A Study On Fertilization Status And Nitrogen Optimization Of Watermelon In China

The planting area and yield of watermelon in China rank first in the world.It has a pivotal position in the international.At present,the regionalized development of watermelon industry in China is accelerating,but there is a lack of research on the current situation of field production in typical watermelon growing areas.The unreasonable fertilizers,pesticides and other agricultural resources not only affects the yield and quality of watermelon,but also causes a series of environmental problems such as non-point source pollution and greenhouse gas emissions.Thus it is urgent to quantify the input status of agricultural resources such as fertilizer in typical watermelon planting areas,evaluate the cost of environmental and resources,then conduct optimization research on key factors based on this.For this reason,this study adopted the method of life cycle assessment to study the three major watermelon cultivation areas in China including north China?NC?,northwest?NW?and southwest?SW?,through the questionnaire survey of farmers.The questionnaire survey coverd fertilizer and other agricultural materials input and output status,then the advantages of different cultivated areas was compared,the same as land resources use?LO?,water resource depletion?WD?,energy depletion?ED?,global warming potential?GHG?,acidification potential?AP?and eutrophication potential?EP?,a total of six aspects of resources and environment cost.The potentiality and the way of increasing the efficiency of watermelon were discussed.On this basis,field experiments were carried out in southwest China,where unit nutrient consumption was the highest,to further optimize the local nitrogen fertilizer application,and to discuss the influence of nitrogen fertilizer dosage under three cultivation modes of long-term facilities,common facilities and open-air cultivation?nitrogen fertilizer dosage of long-term facilities 0,112.5,169,225,281,338,450 kg/hm²;traditional facility cultivation and open-air cultivation 0,113,150,188,225 kg/hm²?and Organic substitution ratio?0,15%,30%and 45%?on growth,nutrient uptake,fruit quality,and the fertilizer use efficiency.It would provide technical support for the management of high yield and high quality nitrogen fertilizer and the ratio of organic fertilizer to nitrogen for watermelon under different cultivation modes in southwest China.The main results were as follows:?1?According to the investigation of farmers,the nitrogen fertilizer inputs in three watermelon cultivation areas were 558 kg/hm²,154 kg/hm² and 208 kg/hm²,higher than the amount recommended by experts.The average yield of watermelon in north China was 56.8 t/hm²,1.7 and2.7 times higher than that in northwest and southwest China.Compared with other crops and fruits,the environmental impact of the three watermelon cultivation areas in China was lower,but the resource and environmental cost of different regions had significant differences.Compared with the cultivation areas in NW and SW,the cultivation areas in NC had the highest consumption of resources and environment per unit area and the lowest consumption of resources and environment per unit yield.Fertilizer and organic fertilizer application were the most important contribution sources of GHG,AP and EP.The contribution rate of nitrogen fertilizer application in the field alone was as high as 85%,followed by phosphate fertilizer and potash fertilizer.Quadrantal analysis showed that the comprehensive index of resources and environment had about 50%optimization space by controlling yield and nitrogen fertilizer efficiency.Among them,the resource and environment cost of low yield and unit yield was the biggest in SW,which was worth further optimization.?2?The results of field experiment in southwest China showed that proper application of nitrogen fertilizer could increase the fruit weight per fruit,promote the fruit setting of watermelon,and increase the fruit weight and yield per fruit.Nitrogen application had different effects on peel thickness,soluble solid,titratable acid,difference value of solid,nitrate content,sucrose and glucose content,lycopene and other quality indexes.According to the analysis of comprehensive yield and various qualities,watermelon yield and fruit quality were the best when the nitrogen fertilizer amount was 225 kg/hm²,and the comprehensive score was 77.3%higher than that without nitrogen