Bioeconomic Evaluation of Agroforestry Practices in the Mountainous Region of Rima’a Valley, Yemen
Shogaa Aldeen, Abdulmoaamen Hamood (2009) Bioeconomic Evaluation of Agroforestry Practices in the Mountainous Region of Rima’a Valley, Yemen. PhD thesis, Universiti Putra Malaysia.
Yemen encounters serious problems of scarcity of natural resources as well as soil erosion and degradation. Agroforestry system is being promoted as a more appropriate land use system than monocropping practices for smallholders worldwide. Unfortunately, detailed studies on the sustainability of different land use systems are limited and in this region land has started to deteriorate and many farmers turned to traditional agriculture. The general objective of the study was to evaluate the sustainability of agroforestry compared to monocropping systems in terms of soil properties and farmers’ perception. The first specific objective of this study was to determine the effects of agroforestry practices on soil properties and compare them with soil properties under monocropping system. The second objective was to simulate the changes over a 20-year period in soil total organic N, total organic P, and organic carbon, and depths which are the most important elements affecting soil productivity. The third objective was to develop a bioeconomic model to determine the role of agroforestry and other factors affecting soil conservation and net farm income. Three different methods were used to achieve the above objectives. First, 72 composite soil samples were collected from two sites (36 from site 1 and 36 from site 2) based on RCBD split plot design (6 systems X 3 replications X 2 depths). Soil N, P, K, organic carbon, and bulk density were determined. Second, the SCUAF model was used to predict the changes in soil properties over a 20-year simulation period. The output was then used in cost benefit analysis. Third, a questionnaire and direct interview with 162 agroforestry farmers and 83 non-agroforestry were conducted to collect data to develop the bio-economic model. The results showed that soil N, P, K and organic carbon were significantly higher under agroforestry practices mixed trees with coffee (S1), and Muringa (Cordia africana L.) with coffee (S2) at the two sites as compared to the Arabian jujube (Ziziphus spina-christi L.) with maize (S3) and the monocropping systems (P<0.01). It was lowest under monocropping maize (S5) in both sites. Other physical soil properties were better under agroforestry practices (S1 and S2) than the monocropping maize (S5). The results of the SCUAF modeling illustrated that soil depth decline was negligible under agroforestry practices (S1 and S2) with soil loss less than 1000 kg/ha/yr even without using chemical fertilizers. The predicted decline of soil depth was highest under S5 followed by S3 which lost 43.1 % and 18 % of the top soil, respectively. Soil organic N and organic P are significantly higher under S1 and S2 systems even without using chemical fertilizers. It declined continuously under other systems at different rates during the simulation period. However adding 55 kg/ha/yr super phosphate (46 % P) and 271 kg/ha/yr urea (46 % N) to the systems (S1, S2, S4, and S6) resulted in maintaining soil fertility and led to sustaining the yield over 20 years of the simulation period. The results of cost benefit analysis showed that by using chemical fertilizers all systems were profitable at this level of the capital cost. The results also showed that Muringa coffee system (S2) and monocropping coffee (S4) obtained the highest net present value (NPV) (YR 1,171,077 USD 6163.6/ha) and (YR 1,117,965 USD 5884/ha), respectively. The lowest NPV (YR 55,116 USD 290.1/ha) was obtained under monocropping maize (S5). Consequently, the agroforestry system (S2) using fertilizers predicted the highest annualized net benefits (ANB) (YR 156,783 USD 825.2/ha/year), to the farmers and the lowest ANB (YR 7378 USD 38.8/ha/yr) was from monocropping maize (S5). The results of soil conservation model showed that educational level, number of terraces and channels maintained during the last ten years, geographical location, water efficiency, farmers’ experience, and agroforestry index are significantly influenced soil conservation in both models (OLS and SUR). The results of income regression model showed that the net income increased in output price and fixed inputs such as farm size, and decreased in input prices mainly wage of labor, and price of fodder in both models (OLS and SUR). The coefficients of the wage of labor (PLAB), fodder price (PFOD), are negative and significantly decreased the net income in both models as well. Farm size and price of cows sold are significantly affected the net farm income in models 1 and 2. The model shows that agroforestry can improve soil properties. The calculated values suggest that soil conservation generated productivity benefits in range of 4 to 9 percent of the current farm income. Ii is equivalent to about 23261 YR/yr (US$ 122.4) for an average area of 0.6 ha for each farmer. It can be concluded that agroforestry practices are more profitable and sustainable compared to monocropping systems.
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