Sustainability of using organic fertilizer in irrigated lowland rice
2007
Javier, E.F. | Grospe, F.S. | Rivera, J.M. | Santin, C.A. | Sebastian, L.S. | Mamaril, C.P., Philippine Rice Research Inst., Maligaya, Science City of Munoz, Nueva Ecija (Philippines)
Plant residues like straw, weeds like the wild sunflower, and poultry wastes or chicken manure are abundant in the farm and seemingly unimportant. But these can be recycled as nutritional amendments into the soil. The use of inoculant enhances decomposition of plant residues with high C/N ratio like the rice straw. The use of pure organic amendments however can either be beneficial or detrimental in the long run. An experiment therefore on the continuous use of these organic fertilizers (OF) was done in Maligaya clay soil series, from 2003 wet season to 2006 dry season, to determine their effect on the sustainability of soil productivity and of rice yield. Rice straw (RS), inoculated rice straw (RSEM), chicken manure (CM), wild sunflower (WSF), commercial organic fertilizers (COF) were against the unfertilized soils and the inorganic NPK fertilizers. Trends of availble soils N and K owing to organic fertilizers increased at 7 days after transplanting (DAT) of rice then decreased at 28 DAT. This implies insufficiencies of the different OF to supply the needs of rice plants all throughout its growth duration. However, after two years of continuous application, RS gave significantly higher soil K content, higher soil Zn, P and N from CM, while considerable N, P, K and Zinc from WSF. Likewise, the slight decrease of soil pH and the slight increase of soil OM after 2 years were similar regardless of whether the fertilizer applied was in inorganic or organic form. Consistent higher yield was observed when OF were applied with inorganic fertilizer. The return of investment (ROI) from the application of OF alone was higher than when they are applied with inorganic fertilizer. For an optimized yield and ROI, the organic amendment + 1/2 of inorganic NPK gave the highest ROI.
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