| Serious soil erosion not only reduces the volume of top soil, but also reduces the quantity of a range of soil nutrients, resulting in low crop yields in the Loess Plateau. The traditional tillage practice exacerbated wind and water erosion by soil disturbance, soil erosion is more serious. No-till farming and crop residue retention both control erosion and maintain crop yields by increasing surface cover and enhancing soil nutrient conversion through changing hydrothermal processes. This study was conducted on a no-till and crop residue incorporating corn-wheat-soybean crop rotation system in the Loess Plateau area after4rotation cycles. Soil organic nitrogen mineralization characteristics were measured by the long-term aerobic incubation method and in-situ incubation method, in order to reveal the mechanism for no-till and crop residue incorporation increasing crop production from the perspective of soil nitrogen cycle. Following are the main results:1. Indoor incubation conditions, the rotation system under three crop phases, the effect of no-till and crop residue on the amount of soil organic nitrogen mineralization all showed vertical differentiation characteristics; the amount of soil organic nitrogen mineralization in the0-5cm layer was improved under no-till treatment, the decline was10.3～35.9%; and in the5-10cm layer it was improve under crop residue treatment, the decline was4.8～28.9%.2. Potentially, mineralized N is differrent with crop phases. In the maize rotation, no-till and crop residue increased potentially mineralized N in the0-5cm and5-10cm soil layers by27.9%and11.3%, respectively. In the wheat rotation, crop residue reduced potentially mineralized N in the0-5cm soil layer by14.1%while the other treatments did not have significant effect on the0-5cm and5-10cm soil layer. In the soybean, rotation, no-till with crop residue enhanced potentially mineralized N in the0-5cm and5-10cm soil layers by49.3%and6.6%, respectively. Wheat soil potentially mineralized N was higher than maize and soybean soil, however it had the lowest proportion of mineralization. Soybean soil was the reverse of this.3. Within the three phases crop rotation system under in-situ incubation conditions, soil organic N nitrification rate increased by an average of490%, mineralization rate increased by an average of130%and nitrate leaching losses were reduced by an average of11.7～42.8%under no-till and crop residue treatment than traditional tillage treatment.4. At11years, compared with traditional tillage treatment, surface0-5cm layer of soil nitrate content significantly increased3.3mg/kg under treatment with both tillage and residue retention, whereas other treatments had no significant effect; In the5-200cm soil layer, soil nitrate content decreased significantly under no-till and crop residue treatments, the decline was17.0～74.8%and the decline in the60-120cm soil layer at harvest was the greatest; soil ammonium nitrogen content in the soil profile was low, the decline in the0-30cm soil layer was greater, the amplitude was0.9～6.4mg/kg and1.3～4.4mg/kg at sowing and havesting, but less in the30-200cm soil layer, the amplitude was3.9～5.3mg/kg and0.9～2.0mg/kg at sowing and havesting. The performance of time series for ammonium nitrogen content showed that the harvest content was higher than sowing content.5. At11years, during the stage of the maize, crop residue treatment significantly increased nitrogen use efficiency by24.9%; no-till significantly reduced soil nitrogen use efficiency, no-till with no crop residue treatment was42.3%,32.8%lower than conventional tillage treatment. |
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