Cassava Agroforestry Systems
Soil Management and Yields
According to a recent study from India, trees and woody tree crops on your farm may control erosion on sloping sites, improve soil physical conditions, fertility, hydrological characteristics. When interplanted with food crops, yields may decline, but the long term benefit to the soil gained from such an intercropping system is considerable. Scientist of the Central Tuber Crops Research Institute of Kerala, India conducted a three year study to determine the interactions between species in an agroforestry system, and to observe their effect on crop yield and soil properties.
The experiment was carried out on sloping laterite soils of south India, and included plantings of: Eucalyptus tereticornis, Leucaena leucocephala, cassava, groundnut, and french beans/cowpea.
Each crop was grown in monoculture as well as in intercropped plots. Five types of intercropping treatments were performed: 1 tree crop + cassava; 2 tree crop + cassava + groundnut; 3 tree crop + cassava + cowpea; 4 tree crop + groundnut; 5 tree crop + cowpea. Each set of treatments were carried out once with Leucaena and again with Eucalyptus.
Effects on Yields
Yields of both cassava and the seasonal intercrops were reduced when grown in association with one of the tree crops. The pod yields of groundnut and cowpea were higher when intercropped with cassava and lower when grown in association with one of the tree crops + cassava. While intercropping with cassava reduced yields of Leucaena, it improved that of Eucalyptus. Forage yield of Leucaena was lowest (4.83 t/ha) when grown in association with cassava, and greatest (7.50 t/ha) when grown with cassava + groundnut.Eucalyptus benefited from association with cassava, as indicated by pre-harvest trunk girth. Cassava + groundnut intercropping resulted in the best growth of Eucalyptus, as judged by percent of trees with a girth greater than 30 cm. The maximum air dried wood yield (43.5 t/ha), however, was reached when the tree was grown with cassava + cowpea. Intercropping had a definite positive effect on Eucalyptus yield since monocropped plantings of Eucalyptus yielded only 30.1 t/ha of wood.
The benefit of intercropping tree crops with cassava is in the reduced run off and soil loss. The disadvantage of intercropping trees with cassava was that yields fell after the first year. Leucaena and Eucalyptus are very efficient in removing nutrients from the soil.
Effect on Soil Qualities
Initially the soil in all the plots was acidic, the organic carbon content was medium to high, and the nutrient availability was low to medium. The pH did not change after three years of cropping. The organic carbon content of the soil improved in plots of monocropped cassava and in plots of cassava intercropped with the tree crops, and showed a decline where tree crops were grown alone. Mono-cropping of Leucaena and Eucalyptus also reduced the available nutrients of the soil. During all three years the nutrient removal by cassava was greater when grown alone, as compared to the cassava-tree crop combinations. Of those combinations, cassava + Eucalyptus had the lowest nutrient removal rate.
Chemical assays of plant parts indicated that cassava utilized more soil nutrients when planted alone, and considerably less when grown with Eucalyptus. These results further demonstrate the aggressive habit of fast growing tree crops; they effectively utilize available nutrients and moisture at the expense of companion crops, and they considerably reduce soil fertility when grown continuously for three years, especially in monocultural plantation forests. If cassava were intercropped with the tree crops, however, the fertility status of the soil could be maintained without much deterioration.
Soil erosion was most effectively controlled in the two tier cropping of tree crop + cassava. Here the soil loss was 70%-80% less than mono crops of cassava, Eucalyptus, or Leucaena. Runoff and soil loss were effectively reduced when cassava was grown on staggered soil mounds along with Eucalyptus and Leucaena, due to better canopy coverage of the soil surface. Canopy coverage by Leucaena and Eucalyptus was restricted by harvesting, thus reducing their erosion and runoff control potential. Intercropping of cassava has great potential to decrease soil loss substantially. Soil erosion which is normally accelerated by deforestation of tropical rain forests can be successfully minimized by a proper combination of agricultural crops with forest species.
S.P. Ghosh, B. Mohan Kumar, S. Kabeerathumma and G.M. Nair. 1989. Productivity, Soil Fertility and Soil Erosion Under Cassava Based Agroforestry Systems. Agroforestry Systems 8:67-82.
For more information contact:
Central Tuber Crops Research Institute