| The topdressing nitrogen fertilizer after transplanting rice seedling was generally applied by artificially spreading on surface in paddy rice, which was one of the factors resulting in low rice yield and inefficiency in nitrogen use, and a major limiting factor in mechanization as well. This study was to investigate the feasibility of mechanical topdressing readily available nitrogen fertilizer and polymercoated urea without additional fertilizing, in a hope to provide a theoretical basis of mechanization of topdressing fertilizer for paddy rice. The experiments were conducted in Jiansanjiangdaxing farm from 2013 to 2014. Under the condition of applying the same total fertilizer and base fertilizer dosages, farmers’ fertilizer practice method(FFP) and method of mechanical topdressing polymer-coated urea with 50 days’ release duration(OPT1) and 60 days’(OPT2) polymer-coated urea were used to assess the effect of mechanical fertilization on rice yield and dry matter accumulation. Meanwhile, laboratory and field experiments were conducted to measure the release rate of polymer-coated urea. The main findings were as follows:The release duration of two kinds of polymer-coated urea(release rate were 80%) were approximately 40 days and 63 days in 25℃ water, respectively. The corresponding release duration in the field is approaching 48 days and 76 days, respectively. The release cycle of the two polymer-coated urea were longer under the field condition. The release rate of two polymer-coated urea reached 1% for 1.4 and 2.9 days in laboratory, while in the field, it was less than 1 days. When releasing amount took no more than 30%, the release rate of the two polymer-coated urea were faster in the field than that in the laboratory. But when the releasing amount reached 50%, there were no difference in the release rate between them.Because a 5 cm-distance between fertilizers and rice roots were established by mechanized topdressing method while transplanting, rice roots could absorb N timely. Therefore, compared with FFP, OPT1 and OPT2 prevented rice from obviously turning green to yellow, promoted early rice growing and tillering quickly, and thus increased rice numbers of panicles at maturity stage. Under the condition that other yield-relevant factors showed little differences, OPT1, in comparation with FFP treatment, increased rice yield by 13.37%(P<0.05) averagely, while OPT2 increased rice yield by 19.59%(P<0.05) averagely. Meanwhile, due to ensuring the rice nitrogen demand during the whole growth stage, nitrogen accumulation and dry matter accumulation in applying OPT1 were increased by 13.98% and 9.33%, respectively. And they were increased by 21.39% and16.68% in applying OPT2, respectively. Mechanical fertilization of OPT1 increased the average income by about 3033.50 yuan per hectare by significantly increasing rice yield, despite the increase in the investment of per unit area. OPT2 created 1537.50 yuan per hectare higher income than OPT1 because of higher yield but lower price in raw material.Compared with FFP of surface application, mechanical topdressing readily available nitrogen fertilizer and polymer-coated urea without additional fertilizing, significantly promtes rice seedlings to turn green, satisfies the rice nitrogen demand during the critical stage(mid and late stage), and ensures a higher rate of tillering, and increases rice numbers of panicles at maturity stage. Meanwhile it enhances nitrogen and dry matter accumulation, and significantly increases rice yield and nitrogen efficiency. Mechanical topdressing readily available nitrogen fertilizer and polymer-coated urea could enable the realization of mechanization in paddy field fertilizers topdressing. Mechanical topdressing polymercoated urea release period with over-70-day release as the best, can increase rice yield and the farmers’ income per hectare for it ensures better rice growth in both stages of tillering and yielding and save the labor cost despite the added investment of machinery. |
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