22 .7 bushels for C103 to 50.7 bushels for W23. Highly significant interactions-~fertilizer x inbred and population x inbred—-indicated that some of the inbreds did not respond alike to fertilizer and plant population. These interactions are illustrated in Figure 1. However, when the error effects were removed from these interaction terms, the components of variance were either very small or negative (Table 6). Thus relatively little importance can be attached to these interactions. Moisture content was not affected by fertilizer or population. The averages are presented in Table 7 to indicate relative maturity of the inbreds. Correlations of yield and moisture content (Table 11) were low, indicating that only a small portion of the difference in yield was associated with maturity of the inbreds. The significant negative correlations in Experiments 5, 8, 9, and 10 indicate that early maturing inbreds tended to be higher yielding than late inbreds in these cases. Table 12 gives r values for yield for all possible combinations 0f Experiments 3-10. Correlations were nearly all highly significant, indicating the inbreds tended to respond alike to fertilizer and Population. Low and negative components of variance for inbred x fertilizer and inbred x population interactions (Table 6) and similarity 9f ranking (Tables 7, 8, 9, and 10) further substantiate the tendency for the inbreds to respond in a similar manner. 22 FIGURE I. YIELDS OF 25 INBREDS WITH AND WITHOUT FERTILIZER AT FOUR PLANT POPULATIONS ............. ............. ..... ........................ ......................... ...... ..... ..................... 1 _ _ Unfertilized 23 TABLE 11. CORRELATION OF PER CENT MOISTURE WITH YIELD FOR EXPERIMENTS 3-10 Experiment n9. r Plants per acre Fertilizer 3 -.0905 7,500 Fertilized 4 -.1105 11,400 Fertilized 5 -.5669* 14,600 Fertilized 6 -.2033 18,300 Fertilized 7 -.0491 7,500 Unfertilized 8 -.4671* 11,400 Unfertilized 9 -.4964* 14,600 unfertilized 10 -.4088* 18,300 Unfertilized t * Significant at 5% level of probability TABLE 12. CORRELATION 0F YIELD FOR ALL POSSIBLE COMBINATIONS OF EXPERIMENTS 3, 4, 5, 6, 7, 8, 9, AND 10 ‘-~———_—_—7 fl Plants per acre . Fertilized ] Unfertilized Experiment 11,400 14,600 18,300 7,500 11,400 14,600 18,300 Innnber 4 5 6 7 8 9 10 .6898** .7569** .6328** .6079** .7630** .7523** .6750** 4- .5762** .5502** .6849** .4965* .5472** .4910* 5 .7851** .3530 .7864** .7826** .7327** 6 .5431** .7030** .7901** .8225** 7 .5257** .6740** .5609** 8 . 9041** . 8089** 9 . 809 5** —-——— - * Significant at 5‘7o level of probability ** Significant at 17. level of probability 24 Duncan's (2) proposal that the logarithm of yield in pounds per plant bears a linear relationship to plant population was applied to 23 of the inbred lines tested. Inbreds C103 and 38-11 have been omitted from these predictions because stands were poor and pollination was not complete. Yields for the four actual populations fell close to a straight line for some inbreds, but not for others. In general, yields predicted by this method for the four populations agreed closely with yields adjusted by covariance analysis (Table 13). Yields predicted by Duncan's method for 23 inbreds at 5,000, 10,000, 15,000, 20,000, 25,000 and 30,000 plants per acre are given in Table 14. Predicted yields for most of the inbreds continued to increase up to 30,000 plants per acre. Some inbreds--B8, Hy2, W70, Oh43, M8132, M8116, M81334, M8211, W10, Oh51, A73, M8130, W64A--continued to increase up to 40,000 plants per acre before yields leveled off. Predicted yields for M824A, M5206, R53, M14, W22, and WR3 reached a peak at about 25,000 plants. These predictions for 20,000 to 40,000 plants were not evaluated by actual field experiments. Figure 11 illustrates the relationship of pounds per plant, logarithms of pounds per plant, and predicted yields for four of the inbreds. Pounds per plant and logarithms of pounds per plant were plotted for the four actual populations. Actual values for W70 and Oh51 fit a straight line very closely. Highest predicted yields were for about 35,000 plants per acre. Logarithms of yield per plant for M8206 and M14 did not fit as closely the predicting line drawn through the highest and lowest points. Since yield per plant decreased more rapidly of lbs. per plant and log. Lbs. per plant FIGURE I I . 25 POUNDS PER PLANT AND LOGARITHMS FOR FOUR ACTUAL PLANT POPULATIONS, AND YIELDS PER ACRE PREDICTED FROM LOGARITHMS FOR POPULATIONS OF 5,000 TO 40,000 FOR FOUR INBREDS ‘80 W70 Log. of lbs. per plan 0 = Actual values 5 Th 15 26 25 50 35 4b ()hSl .’/.-..-. .44 /’ -80 “sh. per acre ./ .3. ~60 Log. of lbs. .2 \ per plant.40 ‘ / 804.- / ‘.\“o ,' Lbs. per plant . l- .20 ®= Actual values 5 16* 515 20 25 36 55' 46 MS206 '80 Bu. per acre 5 10 15 20 OJ - s 1 5 10 15 20 25 30 M14 .4— ‘80 .3J ~60 \ Bu.per acre 9. ""k""’°\.‘ \x ‘0 .2. «" .40 ./ ‘9 I/' {I Lbs. per Log. of ‘plant ~1‘ lbs. per ‘~.