Nitrogen Nutrition And Its Regulation Of Kiwi-orchard In A Small Catchment On The Northern Slope Of The Qinling Mountains

The northern slope of the Qinling Mountains is one of the main kiwifruit producing areas,which accounts for nearly 60% of the total area of kiwi cultivation in China.However,in recent years,excessive application of nitrogen?N?fertilizers in the region is very common due to pursuiting of the high fruit yield and profits by local farmers.As a result,the N surplus in kiwi-orchard has become very severe in the region.Over-application of N fertilizers can never guarantee significant increase in the fruit yield,but could cause the waste of resources and poses a series of environmental threats,which influence the sustainable development of kiwi-fruit industry in a big way.Therefore,we chose Yujiahe catchment,located in Zhouzhi County in the northern slope of the Qinling Mountains,Shaanxi province,as our study base to investigate the nutrient inputs in more than 240 mature kiwi-orchards in years?2012,2013?.We have determined nutrient removals by fruit harvesting and branch pruning of the kiwi-orchards to evaluate the nutrient output during an annual growing cycle.The contents of soil nutrients both in kiwi-orchards and wheat-maize rotation systems were compared to evaluate the effects of long-term fertilization on potential environmental pollution in kiwi-orchard.The nutrient accumulation and movements in 0-200 cm soil profile of orchards on the slope land before and after rainy season during 2-year successive were compared.The effects of reducing N fertilization on fruit yield,quality,and nitrate in soil profiles were evaluated with a 3-year field experiment.Finally,we used the substance flow analysis method analyse of nitrogen flow of the kiwi-orchard in this area.The main conclusions are as follows:1.The results of survey for two consecutive years?2012²013?showed that the manure inputs in this catchment were significantly insufficient,about 36.4% of orchards did not use manure at all,and 94.3% of orchards had an inadequate input of manure.As for chemical fertilizers,the input of N fertilizers was generally high with an average of 891 kg N ha^-1.About 81.8% of orchards overused nitrogen fertilizer,and for the application of phosphorous and potassium,both over-and under-supply existed.We recommended nutrients application rates for N(375⁵00 kg ha^-1),P2O5(186²66 kg ha^-1),and K2O(286³50 kg ha^-1)for a yield target between 24⁴2 t ha^-1.Therefore,it was recommended to increase the application ratio of manure,decrease nitrogen input and rationally using phosphorus and potassium fertilizers can be key points for better nutrients management in this catchment.2.The nutrients concentrations in leaves,fruits,and pruning branches showed no significant differences among the different varieties?Qinmei,Yate,and Huayou?of kiwi-vines?P < 0.05?.According to the average fruit yield of 33.9³9.5 t ha^-1 and pruning rate of 7¹1 t ha^-1?FW?,the nutrients removed by fruit harvest and branch pruning averaged 75.0⁹2.8 kg ha^-1 for N,19.4²4.9 kg ha^-1 for P,90.0¹17.7 kg ha^-1 for K,22.9²7.3 kg ha^-1 for Ca,5.05⁷.00 kg ha^-1 for Mg,and 2.60⁴.89 kg ha^-1 yr^-1 for S during the annual growth cycle.3.The comparison of nutrient balances between kiwi-orchards and wheat-maize rotation croplands showed that the total N,P,and K input?chemical fertilizers,manures,deposition and irrigation?averaged 1201,268,and 615 kg ha^-1 yr^-1 respectively,which is higher than those in croplands(N 425 kg ha^-1 yr^-1,P 59 kg ha^-1 yr^-1,and K 109 kg ha^-1 yr^-1).The apparent N,P,and K surplus in kiwi-orchards were as high as 1081,237,and 491 kg ha^-1 yr^-1,respectively.The nitrate accumulation in 0^-100 cm and 0-200 cm soil depths reached up to 466 and 793 kg N ha^-1,respectively,which were significantly higher than that in croplands.It indicated that the excessive nutrient inputs in kiwifruit orchards resulted in a serious problem of nutrient surplus,especially of nitrogen in the area.4.The study on nutrient accumulation and movements in sloping orchard indicated that the summer rains from May to September was a driving factor.After a rainy season,soil nitrogen moved both vertically and downward along the slope.The vertical movement of nitrogen leads to a large accumulation of nitrate in deep soil layers with a risk to be leached.The downward slope movement resulted in the spatial heterogeneity of nutrients distribution?i.e.,nutrition in upper slope was low,and was high in lower slope?.These processes caused a waste of resources and potential threat to both surface and ground waters.Therefore,we suggest reducing the application rates of N fertilizers in slope kiwi-orchards.Moreover,more fertilizer should be applied in the top of slope and less fertilizer applied in the bottom of slopes.5.The results of field experiment for 3 consecutive years showed that,in comparison with farmer conventional fertilization,reducing nitrogen application rates by 25% in 2013 and 2014,and by 45% in 2015 did not have significant effects on nitrogen nutrition,fruit single weight,yield and fruit quality?P > 0.05?.Meanwhile,reducing fertilization significantly enhanced the partial factor productivity of applied nitrogen and economic profits of local farmers,and decreased nitrate accumulation and leaching into deep soil layers.Compared with common urea,the application of controlled released urea did not have a significant effect on fruit yield and quality,but decreased the risks of nitrate leaching.6.The nutrient flow analysis showed that the nitrogen input in kiwi-orchards was much higher compared with wheat-maize rotation system.The large accumulation of nitrogen in orchards brought a big burden for the quality of soil,atmosphere,and water.Total nitrogen input in kiwi-orchards was 1220 kg N ha^-1,in which 783 kg N ha^-1 remained in soil.Nutrients removal by fruit harvest,branch pruning and plant storage accounted for 27% of the total outputs.Nutrients flowed into water and atmosphere accounted for 46.7% and 26.5%,respectively.The data calculated that the total nitrogen input in water and atmosphere reached 32.6 t N and18.6 t N,which was very higher than wheat-maize rotation croplands?3.98 t N and 5.50 t N?.In conclusion,compared with farmland system,the excessive application of N fertilizers in kiwi-orchards has resulted in high accumulations of nitrate in soil,which decreased nitrogen use efficiency,and increased N loss to deeper soil layers,atmosphere,and water environments.Therefore,controlling the total nitrogen input and using the variable fertilization can be a key to reduce nitrogen losses in order to ensure the healthy and sustainable development of kiwifruit orchards in this catchment.