Effect of change in irrigation frequency and fertilizer level on the yield, water productivity, root traits and water footprint of cowpea

Field research was conducted on cowpea (variety, Pusa Dharani) during the summer season in New Delhi, India. Irrigation frequency was determined based on tensiometer readings corresponding to different soil moisture thresholds during cowpea cultivation. The study aimed to identify the optimum irrigation frequency for improving cowpea yield, water use efficiency and productivity using 4 irrigation treatments and 3 fertilizer treatments. Irrigation was scheduled at soil moisture thresholds of 90%, 80%, 75% and 70% of field capacity, respectively. Based on tensiometer readings, irrigation was applied to restore the soil moisture to the percentage of field capacity. Fertigation at F1:100%, F2:80% and F3:60% of recommended NPK were tested. In the field trial, the highest cowpea yield, of 12.2 t/ha, and maximum water productivity of 3.7 kg/m3 was obtained with irrigation scheduled at a soil moisture threshold of 80% field capacity and 100% of recommended dose of fertilizer (RDF) applied through fertigation. Lower yield was observed under irrigation scheduled at a soil moisture threshold of 70% of field capacity with 60% RDF through fertigation. The depth of irrigation water applied through the drip irrigation system was 330 mm whereas the depth of water applied in surface irrigation was 486 mm. It is recommended to maintain 80% field capacity soil moisture at the effective root zone with alternate day irrigation frequency in order to obtain good yield and maximum water productivity in cowpea. Regression models of cowpea yield were calibrated to different shoot and root parameters for efficient prediction of yield. The rank sum and sustainable yield index (SYI) revealed that treatments with lower rank sums produced higher yield stability, with I2F1 showing the lowest rank sum (6 and 4) and the highest SYI (98.4% and 96.0%). Water footprint analysis further indicated that soil-moisture-based drip irrigation was more efficient, requiring approximately 270 L of water to produce 1 kg of cowpea, compared with 525 L/kg under surface irrigation.