\' plant ' 0= Actual 0. - 25 3b Plants per acre (thousands) per acre Bu. 26 TABLE 13. BUSHELS PER ACRE FOR 23 INBRED LINES ADJUSTED TO FOUR AVERAGE PLANT POPULATIONS BY COVARIANCE ANALYSIS AND BY DUNCAN'S (2) LOGARITHM METHOD - EXPERIMENTS 3-10 “ E Plants er acre L500 11,400 7 14,600 18 300 ovari- Duncan's Covari- Duncan's Covari- Duncan's Covari- Duncan's Inbred ance log. ance log_ ance lo ance log 38 27.4 28.9 39.7 40.5 50.8 48.8 56.7 56.5 Oh51A 31.9 34.4 45.3 46.6 52.0 54.0 61.3 60.1 Hy2 25.3 26.4 34.1 36.6 48.6 43.5 49.4 50.0 W70 33.2 32.4 44.6 44.6 55.4 52.9 60.3 60.1 Oh43 30.1 31.1 43.1 42.7 47.2 50.6 59.3 57.8 M8132 26.6 28.1 40.2 39.1 48.4 46.4 54.3 52.9 W23 32.3 35.4 50.1 47.2 59.6 54.7 60.9 61.1 M8116 25.4 22.9 37.7 32.2 43.4 38.6 52.5 45.1 MSZ4A 25.8 24.1 34.0 31.8 41.0 36.2 45.7 39.9 M81334 22.2 24.0 33.3 34.0 39.3 41.2 48.5 48.4 M3211 24.2 24.2 35.7 34.8 40.6 42.5 51.5 50.3 W10 25.1 26.2 35.0 37.5 41.7 45.4 60.5 53.9 Oh51 29.6 29.7 41.6 42.5 52.9 51.4 61.7 60.8 A73 25.0 26.0 37.6 36.2 44.4 43.5 52.2 50.7 WF9 27.7 28.1 37.2 38.9 43.2 45.9 53.0 52.6 M8206 20.6 24.1 31.1 32.2 40.9 37.3 37.9 41.5 R53 21.0 22.1 35.2 30.5 40.3 36.0 39.6 41.5 M14 32.7 34.0 42.7 42.3 44.9 45.9 43.1 47.4 M8130 25.9 25.2 35.7 35.8 47.2 43.0 48.4 50.3 W64A 34.2 34.6 49.0 47.2 51.9 55.3 61.2 62.7 W22 32.2 32.4 35.5 43.2 46.4 49.8 56.2 54.9 WR3 30.9 31.1 46.1 40.9 50.9 46.4 51.2 51.3 M8131 18.0 20 1 30.7 28 3 34 0 34.4 39.6 40.2 II II C O O 27 TABLE 14. YIELDS FOR 23 INBREDS PREDICTED FOR SIX PLANT POPULATIONS BY DUNCAN'S (2) LOGARITHM METHOD Plants per acre 5,000 10,000 15,000 20,000 25,000 30,000 Inbred Bushels per acre B8 22.1 36.6 49.8 60.0 68.3 73.9 Oh51A 25.0 42.5 54.4 61.8 66.1 67.5 Hy2 18.6 33.2 44.5 52.9 59.4 63.2 w7o 23.4 40.7 54.1 63.2 69.6 73.4 01143 22.1 42.5 49.0 60.7 66.9 71.2 M8132 19.9 35.2 46.9 55.7 61.6 65.9 w23 25.4 43.4 55.4 62.9 67.0 68.6 M8116 16.1 29.1 39.6 47.5 54.5 58.9 MSZ4A 17.5 29.3 36.7 40.4 42.4 41.8 M81334 16.7 30.7 42.1 51.1 58.9 64.3 M8211 16.7 31.1 43.4 53.6 62.5 69.6 W10 18.1 33.4 46.6 57.9 66.1 73.4 Oh51 20.8 38.2 52.5 63.9 73.2 80.9 A73 18.2 32.7 43.7 52.1 58.5 62.7 WF9 19.8 35.4 47.4 56.4 62.5 67.0 M8206 17.4 29.6 37.8 42.9 45.5 42.9 R53 14.8 28.2 37.0 43.6 48.2 48.2 M14 25.5 43.0 45.8 47.5 46.0 42.9 M8130 17.7 32.1 44.2 53.6 61.2 67.5 W64A 24.8 43.0 56.3 65.4 70.5 73.9 W22 23.4 43.2 50.4 56.8 60.3 61.1 WR3 22.6 37.7 47.1 52.5 54.5 54.6 0 5 8 1 2 0 MS = 131 14. 25. 34. 42. 48. 52. 28 as population increased for these two inbreds, predicted yields reached a peak at 25,000 and 20,000 plants per acre and then declined. The 25 inbreds could be classified into three groups based on their response to increasing population from 14,600 to 18,300. (1) Oh51, Oh51A, W64A, Oh43, W22, WF9, M8116, M8211, and M81334 increased yields significantly, 9.2 to 12.1 bushels per acre. (2) 38-11, W10, W70, 38, M8132, A73, M824A, M8131, and M8206 increased 4.7 to 8.2 bushels which was not significant at the 57.. level. (3) W23, WR3, Hy2, M8130, M14, R53, and C103 showed very little or no increase in yield. The six highest yielding inbreds, averaged for all treatments, were W23, W64A, W70, Oh52A, Oh43, and RW3. The six lowest yielding inbreds were M8211, M824A, M81334, R53, M8206, and M8131, excluding C103 and 38—11 since they were very late and stands were poor. 29 Single-cross Hybrids Experiment _2_ A summary of average yields adjusted for stand by covariance, and the analysis of variance are presented in Table 15 for seed produced on single-cross hybrid WF9 x Oh51A grown in 1957 with three levels of complete fertilizer, four nitrogen sidedressing levels, and five plant populations. Since pollination was not controlled as it would be in a double-cross seed production field, the seed produced by open pollination can be considered as pseudo "double-cross" seed. Yields were not affected significantly by complete fertilizer or nitrogen sidedressing treatments. Plant population was the only factor affecting yield significantly in this experiment. Average yields were 43.2, 60.6, 69.4, 88.8, and 91.6 bushels per acre for populations of 6,100, 9,200, 11,200, 15,100 and 17,200 plants per acre. Each increase in pOpulation, except 15,100 to 17,200, produced a significant yield increase. There were no significant effects of complete fertilizer, nitrogen sidedressing, or population on moisture content which averaged 50.37.. The experiment was planted June 2, harvested October 10, and the first killing frost occurred September 27. Seed produced in this experiment was not fully mature when harvested and yields should have been higher 30 TABLE 15. AVERAGE YIELDS ADJUSTED FOR STAND AND ANALYSIS OF VARIANCE FOR SEED PRODUCED ON WF9 x Oh51A SINGLE-CROSS HYBRID AT THREE LEVELS OF COMPLETE FERTILIZER, FOUR NITROGEN SIDEDRESSING LEVELS, AND FIVE PLANT POPULATIONS - EXPERIMENT 2 12-12-12 Nitrogen fertilizer sidedressing Plants per acre pgggd§_pg£ragre pounds per acre 6,10019,200I11,200 15,100 17,2001Averaggg 0 0 48.5 53.2 62.2 81.7 92.4 67.6— 20 54.2 64.8 65.7 91.4 72.6 69.8 40 41.4 62.3 80.9 91.9 92.8 75.7 60 53.0 61.4 75.4 84.6 100.4 75.0 Average 49.3 60.4 73.3 87.4 89.6 72.0 200 0 43.5 56.2 61.1 84.0 86.4 66.2 20 31.9 59.1 71.2 81.5 84.7 65.7 40 38.1 64.7 66.5 84.8 94.7 69.7 60 44.8 59.0 69.1 94.7 88.5 71.2 Average 39.6 59.8 67.0 86.3 88.6 68.2 850 0 43.7 72.4 69.1 103.5 102.2 78.2 20 39.4 54.0 66.2 88.6 99.6 69.6 40 38.3 58.2 69.4 92.1 97.5 71.1 60 41.0 61.4 67.2 86.7 86.7 68.6 Average 40.6 61.5 68.0 92.7 96.5 71.9 Nitrogen 0 45.2 60.6 64.1 89.7 93.7 70.7 x 20 41.8 59.3 67.7 87.2 85.6 68.4 Population 40 39.3 61.7 72.3 89.6 95.0 72.2 60 46.3 60.6 70.6 88.7 91.9 71.6 Average 43.2 60.6 69.4 88.8 91.6 70.7 Analysis of variance Degrees Sum of Mean Source of freedom squares square F Replication 1 480.4 Fertilizer (F) 2 328.6 164.3 18.7 Error a 2 17.5 8.8 Nitrogen (N) 3 210.1 70.1 0.8 F x N 6 929.1 154.8 1.7 Error b 9 812.2 90.2 Population (P) 4 39082.5 9770.7 l78.2** F x P 8 701.9 87.7 1.6 'N x P 12 556.0 46.3 0.8 F x N'x P 24 1850.8 77.1 1.4 Error c 48 2632.6 54.8 Total 119 47601.7 Least significant differences--bushels per acre Level of probability Treatment 5% 1% 12-12-12 fertilizer 2.9 6.6 Nitrogen sidedressing 5.5 8.0 Pepulation 4.3 5.7 $111 two treatment means 24.8 33.0 1**Significant at 1% level of probability 31 if the crop had reached full maturity. Since no measurable effects of treatments on maturity