Cultural methods can be defined as the alteration of growing conditions aimed at suppressing indirectly weed populations by decreasing competitive ability of weeds or directly by encouraging weed growth at a specified period during which time direct control methods can be imposed.
Cultural method consists of the following:
Land preparation can bury existing weeds and reduce the amount of germinating weeds coming into the crop. The key is to disturb the soil (e.g., plow) and then kill the weeds that subsequently germinate (e.g., second plowing or harrow). The weeds will germinate in response to moisture. Thus the timing of the follow-up cultivation depends on the soil moisture conditions, but if the soil is moist, this will usually be most effective about 15-20 days after the initial plowing.
Plowing - Incorporates weeds into soil, often to a depth of 10 to 15 cm.
Harrowing - Early harrowing destroys weeds and encourages weed seeds to germinate. Later harrowing destroys weeds that have germinated since the previous harrowing. Greater numbers of harrowing reduce seed stocks in the soil and, consequently, reduces weed infestations.
Land leveling is widely overlooked as an important management option for reducing weeds. Further, it has been found to be highly successful in both irrigated and rainfed lowland areas. Leveled fields can have up to 40% less weeds due to better water management and crop establishment.
Land leveling is also important in direct seeding. In general, high drier spots have both weeds and crop germinating. In deeper spots, neither the weeds nor the crop can emerge. In between these two are the areas where the crop can establish and weeds have problems.
Unlevel land causes uneven wetting and drying.
Water has been described as the best herbicide in Asia. In general, weed densities decrease as water depth increases. Even as little as 1 to 2 cm of water reduces weed densities. Few weeds occur when a field is flooded to a depth of 15 cm.
Flooding is effective only when the area is submerged from time of planting until the crop forms a continuous canopy. If the water level drops within this period, then conditions become favorable for weed seed germination or re-growth of some weed species.
Weeds vary in response to water.
Weeds can also be managed outside the crop cycle.
Many people are interested in ecology. Ecology can be defined as: The study of organisms in relation to one another and to their surroundings. In summary, this means that the types and numbers of weeds present in a field are a reflection of the long-term management of that field.
In essence, crop rotation like fallow management can be used to change weed flora and to ensure that there are breaks in the weed cycle.
Fertilizers should be applied when they are most beneficial to the crop, not when they would increase weed competition. Early to mid-season application of nitrogen often benefits the rice crop, but if weeds are present, then weed competition may also increase. Weeds should, therefore, be controlled before nitrogen application.
Some weeds can respond better than the crop to fertilizer. e.g., Watergrass out-competes the crop as the nitrogen rate increases