Indian Journal of Agronomy

A long-term field experiment was conducted from 1999–2000 to 2015–16 at Karnal, Haryana, to study the effect of green manuring (GM) and continuous or rotational use of herbicides on weed pressure, crop productivity and soil properties in rice (Oryza sativa L.)-wheat (Triticum aestivum L.) system. Based on data from 2008–09 onward (results from 1999–2000 to 2007–08 published elsewhere), the dry-weight of grassy weeds in rice was lower or similar under GM (103–407 g/m²) as compared to without green manuring (WGM) (153–472 g/m²) except higher dry-weights during 2011 and 2014. The dry-weight of broad leaf weeds (BLW) and sedges under weedy check remained lower or similar under GM (1.5–9.8 g/m²) than WGM (0.3–15.5 g/m²), except being higher during 2013. Continuous and rotational use of herbicides being excellent and as good as weed-free checks in rice provided similar reductions in the dry weights of weeds irrespective of GM and WGM over the years. The dry-weight of small canary grass (Phalaris minor Retz.) in wheat was higher or similar under GM (42–216 g/m²) to WGM (26–156 g/m²) except being lower in 2010–11. The fixed herbicide (Clodinafop) being similar to weed-free was also similar (0.0–13.8 g/m²) to the rotational use of herbicides (0.0–25.4 g/m²) in respect of dry weight of grassy weeds over the years. The dry weights of BLW in wheat were equal to or lower under GM (2.9–35.9 g/m²) than WGM (4.4–44.0 g/m²) in the plots treated with Clodinafop over the years. The rotational use of herbicides resulted invariably in lower dry weights of BLW (0.1–25.8 g/m²) than the fixed herbicide (2.9–35.9 g/m²) in wheat with few exceptions. There were no envisaged signs of herbicide resistance development in the dominant weed barnyard grass [Echinochloa crus-galli (L.) Beauv.] in rice and Phalaris minor in wheat. Grain yields of rice were better under green manuring (6.38–8.30 t/ha under weed-free situations) than without green manuring (5.59–7.63 t/ha). Similarly, the grain yields of wheat were higher under GM (5.25–5.99 t/ha) than WGM (5.08–5.54 t/ha). The productivity of rice-wheat cropping system was higher under GM than WGM by 0.4–1.1 t/ha over the years. The economic returns from rice-wheat system were also more under GM than WGM. The study indicated the long-term sustainability of green manuring and use of herbicides (continuous or rotational) in rice-wheat cropping system. Moreover, there were no signs of development of herbicide resistance in weeds, and it might be avoided or delayed by proper use of recommended herbicides.