had occurred by harvest, it is likely that yields would have increased proportionately for all treatments with a longer growing season. Specifications used for grading seed samples are given in Table 2. Grading percents and bushels per acre of each grade are summarized in Tables 16 and 17, respectively. Yields were not discounted for pollen parent rows necessary in commercial double-cross seed production. Long medium flats are separately listed to show effect of treatment on kernel length, but are included in total medium flats. Complete fertilizer and nitrogen sidedressing treatments did not affect seed grades significantly. Plant population significantly affected grading expressed as either percent or bushels per acre. As population increased, the percent of large flats and long medium flats decreased significantly and small flats increased significantly. The decrease in percent large flats was accompanied by a corresponding increase in percent small flats. Percent of medium flats and rounds were not affected by population. These data indicated that kernel width and length were reduced as population was increased. Since total yield increased with population, bushels per acre of each grade were not affected the same as grading percent. Yield of large flats was not affected while yield of medium flats, long medium flats, small flats, and rounds increased significantly as population increased. ‘Yields of medium flats, the most desirable grade in the seed trade, were 28.5, 40.1, 46.7, 59.8, and 61.2 bushels per acre for the five populations, respectively. All except the last increase were highly significant. 32 TABLE 16. AVERAGE GRADING PERCENT AND ANALYSES OF VARIANCE FOR SEED PRODUCED ON SINGLE-CROSS HYBRID WF9 x Oh51A AT THREE LEVELS OF COMPLETE FERTILIZER, FOUR NITROGEN SIDEDRESSING LEVELS, AND FIVE PLANT POPULATIONS - EXPERIMENT 2 % % Total % Long % Large medium medium Small flats flats flatsl/ flats Rounds 12-12-12 fertilizer-:pounds per acre 0 8.4 67.3 35.4 10.6 5.6 200 8.5 66.0 37.0 11.6 5.6 850 7.9 67.0 40.2 10.8 5.9 Least significant difference 5% 1.3 3.4 19.6 1.7 1.6 Least significant difference 1% 3.1 7.7 45.0 3.8 3.7 Nitrogen sidedressing--pounds per acre 0 6.8 67.2 39.6 11.5 5.7 20 7.7 67.7 37.8 10.8 5.6 40 9.4 66.0 37.0 11.0 5.7 60 9.2 66.0 35.7 10.7 5.6 Least significant difference 5% 2.3 3.8 7.4 1.4 0.6 Least significant difference 1% 3.2 5.4 10.7 2.0 1.0 Plants per acre 6,100 10.9 65.8 41.0 9.2 5.9 9,200 9.6 66.2 39.5 10.3 5.9 11,200 7.5 67.7 37.2 11.2 5.5 15,100 7.2 67.3 36.8 11.6 5.5 17,200 6.2 66.7 33.1 12.8 5.5 Least significant difference 5% 2.0 2.1 4.0 1.3 0.6 Least significant difference 1% 2.6 2.7 5.3 1.7 0.8 Analyses of variance Source DF Mean squares Replication 1 20.9 9.1 49.4 2.4 4.9 Fertilizer (F) 2 4.3 17.6 233.5 12.0 1.0 Error a 2 1.9 12.1 416.0 3.0 2.8 Nitrogen (N) 3 45.2 22.2 75.4. 3.2 0.2 F x N 6 3.5 22.6 74.0 17.3 0.3 Error b 9 14.8 41.8 161.4 5.8 1.2 Population (P) 4 88.6** 14.0 217.2** 42.7** 1.0 F x P 8 23.4 2.7 20.5 9.7 1.2 N x P 12 4.3 22.0 26.9 4.7 1.0 F x N x P 24 8.2 14.4 87.3* 5.4 1.1 Error c 48 11.3 12.6 47.7 5.0 0.9 'l/Long medium flats were separately listed, but included with total medium flats. * Significant at 5% level of probability ** Significant at 1% level of probability 33 TABLE 17. AVERAGE BUSHELS PER ACRE BY GRADE AND ANALYSES OF VARIANCE FOR SEED PRODUCED ON SINGLE-CROSS HYBRID WF9 x Oh51A AT THREE LEVELS OF COMPLETE FERTILIZER, FOUR NITROGEN SIDEDRESSING LEVELS, AND FIVE PLANT POPULATIONS - EXPERIMENT 2 Total Long Large medium medi Small flats flats flats-j flats Rounds T ‘- 12-12-12 fertilizer—-pounds per acre 0 5.9 50.1 26.2 8.0 4.0 200 5.3 44.3 24.8 7.9 3.8 850 5.4 47.5 28.1 7.7 4.2 Least significant difference 5% 0.9 7.2 15.3 0.6 1.1 Least significant difference 1% 2.2 16.6 35.3 1.4 2.5 Nitrogen sidedressing--poundsyper acre 0 4.8 50.0 29.8 8.5 4.2 20 3.7 45.9 25.3 7.6 3.8 40 5.9 45.4 25.2 7.7 3.9 60 6.2 47.7 25.2 7.7 4.0 Least significant difference 5% 1.2 5.9 7.1 1.1 0.7 Least significant difference 1% 1.7 8.5 10.2 1.5 1.0 Plantsyper acre 6,100 4.7 28.5 17.6 3.8 2.6 9,200 5.9 40.1 24.1 6.2 3.6 11,200 5.2 46.7 26.2 7.6 3.7 15,100 6.3 59.8 33.2 10.2 4.9 17,200 5.7 61.2 30.5 11.6 5.1 Least significant difference 5% 1.2 5.0 4.6 1.2 0.6 Least significant difference 1% 1.6 6.6 6.1 1.7 0.7 Analyses of variance Source DF Mean squares Replication 1 10.1 3.3 86.7 4.4 2.1 Fertilizer (F) 2 4.0 341.5 121.2 0.6 1.7 Error a 2 0.9 56.0 253.4 0.4 1.2 Nitrogen (N) 3 14.3 129.4 147.2 5.3 0.1 F x N 6 6.4 305.4 181.5 4.4 1.4 Error b 9 3.9 102.3 146.8 3.3 1.2 POpulation (P) 4 9.6 4533.3**878.4** 236.8** 25.6** F'): P 8 8.6 64.0 49.5 2.4 1.6 N x I’ 12 1.8 67.0 44.8 1.2 0.9 F x N'x P 24 5.4 78.1 71.1 3.7 0.8 Error c 48 4.4 72.6 62.0 4.6 0.9 -l/Long medium flats were separately listed, but included with total medium flats. *' Significant at 5% level of probability ** Significant at 1% level of probability 34 Experiments 1 and 1 Experiment 11 was planted on June 2, 1958 and Experiment 12 on June 10, 1958. The same treatments were applied to both of these experiments grown in the same field as Experiment 2 in 1957. Since stands were poorer in Experiment 12, resulting populations were lower than Experiment 11. Soil test results were slightly lower in 1958 but I still indicated that the field was relatively high in fertility. Plots 3 ‘74" were arranged in two-row strips between five-row lands of inbred plots ~- of Experiments 3-10 to provide additional pollen for the inbreds. Thus, I I" plant competition was reduced to some extent. Moisture contents of corn averaged 48.5 and 46.5% in Experiment 11 and 53.1 and 51.0% in Experiment 