Optimization of fertilizer schedules in fallow and groundnut-based cropping systems and an assessment of system sustainability

Abstract

Low native soil nitrogen (N) and phosphorus (P) availability coupled with their low level of application through fertilizer is a major constraint limiting the productivity of groundnut-based cropping systems in India. We, therefore, evaluated in a 4-year field experiment (1994/1995–1997/1998) the optimum fertilizer-NP schedules for post-rainy season crops and sustainability of groundnut-based cropping systems based on total system productivity (TSP), sustainable yield index (SYI), agronomic efficiency (AE), partial factor productivity (PFP) and soil organic carbon (SOC). One fallow treatment was maintained for comparison. The treatments comprised two rainy season treatments (groundnut and fallow) and five post-rainy season crops (wheat, mustard, chickpea, sunflower and summer groundnut), each crop being tested at four nitrogen and phosphorus levels (0, 50, 100 and 150% recommended NP). The economic optimum NP (kg ha −1) rates of post-rainy season crops estimated from response curves were 203.2 (N=155.9, P=47.3) and 188.5 (N=145.0, P=43.5) for wheat; 68.5 (N=42.5, P=26.0) and 66.3 (N=41.4, P=24.9) for mustard; 28.7 (N=15.1, P=13.6) and 26.2 (N=13.8, P=12.4) for chickpea; 68.6 (N=47.3, P=21.3) and 52.0 (N=35.9, P=16.1) for sunflower; 68.5 (N=36.8, P=31.7) and 55.1 (N=29.6, P=25.5) for summer groundnut in groundnut and fallow-based systems, respectively. The TSP was 128.8% higher in groundnut-based than in fallow-based systems and was in the order, groundnut–groundnut (2.43 t ha −1)> groundnut –chickpea (2.23 t ha −1)> groundnut –wheat (1.96 t ha −1)> groundnut –mustard (1.90 t ha −1)> groundnut –sunflower (1.78 t ha −1). The SYI was greater in groundnut–groundnut (0.673) and low was in the groundnut–mustard (0.376) system. Values of AE for N (AE N) and P (AE P), and PFP for N (PFP N) and P (PFP P) were greater in summer groundnut. The SYI increased significantly due to 100% NP level, whereas AE N, AE P, PFP N and PFP P were greater at 50% NP level than at 100% NP level. The SOC declined in all the treatments after 4 years except in wheat plots. The available P status of soil showed a significant build up due to continuous application of fertilizer NP. Groundnut–groundnut and groundnut–wheat systems were found to be productive and sustainable cropping systems as these had greater TSP, SYI and highly significant effect of SOC on yield ( R 2=0.92 and 0.86, respectively, ∗P<0.05 ).