26. Weed management in a low-input cropping system in the Peruvian Amazon region.
Trop. Agric. (Trinidad), 69, 3, 1992, pp. 250-258
A weed-control study in a five-crop sequence (rice-rice-cowpea-rice-cowpea) following forest clearing in the Peruvian Amazon was carried out.
Previous work has established that continuous cropping systems in the Peruvian Amazon are viable alternatives to shifting cultivation if appropriate amounts of lime and fertilizers are supplied. Herbicides have provided effective but costly weed control in these intensively managed (high-input) systems.
Low input systems are based on acid-tolerant cultivars and rely on moderate amounts of fertilizers and careful recycling of crop residues to maintain soil fertility. But weed control in this management system poses special problems. Complete reliance on herbicides is unacceptable because of the cost, and hand labour is often unavailable.
Weed control in a low-input system must focus on cultural practices that increase the crop's ability to compete with weeds and thereby eliminate some of thecostly control measures needed to maintain yields.
The results of this study revealed that tilled plots had more weeds than untilled in the first crop but fewer in the fifth. Mulching residues had little weed-controlling effect, and crop yields were always higher when residues where incorporated. High planting density reduced weed levels and increased crop yields. Herbicides were as effective as hand weeding in controlling weeds, but herbicide costs sharply limit their use in low-input systems. Rice yields fell by 54-100% in the absence of weed control but were reduced by less than 30% for cowpea. Sedges comprised 84% of the weeds in the first crop following forest clearing, but grasses dominated (79%) in the fifth crop.
As has been shown in other environments a practical and effective weed-management programme for continuously cropped systems must combine cultural practices with chemical and manual methods of control. The observations suggest that a similar integration of control measures is needed during this transitional period that bridges the time-span between forested land and the cultivatable fields of a permanent agriculture.
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Latin America, Mexico, weed control methods, crop rotations, maize, bean, intercropping
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