| In order to evaluate the influence of no-tillage on change of soil available nitrogen, transformation of nitrogen content of paddy field after fertilization, ammonia volatilization, nitrogen leaching, rice uptake nitrogen, soil residue nitrogen, nitrogen balance, rice growth, rice nitrogen content, rice nitrogen efficiency, soil profile properties, soil physical and chemical properties, soil enzyme activities and soil microorganism quantity of paddy field, Field experiments with four treatments, common no-tillage (CNT), no-tillage with rice straw returning (SNT), common conventional tillage (CCT), conventional tillage with rice straw returning (SCT) were carried out.The main results are as follows.1. Transformation of soil nitrogen in no-tillage paddy fieldNitrogen transformation of paddy soil were obviously affected by no-tillage for the change of tillage and fertilization as compared with conventional tillage. Contents of nitrate nitrogen in0-5cm soil layer and alkaline-hydrolyzable nitrogen in5-20cm soil layers were reduced, but contents of ammonium nitrogen, nitrate nitrogen and total nitrogen of soil surface water were increased in1-6days after fertilization under no-tillage condition. Rice straw returning made an obvious influence on nitrogen transformation. Treatment of CNT increased contents of nitrate nitrogen in0-20cm soil layer, contents of alkaline-hydrolyzable nitrogen in0-5cm soil layer before filling stage, but reduced content of ammonium nitrogen in0-5cm soil layer. Treatment of SNT increased contents of nitrate nitrogen and alkaline-hydrolyzable nitrogen in0-5cm soil layer, but declined contents of ammonium nitrogen, nitrate nitrogen and total nitrogen of soil surface water after fertilization as compared with CNT.2. Migration of nitrogen in no-tillage paddy fieldGreat change took place in migration of soil nitrogen in no-tillage paddy field for soil with no ploughing and surface application as compared with conventional tillage. Treatments of no-tillage increased quantity of ammonia volatilization in1-6days after fertilization and each rice growth stage, quantity of leaching nitrogen. Rice straw returning made an obvious influence on nitrogen migration. CNT reduced nitrogen quantity of rice uptake and soil residue, while SNT increased nitrogen quantity of soil residue as compared with treatments of conventional tillage. Treatment of SNT reduced nitrogen amount of ammonia volatilization in1-6days after fertilization and each rice growing stage, amount of leaching nitrogen, amount of rice uptake nitrogen as compared with treatment of CNT.3. Balance of nitrogen in no-tillage paddy fieldNitrogen balance of paddy field was obviously affected by tillage ways and rice straw returning. Nitrogen import amount of CNT was roughly equal to treatment of CCT, but nitrogen import was more, so residual nitrogen of soil was less than CCT. Nitrogen import amount of SNT was roughly equal to treatment of SCT, but nitrogen import was less, so residual nitrogen of soil was more than SCT. The treatment of SNT increased more nitrogen than that of CNT in soil. Rice straw returning plays an important role in maintaining nitrogen balance of paddy field.4. Growth and nitrogen utilization of rice under no-tillageGrowth and nitrogen utilization of rice under no-tillage was obviously affected by tillage ways and rice straw returning. Rice straw returning promoted rice to grow and absorb more nitrogen, so nitrogen recovery efficiency (NRE) of rice was increased. The rice height, amount of rice tillers, amount of rice valid tillers, rice leaf area index, rice leaves nitrate reductase activity, content of rice leaves RuBPcase, rice dry matter accumulation, nitrogen content of rice leaves and stem, total nitrogen accumulation (TNA), NRE and yield of CNT were least, but the nitrogen content of rice spike, nitrogen grain production efficiency (NGPE), nitrogen transportation efficiency (NTE), nitrogen harvest index (NHI) were most among the treatments. The rice height, amount of rice tillers, amount of rice valid tillers, rice leaf area index, rice leaves nitrate reductase activity, content of rice leaves RuBPcase, TNA, nitrogen content of rice leaves and stem, rice nitrogen accumulation, nitrogen agronomy efficiency (NAE), NRE and yield of SNT were more than CCT. 5. Influence