Contributed by Chime G. Mora, University of Ghent, BelgiumAgroforestry is the land use system that combines trees and crops with or without animals on a given piece of land. It has been proven effective in improving the productivity and biodiversity of degraded lands in the tropics. Degraded lands are generally characterized by low soil fertility status and unfavorable soil physical and chemical conditions. Thus, the success of agroforestry on degraded lands greatly depends on the availability of mineral nutrients in the soil. This is because the trees and crops may fail to grow if there is deficient supply of essential nutrients in the soil. Studies have shown that nutrient deficiency is the most important factor limiting early growth of indigenous tree species on degraded soils. There are, however, certain plant species that are capable of thriving even in nutrient stressed environments. These are the slow growing wild plants which usually exhibit a low absorption of nutrients. Such plant species can be suitable for integration in agroforestry systems especially in degraded lands.
The use of native rain forest tree species in agroforestry systems is relatively new as past efforts have largely focused on the planting of leguminous tree species many of which are exotic. In order to know the most suitable native tree species as well as exotic and fruit tree species for use in such land use systems, there is a need to understand their nutrient requirements and their effects on the soil. In a recent study (Mora and Asio, 2009) conducted at two project sites of the ViSCA-GTZ Ecology Project in Leyte (established in the early 1990s) and funded by the Philippine Agroforestry Research and Education Network, the levels of N, P, and K in native tree species, exotic tree species and fruit trees growing in acidic (volcanic) and calcareous (limestone) agroforestry sites were compared, and differences in nutrient status of soils under the three types of tree species were evaluated.
The tree species sampled included: Gmelina arborea, Swietenia macrophylla, and Tectona grandis for the exotic species; Dipterocarpus validus, Dracontomelon dao and Pterocarpus indicus for the native species; and Artocarpus heterophyllus, Chrysophyllum cainito, Persea americana, and Sandoricum koetjape for the fruit trees. Composite soil and leaf samples were collected for nutrient analysis.
Results revealed no clear differences in the effects of the tree species on soil nutrient status although the exotic species tended to result in slightly lower soil organic matter content than the other species. This can be explained by the findings of previous decomposition studies done at the site showing that the leaf litter of exotic tree species decomposes faster than those of the native rain forest tree species.
P. indicus had generally high NPK while T. grandis had low NPK leaf concentrations. G. arborea showed relatively high P and K leaf concentrations while the fruit trees all gave high K leaf levels. There were no consistent differences in the leaf NPK contents between the exotic, native, and fruit trees when the nutrients were considered individually. However, when their ratios were calculated, there appeared to be some differences among them. In general, the exotic species tended to have lower N:P ratios, whereas the native species and fruit trees tended to have higher N:K and K:P ratios, respectively.
Reference
Mora, CG. and VB Asio 2009. Nitrogen, phosphorus and potassium status of trees and soils in an agroforestry system in Leye, Philippines. The Icfai University Journal of Soil and Water Sciences 2: 77-90. Available at SSRN: http://ssrn.com/abstract=1415861 and also at http://www.iupindia.org/SoilandWater_Sciences.asp
The use of native rain forest tree species in agroforestry systems is relatively new as past efforts have largely focused on the planting of leguminous tree species many of which are exotic. In order to know the most suitable native tree species as well as exotic and fruit tree species for use in such land use systems, there is a need to understand their nutrient requirements and their effects on the soil. In a recent study (Mora and Asio, 2009) conducted at two project sites of the ViSCA-GTZ Ecology Project in Leyte (established in the early 1990s) and funded by the Philippine Agroforestry Research and Education Network, the levels of N, P, and K in native tree species, exotic tree species and fruit trees growing in acidic (volcanic) and calcareous (limestone) agroforestry sites were compared, and differences in nutrient status of soils under the three types of tree species were evaluated.
The tree species sampled included: Gmelina arborea, Swietenia macrophylla, and Tectona grandis for the exotic species; Dipterocarpus validus, Dracontomelon dao and Pterocarpus indicus for the native species; and Artocarpus heterophyllus, Chrysophyllum cainito, Persea americana, and Sandoricum koetjape for the fruit trees. Composite soil and leaf samples were collected for nutrient analysis.
Results revealed no clear differences in the effects of the tree species on soil nutrient status although the exotic species tended to result in slightly lower soil organic matter content than the other species. This can be explained by the findings of previous decomposition studies done at the site showing that the leaf litter of exotic tree species decomposes faster than those of the native rain forest tree species.
P. indicus had generally high NPK while T. grandis had low NPK leaf concentrations. G. arborea showed relatively high P and K leaf concentrations while the fruit trees all gave high K leaf levels. There were no consistent differences in the leaf NPK contents between the exotic, native, and fruit trees when the nutrients were considered individually. However, when their ratios were calculated, there appeared to be some differences among them. In general, the exotic species tended to have lower N:P ratios, whereas the native species and fruit trees tended to have higher N:K and K:P ratios, respectively.
Reference
Mora, CG. and VB Asio 2009. Nitrogen, phosphorus and potassium status of trees and soils in an agroforestry system in Leye, Philippines. The Icfai University Journal of Soil and Water Sciences 2: 77-90. Available at SSRN: http://ssrn.com/abstract=1415861 and also at http://www.iupindia.org/SoilandWater_Sciences.asp
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