CROP YIELDS AND DYNAMICS OF SOIL ORGANIC MATTER, NITROGEN, PHOSPHORUS, POTASSIUM, MICROBIAL BIOMASS N AND MICROORGANISMS AS INFLUENCED BY BIO-ORGANICS

摘要

Field experiments were conducted for 3 yr to assess the influence of bio-organics on: (a) the yields of various crops and (b) the dynamics of NPK, organic matter, microbial biomass N (MBN) and microbial populations. Bio-organics significantly improvedthe average yield of six crops for 3 continuous yr over the control by 98% but the improvement was much higher (153%) when 50% of the chemical fertilizer N was substituted with bio-organics N. For the chemical fertilizer N, however, the average yield increment over the control for the six crops was 195%. While a 50:50 proportion of bio-organic and inorganic fertilizer was helpful, it would take sometime for the yield to be comparable with that of purely inorganic fertilizer. Furthermore, it is not advisable to suddenly shift from inorganic to completely bio-organic fertilizer since it would substantially decrease the yield. Soil organic matter declined continuously following a quadratic pattern except for the bio-organics treatment. The addition of Nfrom either inorganic fertilizer or bio-organics increased the total soil N initially but after 21 cropping months, its level started to decline. Available P increased with bio-organics addition during the first 21 cropping months but a rapid decline wasobserved afterwards. The levels of exchangeable K decreased exponentially throughout the cropping months regardless of fertilizer treatments. MBN increased quadratically as a result of the application of either inorganic fertilizer or bio-organics and it was positively and significantly correlated with the yields of pechay and green corn. Bacterial population responded positively to bio-organics addition and bacteria appeared to be more sensitive than either actinomycetes or fungi as microbial indicator of soil environmental quality in continuously cropped production systems.