EFFECT OF CONTINUOUS APPLICATION OF DIFFERENT CHEMICAL FERTILIZERS AND ORGANIC MANURE ON SOIL ENVIRONMENT IN A SUB- TROPICAL RICE-RICE ECO- SYSTEM OF EASTERN INDIAP. Majhi, S. Mondal, K.K. Rout, M. Mandal and M. Singh
A long term fertilizer experiment conducted on rice-rice system since 2005 in a sub tropical Eastern Indian state of Odisha was used for studying the effect of continuous application of NPK fertilizers alone or with Zn, B and S fertilizers and FYM on soil environment comprising of soil organic carbon (SOC) stock and sequestration and activities of three important soil enzymes, dehydrogenase, urease and phosphatase. The experiment was conducted on an acidic sandy loam inceptisol of Central Research Station of OUAT, Bhubaneswar, capital city of Odisha with 7 manurial treatments. Within 9 years (2005-2014) of continuous manuring, SOC content of surface (0-15cm) soil increased from 4.3g kg-1 to 4.59 - 5.84 g kg-1 in fertilized treatments and decreased to 3.95 g kg-1 in unfertilized control. Highest content of SOC was measured in 100% NPK +FYM treatment. Application of Zn, B and S did not exert any significant impact on SOC. Combined application of Zn and B caused a fall in total organic carbon stock. Carbon sequestration in all fertilized plots varied from 7 kg ha-1 yr-1 to 206 kg ha-1 yr-1 with highest recorded in NPK+FYM. In control it was negative. Dehydrogenase activity was greater in control and 100% NPK + FYM treatment than soils that received only fertilizers NPK plus other nutrients. Lower dehydrogenase in NPK fertilizers alone or with Zn, B and S fertilizers can be attributed to negative effect of K on fungi and algae and Zn on algae. Dehydrogenase poorly correlated with SOC(r=0.19). On the other hand urease and phosphatase strongly correlated with SOC content and increased substantially with fertilizer application. This difference between dehydrogenase and these two enzymes can be attributed to different extracellular sources other than microbes incase of the urease and phosphatase. Addition of FYM along with NPK fertilizers recorded highest urease and phosphatase activity due to increase in SOC and microbial population. Continuous application of Zn alone or with B or S for 18 cropping cycles did not have any significant effect on urease activity. The effect was positive with Zn and S combination and negative with Zn and B combination. But in case of phosphatase activity all the three nutrients had positive effect which was significant with combined application of Zn and S.
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