of no-tillage on profile morphological characteristics of paddy soilNo-tillage of paddy field made an deep influence on profile morphological characteristics of paddy soil.There were obvious difference between soil profile morphological characteristics formed with rice straw returning and that formed without rice straw returning. The morphological characteristics of Ap layer (plow sole), W layer (waterloggogenic horizon) and C layer (parent material horizon) were not obviously affected by no-tillage of paddy field, but great changes took place in that of Aa layer (arable horizon). The Aa sub-constitution formed by CNT is Aal-Aa2-Aa3, while by SNT is O-Aal-Aa2-Aa3. O layer, litter layer consisted of rice straw in differently decomposed level is unique profile horizon of SNT. Aal layer of no-tillage treatments is thinner, but blacker in color, less in soil bulk density, granular in structure, lower in pH value, more root, more pore, looser than that of conventional tillage. Aa2and Aa3layer of CNT is lighter in color, bigger in soil bulk density, less root, and pore, less iron-humus mottling, with higher position of fissure and solider than that of CCT. The Aa2and Aa3layer properties of SNT are equal to that of conventional tillage.6. Influence of no-tillage on physical properties of paddy soil No-tillage increased soil water retention properties in0-5cm layer, and added amount of> lmm water stable macro-aggregate in0-5cm layer. The soil water retention properties, available moisture, amount of water stable macro-aggregate of SNT in5-20cm layer were equal to those of conventional tillage, but CNT reduced the soil water retention properties, available moisture, quantity of water stable macro-aggregate in5-20cm layer as compared with conventional tillage.7. Influence of no-tillage on chemical properties of paddy soilContent of organic carbon, nitrogen, phosphorus, potassium in upper soil layer are higher than that in lower soil layer under no-tillage. No-tillage increased content of humus, cation exchange capacity, available zinc, available boron in0-5cm soil layer, and reduced content of exchangeable calcium, exchangeable magnesium and available copper in0-5cm soil layer, lowered pH value in upper soil layer. As compared with conventional tillage, content of organic carbon, humus, total nitrogen, total phosphorus, total potassium, alkaline-hydrolyzable nitrogen, rapidly available phosphorus, rapidly available potassium, cation exchange capacity, exchangeable calcium, exchangeable magnesium, available zinc, available boron in5-20cm soil layer of no-tillage were lowerer than that of conventional tillage, and between SNT and CNT, the least reduced range was CNT. Content of alkaline-hydrolyzable nitrogen, rapidly available potassium, exchangeable calcium, exchangeable magnesium and available copper in Ap layer, W layer and C layer, content of available zinc, available boron in W layer and C layer of no-tillage tended to become higher than that of conventional tillage.8. Influence of no-tillage on soil enzyme activities of paddy soilAs compared with conventional tillage, treatments of no-tillage increased activities of sucrase, urease, protease, catalase, polyphenol oxidase in0-5cm soil layer, and between SNT and CNT, the most increased range was SNT, but reduced activities of sucrase, urease, protease, catalase, polyphenol oxidase in0-5cm soil layer, and between SNT and CNT, the least reduced range was CNT.9. Influence of no-tillage on soil microorganism quantity of paddy soilAs compared with conventional tillage, treatments of no-tillage increased quantity of fungus, actinomyces in0-5cm soil layer, and between SNT and CNT, the most increased range is SNT. Treatments of no-tillage reduced quantity of bacteria, fungus, actinomyces, anaerobic nitrogen-fixing bacteria, aerobic cellulose decomposing bacteria, anaerobic cellulose decomposing bacteria in5-20cm soil layer, and between SNT and CNT, the least reduced range is CNT. The quantity of ammonifying bacteria in0-20cm soil layer, quantity of fungus and actinomyces in5-12cm soil layer of SNT were more than other treatments.Therefore, the effects of SNT on growth, yield, nitrogen utilization of rice and soil fertility properties are superior to those of CNT. |
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