| Three experiments with Chuanguyou 7329 as materials were conducted from 2015 to2017 to investigate the effects of slow-release urea reduced and combined with conventional urea on nitrogen utilization and yield formation of mechanical-transplanted rice under different plant spacing:(1)Effects of slow-release urea reduced and combined with conventional urea on nitrogen utilization and yield formation of mechanical-transplanted rice under different nitrogen application rates:two nitrogen level,high nitrogen level(180 kg/hm~2)and conventional nitrogen level(150 kg/hm~2),combined with five different ratio of slow-release urea and conventional urea(10:0,7:3,5:5,3:7,and 0:10)were set in this experiment;(2)Effects of slow-release urea reduced and combined with conventional urea on nitrogen utilization and yield formation of mechanical-transplanted rice under different plant spacing:three different plant spacing(16 cm,18 cm,and 20 cm)with 30 cm of row spacing and four slow release application rates(36 kg/hm~2,66 kg/hm~2,96 kg/hm~2,and 126 kg/hm~2)combined with 54 kg/hm~2of conventional urea were set in this experiment;(3)Effects of conventional urea reduced and combined with slow-release urea on nitrogen utilization and yield formation of mechanical-transplanted rice under different plant spacing:three different plant spacing(16 cm,18 cm,and 20 cm)with 30 cm of row spacing and four different nitrogen application patterns(96 kg/hm~2of slow-release urea combined with 24 kg/hm~2of conventional urea as basal fertilizer with no top-dressing;96 kg/hm~2 of slow-release urea as basal fertilizer and 24 kg/hm~2of conventional fertilizer as top-dressing;96 kg/hm~2of slow-release urea combined with 54 kg/hm~2 of conventional urea as basal fertilizer with no top-dressing;and 96 kg/hm~2of slow-release urea combined with 30 kg/hm~2of conventional urea as basal fertilizer and 24 kg/hm~2 of conventional urea as top-dressing)were set;and no fertilizer application treatment was set as control in all experiments.This research systematically studied the effects of combined application of slow-release urea and conventional urea with different plant spacing on nitrogen utilization and yield formation of mechanical-transplanted rice,soil physical and chemical properties,and as well as the relationships between photosynthetic production,nitrogen utilization,and grain yield.The main results are as follows:1.The effects of nitrogen fertilizer reduction and plant spacing on grain yield and its components of mechanical-transplanted riceThe yield of mechanical-transplanted rice in high nitrogen level was significantly higher than that in conventional nitrogen level.Compared with no nitrogen treatment,the yield of rice under the different nitrogen application treatments were significantly higher and increased by 12.81%to 26.60%.The treatment with 7:3 of the ratio of slow-release urea and conventional urea could significantly increase the number of effective panicle,spikelet number per panicle,and grain yield of rice,which was the best treatment in this study.Based on the best ratio(7:3)of slow-release urea and conventional urea,we continued to study the effects of slow-release urea reduced combined with the same amount of conventional urea(54kg/hm~2),namely,the varied nitrogen level,on yield formation of mechanical-transplanted rice under the different plant spacing.The results showed 96 kg/hm~2of slow-release urea combined 54 kg/hm~2 of conventional urea(150 kg/hm~2 of total nitrogen application)could guarantee enough effective panicle number,strong culm,and large panicle,increase the spikelet number per panicle,and gain the higher seed-setting rate and grain yield;and the yield of 150 kg/hm~2 of total nitrogen application increased by 2.76%to 13.98%when compared to 126 kg/hm~2 of slow-release urea combined 54 kg/hm~2 of conventional urea(180kg/hm~2 of total nitrogen application).Besides,18 cm of plant spacing with 30 cm of row spacing could significantly increase grain yield of mechanical-transplanted-rice.Under the condition of various plant spacing,the treatment that 96 kg/hm~2 of slow-release urea combined with 30 kg/hm~2 of conventional urea as basal fertilizer and 24 kg/hm~2 of conventional urea as top-dressing had the advantages in effective panicle number and spikelet number,maintained the higher seed-setting rate and 1000-grain weight.So,the treatment of18 cm of plant spacing with 30 cm of row spacing with 96 kg/hm~2 of slow-release urea combined with 30 kg/hm~2 of conventional urea as basal fertilizer and 24 kg/hm~2 of conventional urea as top-dressing was the best nitrogen application method for high yield in mechanical-transplanted rice.2.The effects of nitrogen fertilizer reduction and plant spacing on nitrogen utilization of mechanical-transplanted riceThe photosynthetic production,nitrogen uptake,nitrogen translocation,and nitrogen use efficiency of rice during