The composite effects of two irrigation frequencies (one irrigation at crown root initiation stage and five irrigations at five critical physiological stages of wheat), eight nutrient treatments consisting of N, P and K either applied alone or in combinations at the recommended doses (N:P2O5:K2O at 120:60:40 kg/ha) on population and dry weight of weeds and on the growth, nutrient uptake and yield of wheat were investigated. Observations on the components of the weed population and their biomass made at 60 DAS did not reveal any significant difference between the high and low frequency irrigation. Among the nutrient treatments, the N-treated plots (N, NP, NK and NPK) had a higher population and biomass of grass weeds, whereas sole P and K application or their combination produced the greater growth of broad-leaved weeds. However, the overall weed competition was significantly higher in the P- and K-treated plots than in the N-treated plots. The NP, NPK, NK and N treatments produced significantly higher values for dry weight, crop growth rate, leaf area, number of tillers, nutrient uptake, number of ear-bearing tillers, protein content and grain yield than the other treatments. Weeds in unweeded control plots did not significantly affect wheat growth (CGR, dry weight, tillers/plant) and uptake of the nutrients except of the P at 60 DAS. However, the number of ear-bearing tillers, grains per ear and yield were significantly higher in the weed-free plots than in the unweeded control treatment.

Soybean is the most important oilseed crop that is grown in India. Horse purslane (Trianthema portulacastrum L.) infests soybean heavily, causing enormous yield losses and threatening the sustainability of the soybean production system. Information on the interference and economic threshold of horse purslane will be useful for the effective management of horse purslane in soybean. This will lead to the rationalization of herbicide use and the reduction of herbicide input into the environment. It was observed in this study that "a composite stand of weeds including horse purslane", and 200 horse purslane plants per m 2 were equally competitive to soybean.These two treatments resulted in a higher dry weight, growth rate, and uptake of N, P, and K by the weeds and/or horse purslane, compared to the other treatments.They caused more reductions in soybean growth (dry weight, height, crop growth rate, net assimilation rate, and leaf area index) and resulted in a more significant yield reduction than did the other treatments. The weed density-crop yield and the relative leaf area-crop yield models were found to be equally effective in simulating soybean yield losses in relation to a wide range of horse purslane densities and the regression equations were a good fit.The quadratic equations revealed that a density of approximately six, five, and four horse purslane plants per m 2 would be the economic threshold levels of horse purslane in soybean cultivation, when considering the 70, 80, and 90% horse purslane control efficiencies, respectively, of the herbicide, lactofen.

Crop husbandry practices, i.e. sowing method, row spacing, and nitrogen (N) fertilisation, influence weed competition in a crop and play a role in ecological weed management. Missing-row sowing is a novel method of sowing wheat, with one row left unsown after several rows of continuous sowing. It affects density and spatial uniformity of wheat, which may influence the wheat plants’ competitiveness and weed suppression. It may have interactions with row spacing and N, which may further improve crop–weed balance, but is rarely studied in India or elsewhere. We undertook this study to optimise the method of missing-row sowing of wheat in combination with row spacing and N application. The results revealed that leaving 20% of rows unsown significantly reduced weed populations and dry weights, and increased the competitiveness of wheat plants through greater leaf area, numbers of ear-bearing tillers, and uptake of N. Leaving 20% of rows unsown increased wheat yield by 10.9%, 17.3%, and 8.2%, respectively, during the first, second, and third year compared with conventional sowing (no missing rows). An 18.5-cm row spacing resulted in a more weed suppression than 22.5-cm row spacing, but the latter gave higher yield. Application of N at 120 kg/ha resulted in higher yield than N at 60 kg/ha, due to a significant reduction in weed growth. A practice that combines 20% of rows unsown, 22.5-cm row spacing, and 120 kg N/ha will yield more through better suppression of a moderate weed infestation.

Purple nutsedge (*nutsedge) is an important perennial weed, which infests soybean in India and causes high yield losses. Selective pre-emergence herbicides hardly control nutsedge. Post-emergent application of imazethapyr is effective against nutsedge with almost 70 % efficiency. Information on the interference effect of nutsedge across densities on soybean and its economic threshold (ET) is hardly available, but would be useful for its management, and saving herbicide treatments with lower densities. An experiment was designed to evaluate the interference of nutsedge in pure stands, and that of natural weed infestations on soybean. Moreover, it was aimed to determine ET of nutsedge in soybean. The dry weights of weeds in the treatments 'natural weeds including nutsedge' and the one of nutsedges in the pure stand density of nutsedge 200 plants/m 2 were similar and higher than weed biomass in other nutsedge densities. The 'natural weed infestation both including and excluding nutsedge' and the treatment of 200 nutsedge plants/m 2 caused greater reductions in soybean yields and were the most competitive. The ET of nutsedge in soybean was 19-22 (*mean 21) plants/m 2 , considering 70 % efficiency of the herbicide imazethapyr. It predicts that a density of 21 nutsedge plants/m 2 can cause 9.1-11.5 % yield losses, which are an economic loss under this situation. This ET would help in making decisions for nutsedge management and fitting models and could be used for other similar sites with nutsedge dominance. This ET, considering several production factors, is more precise and reliable than the ET determined with only yield losses.