The effect of two tree species, karit6 (Vitellaria paradoxa) and nrr6 (Parkia biglobosa) on soil condition, development and production of cotton, sorghum and pearl millet, main crops in South Mali, has been investigated.The soil under the trees is slightly richer (organic matter content and several cations) compared to adjacent tree-less sites. Also tree-specific effects exist.Soil enrichment, however, is mainly a matter of redistribution of locally available nutrient resources.Of the six associations studied, only karitr-cotton shows no tree-induced reduction in crop production. All other associations suffer greatly from reduced crop outputs caused by the trees, usually in the order of 60%.There are at least two reasons that explain tree-induced yield reduction. Because of increased humidity in the immediate surroundings of trees, in both soil and air, lower numbers of crop plants survive up to maturity, presumably because plants are attacked by fungi. Secondly, crop plants that mature show reduced output because of inter-specific competition for light and nutrients.In case of n&6, in order to minimize the trees' negative influence lopping is advised. Such practice, however, is less suitable in case of karitr, because of its assumed lower potential to regenerate, as compared to nrrr.
The decomposition of the leaf mulches of Leucaena leucocephala, Gliricidia sepium and Flemingia macrophylla has been studied under field conditions. Mulch samples were analysed over a period of 70 days on carbon, nitrogen, phosphorus, potassium, calcium and magnesium left. Loss rates for the elements show similar patterns for the three mulches. Losses of mulch material are caused by. decomposition as well as removal by soil-dwelling fauna (insects, arthropods, etc.) feeding on the mulch.Based on the data decomposition-and nutrient release functions are developed for the three mulches. These functions are useful in alley-cropping system analysis and models.
Abstract. The performance of the leaf mulches of Leucaena leucocephala, Gliricidia sepium and Flemingia macrophylla in weed control has been tested in two trials. The length of the period during which a mulch layer yields significantly less weedbiomass compared to the control plots is called the 'effective life-span' of the mulch.Of the three mulch materials only that of F. macrophylla shows promise in retarding weed development.In the second trial 17. macrophylla leaf mulch was applied at rates of 3, 6 and 9 tons dry matter per ha. The effective lifespan of a mulch layer of 3 tons is between 12 and 13 weeks. The treatments 6 and 9 tons have effective life-spans of over 14 weeks.For moderate quantities (up to 5 tons of dry leaf mulch per ha) the effective life-span is estimated at about a 100 days.The value of mulching in weed control is limited to the control of weed species that multiply by seed. Regrowth originating from roots or stumps from former vegetation is unlikely to be checked by a mulch layer.
Leaf dry matter productivity has been measured at the end of regrowth cycles of 3 months for stands of Leucaena leucoeephala, Gliricidia sepium and Flemingia macrophylla, all three species belonging to the Leguminosae. The effective period of observation was minimally 24 months, or 8 regrowth cycles, after a period of establishment of slightly more than a year. Using systematic trial designs, originally developed by NELDER, yield figures have been acquired for a broad range of plant densities. At a plant density of 10,000 trees per hectare the average yearly leaf DM productivity amounted to 15.4 ton for Leucaena leucocephala, 12.4 ton for Flemingia macrophylla and 10.5 ton for Gliricidia sepium.Productivity figures and leaf area indices are compared with those of relevant cropping systems.
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