Bio-organics: influence on crop yields and dynamics of major soil nutrients and microbial populations
2003
Manguiat, I.J. (Philippines Univ. Los Banos, College, Laguna (Philippines). Dept. of Soil Science)
Field experiments were conducted for three years (six cropping seasons) to assess the influence of bio-organics on: a) yields of six upland crops, and b) dynamics of major soil nutrients and microbial populations. Results revealed that on the average, bio-organics improved significantly the yields of six crops over the control by 98%. However, compared with the inorganic fertilizer, bio-organic reduced the yields by 32%. By substituting 50% of N from ammonium sulfate with 50% of N from bio-organics in the form of chicken manure, the fertilization cost for upland rice, vegetable corn, and green corn could be reduced without significant yield reductions. Based on the dynamics of N, P, and K, bio-organics did not show any influence on K. The exchangeable K levels decreased exponentially throughout the 3-year period indicating the lack of nutrient sustainability in the uplands. Apparently, exchangeable K levels could serve as a nutrient indicator of the general fertility status of upland soils subjected to continuous cropping. Microbial biomass N (MBN) was positively and significantly correlated with either available N, organic matter, available P, or exchangeable K among others. Predictive equation were formulated to allow an estimation of MBN based on the aforementioned parameters. More importantly we were able to establish for the first time that MBN is positively and significantly correlated with crop yield, specifically for pechay (Brassica naphus) and green corn (Zea mays). Results showed also that the bacterial population is very responsive to bio-organics addition. It appears that with continuous cropping and bio-organics addition, bacterial population could serve as microbial indicator of soil environmental quality. The institutionalization of bio-organic farming is a national goal. The Congress of the Philippines is exerting great efforts to pass a law to be known as "Promotion of Bio-organic Farming in the Philippines"
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