Nutrient uptake by weeds as influenced by nutrient levels and weed management practices in aerobic rice

Weed crop competition for nutrients is a major constraint in aerobic rice production, especially under sub-optimal nutrient supply and inadequate weed management. A field experiment was conducted during Kharif 2023 and 2024 at the Zonal Agricultural and Horticultural Research Station, Navile, Shivamogga, to evaluate the influence of nutrient levels and weed management practices on nutrient uptake by weeds in aerobic rice. The experiment was laid out in a factorial randomized block design with three nutrient levels (N₁: 75:37.5:37.5 NPK kg ha^-1, N₂: 100:50:50 NPK kg ha^-1, N₃: 125:62.5:62.5 NPK kg ha^-1) and four weed management practices (W₁: Hand weeding + Intercultivation (20 and 40 DAS), W₂: Pyrazosulfuron ethyl 10% WP @ 100 gm ha^-1 (PE) + sunhemp, W₃: Pyrazosulfuron ethyl 10% WP @ 100 gm ha^-1 (PE) + Bispyribac sodium 10 SL 0.4 ml ltr^-1 (POE), W₄: Weedy check). Results revealed that weed nutrient uptake increased significantly with higher nutrient levels, as enhanced soil nutrient availability stimulated vigorous weed growth. Across both years, the highest nutrient uptake by weeds was recorded under N₃ combined with the weedy check. Effective herbicide treatments reduced N, P and K removal by weeds by restricting weed density and biomass throughout the crop growth period. Among weed flora, sedges contributed the highest share of total NPK uptake, followed by grasses and broad-leaved weeds. Interaction effects (N × W) were significant for all nutrient uptake parameters, confirming that nutrient application without proper weed control aggravates nutrient losses to weeds. Overall, the study highlights that integrated weed management combined with optimal nutrient application (125:62.5:62.5 NPK kg ha^-1) is essential to minimize nutrient depletion by weeds and improve nutrient use efficiency in aerobic rice systems.