Effect Of Water And Nitrogen Regulation On Vegetable Yield And Nitrogen Fate In Sunlight Greenhouse

As an important form of modern agriculture,solar greenhouses are widely distributed in the northern region of China.Due to the high input and benefit of solar greenhouse,farmers often invest a lot of water and fertilizer in order to obtain high yield when planting greenhouse crops which leads to serious excessive water and nitrogen input in the production of solar greenhouses in China.Excessive input of water and nitrogen will not only lead to a decrease in water and nitrogen utilization,but also caused the leaching of nitrogen fertilizers into the lower soil layer and groundwater,thus causing serious environmental pollution.In order to explore the pattern of nitrogen under different water and nitrogen conditions in the solar greenhouse.Solar greenhouses located in the southern part of the Loess Plateau were taken as study site.We determine the effects of different water and nitrogen treatments on vegetable yield,nitrogen absorption and nitrogen fertilizer residual using field plot of1m×1m experiment combined with stable isotope ¹⁵N method.The pattern of residual effect of nitrogen in the solar greenhouses were continuously tracked.Four water and nitrogen treatments were set up in the experiment:no nitrogen+conventional irrigation（N0+FI）,conventional nitrogen+conventional irrigation（FT+FI）,and optimization nitrogen application+conventional irrigation（OPT+FI）and optimized nitrogen application+optimized irrigation（OPT+OI）.The main conclusions obtained are as follows:1)According to the continuous monitoring of water and nitrogen in the solar greenhouse,it was found that compared to the conventional nitrogen application and irrigation treatment,the reduction of nitrogen application and irrigation amount had no significant impact on the crops yield and biomass;There was no significant difference in the total nitrogen carrying amount in the five seasons after nitrogen reduction and water control indicating that nitrogen reduction and water control did not affect the nitrogen carrying amount of greenhouse crops;Appropriate reduction of nitrogen fertilizer balance can significantly increase the nitrogen use efficiency.There is no significant difference in nitrogen use efficiency after water control,which indicates that there is an excessive phenomenon of nitrogen input and irrigation in different cultivation mode of solar greenhouse.Thus,the optimization of nitrogen application and irrigation measures has great potential in actual production.2)The experiment in solar greenhouse cultivation showed that ¹⁵N fertilizer values varied between 7.7-11.8%,and were low in the conventional nitrogen application.Whereas,the ¹⁵N residual efficiency utilization rate from the second to fourth seasons were 3.15-4.30%,1.39-1.57%,0.27-0.47%respectively,and the total nitrogen utilization rate in the five seasons changed 12.7-18.7%;¹⁵N fertilizer applied to the soil mainly only exists in the mineral nitrogen form.After the end of the first season,the residual rate of fertilizer nitrogen in the 0-60 cm soil of each treatment was 72-81%,and 34-47%,after the end of the third season.The residual rate of soil mineral nitrogen decreased from 53-67%to 17-31%and the mineral nitrogen（Ndff）of each soil layer has an obvious downward trend.After the end of the fifth season,the residual rate of ¹⁵N total nitrogen in 0-60 cm soil of each nitrogen treatment was only 11.0-16.8%,while the residual rate of 15N mineral nitrogen was only 7.6-12.7%.The residual rates of total nitrogen and mineral nitrogen in 0-60 cm soil layer were significantly increased by reducing N and controlling water on the basis of conventional water and nitrogen.3)In the first three seasons,there was no significant change in NO₃-N content in 0-200cm soil under different treatments.Organic fertilizer was stopped and stopped in the fourth season.In the fifth season,NO3-N content in 0-100 cm soil layer decrease rapidly and significantly.The nitrate accumulation in 0-200 cm soil layer of all treatments decreased,while N0+FI treatment gradually decreased from the first season by 59%,but there was no significant difference in FT+FI treatment.In addition,a reduction of 46%and 37%were observed in OPT+FI and OPT+OI treatment respectively.By monitoring the nitrate nitrogen in 0-500 cm soil,it was found that the peak value of nitrate nitrogen content in all the treated soil occurred in 150-250 cm,and the nitrate nitrogen content at the peak value was 164-191mg·kg^-1.The accumulative amount of 0-500 cm nitrogen treatment was 5590.2-6829 kg Nha^-1,while that of no nitrogen treatment was only 3697.4 kg N ha^-1.In summary,the problem of excessive nitrogen application in solar greenhouses is prominent,leading to low nitrogen utilization and a large amount of nitrate nitrogen accumulating in the soil.Nitrogen reduction and water control can effectively improve nitrogen use efficiency and reduce nitrogen leaching loss on the basis of ensuring crop yields,thereby achieving a win-win situation for economic and environmental benefits.