Effect of Irrigation Regime and Soil Nutrients on the Growth of the Paddy Weed Heteranthera reniformis and Rice Grain Yield

The growth of Heteranthera reniformis, an invasive alien paddy weed, can be affected by cultivation practices. The experiments were conducted using herbicide-free soil to understand the effects of irrigation regimes and nutrient treatments on the growth of H. reniformis, as well as yield parameters while competing with a pre-existing seedbank. The pot experiments were conducted in a randomized complete block design (RBCD) with three replicates and twelve treatments. The four irrigation regimes (IRs): continuous irrigation (CI), soil condition at near saturation (non-puddled) (S), alternate wetting and drying (AWD) irrigation under two conditions [rewatered when the soil water potential reached −25 kPa (25P) and −35 kPa (35P)], and three nutrient treatments (NTs) of 0–0–0 NPK (NT0), 40–25–30 NPK (NT1), 80–50–60 NPK (NT2), kg ha−1 were established. The IRs had a significant effect on the growth of H. reniformis and other paddy field weeds, and the growth of H. reniformis was suppressed in the AWD regimes. NT2 resulted in more rice panicles, higher grain yield, and increased irrigation water use efficiency (IWUE). The highest grain yield and protein content were observed in S–NT2 and 25P–NT2 treatments. The IR and NT can be maintained to prevent yield penalties and reduce the invasiveness of weeds.