the main growth stages in high nitrogen level were significantly higher than those in conventional nitrogen application.Compared with the conventional urea application,the treatment with 7:3 of the ratio of slow-release urea and conventional urea could improve photosynthetic production,dry matter accumulation,and nitrogen uptake and translocation;nitrogen increment in panicle increased by 34.85%to 48.00%;nitrogen apparent use efficiency increased by 67.00%to 88.75%;nitrogen agronomy efficiency increased by 67.30%to 90.51%;and partial factor productivity of applied nitrogen increased by 9.23%to 9.72%;especially,the higher nitrogen accumulation and nitrogen use efficiency were observed in high nitrogen level.When reducing the amount of slow-release urea combined with 54 kg/hm~2 of conventional urea and introducing the plant spacing,the results showed dry matter accumulation,population photosynthetic traits,nitrogen uptake and translocation,and nitrogen use efficiency of rice of the treatment 18 cm of plant spacing with30 cm of row spacing were higher than those of 16 cm or 20 cm of plant spacing with 30 cm of row spacing.Besides,under the condition of 18 cm of plant spacing and 30 cm row spacing combined with 96 kg/hm~2 of slow-release urea and 54 kg/hm~2 of conventional urea(150kg/hm~2 of total nitrogen application),the dry matter accumulation,population growth rate,nitrogen accumulation,nitrogen translocation,and nitrogen use efficiency of rice showed a significant increase,partial factor productivity of applied nitrogen increased by 20.43%to59.72%,and nitrogen agronomy efficiency increased by 28.65%to 75.94%when compared to other nitrogen application methods.Furthermore,when reducing the amount of conventional urea and changing the nitrogen application method,the treatment of 18 cm of plant spacing with 30 cm row spacing could significantly improve the nitrogen use efficiency of mechanical-transplanted rice during grain filling stage.Under the various plant spacing,the treatment that 96 kg/hm~2 of slow-release urea combined with 30 kg/hm~2 of conventional urea as basal fertilizer and 24 kg/hm~2 of conventional urea as top-dressing could get the best performance of dry matter,nitrogen and carbon accumulation,nitrogen translocation,carbon-nitrogen ration,partial factor productivity of applied nitrogen,and nitrogen agronomy efficiency.Correlation analysis showed that,leaf area index,net photosynthetic rate at grain filling stage,and photosynthetic potential from jointing stage to full heading stage were positively correlated with dry matter accumulation,effective panicle number,and grain yield(0.36*to 0.96*);nitrogen translocation from full heading stage to maturity stage,nitrogen and carbon accumulation at maturity stage,nitrogen use efficiency were significantly positively correlated with dry matter accumulation,effective panicle number,spikelet number,and grain yield(0.38**to 0.99**)under the reduced nitrogen application and plant spacing;especially,the highest relationship was found between photosynthetic potential from jointing stage to full heading stage,nitrogen accumulation at maturity and grain yield of rice.3.The effects of nitrogen fertilizer reduction and plant spacing on soil physical and chemical properties in mechanical-transplanted riceThe organic content in paddy field showed no difference between the two nitrogen application rates;and nitrogen content and urease activity in paddy field were higher in high nitrogen level condition.Under the different combination of slow-release urea and conventional urea,the nitrogen content and organic content in paddy field at grain filling stage were highest in the treatment with 7:3 of the ratio of slow-release urea and conventional urea;and urease activity in paddy field were higher in 10:0 and 7:3.These results indicated treatment with 7:3 of the ratio of slow-release urea and conventional urea was suitable for urease activity and maintained higher organic content and nitrogen content in the soil.While the amount of slow-release urea was reduced under different plant spacing,the urease activity and nitrogen content were the highest in 18 cm of plant spacing with 30 cm of row spacing,followed by 16 cm of plant spacing with 30 cm of row spacing.The highest urease activity and nitrogen content were detected in 18 cm of plant spacing with 30 cm of row spacing combined with 150 kg/hm~2 of total nitrogen application(96 kg/hm~2 of slow-release urea and54 kg/hm~2 of conventional urea).Furthermore,the treatment that 96 kg/hm~2 of slow-release urea combined with 30 kg/hm~2 of conventional urea as basal fertilizer and 24 kg/hm~2 of conventional urea as top-dressing,especially combined with 18 cm of plant spacing with 30cm of row spacing,was beneficial to nitrogen content,urease activity,and organic content in paddy field at grain filling stage. |
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