Study On Utilization And Fate Of Nitrogen Fertilizer Under Different Irrigation And Nitrogen Conditions In Solar Greenhouse

The solar greenhouse is the main mode of cultivation in the northwestern China,and it plays a pivotal role in the development of regional agriculture facilities.Farmers generally apply excessive amounts of fertilizer and irrigation to ensure high yields.Nitrogen fertilizer application has greatly improved the food production,but the risk of environment has increased dramatically,which has restricted the sustainable development of solar greenhouses.The field experiment was carried out at Dazhai village located in Yangling Demonstration Zone of Shaanxi Province.Greenhouse tomatoes?Lycopersicon esculentum Mill.?were chosen as plant materials.The effects on yield,quality and nitrogen utilization of crops as well as the fate of N fertilizer were studied by combining field research with ¹⁵N isotopic tracing technology.Four treatments included no nitrogen input+common irrigation,farmers'nitrogen input+common irrigation,optimum nitrogen input+common irrigation and optimum nitrogen input+optimum irrigation under drip fertigation conditions.The aim of the study was to reveal the relevant mechanism for the efficient management of nitrogen and irrigation under greenhouse cultivation.Through the research,the main conclusions we got are as follows:?1?The effects of reducing water and nitrogen fertilizer rates showed that compared with the conventional use of nitrogen and water by farmers in the region,the combination of optimum nitrogen and optimum irrigation did not decrease the yield,content of soluble sugar,titratable acids and Vitamin C?Vc?of tomato,but it decreased the nitrate content in fruit by66.3%.When the irrigation amount was similar,the yield of mini-watermelon with 40%reduction in N fertilizer input was 13.1%higher than that of farmers'nitrogen input.The content of soluble sugar,titratable acid and Vc in fruit of the combination of optimum nitrogen and optimum irrigation treatment were significantly higher than that of the control treatment.The nitrogen distribution proportion illustrated as fruit>leaf>stem>root.With the growth of tomato,the nitrogen distribution proportion in fruit and stem increased from62.4%and 5.9%to 67.1%and 6.3%,while it decreased in root and leaf,and the combination of optimum nitrogen and optimum irrigation treatment promoted the transport of nitrogen from vegetative organs to fruit.In summary,the treatment of optimum nitrogen and optimum irrigation,which reduced nitrogen by 46%and saved water by 15%during two seasons,could not only obtain the yields and nitrogen uptake of crop but also promote the quality of fruit.It indicated that the farmers'nitrogen and irrigation input in the solar greenhouse was significantly excessive,so there is a certain potential in reducing the application of water and fertilizers under current cultivation conditions.?2?The ¹⁵N microplot experiment was conducted to study the fate of nitrogen fertilizer in different combinations of irrigation and fertilization.The results showed that20.87%-26.32%of nitrogen assimilated by tomato came from fertilizer.The nitrogen use efficiency ranged from 7.72%to 11.77%in the first season,and it decreased with the increase of N fertilizer rate.71.69%-80.8%of the residual fertilizer nitrogen accumulated in the 0-100 cm soil layer was centralized in 0-40cm soil layer,and 63.7%-72.4%of which was in the form of NO₃^--N.The residual amount of ¹⁵N fertilizer in the soil profile decreased with the increasing of soil depth.After the tomato harvest,the ¹⁵N fertilizer was found lost at a rate of 8.99%-20.59%.The amount of residual fertilizer assimilated by mini-watermelon accounted for 11.74%-14.63%of the total nitrogen uptake.The ¹⁵N reutilization rates(defined as the ratio of ¹⁵N uptake by the subsequent crop to the total applied ¹⁵N)were2.78%-4.54%.Compared with conventional treatment,optimum nitrogen and irrigation had no significant effect on nitrogen uptake and utilization of crop,but significantly increased residual rate of labeled ¹⁵N in soil and decreased its loss rate.In summary,this model has good economic and environmental benefits.?3?Through the analysis of 43 domestic and foreign published papers related to the nitrogen utilization of tomato and the data of this experiment,the results showed that the differences of cultivation forms and planting season caused the differences in nitrogen absorption characteristics of tomato.Yield,above-ground N uptake and N needed per 1000kg fruit of tomato had significant variations.The average yield of tomato was 84.9 t/hm²,among which the yield of tomato in greenhouse cultivation in spring was the highest?98.5t/hm²?,followed by in autumn-winter?77.3 t/hm²?,and the lowest in the open field?75.4t/hm²?.The average nitrogen requirement for forming 1000 kg fruit was 2.52 kg,the highest nitrogen requirement was 2.75 kg in greenhouse cultivation in autumn-winter,and which in spring and the open field were 2.43 kg and 2.44 kg,respectively.The above-ground N uptake increased significantly with increasing tomato yields,and there was a significant linear relationship between them.The nitrogen requirement for 1000 kg tomato fruit decreased with the increase of yield level,which were 3.17,2.38,2.27,2.25 and 2.25 kg for tomato yields<55,55-85,85-115,115-145,>145 t/hm²,respectively.So the differences of cultivation conditions of different districts,combined with target yield and N requirement of tomato should be taken into account for determining reasonable nitrogen fertilizer rate.