| At present, the total consumption of chemical fertilizers in China has accounted for about one third of the world's total consumption, while the consumption per unit field has far exceeded the world's average level, furthermore, applying chemical fertilizers massively and ignoring organic fertilizers have been the outstanding problems in rice production in China. Low fertilizer-N Use Efficiency, low ratio of output/input and environment pollution, etc, are the new problems need to solve. It's very useful if we can mixed the organic fertilizer which from agricultural production system and inorganic fertilizer to maintain the long term sustainability of rice production.The objectives of this dissertation were:(1) Prove the effects of tillage and straw return on the growth and rice grain yield; (2) Study the effects of tillage and straw return on fertilizer absorption and fertilizer-N use efficiency; (3) Investigate the effects of site-specific nitrogen management on the growth, grain yield and fertilizer-N use efficiency of rice; (4) Explore the effects of combining tillage and straw return with nitrogen management on the yield and fertilizer-N use efficiency of rice; (5) Study the effects of the mixed application of chemical fertilizers and organic fertilizers on the yield and fertilizer-N use efficiency of rice. In this study, field and pot experiments were conducted, and the following results were obtained:(1) Compared with conventional tillage, zero tillage had the comparable rice yield in our experiment. Influence mechanism of rice growth and yield under different tillage model were studied, the results suggested that, compared with conventional tillage, although the maximum root length and tiller number were litlle lower at early growth stage under zero tillage treatment, however, it had comparable leaf area index, leaf N content (SPAD value) and effective panicles at maturity stage through increased spike rate, moreover, the root bleeding sap increased by 14.3% compared with conventional tillage, and the N, P, K accumulation at maturity stage were no difference between them too.(2) Grain yield was increased after straw returned when no N fertilizer applied, however, yield increasing effect of rice straw return was covered by the increasing effect of fertilizer-N when the amount of N fertilizer applied between 100 kg N ha-1 to 150 kg N ha-1 in our experiment, so no difference was found between straw returned treatment and removed treatment. All straw return and half straw return treatments were not decreased grain yield through site-specific nitrogen management and reasonable water management. In our experiment, compared with no straw return treatment, grain yield of straw return treatment increased from 10.3% to 16.7% when no N-fertilizer applied. That's because the straw has high C:N ratio, the inorganic N of soil was immobilized by microorganism in shot-term after returned, the leaf SPAD value was lower compared with no return treatment in early growth stage, while with the plant growth, roots can absorb much more nutrient from soil after straw decomposed, so the leaf SPAD was higher compared with no straw return at middle and late growth stage, and increased root activity, so the rate of dry matter accumulation was higer, it benefit to increase the biomass and spikelets per m2, and lead to yield increasing. However, the increasing effect was not significant after straw return under N-fertilizer treatment, that's the reason of no yield difference between straw returned and no returned treatment.(3) In our experiment, compared with farmers'N-fertilizer practice (FFP), the amount of applied N-fertilizer was dcreased by 16.7%-32.0%, but grain yield of site-specific nitrogen management (SSNM) showed difference trend in different year, no difference was found in 2004 and 2005, however grain yield increased significantly in 2006, the reasons were spikelets per panicle, spikelets per m2 and harvest index increased significantly.(4) Straw return improved the N uptake of rice plant. In our expertiment, compared with straw removed treatment, N uptake was increased by 12.1%,11.1% and 5.6% in three years, respectively, moreover, N uptake was increased more significantly under no fertilizer-N application, and increased by 14.4%,25.7% and 25.8% comparing with no straw return, respectively.(5) Compared with no straw returned treatment, fertilizer-N use efficiency was increased significantly under the straw returned treatment, agronomic use efficiency of fertilizer-N (AE) increased from 14.8% to 20.6%, partial fator productivity (PFP) increased from 1.9% to 8.4%, and physiology use efficiency (PE) increased from 4.3% to 36.3%. Under the different tillage and straw return treatment, we compared the fertilize N use efficiency between SSNM and FFP, the results showed that, AE, PE and recovery efficiency (RE) of SSNM were all significantly higher than that of FFP treatment, 40.5%-54.2%,26.5%-50.1% and 27.7%-62.0% increased, respectively, because compared with FFP treatment, the yield of SSNM treatment is comparable or increased significantly, however, its nitrogen application amount was decreased greatly.(6) Mixed application of organic and inorganic fertilizer increased the rice yield from 12.5% to 22.3% in our experiment, the reasons were significant higher dry matter accumulation and larger sink (panciles per m2, spikelets per panicle and spikelets per m2). After organic fertilizer applied, the length, width and leaf area of rice top three leaves increased, that lead to the leaf area index increased, leaf N content (SPAD value) was higher in whole growth stage, and the root bleeding sap at middle and late growing stage was larger, meanwhile the dry matter accumulation stage was higher, that's all the basis of the yield increase. After analyzed the response curve of grain yield, the results showed that, with the increase of organic fertilizer applied, fertilizer N amount was decreased when got the highest grain yield, so, we need adjust the amount of fertilizer N when we mixed application of organic and inorganic, to improve the organic and inorganic fertilizer effect together. In our experiment, residual effect of organic and inorganic fertilizer applied in early season was found, grain yield of late season rice was significantly higher when the amount of organic and inorganic fertilizer applied higher in early season. |
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