| Water quality worsening of Erhai Lake is mainly caused by nitrogen leaching from farming fields in Erhai lake basin which is seriously agricultural non-point source pollution areas. It is necessary to seek the appropriate agronomic techniques that can effectively improve physical and chemical characteristics of soil and reduce potential nitrogen leaching. A field experiment had been carried out with a typical garlic-rice rotation mode to study the effects of5agronomic techniques (No-tillage and straw mulching&optimized N fertilization, Doubling cow manure&nitrogen regulation, Nitrogen regulation, Cow manure, Conventional fertilization) on soil properties, the growth of plant and the risk of nitrogen loss in northern Erhai lake basin. The results indicated that:1. No-tillage and straw mulching treatment could significantly improve the soil water content, its soil water content of0-20cm soil was up to13.2%higher than the others, and its soil bulk density was higher than the others slightly. Conventional fertilization treatment aggravated the soil acidification; its soil pH value was lower than the others.2. The amount of>0.25mm water-stable aggregates of the three treatments of no-tillage&straw mulching, doubling cow manure combined nitrogen regulation and nitrogen regulation was about82.31%,81.1%and80.57%respectively, compared with conventional fertilization treatment (79.62%) and CK(76.53%), increased2.14%and5.77%averagely. The three treatments improved soil aggregation stability and soil properties.3. No-tillage&straw mulching and doubling cow manure combined nitrogen regulation treatments increased significantly total organic carbon and total nitrogen respectively. No-tillage and straw mulching treatment increase significantly the C/N ratio, which was up to11.40%higher than conventional fertilization treatment.4. The the treatments in no-tillage&straw mulching, nitrogen regulation and doubling cow manure combined nitrogen regulation increased the content of soil microorganism using and mineralization nitrogen, increased soil microbial quantity and more fixed nitrogen, to decrease the risk of nitrogen loss. The content of dissolved organic nitrogen of the above first two treatments was significantly higher than conventional fertilization treatment in tilth soil, about28.20%and28.68%respectively. The soil microbial biomass carbon of the above latter two treatments increased74.77%and32.43%, and soil microbial biomass nitrogen increased68.54%and20.94%.5. The different agronomic techniques had significant effect on the agronomic characteristics. The height and chlorophyll content in Rice of no-tillage&straw mulching was down to4.90%and6.60%respectively lower than conventional fertilization treatment. The height, dry weight and chlorophyll content in garlic/rice of only cow manure treatment was respectively lower than conventional fertilization treatment.6. The no-tillage and straw mulching, doubling cow manure combined nitrogen regulation and nitrogen regulation treatments could guarantee yield. Compared with conventional fertilization treatment, garlic economic benefit of the three treatments increased by4.35%,6.64%and7.58%4.39%respectively; the yield of cow manure treatment in garlic and rice reduced by19.46%and19.81%respectively.7. The no-tillage and straw mulching, doubling cow manure combined nitrogen regulation and nitrogen regulation treatments could reduce the risk of nitrogen loss. Compared with conventional fertilization treatment,0-20cm soil nitrate residue of above three treatments reduced by71.55%,71.39%and62.81%in garlic harvest, and the total dissolved nitrogen content reduced by57.94%,33.10%and55.78%during the week after rice planting.In conclusion, optimized application of fertilizer, applying organic manure combined with no-tillage and straw mulching can improve soil properties, increase soil fertility and reduced effectively the risk of nitrogen loss, is a good choice for the agronomic techniques in Erhai lake basin. |
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