How to control nutgrass (motha) permanently in my field?

Nutgrass or motha (Cyperus, a sedge, usually purple or yellow nutsedge) is one of the hardest weeds to control because it spreads by underground tubers (nutlets) that survive in the soil for years, and pulling the top only triggers new shoots from the tubers below. True permanent eradication is very hard, so think of it as steady, long-term run-down rather than a one-shot kill. The most effective approach is integrated: repeatedly exhaust the tubers and never let the plant rebuild them. Repeated shallow tillage in the dry season brings tubers to the surface to dry in the sun. In the cropping season, dense, competitive crops shade the sedge out. Where a registered herbicide is available for your crop, sedge-active products such as halosulfuron or appropriate sulfonylureas can suppress it, but they must match the crop and be repeated, because one spray does not clear the tuber bank. Summer ploughing and solarisation in fallow fields, and keeping bunds and channels clean so it does not re-invade, all help. Be patient: it usually takes a few seasons of pressure to bring motha down to a low level. Use only herbicides registered for your specific crop, follow the label, and confirm with your KVK, since the wrong product can damage the crop and many common herbicides do not touch sedges.