12 for the 0 and the 550 pound fertilizer treatments, respectively. Significant differences of 1.7 to 2.3% higher moisture contents for the three highest populations occurred in Experiment 11. The effect of population on moisture content was not significant in Experiment 12. Relative maturity (earliest to latest) of the five single crosses is normally Oh51 x R53, M8116 x M8211, W23 x M824, WF9 x Oh51A, and WF9 x M14. The first three hybrids are early maturing while the last two are midseason and late maturing. This order was not followed in these experiments since moisture contents of WF9 x Oh51A and WF9 x M14 averaged slightly less than those for the earlier hybrids. No explanation was apparent. Differences in shelling percent were not significant in Experiment 11 for any factor. Differences between shelling percents for the hybrids were significant in Experiment 12. since the effects on stand, moisture content, and shelling percent were either small, or inconsistent, the summarized data are not presented. 35 Fertilizer increased yields significantly, 8.7 and 7.3 bushels per' acre for Experiments 11 and 12 (Tables 18 and 19). Yields also nnxreased significantly as population increased. Average yields were 58.1, 71.4, 76.6, and 89.1 bushels per acre for populations of 7,300, 10,400, 12,800, and 17,100 plants per acre in Experiment 11 (Table 18), and 46.9, 59.2, 63.8, and 74.7 bushels per acre for average stands of l .1 7,000, 9,400, 11,200, and 14,000 plants per acre in Experiment 12 ;- T (Table 19). ; fl LBJ Grading percent was unaffected by fertilizer treatments except for the long medium flat grade in Experiment 11 where fertilizer treatment produced a significant increase in kernel length (Tables 20 and 21). Although the differences were not all significant, the percent of large flats, long medium flats, and rounds tended to decrease as population increased. Percent of medium flats was not changed significantly while percent of small flats increased significantly with increased population. ‘There were no significant differences in grading percent among the five single-cross hybrids. Yields of large flats were not affected by fertilizer or plant Ixypulation (Tables 22 and 23). Yields of all other grades tended to ixu2rease with fertilizer and higher plant populations although not all cxf the differences were significant. There were no significant ctifferences among hybrids for any of the grades in Experiment 11. Hybrid djxfferences in Experiment 12 were due to lower yields of medium flats and rounds for M8116 x M8211. 36 TYXBLE 18. AVERAGE YIELDS ADJUSTED FOR STAND AND ANALYSIS OF VARIANCE FOR SEED PRODUCED ON FIVE SINGLE-CROSS HYBRIDS WITH AND WITHOUT FERTILIZER AT FOUR PLANT POPULATIONS - EXPERIMENT ll Single-cross hybrid Plants WF9 x Oh51 x W23 x M8116 x WF9 x Fertilizer per acre Oh51A R53 M824 M8211 M14 Averaggs_ Unfertilized 7,300 55.7 58.9 53.0 54.1 54.7 55.3 10,400 69.5 63.9 67.8 65.1 74.3 68.1 12,800 69.4 71.0 73.6 73.5 68.0 71.1 lLlOO 84.7 80.9 80.4 95.5 74.9 83.3 Averages 69.8 68.7 68.7 72.0 68.0 69.5 Fertilized 7,300 59.7 58.6 57.3 68.4 60.4 60.9 10.400 84.1 77.4 76.1 67.7 68.3 74.7 12,800 77.6 84.6 92.6 76.5 79.1 82.1 17,100 93.7 103.2 90.2 93.2 94.4 94.9 Averages 78.8 81.0 79.1 76.5 75.6 78.2 Population 7,300 57.7 58.8 55.2 61.3 57.6 58.1 x 10,400 76.8 70.7 72.0 66.4 71.3 71.4 Hybrid 12,800 73.5 77.8 83.1 75.0 73.6 76.6 17,100 89.2 92.1 85.3 94.4 84.7 89.1 Hybrid averages 74.3 74.9 73.9 74.3 71.8 73.9 Analysis of variance Degrees Sum of Mean Source of freedom sqgares square F Replication 2 316.1 Fertilizer (F) 1 2267.2 2267.2 56.8* Error a 2 79.8 39.9 Population (P) 3 14859.5 4953.2 34.1** F x P 3 210.3 70.1 0.5 Error b 12 1742.2 145.2 Hybrid (H) 4 135.9 34.0 0.3 F x H 4 213.9 53.5 0.5 P x H 12 1128.9 94.1 1.0 F x P x H 12 1179.4 98.3 1.0 Error c 64 6231.1 97.4 Total 119 28364.5 Least significant differences-~bushels per acre Level ofyprobability Treatment 5% 1% Fertilizer 5.0 11.4 Population 6.8 9.5 Hybrid 5.7 7.6 w two treatment geans 27.1 35.8 * Significant at 5% level of probability id: Significant at 1% level of probability 37 TABLE 19. AVERAGE YIELDS ADJUSTED FOR STAND AND ANALYSIS OF VARIANCE FOR SEED PRODUCED ON FIVE SINGLE-CROSS HYBRIDS WITH AND WITHOUT FERTILIZER AT FOUR PLANT POPULATIONS - EXPERIMENT 12 Single-cross hybrid Plants WF9 x Oh51 x W23 x M8116 x WF9 x Fertilizer per acre Oh51A R53 M824 M8211 M14 Averages Unfertilized 7,000 45.5 44.0 41.5 39.3 46.4 43.4 9,400 59.3 54.5 50.2 54.5 58.9 55.5 11,200 58.2 60.4 60.4 61.6 65.6 61.2 14,900 80.5 69.8 83.2 39.3 76.5 69.9 Averages 60.9 57.2 58.8 48.7 61.9 57.5 Fertilized 7,000 51.6 54.8 51.1 48.1 46.7 50.4 9,400 65.1 64.7 62.3 63.2 59.2 62.9 11,200 66.3 67.7 73.3 56.4 68.1 66.4 14,000 79.5 73.6 89.2 70.2 85.0 79.5 Averages 65.7 65.2 69.0 59.5 64.8 64.8 Population 7,000 48.6 49.4 46.3 43.7 46.6 46.9 x 9,400 62.2 59.6 56.3 58.9 59.1 59.2 Hybrid 11,200 62.3 64.1 66.9 59.0 66.9 63.8 14,000 80.0 71.7 86.2 54.8 80.8 74.7 Hybrid averages 63.3 61.2 63.9 54.1 63.3 61.2 Analysis of variance Degrees Sum of Mean Source of freedom squares square F Replication 2 40.1 Fertilizer (F) 1 1608.2 1608.2 28.0* Error a 2 114.9 57.5 Population (P) 3 11909.2 3969.7 14l.2** F x P 3 77.3 25.8 0.9 Error b 12 337.0 28.1 Hybrid (H) 4 1600.5 400.2 6.5** F x H 4 277.7 69.4 1.1 P x H 12 2509.0 209.1 3.4** F x P x H 12 1154.0 96.2 1.6 Error c 64 3935.9 61.5 Total ‘ 119 23563.9 Least significant differences--bushels per acre Level of probability Treatment 5% 1% Fertilizer 6.0 13.7 Population 3.0 4.2 Hybrid 4.5 6.0 Any two treatment means 19.7 26.1 * Significant at 5% level of probability ** Significant at 1%‘leve1 of probability 