treatment.Dry matter and nitrogen accumulation were significantly affected by nitrogen content.In seedling stage and stretching stage,low nitrogen treatment grew well,and medium nitrogen treatment after fruit setting was better than low nitrogen treatment and high nitrogen treatment.The optimum nitrogen treatment?225 kg/hm²?had the highest agronomic efficiency,reaching 80 kg/kg N.At this time,the physiological utilization rate of nitrogen fertilizer and the absorption utilization rate of watermelon nitrogen fertilizer were 735 kg/kg and 8.9%,respectively.The changes of soil nutrient content of watermelon after nitrogenous fertilizer application were mainly presented in the 0-20 cm soil layer,and the ¹⁵N residual amount was as high as 0.49kg/hm²,which was 4.1 times and 2.8times of that in the 20-40 cm and 40-60 cm soil layers.Only 4.25%of ¹⁵N labeled nitrogen fertilizer was absorbed by watermelon,and the loss rate was as high as 88.9%.From the perspective of nutrient demand,the nutrient absorption amount of watermelon from high to low was potassium>nitrogen>phosphorus>calcium>magnesium.Under the optimal fertilization condition,it needs1.26 kg of nitrogen,0.29 kg of phosphorus,3.49 kg of potassium,0.56 kg of calcium and 0.19 kg of magnesium was absorbed for every 1000 kg watermelon.?3?The results of the experiment on the amount of nitrogen fertilizer for watermelon under raditional facility cultivation and open-air cultivation showed that the maximum yield of watermelon was 28.1 t/hm² and 26.0 t/hm²,and the corresponding amount of nitrogen fertilizer was 205 kg/hm² and 05 kg/hm²,74.5%and 43.8%higher than that without nitrogen treatment.In terms of overall yield and quality,the optimal nitrogen application amounts for both raditional facility cultivation and open-air were 150 kg hm² and 188 kg/hm²,respectively.With the increase of nitrogen supply level,the partial productivity of nitrogen fertilizer,agricultural efficiency and nitrogen absorption efficiency all showed a trend of decline,while the fruit harvest index and nitrogen harvest index showed a trend of first increase and then decrease.Under the conditions of facilities and open cultivation,the main nutrient requirements were potassium>nitrogen>phosphorus>calcium>magnesium respectively.And there was no significant difference between the nutrient requirements per unit yield and the cultivation in the long season.?4?The ratio test of organic fertilizer replacing nitrogen fertilizer showed that under the regulation of organic fertilizer replacing 30%chemical nitrogen fertilizer,the yield of facility cultivation and open air cultivation was the highest,reaching 29.8 and 28.9 t/hm²,respectively,and the yield was 10.0%and 4.7%higher than that of pure fertilizer treatment.At the same time,the replacement of partial fertilizer nitrogen by organic nitrogen is beneficial to reduce the thickness of the peel,promote the transformation and accumulation of sugar and acid in the fruit?TSS/TA?,enhance the taste.And the functional substance lycopene was higher,the content of nitrate got down.The yield and quality of watermelons in southwest China were the best when the total nitrogen content of watermelons in raditional facility cultivation and open-air within 188 kg/hm²,the organic nitrogen replacement ratio was 30%and 45%,respectively.The higher the ratio of organic nitrogen substitution was the higher the content of soil organic matter will be after the harvest.In addition,the content of pH value,alkali-hydrolyzed nitrogen,available phosphorus and available potassium in the soil treated with organic nitrogen substitution and inorganic nitrogen was higher than that treated with pure chemical fertilizer.To sum up,the three cultivation areas of watermelon in China had large nutrient input,large yield difference and strong regional resource and environmental cost.Especially,the cultivation areas in southwest China had low yield and high resource and environmental cost per unit yield.Among them,the contribution rate of nitrogen fertilizer application was the highest,which needed to be further optimized.The field experiment preliminarily proved that the cultivation area in southwest China could achieve high yield,high quality and environmental friendliness of watermelon through nitrogen regulation and organic fertilizer replacing part of nitrogen fertilizer,which was helpful to realize the improvement of quality and efficiency and green development of watermelon industry.