Nutrient losses due to harvesting of agricultural crops planted in agroforestry systems

The investigation was carried out at Srisakaet in northeastern Thailand. Twenty-four sample plots of agroforestry system, 20 x 20 square meter in size, were temporarily established on the basis of 6 treatments with 4 replications. Eucalyptus camaldulensis Dehnh, was treated as a primary crop, while six species of cash crop, ie. upland rice, maize, mungbean, groundnut, kenaf and cassava were considered as treatments. Biomass production was estimated, then different sections of plant samples as well as soil collected from all planting sites were analyzed for major elements. The results of soil analyses revealed that both surface soils and subsoils were acidic and infertile, having 0.93-1.58 percent organic matter, 0.3-0.8 percent N, 0.3-48 ppm P, and 4-24 ppm K with the levels of Ca and Mg tended to be relatively high. Maximum total biomass was recorded for cassava (8.80 t/ha), followed by upland rice (3.79 t/ha), mungbean (3.75 t/ha), maize (2.98 t/ha), groundnut (2.09 t/ha) and kenaf (1.08 t/ha). However, the amounts of commercial dry matter lost from the sites due to crop removal were 6088 kg/ha for cassava, 2275 kg/ha for upland rice, 1238 kg/ha for mungbean, 1219 kg/ha for groundnut, 1031 kg/ha for maize, and 419 kg/ha for kenaf. Based on plant analysis, higher nutrient concentrations of all crops were observed from above ground portions in comparison to their root systems. For each intercrop, the maximum nutrient concentration was found in foliage while the minimum was found in roots. The order of abundance was as follows: Cassava : leaf stem root; Kenaf : leaf stem = root; Groundnut : leaf seed stem = root; Mungbean: leaf seed stem = root; Maize: leaf grain stem = root; Upland rice : stem straw grain root. Nutrients lost through the removal of agricultural crops were estimated on the basis of nutrient concentration in connection with biomass to be removed. The total amount of N, P, K, Ca and Mg lost due to crop removal was highest in cassava (73.94 kg/ha), followed by groundnut (67.19 kg/ha), mungbean (59.63 kg/ha), upland rice (36.81 kg/ha), maize (19.75 kg/ha), and kenaf (7.19 kg/ha)