Tilth index: an approach to optimize tillage in rice–wheat system

This study was conducted to determine a tilth index from tillage induced soil physical properties and grain yield to optimize tillage in rice–wheat system. The experiment was conducted in a silty clay loam (Aquic hapludoll) associated with a shallow water table fluctuating between 0.02 and 0.96 m from the surface. Tillage treatments for rice were puddling by four passes of rotary puddler (PR), reduced puddling (ReP), conventional puddling (CP) and direct seeding without puddling (DSWP) in four replications. Tillage treatments for wheat were zero tillage (ZT) and conventional tillage (CT) superimposed over the plots of rice tillage treatments. Measurements were made of puddling index and specific volume (only in the rice season), bulk density, saturated hydraulic conductivity, infiltration rate, plasticity index, porosity and organic carbon in the rice and wheat seasons. Rice yield in the PR plots was highest and statistically equal to that in the ReP plots but wheat yield was highest in the DSWP plots under ZT condition and was statistically equal to that in the ReP plots. index (TI) was determined in two ways: one by the model suggested by Singh et al. [Trans. ASAE 35 (6) (1992) 1777] and the second by a proposed regression model. The proposed regression model utilizes soil physical properties having significant influence on crop yield. As per the Singh et al. model, wheat yield increased linearly with increasing TI from 0.75 to 0.89 but rice yield decreased with increasing TI from 0.67 to 0.81. Both TI and its relation with rice yield were contrary to their observations. The proposed regression model showed a value of TI in the range of 0.74–0.87 for rice soils and 0.86–1.0 for wheat soils as indicators of TI for optimum yields of rice and wheat. A high TI corresponds to low tillage both for rice and wheat. The optimum yield with minimum tillage operations coincided with TI obtained in ReP plots of rice and in ZT plots of wheat under ReP conditions. Results thus show that the quality of soil puddle obtained by half the efforts in PR and CP was sufficient for optimum yields of rice. Similarly, wheat sowing by zero-till drill in such a reduced puddling plots of rice was sufficient for optimum yields of wheat in Tarai soils associated with shallow water tables. The proposed regression model is simple and compatible to use in the existing crop growth models, such as in DSSAT 3.5, with suitable alterations.