Response of Rice to Tillage, Wheat Residue and Weed Management in a Rice-Wheat Cropping System

In Nepal and elsewhere in the Indo-Gangetic plains where rice-wheat is a major crop rotation, interest in conservation practices such as direct-seeding of rice on zero-tilled soil and retention of crop residue is increasing. However, the use of herbicide is increasing in the region due to a shortage of labor and its ease of operation compared to manual weeding. This field experiment was conducted to identify the response of rice to tillage and planting systems, level of wheat residue retention and weed managements under rice-wheat cropping system. This study was conducted during three growing seasons of rice (June through November) in 2014, 2015 and 2016 at the National Wheat Research Program (NWRP), Rupandehi, Nepal. The experiment was conducted in a split-split plot design. Tillage and planting systems were the main plots where rice was either transplanted on puddled field managed with conventional tillage (CT) or direct seeded on zero till (ZT) soil. The level of residue retention was the sub-plot which included three levels of residue retention as whole (WR), partial (PR) or no (NR) retention. Forms of weed management were the sub-sub plots with manual weeding (MW) compared with chemical weeding (CW) through the application of bispyribac-sodium. Each treatment combination consisted of three replicated units. Averaged across the years, grain yield of rice under the CT system (4.8 t ha⁻¹) was significantly higher than ZT (4.4 t ha⁻¹). Increased level of wheat residue retention increased grain yield consistently in all three years. Grain yield was not influenced by systems of weed management. The following conclusions were drawn from the results: (i) rice grain yield might decrease under a direct-seeded ZT system more than the conventional system, (ii) wheat residue retained in the field can increase rice grain yield significantly, and (iii) application of bispyribac-sodium could be equally effective as manual weeding for weed control in both tillage/planting systems of rice.