Influence of phosphorus in soil on biomass production and quality of Sesbania rostrata as green manure for rice in North Eastern paddy soils
1997
Prasert Sripairoch
This thesis had 3 main experiments : Transformation of fertilizer P into soil P forms after one crop of P fertilizer rate trial for rice; Response to the residual P of Sesbania rostrata ; and Mineralization of organic N and P from different quality of S. rostrata by anaerobic incubation. First experiment used 5 important soil series in the Northeast : Buntric (Bt), Phimai (Pm), On (On), Roi-Et (Re) and Ubon (Ub) which were treated with 5 P rates : 0, 15, 30, 60 and 120 ppm P for rice trial for one crop. Results of this experiment showed that amount of T-P, Bray II-P, O-P and all forms of I-P significantly increased upon the increase P rates and both T-P and Bray II-P were good indicators of all other P forms but the slope of the equations differed from soil to soils. Second experiment tested response of S. rostrata in aspect of growth and quality indicators as a source of green manure for rice on the residual P studied. Results of the experiment clearly showed good agreement of the growth indicator (height, fresh and dry mass) and the residual P contents. Such green manure qualities as : P content and N2 fixed positively correlated with the T-P and Bray II-P. Such organic carbon compounds as crude lipid, resin, soluble carbohydrate, hemicellulose, cellulose and lignin as well as crude protein, total hydrolyzable-N, ammonium-N, (ammonium+hexosamine)-N and amino acid - N produced in the one plant basis also closely correlated to the residual P contents indicated by T-P and Bray II-P. The last experiment investigated releases of NH4-H, H2PO4 - P, Fe++ - Fe and Mn++ - Mn from different quality of S. rostrata under anaerobic incubation at 2, 4 and 6 weeks. Results showed that 2 months old S. rostrata gave highest ammonification. The H2PO4 - P release increased continuously but that of NH4 - N, Fe++ - Fe and Mn++ - Mn were opposite.
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