| Application of farm waste combined with chemical fertilizers are the effective ways to improve soil quality, avoid environmental pollution and promote the recycling of agricultural waste. The objectives of this research is to explore the soil nitrogen and enzyme activities under different ratio of pig manure and chemical fertilizer application. By using the field test method at Tianma Town in Dujiangyan City of Sichuan Province, we designed six treatments including no fertilizer control, chemical fertilizer only,10% pig manure nitrogen (N) plus 90% fertilizer N,20% pig manure N plus 80% fertilizer N,30% pig manure N plus 70% fertilizer N,100% pig manure. In this paper, we mainly study the content change of soil total nitrogen (TN), ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3--N), soluble organic nitrogen (SON) and microbial biomass nitrogen (MBN), soil urease, protease, nitrate reductase, L-asparaginase, and the relationship between soil nitrogen and the enzyme activities. The dynamic relationship between the changes of soil nitrogen and the enzyme activities of nitrogen transformation was analyze. The main conclusions were as follows.(1) The effect of organic and inorganic fertilizer treatments on soil TN content was not significant in the short term (P>0.05), but the contents of NH4+N?NO3-N?SON and MBN in soil were affected differently. After one year of rice-wheat rotation, content of soil TN showed no significant change, contents of soil NH4+-N?NO3--N decreased, contents of SON and MBN increased, and its growth rate was higher than control treatment of 17.94-59.95% and 16.72-31.16%, and higher than chemical fertilizer only treatment of 2.54-40.83% and 8.35-21.55%, which revealed that compared with no fertilizer control and chemical fertilizer only treatment, organic and inorganic fertilizer treatments were not only more helpful to slow down the NH4+-N?NO3--N loss of in soil, but also more conducive to promote the contents of soil SON and MBN. Among the six treatments, the treatments of 20% pig manure N plus 80% fertilizer N and 30% pig manure N plus 70% fertilizer N showed the best promotion effect, the increase rates of SON contents were higher than no fertilizer control of 50.62-54.00% and 49.11-59.95%, and higher than pure chemical fertilizer treatment of 34.89-35.23% and 33.72-40.83%, besides, the increase of MBN contents were higher than no fertilizer control of 25.28-31.16 and 23.45-26.95%, and higher than pure chemical fertilizer treatment of 13.67-21.55% and 13.83-15.34%.(2) Organic and inorganic fertilizer treatments could have a significant effect on the activity of soil nitrogen transformation enzymes in the short term. After one year of rice-wheat rotation, urease, nitrate reductase and asparaginase activity increased respectively in spite of the slight decrease of protease activity. The activities of urease, protease, nitrate reductase and L-asparaginase were 1.05-1.47 times,1.04-1.47 times? 1.24-2.03 times?1.17-1.82 times to no fertilizer control treatment, and were 1.03-1.27 times,0.97-1.34 times,.07-1.41 times,1.03-1.39 times of chemical fertilizer only treatment. Soil enzymes activities of pig manure only treatment and organic and inorganic fertilizer treatments were significantly higher than control and chemical fertilizer only treatment at most growth stages of two crops. And among the three organic and inorganic fertilizer treatments, the treatments of 30% pig manure N plus 70% fertilizer N showed the best promotion effect, and were significantly higher than pig manure only treatment,10% pig manure N plus 90% fertilizer N treatment and 20% pig manure N plus 80% fertilizer N treatment at most growth stages of two crops.(3) The correlation between the soil nitrogen indexes and the soil enzyme indexes showed obvious dynamic change in the crop growth period, and the correlation of the indexes were similar in different soil depth. During one year of rice-wheat rotation, NH4+-N?NO3-N showed significant positive correlations(P<0.05) with TN at the early stage of crop growth, SON and MBN showed significant positive correlations(P<0.05) with TN at the later period of crop growth stages, NH4+-N?NO3--N showed significant positive correlations(P<0.05) with SON?MBN, SON and MBN showed significant positive correlations(P<0.05) with each other throughout the crop growth stages. Except for very few of situations, soil urease, protease, nitrate reductase and L-asparaginase showed significant (P<0.05) or extremely significant positive correlations (P<0.01) with each other. All of these showed that the soil nitrogen transformation enzyme could be used as the most sensitive indicator of soil nitrogen change.(4) Soil urease, protease, nitrate reductase and L-asparaginase were closely related to the transformation process of soil nitrogen, and the correlation between soil nitrogen and nitrogen transformation enzyme showed obvious dynamic change in the crop growth period, and showed a similar correlation in the soil layer at different depths. Soil TN showed significant (P<0.05) or extremely significant positive correlations (P<0.01) with the four soil enzymes at the later period of crop growth stages, which indicated that the soil TN could reflect the changes of enzymes in the later period of crop growth stages. Soil SON and MBN showed extremely significant correlations with the four soil enzymes at almost all stages of crop growth, which indicated that they were the most sensitive indicators of soil enzyme activities and their dynamic changes.(5) Compared with single application of chemical fertilizer and single application of organic fertilizer treatments, inorganic fertilizer combined with organic pig manure treatments were more helpful to improve the yields of rice and wheat. And the treatments of 30% pig manure N plus 70% fertilizer N enhanced the ability to increase crop yield best. |
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