Effect of turning over Chinese milk vetch (Astragalus sinicus L.) on soil nutrients and microbial properties in paddy fields
Objectives] Chinese milk vetch ( Astragalus sinicus L.) is a major green manure planting in southern paddy fields .In this study , the effects of turning over Chinese milk vetch on crop yield , soil nutrients and microbial properties were investigated to determine the appropriate application rates of chemical fertilizers.[Methods]Rice-Chinese milk vetch ( MV) rotation Experiment Station was established in 2009.Five fertilization treatments with three replicates ( each replicate plot was 15 m2 ) were designed as control ( CK) , 100%chemical fertilizer (100%F) , 18000 kg/ha milk vetch +100% chemical fertilizer ( MV+100% F) , 18000 kg/ha milk vetch +60% chemical fertilizer ( MV +60% F ) , 18000 kg/ha milk vetch alone ( MV ) .Soil samples were collected after rice harvest in October, 2012, and crop yield, soil nutrients, soil microbial biomass carbon ( SMBC) and soil microbial biomass nitrogen ( SMBN ) , number of culturable microorganisms and soil enzyme activities were determined.[Results]1) There was no significant difference in the crop yields between the 100%F and MV+60%F treatments which demonstrated MV could substitute 40%of chemical fertilizer.2 ) Compared to the 100%F treatment, the MV+F treatments could increase the contents of soil organic matter and total nitrogen, but not those of total phosphorus and total potassium; the MV+100% F treatment could increase the content of available nitrogen;MV and MV+60%F treatments could decrease the content of available phosphorus.The 100%F treatment had the highest content of available potassium.There were no significant differences in pH values from all treatments.3) The number of bacteria in the 100% F and MV+100% F treatments were significantly higher than that in the CK treatment, but there were no significant differences between the MV+60% F, MV and CK treatments.These results imply that bacteria were obviously dependent on the soil nutrients.Chemical fertilizer with MV could increase the number of fungi and actinomyces.4 ) Correlation analysis showed that the contents of available nitrogen, available phosphorus and available potassium in soils were significantly correlated with the number of bacteria, and NH+-N content was significantly correlated with the number of fungi and actinomyces.5) In comparison with 100% F treatment, chemical fertilizer with MV treatments could increase the contents of soil microbial biomass carbon and nitrogen.6 ) Soil enzyme activities in chemical fertilizer with MV treatments were significantly higher than those in the 100% F or MV treatments.7 ) Soil enzyme activities and microbial biomass were significantly correlated with the soil nitrogen content.Invertase, urease and acidic phosphatase activities were significantly correlated with the rice yield.[Conclusions]Compared to the 100% F, the MV+60%F treatment could achieve equivalent rice yield, indicating that application of 60% fertilizer could be considered as the best fertilization model in our study.Contents of soil organic matter, total nitrogen, available nitrogen, microbial properties and enzyme activities in 100% F treatment were lower than those in chemical fertilizer with MV treatmetns.
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