Evaluation of phosphate availability in rice-soybean system cultivated in Lampang soil series
1988
Virojn Vajanarnvach | Vichit Kajornmalee | Chakranopakhun Tongyai, M.L.
Assessment of availability of TSP. and Rock Phosphate applied during paddy growing season on available phosphorus in soils and soybean yields in the rice-soybean cropping system in Low Humic Gley Soils (Typic Tropagualfe) in Northern Region is made based on results form trials in farmers' field in Chompoo Sub'district, Muang District, Lampang Province. Experimental results in the first year indicate that paddy rice does not respond to phosphate fertilizers but shows significant increase at 0.01 level in terms of total phosphorus uptake in plant and available phosphorus in the soils (Bray II when two types of phosphate fertilizers are applied). There are significant increases at 0.01 level of soybean yields grown after paddy in the check plot with no residual effect and in the plot with residual effect of TSP. from paddy growing season when Super phosphate fertilizer is newly applied. Soybean does not respond to the newly applied Super phosphate in the plots with residual effect of Rock phosphate for both rates. In years 2 and 3, it is discovered that paddy rice does not respond to residual effect of the first year phosphate fertilizers but soybean has obviously higher yield due to residual effect of the first year Rock Phosphate for both rates. In the meanwhile, residual effect of Super phosphate fertilizer at a high rate applied to soybean in the first year gives marginally higher yield when compared with plots with no previous Phosphate fertilizer application. Based on the above results, it indicates that Rock Phosphate can be effectively used to give phosphorus in paddy field where the rice-soybean cropping system is prevalent.
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