Cultural methods or cropping methods and competitive methods –
Several cultural practices like tillage, planting, fertilizer application, irrigation etc., are employed for creating favourable condition for the crop. These practices if used properly, help in controlling weeds. Cultural methods, alone cannot control weeds, but help in reducing weed population.
They should, therefore, be used in combination with other methods. In cultural methods, tillage, fertilizer application, and irrigation are important. In addition, aspects like selection of variety, time of sowing, cropping system, cleanliness of the farm etc., is also useful in controlling weeds.
1. Field preparation – The field has to be kept weed free. Flowering of weeds should not be allowed. This helps in prevention of build up of weed seed population.
2. Summer tillage – The practice of summer tillage or off-season tillage is one of the effective cultural methods to check the growth of perennial weed population in crop cultivation. Initial tillage before cropping should encourage clod formation. These clods, which have the weed propagules, upon drying desiccate the same. Subsequent tillage operations should break the clods into small units to further expose the shriveled weeds to the hot sun.
3. Optimum plant population – Lack of adequate plant population is prone to heavy weed infestation, which becomes, difficult to control later. Therefore, practices like selection of proper seed, right method of sowing, adequate seed rate protection of seed from soil borne pests and diseases etc., are very important to obtain proper and uniform crop stand capable of offering competition to the weeds.
4. Crop rotation – The possibilities of a certain weed species or group of species occurring is greater if the same crop is grown year after year. In many instances, crop rotation can eliminate at least reduce difficult weed problems. The obnoxious weeds like Cyperus rotundus can be controlled effectively by including low land rice in crop rotation. Inclusion of smothering crop or competitive crops like sunflower, sorghum, sweet, potato, fodder grasses in rotation will effectively control the weeds. The selected crops should grow thickly and develop dense canopy and shade to suppress the weeds. Competitive plants- Parthenium hysterophorus can be effectively controlled by growing Cassia sericea Parthenium through allelopathic effect. Brachiaria mutica (Para grass) is highly competitive to the growth of Typha sp. in ditches.
5. Growing of intercrops – Inter cropping suppresses weeds better than sole cropping and thus provides an opportunity to utilize crops themselves as tools of weed management. Many short duration pulses viz., green gram and soybean effectively smother weeds without causing reduction in the yield of main crop.
6. Mulching – Mulch is a protective covering of material maintained on soil surface. Mulching has smothering effect on weed control by excluding light from the photosynthetic portions of a plant and thus inhibiting the top growth. It is very effective against annual weeds and some perennial weeds like Cynodon dactylon. Mulching is done by dry or green crop residues, plastic sheet or polythene film. To be effective the mulch should be thick enough to prevent light transmission and eliminate photosynthesis.
7. Solarisation – This is another method of utilization of solar energy for the desiccation of weeds. In this method, the soil temperature is further raised by 5–10ºC by covering a presoaked fallow field with thin transparent plastic sheet. The plastic sheet checks the long wave back radiation from the soil and prevents loss of energy by hindering moisture evaporation.
8. Stale seedbed – A stale seedbed is one where initial one or two flushes of weeds are destroyed before planting of a crop. This is achieved by soaking a well-prepared field with either irrigation or rain and allowing the weeds to germinate. At this stage a shallow tillage or non-residual herbicide like paraquat may be used to destroy the dense flush of young weed seedlings. This may be followed immediately by sowing. This technique allows the crop to germinate in almost weed-free environment.
9. Blind tillage – The tillage of the soil after sowing a crop before the crop plants emerge is known as blind tillage. It is extensively employed to minimize weed intensity in drill sowing crops where emergence of crop seedling is hindered by soil crust formed on receipt of rain or irrigation immediately after sowing.
10. Crop management practices – Good crop management practices that play an important role in weed control are:
• Vigorous and fast growing crop varieties are better competitors with weeds.
• Proper placement of fertilizers ensures greater availability of nutrients to crop plants, thus keeping the weeds at a disadvantage.
• Better irrigation practices to have a good head start over the weeds.
• Proper crop rotation programme.
• Higher plant population per unit area results in smothering effect on weed growth.
• Low cost for weed control
• Easy to adopt
• No residual problem
• Technical skill is not involved
• No damage to crops
• Effective weed control
• Crop-weed ecosystem is maintained
• Immediate and quick weed control is not possible
• Weeds are kept under suppressed condition
• Perennial and problematic weeds can not be controlled
• Practical difficulty in adoption
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