38 TABLE 20. AVERAGE GRADING PERCENT AND ANALYSES OF VARIANCE FOR SEED PRODUCED ON FIVE SINGLE-CROSS HYBRIDS WITH AND WITHOUT FERTILIZER AT FOUR PLANT POPULATIONS - EXPERIMENT 11 % % Total % Long % Large medium mediuT/ Small % flats flats_1:q flats— flats Rounds Fertilizer Unfertilized 16.4 59.0 54.4 9.2 11.5 Fertilized 15.2 58.6 61.7 11.3 11.9 LSD 5% 3.6 4.9 4.8 2.2 0.3 LSD 1% 8.4 11.2 11.0 5.2 0.7 Population 7,300 17.6 59.1 63.7 7.5 13.2 10,400 16.6 58.1 59.4 10.5 11.7 12,800 15.8 59.0 58.3 11.0 11.0 17,100 13.2 58.9 50.8 12.1 11.1 LSD 5% 3.2 3.0 10.6 2.9 1.8 LSD 1% 4.5 4.1 14.8 4.1 2.5 Hybrid WF9 x Oh51A 18.8 57.9 52.8 9.1 11.3 Oh51 x R53 14.5 57.8 57.2 12.8 11.5 W23 x M824 17.8 59.3 64.7 7.4 12.5 M8116 x M8211 11.7 61.1 58.7 11.0 11.8 'WF9 x M14 16.3 57.7 57.1 11.0 10.6 LSD 5% 9.3 6.4 9.2 5.8 1.9 LSD 1% 12.4 8.5 12.2 7.7 2.5 Analyses of variance Source SIDFri Mean squares Replication 2 5.8 56.4 61.3 62.8 1.7 Fertilizer (F) 1 41.1 5.9 1562.4* 132.9 4.9* Error a 2 21.5 38.6 37.1 8.1 0.2 Population (P) 3 103.1 5.7 862.8 118.4* 30.7** F x P 3 6.9 18.0 95.7 18.6 7.1 Error b 12 32.9 27.6 373.7 27.0 3.4 Hybrid (H) 4 191.9 50.8 443.6 103.2 4.5 F x H. 4 33.2 21.8 221.6 10.1 4.6 P x.li 12 300.0 125.6 549.9* 101.0 20.5* F x P x H 12 290.2 120.5 698.6** 100.4 27.3** 'Egrpr'c 64 261.6 121.7 253.3 101.6 10.2 -' J LSD - Least significant difference -l/Percent long medium flats is the percent of total medium flats which *were long. Long medium flats were separately listed, but included with total medium flats. '* Significant at 5% level of probability '** Significant at 1% level of probability 39 TABLE 21. AVERAGE GRADING PERCENT AND ANALYSES OF VARIANCE FOR SEED PRODUCED ON FIVE SINGLE—CROSS HYBRIDS WITH AND WITHOUT FERTILIZER AT FOUR PLANT POPULATIONS - EXPERIMENT 12 % % Total % Long % Large . medium medium Small % flats flats flatsl/ flats Rounds Fertilizer Unfertilized 13.8 59.7 33.6 12.6 9.6 Fertilized 14.4 59.3 39.3 11.8 10.8 LSD 5% 3.0 2.1 5.9 2.3 3.0 LSD 1% 6.9 5.0 13.5 5.3 6.7 Population 7,000 17.9 57.3 42.0 9.5 11.7 9,400 15.3 59.7 35.9 11.1 10.3 11,200 12.3 60.0 34.3 13.7 9.9 14,000 10.9 61.0 33.6 14.7 9.0 LSD 5% 2.1 2.9 9.8 2.9 1.8 LSD 1% 2.9 4.1 13.7 4.1 2.5 Hybrid WF9 x Oh51A 19.2 59.4 34.8 8.0 11.0 Oh51 x R53 15.0 58.4 30.8 12.3 10.0 W23 x M824 10.9 61.5 39.8 13.6 9.5 M8116 x M8211 13.1 59.3 32.1 13.8 8.0 WF9 x M14 12.5 59.0 44.8 13.5 11.6 LSD 5% 9.1 6.0 13.0 6.0 2.0 LSD 1% 12.1 8.0 17.3 7.9 2.6 Analyses of variance Source ‘jlngQL Mean squares Replication 2 3.4 36.5 22.5 93.7 26.3 Fertilizer (F) 1 11.0 7.8 991.9 17.3 41.2 Error a 2 14.6 7.5 55.6 8.5 13.6 Population (P) 3 29l.1** 73.0 431.3 165.1** 38.4* F x P 3 31.2 30.2 528.4 7.1 8.2 Error b 12 13.3 26.8 303.7 27.2 10.1 Hybrid (H) 4 246.5 33.9 808.3 145.9 26.4 F x H 4 295.5 80.3 794.9 230.7 17.6 P x H 12 152.2 98.6 377.7 96.4 22.6* F x P x H 12 220.6 140.6 553.3 67.4 9.4 Error c 64 250.9 108.7 508.8 106.6 11.4 LSD - Least significant difference l/Percent long medium flats is the percent of total medium flats which were long. Long medium flats were separately listed, but included with total medium flats. * Significant at the 5% level of probability ** Significant at the 1% level of probability 40 TABLE 22. AVERAGE BUSHELS PER ACRE BY GRADE AND ANALYSES OF VARIANCE FOR SEED PRODUCED ON FIVE SINGLE-CROSS HYBRIDS WITH AND WITHOUT FERTILIZER AT FOUR PLANT POPULATIONS - EXPERIMENT 11 Total Long Large medium medium Small flats flats flatsl/ flats Rounds Discard Fertilizer Unfertilized 11.1 41.0 22.1 7.4 8.0 2.5 Fertilized 11.8 45.6 28.3 8.5 9.4 2.4 LSD 5% 3.9 6.0 5.7 3.2 0.7 1.0 LSD 1% 9.0 13.9 13.0 7.4 1.6 2.1 Population 7,300 10.4 34.3 22.2 4.5 7.7 1.3 10,400 12.1 41.2 24.7 7.2 8.5 2.5 12,800 12.2 45.2 27.0 8.2 8.6 2.5 17,100 11.0 52.5 26.9 12.1 10.0 3.7 LSD 5% 2.3 5.4 6.3 2.8 1.0 0.7 LSD 1% 3.3 7.6 9.0 4.0 1.3 1.0 Hybrid WF9 x Oh51A 14.0 42.9 23.6 6.8 7.6 2.5 Oh51 x R53 9.6 43.4 24.0 9.5 8.5 2.9 W23 x M824 13.5 43.6 28.4 6.6 9.3 1.9 M8116 x M8211 8.4 45.4 26.8 9.0 8.9 2.7 WF9 x M14 11.7 41.2 23.2 8.1 7.5 2.5 LSD 5% 6.7 5.7 5.8 5.0 1.8 1.1 LSD 1% 8.9 7.6 7.8 6.6 2.4 1.5 Analyses of variance Source IDFJT Mean squares Replication 2 8.1 33.4 42.2 34.2 0.3 0.5 Fertilizer (F) 1 13.9 18.8 1161.3* 38.1 56.6* 0.3 Error a 2 24.7 58.7 51.5 16.6 0.8 1.3 Population (P) 3 22.3 l754.4** 156.3 299.3** 25.1** 27.4** F x P 3 9.8 43.0 67.0 33.6 6.4 1.5 Error b 12 17.3 92.5 127.3 25.0 2.9 1.6 Hybrid (H) 4 141.5 55.8 126.4 37.6 3.3 3.5 F x H 4 25.8 28.8 16.3 13.8 1.6 2.6 P x H ' 12 172.1 32.3 108.0 54.8 15.8 3.5 F x P x H 12 146.3 48.7 116.5 57.4 16.7 2.3 Error c 64 133.8 98.4 101.5 74.6 9.7 3.9 LSD - Least significant difference / "Long medium flats were separately listed but included with total medium flats. * Significant at 5% level of probability ** Significant at 1% level of probability 41 TABLE 23. AVERAGE BUSHELS PER ACRE BY GRADE AND ANALYSES OF VARIANCE FOR SEED PRODUCED ON FIVE SINGLE-CROSS HYBRIDS WITH AND WITHOUT FERTILIZER AT FOUR PLANT POPULATIONS - EXPERIMENT 12 Total Long Large medium medium Small _ flats flats flatsl/ flats Rounds Discard FErtilizer Unfertilized 7.9 34.6 12.5 7.4 5.6 2.4 Fertilized 9.0 38.6 15.0 7.6 6.9 2.5 LSD 5% 1.4 8.0 0.8 4.4 1.3 0.1 LSD 1% 3.2 18.3 1.7 10.1 3.0 0.3 Population 7,000 8.5 26.8 11.6 4.4 5.5 1.7 9,400 9.2 35.4 13.3 6.4 6.2 2.2 11,200 8.0 38.2 14.1 8.6 6.5 2.7 14,000 8.1 46.0 16.1 10.8 6.9 3.2 LSD 5% 1.5 3.7 4.4 1.9 1.2 0.5 LSD 1% 2.1 5.2 6.2 2.7 1.7 0.8 Hybrid WF9 x Oh51A 12.2 37.5 13.2 5.0 7.0 1.6 Oh51 x R53 8.8 36.1 11.0 7.6 '6.0 2.7 W23 x M824 6.6 39.6 16.2 8.8 6.0 2.9 M8116 x M8211 7.0 32.4 11.3 7.3 5.1 2.5 WF9 x M14 7.5 37.4 17.2 9.0 7.3 2.4 LSD 5% 5.4 4.3 5.7 3.8 1.5 0.9 LSD 1% 7.2 