Impacts of herbicides on weeds, water productivity, and nutrient-use efficiency in dry direct-seeded rice

Abstract

Direct-seeded rice (DSR) is an emerging resource-saving rice production practice. It can be alternative to input-intensive conventional transplanted puddled rice, which has encountered problems, relating to water, nutrients, energy, and environment. DSR can save water, labour, and energy, reduce greenhouse gases emission and improve soil properties. But, weeds are major constraint, which can cause complete failure of rice. Effective weed management is essential to achieve higher yield and resource-use efficiencies. Herbicide is a more effective and economical option than other weed control methods. But, its efficacy is influenced by herbicides and their use rates, and the weed species that vary across locations, depending on climate and soil. Therefore, this field experiment was carried out to evaluate the combinations of pre-emergence (~ PE) and post-emergence (~ PoE) herbicides as sequential applications, and their impacts on weeds, crops, economics, water productivity, and major nutrients-use efficiencies. It was observed that weed control treatments reduced weed density by 68–84.5% and weed dry weight by 71.6–86.7% at 60 days after sowing (DAS) compared to unweeded control (UWC). Among them, the pendimethalin 1000 g ha^–1 PE at 1 DAS followed by (~ fb) penoxsulam + cyhalofop-butyl 130 g ha^–1 (pre-mix) PoE at 25 DAS resulted in significant reduction in weed density (~ 84.5%) and weed dry weight (~ 86.7%) at 60 DAS. These sequential herbicides application increased effective tillers (233.3 m^–2), grains weight per panicle (2.54 g), and grain yield (3.92 t ha^–1) of rice, and irrigation (0.87 kg m^–3) and total water productivity (0.31 kg m^–3) by 288.2%, 75.2%, 378.9%, 378%, and 380%, respectively, than those in UWC. This resulted in 17.9% and 73.3% higher net returns and net benefit: cost, respectively, than even weed-free control (WFC) and was superior to all. Contrast analysis revealed that the brown manuring (BM) fb almix 20 g ha^–1 (pre-mix) applied at 40 DAS was similar to it, reducing weed density by 82.7% and dry weight by 83.3%. This study suggests that the sequential applications of herbicides or integration of herbicides with BM would provide broad-spectrum weed control and higher productivity and profitability in DSR. Controlling weeds may also reduce/economize water use and increase use efficiencies of N, P, and K in DSR.