Statistical Modeling and Assessment of Effects of Rainfall and Fertilizer on Sustainable Soybean Productivity under Semi-Arid Vertisols

An attempt is made in this paper to assess the fertilizer treatment effects on soybean yield under permanent manorial experiments conducted during 1999 to 2006 and select an efficient treatment for attaining sustainable yield in a semi-arid vertisol at Indore. The trials were conducted in maize, soybean and soybean + maize blocks with 12 treatment combinations of N through urea, compost and green leaf sources along with a common dose of P. 80 kg N + 60 kg P/ha gave a significantly higher mean soybean equivalent yield of 1927, 2297 and 1760 kg/ha with a yield increase of 67.0, 55.5 and 42.0% over control in maize, soybean + maize and soybean blocks respectively. The regression models indicated that June and September rainfall had a positive effect, while July and August rainfall had a negative effect on yield attained in maize and soybean + maize blocks. However, July and September rainfall had a positive effect compared to negative effect of June and August rainfall in soybean block. The yield had a better predictability of 0.56 (15 kg N (green leaf) + 10 kg N (urea)) to 0.78 (15 kg N (green leaf) + 20 kg N (urea)) in soybean + maize, followed by 0.42 (80 kg N + 60 kg P/ha and 15 kg N (compost) + 10 kg N/ha (green leaf)) to 0.61 (control) in maize and 0.15 (40 kg N + 30 kg P/ha) to 0.32 (25 kg N (compost) + 15 kg N (urea) + Azotobacter @ 2 kg/ha) in soybean block. 80 kg N + 60 kg P/ha had a maximum sustainable yield index of 45.0% in soybean + maize and 47.8% in soybean block, while 40 kg N + 30 kg P/ha had a maximum of 33.2% in maize block. Based on ranks assigned to treatments for yield and regression parameters, 80 kg N + 60 kg P/ha was superior in soybean + maize and soybean blocks, while 40 kg N + 30 kg P/ha was superior in maize block for attaining sustainable yield over years in a semi-arid vertisol.