Long-term effects of organic amendment and mineral fertilizers on soil fertility in a rice-rice-wheat cropping system in Nepal
1994
Regmi, A.P.
Long-term application of FYM [farmyard manure] increased OM, total N, available P, total P, CEC, Mg, contents of soil and lowered the soil pH of the calcareous soil. Long-term application of NP or NPK fertilizers increased OM, total N, available P, total P, content of soil compared to mineral fertilizer treatments lacking P. Application of nitrogen alone had similar effects on soil properties as treatments without fertilizer. Application of K in combination with N increased the K content of the soil because less K was removed by the grain and straw in the absence of P. Phosphorus-supplying capacity severely decreased through continuous cropping without P fertilizers. Application of moderate dose of P (46 kg P/ha/year) was not sufficient to maintain the P status of the soil in the rice-rice-wheat system. Application of 30 t/ha/yr FYM significantly increased the P status of the soil but did not balance K removal. Potassium supplying capacity was found low even with the application of 75 kg K/ha/yr. More than 95% of applied P was sorbed. P sorption was higher under reduced than under oxidized condition. Desorption of freshly adsorbed P was higher in oxidized than reduced soils. P fertilizer requirement to achieve a concentration of 0.12 microgram P/ml in the soil solution, a critical level for maximum growth, was high in these soils. The soil which received NPK fertilizers for 13 years required the most with 273 microgram P/g soil. Long-term application of FYM 30t/ha/yr showed the highest P concentration in all pools followed by application of mineral P
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