Soybean-chickpea rotation on Vertic Inceptisols II. Long-term simulation of water balance and crop yields

In rainfed agriculture, climatic variability has profound effects on the pe rformance of management systems in improvements of productivity and use of natural resources. A held study was conducted on a Vertic Inceptisol during 1995-1997 seasons at the ICRISAT Center, Patancheru, India, to study the e ffect of two landforms, i.e., broadbed-and-furrow (BBF) and flat, and two s oil depths (shallow and medium-deep) on crop yield and water balance of a s oybean-chickpea rotation. Using two seasons experimental data, a soybean-ch ickpea sequencing model was evaluated and used to extrapolate the results o ver 22 years of historical weather records. The simulation results showed t hat in 70% of years total runoff for BBF was greater than 35 mm (range 35-1 90 mm) compared to greater than 60 mm (range 60-260 mm) for flat on the sha llow soil. In contrast on the medium-deep soil it was greater than 70 mm (r ange 70-280 mm) for BBF compared to greater than 80 mm (range 80-320 mm) fo r the flat landform. The decrease in runoff on BBF resulted in a concomitan t increase in deep drainage for both soils. In 70% of years, deep drainage was greater than 60 mm (range 60-390 mm) for the shallow soil and ranged fr om 10 to 280 mm for the medium-deep soil. In 70% of years, the simulated so ybean yields were greater than 2200 kg ha(-1) (range 2200-3000 kg ha(-1)) a nd were not influenced by landform or soil depth. In the low rainfall years , yields were marginally higher for the BBF than for the flat landform, esp ecially on the shallow soil. Simulated chickpea yields were higher for the medium-deep soil than for the shallow soil. In most years, marginally highe r chickpea yields were simulated for the BBF than for the flat landform on both soil types. In 70% of years, the chickpea yields were greater than 500 kg ha(-1) (range 500-1500 kg ha(-1)) for the shallow soil, and greater tha n 800 kg ha(-1) (range 800-1960 kg ha(-1)) for the medium-deep soil. Total productivity of soybean-chickpea rotation was greater than 3000 kg ha(-1) ( range 3000-4150 kg ha(-1)) for the shallow soil and greater than 3450 kg ha (-1) (range 3450-4700 kg ha(-1)) for the medium-deep soil in 70% of years. These results showed that in most years BBF, landform increased rainfall in filtration into the: soil and had marginal effect on yields of soybean and chickpea. Crop yields on Vertic Inceptisols can be further increased and su stained by adopting appropriate rain water management practices for exploit ing surface runoff and deep drainage water as supplemental irrigation to cr ops in a watershed setting. (C) 1999 Elsevier Science B.V. All rights reser ved.