5.7 7.6 5.0 2.0 1.2 Analyses of variance Source [DFI Mean squares Replication 4*72 1.3 2.6 19.3 38.6 12.5 0.7 .Eertilizer (F) 1 37.5 469.3 l84.5** 1.4 53.1* 0.3 ‘Error a 2 3.2 102.9 0.9 31.3 2.7 0.1 Population (P) 3 8.5 1882.3** 105.2 228.9** 8.9 l3.3** F x P 3 13.6 23.7 98.8 0.5 3.5 2.2 Error b 12 7.1 43.6 61.9 11.6 4.5 0.9 Hybrid (H) 4 122.9 171.0* 190.2 60.8 19.0* 5.5* .F x H 4 95.2 45.9 80.4 28.7 6.6 3.1 P x H 12 62.9 92.7 91.2 56.2 10.2 2.5 IF x P x H 12 63.2 60.0 88.8 26.4 4.2 3.2 Error c 64 87.3 55.5 98.9 42.7 6.5 2.3 ZLSD - Least significant difference JL/Long medium flats were separately listed but included with total medium flats. *r Significant at 5% level of probability ** Significant at 1% level of probability 42 The 4.6% higher moisture and 3.3% lower shelling percent of Experiment 12 probably resulted from planting eight days later than Experiment 11. While plant population averaged 11,900 and 10,400 for the two experiments, at least part of the 12.7 bushel yield difference was due to the difference in planting dates. Average grading percents were 15.8 and 14.1% large flats, 58.8 and 59.5% total medium flats, 58.1 and 36.5% long medium flats, 10.3 and 12.2% small flats, and 11.7 and 10.2% rounds for Experiments 11 and 12, respectively (Tables 20 and 21). Average income per acre (Table 24) for Experiment 11 was $316, $380, $404 and $463 for unfertilized plots and $345, $416, $458 and $524 for fertilized plots at populations of 7,300, 10,400, 12,800, and 17,100 plants per acre, respectively. Estimated wholesale prices for Michigan certified seed were used in these calculations. Yields were reduced 25% to compensate for pollen parent rows not usually harvested for seed. The usual planting pattern for double-cross seed production is six seed parent rows and two pollen parent rows. 43 TABLE 24. AVERAGE YIELDSl/ AND GROSS INCOME FOR GRADES OF SEED AT ALL LEVELS OF SOIL FERTILITY AND PLANT POPULATION FOR ALL HYBRIDS IN EXPERIMENT 11 Bushelsyper acre for each grad; — Fertilizer Total Plants Pounds Large medium/ Small Pollen per acre per acre flats flats— flats Rounds Discard parent Total 7,300 None 7 6.3 24.1 2.6 5.0 3.5 13.8 55.3 550 7.7 25.6 3.4 5.3 3.8 15.1 60.9 10,400 None 8.3 28.2 4.2 5.5 5.3 17.0 68.5 550 8.1 31.1 5.5 5.9 5.0 18.6 74.2 12,800 None 8.3 29.7 6.1 5.0 5.6 18.0 72.7 550 8.2 35.5 5.0 6.5 5.2 20.0 80.4 17,100 None 7.1 35.6 7.1 6.0 6.8 20.8 83.4 550 7.7 39.3 9.2 7.4 7.5 23.8 94.9 Gross income from seed Grade and wholesale price per bushel Total Fertilizer Large medi / Small Pollen Plants Pounds flats flats- flats Rounds Discard parent Total per acre yper acre $6.50 $8.90 $5.50 $5.50 $1.00 $1.00 ($12 7,300 None 41 215 14 28 4 14 316 550 50 228 19 29 4 15 345 10,400 None 54 251 23 30 5 17 380 550 53 277 30 32 5 19 416 12,800 None 54 264 34 28 6 18 404 550 53 316 28 36 5 20 458 17,100 None 46 317 39 33 7 21 463 550 50 350 51 41 8 24 524 l/Yields of graded seed were discounted 25%, to compensate for pollen parent rrnws not usually harvested for seed, and an additional 10% (included in dijuzard) to adjust these yields for short and damaged kernels which would normally be graded out. 33./Since long and short medium flats normally sell for the same price, only total medium flats were reported for income computing purposes. DISCUSSION Inbred Lines Seed yields on inbred plants were as high as 46.9 bushels per acre for Oh51 in 1957 and 69.6 for W23 in 1958. These yields were considerably higher than those usually reported for foundation inbred and single-cross seed in Michigan. In commercial foundation single-cross seed production fields, one row of the pollinator inbred usually provides pollen for two to four rows of the detasseled or male-sterile seed parent inbred depending on amount of pollen produced by the pollinator. Adequate pollen at the right time is frequently a limiting factor in single-cross seed production. The objective in these experiments was to investigate the effects of fertilizer and plant population on single-cross seed yields without the variation due to pollination. Therefore, two rows of single—cross hybrids were planted later between every five or six rows of inbreds to provide pollen in addition to that of the inbreds. Thus, pollination was not a limiting factor except for the two late inbreds C103 and 38-11 which also had poor stands. In commercial single-cross seed production, 20% to 33 1/3% of the seed is discarded as sib-pollinated from the pollinator parent. Acre yields reported from these experiments have not been discounted for pollinator rows. 45 Obtaining a satisfactory stand from inbred seed is a major factor in commercial single-cross seed production. Cold-test germination and seed treating will aid in calculating the seeding rate to more nearly assure a given plant population. Starter fertilizer placed to the side and below the seed in the row may promote faster seedling growth and thereby aid in weed control. Variations in stand also occurred in these I experiments. These effects were adjusted by covariance analyses which p adjusts the yield of each plot for its deviation from the average stand * of the particular treatment involved. [ 1 Neither WF9 nor Oh51 were fully matured in Experiment 1 and only three (W23, M8206, and R53) of the 25 inbreds were mature--below 40% moisture at harvest-~in Experiments 3-10. These experiments were planted on June 2 and May 24. Since fertilizer and population treatments did not affect maturity, it is likely that yields would have increased jproportionately for all treatments with full maturity and that main (effects and interactions of treatments would change very little. Inbreds (Develop and mature more slowly than hybrids. Early planting and a favorable growing season are necessary to reach full maturity and obtain Inaxinnmlyields. Since germination and seedling vigor of inbred seed are laner than for hybrid seed, planting is usually delayed until soil temperatures have warmed to 50°F or above. High residual soil fertility as indicated by soil tests may have liJnited the response to fertilizer. Also, plant populations may not have 'beeui high enough to effectively utilize the added fertilizer. All inbreds prtflaably would not respond to further increases in population since some dirl not show much increase at the highest population. 