Optimizing dry and wet tillage for rice on a Gangetic alluvial soil: Effect on soil characteristics, water use efficiency and productivity of the rice–wheat system

The effect of puddling in reducing water and nitrogen losses, and increasing rice (Oryza sativa L.) yields and N uptake depends on its intensity and also on the level of pre-puddling tillage, although an increase in the intensity of these operations involves excessive energy and may lead to a negative effect on the yield of succeeding wheat (Triticum aestivum L.) due to sub-soil compaction. A 3-year field experiment was conducted on a sandy loam (Typic Ustochrept) soil of Modipuram, India to study the interactive effects of pre-puddling tillage and puddling intensity on irrigation water productivity (IWP) in rice, the concentration of nitrate-N in the soil profile, and the performance of rice and wheat crops. Treatments included 3 levels of pre-puddling tillage – discing followed by a tine-cultivation and planking (T₁), discing followed by 2 tine-cultivations and planking (T₂), or discing followed by 4 tine-cultivations and planking (T₄); and 3 puddling intensities, i.e. 1, 2 or 4 passess of a puddler in ponded water (P₁, P₂ and P₄, respectively), each followed by planking. Increasing tillage levels from T₁P₁ to T₄P₄ decreased irrigation water requirement by 22–25%, and increased rice grain yield by 1.6–2.2tha⁻¹ and IWP by 0.26–0.34kgm⁻³ in different years. The post-rice nitrate-N concentration in the soil further indicated the advantage of puddling in retaining more nitrate-N in the upper profile, i.e. effective root zone. There was a significant (p≤0.05) interaction between pre-puddling tillage and puddling intensity on puddling index, which was the highest (0.63–0.65) under T₄P₄ during all years. Treatment T₄P₄ also increased bulk density over T₁P₁, especially at 28–33cm depth. This sub-soil compaction led to decreased wheat root mass density and wheat grain yield; the adverse effect of excessive puddling on wheat yield increased with time. The present study indicated 2 pre-puddling tillage operations followed by 2 passes of puddler, i.e. T₂P₂ as the optimum tillage combination with respect to energy efficiency in rice, total annual productivity and economic returns of the rice–wheat system.