| Hengshao basin is the main grain producing area in Hunan province,its rice production accounts for more than a quarter of the total grain output of Hunan province.However,it has been confronted perennially with the problems of excessive fertilizer rate and low fertilizer utilization efficiency.This study focused on the subject of double cropping rice in south Hunan,studied the effects of nitrogen application rate and nitrogen fertilizer management ways,the combined application of calcium cyanamide granular fertilizer and urea on rice growth and development,rice yield and quality,nitrogen use efficiency and soil physical and chemical properties,respectively.This study aimed to explore the key technologies of rice nitrogen use efficiency,and to lay the foundation for the construction of rice nitrogen high efficiency utilization system in south Hunan.The main results were as follows:1)The nitrogen application rate and nitrogen fertilizer management text showed that thenitrogen ratehad no main effect on yield of early and late rice.Early rice yield and panicles sharply increased when the proportion of basic-tiller nitrogen fertilizer decreased at 180 kg/hm~2 nitrogen level.Late rice yield could improve significantly when the proportion of panicle nitrogen fertilizer reached 30%,and the late rice yield increased by 18.7%,16.0%,4.7% than that without panicle nitrogen fertilizer at 150,180,210 kg/hm~2 nitrogen rate levels,respectively.High nitrogen levels(210 kg/hm~2)+ delayed nitrogen application treatments could effectively improve the early and late rice quality.There was no significant difference in rice quality between the different nitrogen rates and nitrogen management ways,except the rice crude protein content.The early and late rice crude protein content improved regularly with the increaseof panicle nitrogen fertilizer proportion.There was no significant effect on organic matter content in the soil which treated by different nitrogen fertilizer rates and nitrogen management ways in the short term.Soil alkali-hydrolysable nitrogen content and urease activity had a certain increase with the increase of nitrogen fertilizer rate in early rice season,while it had no obvious change in late rice season.Nitrogen management ways had been proved to be invalid on soil alkali-hydrolysable nitrogen content and urease activity.Nitrogen fertilizer rate increase significantly decreased the nitrogen partial productivity,nitrogen agronomy efficiency and nitrogen recovery efficiency of early and late rice.Abnormally,early rice nitrogen partial productivity,nitrogen agronomy efficiency,nitrogen harvest index,nitrogen physiological efficiency and nitrogen transportation efficiency improved with the basic-tillering nitrogen fertilizer raising.However,it could significantly improve the late rice nitrogen partial productivity,nitrogen agronomy efficiency and nitrogen recovery efficiency when the panicle nitrogen fertilizer proportion increased,while the nitrogen transportation efficiency decreasedinstead.Correlation analysis showed that there was almost no correlation between the nitrogen fertilizer rate and yield in early and late rice.It showed that the nitrogen fertilizer rates were negatively related with the rice nitrogen partial productivity,nitrogen agronomic efficiency,nitrogen harvest index and nitrogen physiological efficiency.On the whole,the proportion of panicle nitrogen fertilizer on 180 kg/hm~2 nitrogen levels in the early and late rice yield and nitrogen utilization ratio had positively correlated relationship.2)Calcium cyanamide granular fertilizer was proved to be toxic to early rice,and hindered its growth and sharply decreased the yield.Combined application of urea and calcium cyanamide granular fertilizer(300 kg/hm~2)could significantly increase the late rice yield and panicles,and the yield increased by 3.1%(2015)and 28.7%(2016)than that of the conventional nitrogen treatment.There was no significant difference in rice quality between the different nitrogen combined application ways,identically,except the rice crude protein content.The late rice crude protein content rose slightly with the increased of calcium cyanamide granular fertilizer.Calcium cyanamide granular fertilizer application had proved to be ineffective on soil organic matter content and urease activity,while decreased the soil alkali-hydrolysable nitrogen content.Significantly increase was observed in rice plant nitrogen content,nitrogen accumulation and rice nitrogen partial productivity,nitrogen agronomic efficiency and nitrogen recovery efficiency when 300 kg/hm~2 calcium cyanamide granular fertilizer was applied.Calcium cyanamide granular fertilizer application was significantly positively related to the rice yield and panicles.Furthermore,the roughly positive correlation had been also found between the calcium cyanamide granular fertilizer application rate and nitrogen partial productivity,nitrogen agronomic efficiency and nitrogen recovery efficiency.3)In this test,overall,the nitrogen rates(150 kg/hm~2,180 kg/hm~2 and 210 kg/hm~2)made no main effect on early and late rice yield in south Hunan;Delayed nitrogen application increased the late rice yield significantly,while it did not work on early rice.Delayed nitrogen application in 180 kg/hm~2 nitrogen rate could significantly improve the early and late rice yield and nitrogen use efficiency.Calcium cyanamide application could dramatically decreased the early rice yield in south Hunan,while combined application of urea and calcium cyanamide granular fertilizer(300 kg/hm~2)could significantly increase the late rice yield and nitrogen use efficiency. |
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