46 When Duncan's method (2) of predicting yields at various populations was applied to the data in Experiments 3-10, the predictions indicated that population for some inbreds could be increased to 35,000 plants per acre before yields failed to increase. The highest predicted yield at 30,000 plants per acre was 82.0 bushels per acre for Oh51 compared to the actual yield of 61.7 bushels with 18,300 plants. Duncan (2) reported I that yields of dwarf and semi-dwarf corn maintained a linear relationship 4 to 78,000 plants per acre. Since competition by inbred plants for plant : nutrients and moisture would be less than that of hybrid plants, inbred I plant populations might be increased more than hybrid populations for maximum production. Only one year's data are provided by these experiments to classify the 25 inbreds for predicting hybrid combinations that might be adapted to high levels of fertility and plant population. Since interactions of inbreds with environment are usually greater than interactions of hybrids, further testing of these lines would be helpful and necessary for more precise classification. Correlations of inbred and hybrid performance for many characteristics including combining ability are usually low so that prediction of hybrid performance from inbred data is difficult. Sixuze relatively little information is available on the correlation of ixflyred with hybrid response to fertility and population stress, it seemed desirable to attempt to classify a group of inbreds and then evaluate their hybrid progeny. Single-cross and double-cross hybrids from inbreds in groups 1 arui 3 should be compared for their ability to respond under high 47 population pressure. Using the letters H and L to indicate inbreds in groups 1 and 3, respectively, and numeral subscripts to indicate inbreds within a group, the following pedigrees are examples of some comparisons that should be evaluated. (H1 x (L1 x (H1 X (H1 X (H1 X (H1 x If ability to respond to H2) (H3 x L2) (L3 X population H4) 1.4% L 1 L2) L2) pressure proves to be dominant in its inheritance, then one or two lines with low ability in the double-cross pedigree may not greatly alter the performance contributed by the other two or three inbreds possessing high abilities. If this ability proves to be largely recessive, then probably all four inbreds in the pedigree will need to be capable of responding to population pressure. Information concerning dominance relationships can be obtained from the single-cross data when it is available. from the single-cross data will also aid in determining the double-cross pedigrees to be evaluated. Single-cross Hybrids Experiments with single-cross hybrids to study double-cross seed production were conducted during two seasons, 1957 and 1958, in the same field. The Conover loam soil was in relatively high state of fertility as indicated by soil tests. In 1957,following alfalfa, there was no significant effect from 12-12-12 fertilizer applied either as 200 pounds of 12-12-12 in the row or 650 pounds plowed down and 200 pounds in the row. Double-cross predictions :fififll . ' \LJ 48 Sidedressed nitrogen at 20, 40, and 60 pounds per acre did not affect yields. Soil tests for the 1958 crop were a little lower than 1957 but still indicated relatively high fertility. There were no consistent differences in soil tests on 1958 samples taken from the three 1957 fertility levels. Significant average increases of 8.7 and 7.3 bushels were obtained in 1958 from 550 pounds of 15-15-15 applied in the row and 40 pounds sidedressed nitrogen for the two dates of planting, June 2 (Experiment 11) and June 10 (Experiment 12). The average increases from fertilizer in Experiment 11 were 5.6, 6.6, 11.1,andlju6 bushels per acre for populations of 7,300, 10,400, 12,800, and 17,100, respectively. In Experiment 12, fertilizer increased average yields 7.0, 7.4, 5.2, and 9.6 bushels per acre for populations of 7,000, 9,400, 11,200, and 14,000. Benefits from fertilizer were increased at the higher populations. These results illustrate the importance of maintaining high populations to utilize the added fertilizer. While significant increases from fertilizer may not always occur, the possibilities for appreciable gain warrant judicious fertilizer applications based on soil test, previous cropping history, soil type, and plant population. All three experiments were planted late (June 2 and 10) and none of the seed had reached full maturity at harvest. Since there were no consistent fertilizer effects on maturity, it does not seem likely that a longer growing season would have changed the relative differences between yields from fertilized and unfertilized plots. 