Organic weed management

Y Sanatombi Devi, M Sumarjit Singh, Priyaka Irungbam and Y Bebila Chanu
Weed are no strangers to man. They have been there ever since man started to cultivate crops about 10,000 BC and undoubtedly recognized as a problem, from the beginning. In India, the manual method of weed control is quite popular and effective. Of late, labour has become non-available and costly, due to intensification, diversification of agriculture and urbanization. The use of herbicides in India and elsewhere in the world is increasing due to possible benefits to farmers. At the same time, the continuous use of the same group of herbicides over a period of time on a same piece of land leads to ecological imbalance in terms of weed shift, herbicides resistance in weeds and environmental pollutions. Application of herbicides for controlling aquatic weeds in a pond also reduces dissolved oxygen and pH and increase biological oxygen demand. The complexity of these situations has resulted in a need to develop a holistic sustainable eco-friendly weed management programme throughout the farming period. Sustainable development is the management and conservation of the natural resource base and the orientation of technological and institutional change in such a manner as to ensure the attainment and continued satisfaction of human needs for present and future generations. There are three different approaches are involved in sustainable weed management are as follows:
· Cultural method
· Mechanical method
· Biological method
Cultural methods: Cultural practices of weed control exploit the crop’s competitive behaviour, growing environment and crop management practices towards smothering of wees. Cultural practices including crop rotation, intercropping, mulching, soil solarization, sowing crop (seed rate) etc. are important tools in farming system. These practices can also have secondary benefits for soil fertility, disease and pest management. These practices if used properly help in controlling weeds. Cultural practices alone cannot control weeds, but help in reducing weed population.
Crop rotation: Crop rotations should be designed that make it difficult for weeds to grow and reproduce. It is way to avoid use of herbicides. Certain crops can suppress weeds by out-competing them for water and nutrients, or by shading them so they cannot receive adequate sunshine. Choice of crop rotation strongly affects the abundance and diversity of weed flora. Rotation crop with different life cycles can disrupt the development of weed crop associations through different planting and harvest dates preventing weed establishment and therefore weed seed production. Weed densities were lower when a crop was grown in rotation.
Intercropping: In organic or other system where herbicides are not used, intercropping can reduce the yield loss potential and provide stability in the system. Intercropping system and enhance the utilization of resources such as light, heat and water. These practices can also help to suppress weeds and increase the likelihood of being able to reduce herbicide use in the cropping system. Weed suppression, the reduction of weed growth by crop interference, has been referred as one determinant of yield advantage of intercropping, being a viable alternative to reduce the reliance of weed management on herbicide use.
Soil solarization: The basic principle behind soil solarization is that light received from the sun is in the form of electromagnetic short waves, which easily pass through the transparent colourless polythene films and reach the soils. As a result soil is heated upend emits long wave terrestrial radiation which, however can’t pass through transparent polythene film and result in build-up or trapping of heat. Weed seeds and young seedlings are killed by the heat and moisture and through direct contact with the plastic, which causes scorching. Thinner transparent sheet (0.05 mm)   were better in controlling weeds than thicker one (0.1 mm) due to low cost and has high strength.
Guidelines for using soil solarization:
· Soil must be finely tilled, and plastic trap must fit tightly over the soil.
· The recommended soil temperatures for solarization are 1400F at a depth 2 inches and 1020F at a depth of 18 inches.
Mulching: The mulch provides a physical barrier on the soil surface and must block nearly all light reaching the surfaces so that the weeds which emerge beneath the mulch do not have sufficient light to survive. Mulching reduces the deterioration of soil by way of preventing the runoff and soil loss, minimizes the weed infestation and reduces water evaporation. Mulches of organic material, such as straw, stubble, crop residue left on the surface can also effectively block sunlight and are more commonly used in organic row crop production systems.
Certain cover crops also may be used as living mulches. Living mulches can be established before planting, or they can be seeded with or after the main crop has been planted. Living mulch suppress the weeds by shading and cooling the soil.
Stale seed Bed:
A stale seedbed is one where initial one or two flushes of wees are destroyed before planting of a crop. This is achieved by soaking a well-prepared field with either irrigation rain and allowing the weeds to germinate. At this stage a shallow tillage may be used to destroy the dense flush of young weed seedlings. This technique allows the crop to germinate in almost wee-free environment.
Crop Sowing
Seed rate : Lowest seed rate recorded significantly, higher weed density and dry matter accumulation than higher seed rate.
Higher seed rate significantly influence weed population and their dry weight by securing an optimum plant population which shows excellent smothering effects on weeds and improving productivity and profitability of the crop.
Mechanical method
Hand weeding: It is done by physical removal or pulling out weeds by hand.

(To be contd)