Weed management in direct-seeded fine rice using allelopathic crop residue mulches and nitrogen for sustained yields in Pakistan

Direct seeding of rice is a new method of rice production; however, weeds pose serious threat to its productivity. Using residues of allelopathic crops as mulches on soil surface along with appropriate nitrogen (N) application may become an environmental friendly and sustainable way to manage weeds. This two-year field study was conducted to explore the impact of mulching with residues of three allelopathic crops (wheat, rice and sorghum) and three N sources (urea, calcium ammonium nitrate (CAN) and ammonium sulphate (AMS) on weeds and productivity of direct-seeded fine rice. Treatments with plastic mulch and no mulch were established as controls. Results showed that all mulches significantly (P ≤ 0.05) influenced the density and dry biomass of broad leaf weeds (BLWs), narrow leaf weeds (NLWs) and sedges. Maximum suppression of density (90.8, 87.9, and 85.5% of BLWs, NLWs and sedges, respectively) and dry biomass (92.2, 88.0, and 90.5% of BLWs, NLWs and sedges, respectively) of weeds was noticed with plastic mulch over control. Amongst allelopathic crop residue mulches, maximum suppression of the density (69.5, 57.7 and 61.3% of BLWs, NLWs and sedges, respectively) and dry biomass (71.6, 55.8 and 53.2% of BLWs, NLWs and sedges, respectively) was observed with wheat mulch over control. Nitrogen application overall increased the growth of weeds in terms of its dry biomass, compared with the control. However, wheat mulch with all N sources substantially reduced the density of BLWs at 75 DAS during the year 2014 and dry biomass of all kind of weeds at 60 and 75 DAS of rice in both the years over control. Significant negative correlation of density and dry biomass of all weeds was observed with water soluble phenolics in the soil indicating strong influence of allelopathic mulches on weeds. Maximum paddy yield improvement (30.2%) was observed with the plastic mulch; however, amongst the crop residue mulches, maximum improvement (25.6%) of paddy yield was observed with wheat mulch over control. Overall, allelopathic crop residue mulches, especially wheat mulch, in association with N fertilizers suppressed weeds and improved paddy yield by improving competitiveness of crop plants against weeds and therefore may be used to manage weeds and sustain productivity of rice.