49 Immaturity, 50.3%, 47.5%, and 52.1% average moisture at harvest for the three experiments planted June 2 and 10, demonstrates the importance of earlier planting to obtain maximum seed yields and quality. Killing frosts occurred on September 27, 1957 and October 6, 1958 and the experiments were harvested October 10, 1957 and October 15, 1958. Plant population was the most important factor affecting double- l cross seed yields. In 1957 (Experiment 2), average seed yields increased :6 f progressively from 43.2 to 91.6 bushels per acre as population increased I i from 6,100 to 17,200. In 1958, average yields increased from 58.1 to 3‘44 89.1 bushels as population increased from 7,300 to 17,100 in Experiment 11 ' and from 46.9 to 74.7 with population increases from 7,000 to 14,000 in Experiment 12. In double-cross seed fields, plant populations are usually less-- about 10,000 to 12,000--than those used for grain production. Seed producers have felt that the production of the preferred medium flat grade would be reduced at higher populations. In some cases with seed parents that grade a high percent large flats, population has been increased in order to increase the production of medium flats. Detasseling can be more accurate and easier at lower populations. Increasing use of male sterile seed parents to eliminate detasseling would seem to remove the latter objection of seed producers toward increased population in seed fields. Kernel width and length were reduced as population increased. These changes in kernel dimensions were reflected in a decrease in percent large flats and a corresponding increase in small flats. The percent medium flats remained relatively unchanged with increased population. 50 Percent long medium flats decreased at higher population but this is of relatively little consequence since the long and the shorter medium flats are both marketed as medium flats. When expressed as bushels of graded seed per acre, the production of large flats remained the same, and the production of medium flats, small flats, and rounds increased. The consistent results obtained from increased plant population I for the seed parents used in these experiments seem to warrant more 5 serious consideration by seed producers toward increasing plant population in double-cross seed production. { SUMMARY Several fertilizer and plant population treatments were evaluated for effects on seed production with inbred lines and single-cross hybrids in 1957 and 1958 on a Conover loam soil, testing high in residual fertility, in Ingham County, Michigan. Corn did not reach full maturity in any of the experiments. Average increases in yields from fertilizer were not significant for inbreds in either year, nor significant for single-cross hybrids in 1957, but were significant for single-cross hybrids in 1958. Plant population was the most important factor affecting seed yields. Inbred lines Seed yields on WF9 and Oh51 inbreds in 1957 were not affected significantly by complete fertilizer treatments of either 200 or 850 pounds 12-12-12 per acre. Sidedressed nitrogen applications of 20 and 40 pounds per acre did increase yields significantly but there was no difference between the 20 and 40 pound rates. Average yields increased signigficantly from 17.8 to 38.4 bushels per acre as population was increased from 5,500 to 16,000. The highest seed yields were 43.1 and 46.9 bushels per acre for these two inbreds. Fertilizer effects on seed yields of 25 inbreds in 1958 were not significant. Average yields increased significantly frmm 26.8 to 50.3 Insshels per acre as population increased from 7,500 to 18,300. Good 52 agreement was obtained between actual yields and predicted yields using Duncan's method (2). Predicted yields continued to increase up to 30,000 plants per acre for most inbreds and a few predicted yields increased to 40,000 population. As population was increased from 14,600 to 18,300: (1) yields of Oh51, Oh51A, W64A, Oh43, W22, WF9, M8116, M8211, and M81334 increased significantly 9.2 to 12.1 bushels, (2) 38-11, W10, W70, B8, M8132, A73, M824A, M8131, and M8206 increased 4.7 to 8.2 bushels which were not significant at the 5% level, and (3) W23, WR3, Hy2, M8130, M14, R53, and C103 showed little or no increase in yield. Single-cross hybrids In 1957 (Experiment 2), average yield and grading of seed from WF9 x Oh51A were not significantly affected by complete fertilizer and nitrogen sidedressing treatments. Yields averaged 43.2, 60.6, 69.4, 88.8, and 91.6 bushels at populations of 6,100, 9,200, 11,200, 15,100, and 17,200 plants per acre, respectively. Each increase except the last was significant. In 1958 (Experiments 11 and 12), five single-cross hybrids averaged 11.6 and 9.6 bushels more when fertilized with 550 pounds of 15-15-15 and 40 pounds sidedressed nitrogen per acre at the highest plant populations. As population increased from 7,300 to 17,100 in Experiment 11, average yields increased significantly from 58.1 to 89.1 bushels. When population increased from 7,000 to 14,000 in Experiment 12, average yields increased from 46.9 to 74.7 bushels. 53 In both years, kernel width and length were reduced as population increased. about the increased. increased increased. Percent large flats decreased and small flats increased same amount while medium flats remained unchanged as population Production per acre of medium flats, small flats, and rounds and production of large flats remained unchanged as population LITERATURE CITED 1. Airy, John M., in Sprague, Corn and Corn Improvement, Academic Press, New York, 1955, pp. 383-386, 404, 405. 2. Duncan, W. G., The relationship between corn population and yield, Agronomy Journal, Vol. 50:82-84, 1958. 3. Rather, H. C., and Marsten, A. R. A study of corn maturity, Michigan Agricultural Experiment Station Quarterly Bulletin, Vol. 22, No. 4, 1940. 100:8 P . . T:- ..p {Ev}; «I 13.x. 02$ 1 L "Y UNI "1111111111111” 1 ”11111111111311411“ 3 129314082 6931