Effects Of Water And Fertilizer Reduction And Combined Organic-inorganic Fertilization On Nutrient Uptake,distribution And Growth Of Melon

China is the largest melon production country with the largest cultivation area and the highest yield.Because of its short growth cycle and high economic benefits,it has become a key industry to increase farmers’income in some major producing areas.However,the problem of excessive fertilization in actual production is prominent,and the experience management mode of’one shot dose’is still adopted under the integration of water and fertilizer.The accumulation of large amounts of nutrients in the soil cause potential ecological environment problems,which affecting the sustainable development of melon industry.Determining the appropriate fertilization rate is the key to obtain the target,maintain the soil fertility level and reduce the environmental risk.The correct time and place to provide the correct source and rate of fertilizer to plants is the basis for achieving precise fertilization and reducing losses.At present,the results of nutrient uptake characteristics of melon in the existing literature are quite different,and there is still a lack of systematic study on the nutrient uptake and distribution characteristics of different melon cultivars and their response to fertilization stage.Therefore,we studied the nutrient uptake characteristics of nitrogen,phosphorus and potassium in different melon cultivars by field experiment and pot experiment;The influence of optimized water and fertilizer on melon yield,quality and nutrient uptake and utilization were studied by continuous field positioning experiments;The uptake,distribution and utilization of nitrogen fertilizer at different melon growth stages were further studied by ¹⁵N isotope tracer technique.Through the above study,the nutrient uptake law of melon was clarified,and evaluate the field effect and sustainability of optimized water and fertilizer to provide scientific basis and technical support for accurate application on demand and efficient utilization of melon.The main results are as follows:（1）The dry matter accumulation of melon was low from seedling stage to fruit-setting stage,and the leaf was the accumulation center of dry matter.The dry matter accumulated rapidly on the fruit after fruit setting.Differences in dry matter accumulation among different melon cultivars:netted melon Tianshanmi had high dry matter accumulation,but its dry matter distribution in fruit was only 46.7%.Thin-skinned Shuntianyujiao and Lvyuanshuai had high dry matter accumulation in leaf during growth stage,and the dry matter proportion in fruit was61.8%.The thick-skinned Huozhoucuili and Jiashuai 209 had the lowest dry matter accumulation,but the distribution ratio in fruit was 75.3%.The thick-skinned Huozhoucuili and Jiashuai 209 had strong ability to transport assimilates to fruit.（2）The nutrient uptake of N,P₂O₅ and K₂O per unit economic yield of the five tested melon cultivars was1.79-3.87 kg,0.46-1.23 kg and 3.34-6.45 kg,and the nutrient uptake of thick-skinned melon was significantly lower than thin-skinned.Nutrient uptake ratio of N,P₂O₅,K₂O averaged 1:0.32:1.73.The nutrient uptake of melon is relatively small before fruit setting,and it absorbs nutrients rapidly after fruit setting.The proportion of nitrogen,phosphorus and potassium uptake of expanding stage in the whole growth stage was 68.6%,74.7%and 70.6%,which was the maximum efficiency stage of nutrient uptake.（3）Optimization water and fertilizer compared with conventional water and fertilizer,chemical fertilizer N,P₂O₅,K₂O inputs were reduced by 65%,84%,68%,irrigation water was reduced by 24%.Compared with conventional water and fertilizer,the dry matter quality,nutrient uptake,yield and quality of melon in optimized water and fertilizer reduction did not decrease.The irrigation use efficiency increased by 30.2%–33.1%,and the nutrient use efficiency of N,P₂O₅ and K₂O increased respectively by 13.6-20.0,3.6-6.0 and 6.5-9.3percentage points.The partial productivity of fertilizer increased respectively by 60.9-64.4%,60.7-64.1%and 24.9-27.6%.The recommended fertilization rate for optimization water and fertilizer is is scientific and reasonable,and can be widely promoted and applied in production.（4）Manure combined with reasonable amount of nitrogen fertilizer could significantly improve the yield,quality,dry matter quality and nitrogen absorption of melon.The nitrogen fertilizer applied before fruit-setting stage was mainly stored in the leaf and stem,while the nitrogen fertilizer applied during expanding stage was mainly transported and distributed in the fruit.There was little difference in the ¹⁵N use efficiency of nitrogen fertilizer at different stages,but the application of expanded nitrogen fertilizer could improve the accumulation and distribution of nitrogen in fruit,which was conducive to yield increase and quality improvement.Reasonable combination of Manure and chemical fertilizer can significantly improve the chemical nitrogen use efficiency.In production,attention should be paid to the application of nitrogen fertilizer in the expansion stage,the total amount of nitrogen fertilizer application and the proportion of nitrogen fertilizer application in each growth stage should be controlled,and the vegetative growth and reproductive growth should be coordinated to achieve the goal of reducing fertilizer application and increasing efficiency.