| The inefficient utilization of nutrient resources as result of irrational fertilization input has become common problems in rice-wheat rotation in southern Jiangsu province of China.However,the study about soil nutrient supply capacity in southern Jiangsu province which was very important for reducing nutrient losses was rare.Most of the previous studies about the effect of reduction of fertilization,optimized fertilization on soil fertility and crop production were short-term trials.For this,a long-term fertilization experiment was conducted in rice-wheat rotation in the middle-lower Yangtze area of China.Nutrient deficiency treatments were set from June 2012 to study soil nutrient supply capacity of paddy-upland rotation system in southern Jiangsu province.(1)CK:without nitrogen fertilizer,phosphorus fertilizer and potassium fertilizer;(2)PK:no nitrogen fertilizer;(3)NK:no phosphorus fertilizer;(4)NP:no potassium fertilizer;(5)NPK:with nitrogen fertilizer,phosphorus fertilizer,potassium fertilizer.In addition,Three different fertilization treatments(FFP(farmers' fertilization practice),(OF,optimized fertilization through optimal application times)and(ORF,optimization of reducing fertilization))were utilized to evaluate the effects of reduced N application on the productivity,nutrient uptake,soil fertility and nutrient balance in the rice-wheat(R-W)cropping system in southeast China,over a 6-year period.The results of the field experiment showed as follows:(1)Nutrient supplying capacity of soilThe N,P and K natural supplying capacities of soil and the basic productivity of soil and their varieties were studied with long-term fertilization experiment in the wheat-rice rotation system.The results of the experiment indicated that the contribution of the natural productivity of soil for the yields of wheat and rice were in 56.0%and 26.5%.The contributions of chemical fertilizers for the yield increases of rice and wheat were in 44.0%and 73.5%.The amount of nutrient demand in wheat was higher than that in rice.The average natural supplying amounts of nitrogen,phosphorus and potassium from soil were 37.4,11.1 and 53.8 kg hm2 in wheat seasons,and were 86.1,36.3 and 153.7 kg hm2 in rice seasons,respectively.In rice-wheat rotation system,the amounts of N natural supplying by soil gradually decreased in wheat season year by year,the amounts of K natural supplying by soil gradually decreased in rice seasons.The natural productivity of soil could support some yields of crop,which were about 1.4t/hm2 for wheat and 5.6 t/hm2 for rice.(2)Dynamic process of soil fertility between seasonsDifferent fertilization treatments were conducted to research the dynamic process of fertility factors in paddy-upland rotation.The results showed that:there were obvious"wave" variations in soil pH,TN,AP,and AK for paddy-upland rotation.The pH increased in rice but decreased in wheat season,while AP and AK went with the opposite way.After rice harvest by 2015,compared with the FFP treatment,total soil nitrogen,and available potassium of the OF treatment were increased significantly.And organic matter,total phosphorus,available nitrogen and available phosphorus were increased.There was no significant difference in parameters of soil fertility between the FFP treatment and the ORF treatment.That is to say long-term reduction of fertilizer application did not significantly reduce soil fertility,Optimized fertilization(OF)increased soil fertility.(3)Yield and nitrogen uptake of rice and wheatA distinct reduction in fertilizer N application rates to summer rice and winter wheat crops is possible without a significant decrease in mean grain yields because of the filled-grain percentage and 1000-grain weight of ORF treatment increasing.The total number of spikelets of OF treatment was increased,then crop yields of OF treatment is higher than the FFP treatment.Compared with the FFP treatment,the apparent N recovery efficiency(REN)of the OF and ORF treatments increased by 7.6%and 11.8%on average for rice(p<0.05)and increased by 1.7%and 1.3%on average for wheat(p>0.05).(4)Nutrient uptake and apparent nutrient budgetsAt mature stage of wheat,compared with the FFP treatment,the ORF treatment had no effect on the uptake of N?P?K,the OF treatment significantly increased the amount of nitrogen and potassium uptake by 14.9%and 25.0%.At mature stage of rice,nutrient uptake by rice was promoted by the OF treatment but limited by the ORF treatment compared with the FFP treatment across all years.The amount of nitrogen and phosphorus uptake by rice was significantly reduced by 14.7%and 8.5%.Apparent nutrient budgets showed positive nitrogen and phosphorus balances but negative potassium balance in all treatments.Compared with FFP,ORF led to much lower N surplus due to less nutrient inputs while OF led to lower N surplus due to the nitrogen application were postponed. |
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