Potential of timber based hedgerow intercropping for smallholder agroforestry on degraded soils in the humid tropicss of Southeast Asia: an assessment of timber based fallow systems

Timber hedgerow intercropping system is a frontier issue in the humid tropics of sotheast Asia particularly in Philippines.It has two phases: simultanious and sequential are fallow.The fallow phase is the consicuence of the simultaneous phase when trees have developed canopies to shade and make the associated annual food crops less productive. During the simultanious phase, it was found that Acacia mangium is apotential species as hedgrow to sustain production of associated annual crops, such as upland rice and maize. Gmalina arborea, on the othe hand, was found out to be more competitive with crops.These two spcies are popular choices of farmers. These speces are being campared together with natural grass or shrub fallow, which is the traditional method of addressing soil fertility.This one year report covers only the fallow phase, and dwells on the system's assessment on above ground biomass,nutrient uptake,litter fall,soil nutrient status and nitrogen fixation of acacia mangium in relation to the studied chronosequence:3-4,5-6,7-8,9-10 and more than 10 years old trees.Acacia mangium fallow waas superior to Gmelina, and grass or shrub fallows in above ground biomass,litter falls,nutrient uptake, such as N, C, P, K, Ca and Mg by a factor of 4 and 10, respectively across all ages fallow. Soil parameters indicated that Acacia mangium fallow resulted in slightly lower PH compared to either Gmelina arborea and natural fallow.No significant differences in soil available P and K were found ,but slightly higher soil N and C contents. Acacia mangium N2-fixation declined from 70-50%as the trees matured.Tress fallows were superior compared to natural grass or shrub fallow in in all facets of above and below ground parameters. The intergration of trees into the farming system enhanced its productive and protective functions,thus promoting sustainability.However, further study is necessary to be able to reduce uncertainty in the estimates of above ground biomass, by improving local allometric equation through sampling a wide range of stem diameter sizes, monitoring changes of fertility over time, impacts on soil chemical and physical properties at lower deptshs, long term litter falls and litter quality as determinants of decomposition rate,and improving estimates of N2- fixation.Understanding the impact of soil fertility and crop productivity due to biomass export as timber of fuel is important as these are determinants of systems sustainability, and appropriateness of the system on the context of small holder agroforestry on degraded soils in Southeast Asia.

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