Evaluation of pigeonpea - white yam (cajanus cajan [l] millsp - dioscorea rotundata [l] poir) cropping system for improved yam productivity and livelihood of smallholder farmers

Yam (Dioscorea spp.) production along the West Africa yam belt is a major contributor to deforestation and soil degradation resulting from shifting cultivation practice in search of fertile land and stakes for yams to climb. This study reports on, field evaluation, simulation evaluation, and economic analysis of integrating pigeonpea into the yam cropping system described as pigeonpea-yam cropping system for improved and sustained yam production on continuously cropped fields. The study was conducted in the forest and forest-savannah transition agro-ecological zones of Ghana in 2017, 2018, and 2019 cropping seasons. In 2017, pigeonpea arrangement options of pigeonpea in an alley (PA), pigeonpea as a border (PB), sole pigeonpea, and no pigeonpea field were laid-out at Fumesua and Ejura in the forest and forest-savannah transition zones respectively. These arrangements considered the ability to obtain enough pigeonpea biomass and stakes for the yam production in the 2018 and 2019 cropping seasons. The study used an integrated soil fertility management of pigeonpea biomass and fertilizer for yam production in both locations in the 2018 and 2019 cropping seasons. The treatments were arranged in a split-plot design in 3 replications with cropping system (yam in PA, Yam in PB and sole yam) and inorganic fertilizer level (No fertilizer, half rate - 23-23-30 N-P2O5-K2O kg/ha and full-rate - 45-45-60 N-P2O5-K2O kg/ha) as main plot and subplots respectively. Significantly (P < 0.05) higher sunlight reached the yam leaves above-canopy (AC), mid-canopy (MC), and below-canopy (BC) of the sole yam fields than the leaves of yam in PB and PA. The lower sunlight reaching these various canopy levels resulted in a significant (P < 0.05) suppression of weeds in the PA than PB compared to sole yam fields for both locations and years. The N and other nutrient contributions, moisture conservation from the pigeonpea biomass and maintained bulking medium (ridges), resulted in a significant (P < 0.05) higher and similar tuber yield per stand and total tuber yield recorded for the pigeonpea-yam fields with a half and full fertilizer rates in both locations and years. Land Equivalent Ratio (LER) indicated productivity efficiency with the pigeonpea-yam intercropping systems than sole yam production with about 27 - 63% and 34 - 68% more land needed for the sole yam to produce yam as in a pigeonpea-yam intercrop for Fumesua and Ejura respectively across years. The Systems Approach to Land Use Sustainability (SALUS) crop model evaluated the long-term (10 years) implication on Integrated Soil Fertility Management (ISFM) of pigeonpea residue and fertilizer. The results revealed, the use of pigeonpea residue, pigeonpea residue in addition to a half and full recommended inorganic fertilizer rate improved the dry tuber yield range to 4.52-7.26 t/ha, 5.80-8.84 t/ha and 7.0-9.99 t/ha, respectively, indicating the influence of the pigeonpea residue in sustaining long-term yam tuber yield. Even when a farmer has no access to fertilizer, the use of pigeonpea residue alone presents a better sustainable yam production option than the use of inorganic fertilizer alone for sole yam production. The economic analysis results revealed, planting yam with pigeonpea (PA and PB) without fertilizer had better IER than planting sole yam with full fertilizer rate in both locations. Planting yam with pigeonpea (PA and PB) with half fertilizer rate presented a slightly lower Net Profit Value (NPV) and Internal Rate of Return (IRR) than planting yam with pigeonpea (PA and PB) with full fertilizer rate; however, the difference in values would only result in marginal income gain. These evaluations thus indicate Integrated Soil Fertility Management (ISFM) with pigeonpea in a pigeonpea-yam cropping system would provide stakes for staking the yams, biomass for improving soil and yam productivity, and profit to smallholder farmers. Therefore, promoting farmers' adoption would sustain yam production on continuously cropped fields to address the deforestation associated with yam production along the West Africa yam belt.