Effects Of Continuous Cropping Duration And Fertilization Regimes On Nitrogen Transformation And Crop Nutrient Uptake Under Greenhouse Vegetable Cultivation

In recent years,greenhouse vegetable cultivation in China has developed rapidly.However,due to people’s excessive pursuit of maximizing crop yields and facility utilization,it is very common as continuous cropping and the surfeit use of fertilizer during the vegetable production.As a result,it leads to an accumulation of soil salt and nutrients.Soil acidification and salinization occur,microbial activity is reduced,and soil environmental quality is reduced,which seriously restricts the sustainable development of greenhouse cultivation.Subsequently,soil acidification and salinization occurred gradually.microbial activity and soil environmental quality decrease,which seriously restricted and hindered the sustainable utilization of greenhouses.Many studies showed that replacing chemical fertilizer with organic fertilizer is an effective measure to control the deterioration of soil environment.Therefore,the change of soil nutrients under the condition that organic fertilizers replace chemical fertilizers has become the focus of scholars.As an important component of soil nutrients,nitrogen not only affects soil quality and crop growth,but also affects environmental problems and even global changes.Soil nitrogen exists in different forms such as organic nitrogen and inorganic nitrogen.It is transformed in a complex process,and these transformation rates control the change of nitrogen content in soil.Therefore,it is of great significance to study the whole process of soil nitrogen transformation,quantitatively describe it,and clarify its occurrence intensity and influencing factors for formulate a reasonable fertilization management,improve soil environment,and improve the sustainable development of greenhouse vegetable cultivation.In view of this,this study was based on greenhouse tomato cultivation,and soil samples were collected under different continuous cropping years and different fertilization measures.We measured soil pH,electrical conductivity,nutrient content and microbiological properties.and measured the gross nitrogen transformation rates by 15N dilution technology,in order to understand response between soil nitrogen transformation and these indicators under vegetable cultivation.The results showed that:(1)Under greenhouse cultivation,soil pH value decreased and EC value increased,resulting in soil acidification and salinization with the increase of continuous cropping years.The application of organic fertilizer can increase soil pH and decrease EC value.The contents of soil total carbon,total nitrogen,soluble organic carbon.ammonium nitrogen and nitrate nitrogen did not decrease,but increased with the increase of continuous cropping years.(2)It will increase the soil gross mineralization rate and the assimilation rate of ammonium nitrogen,and decrease the rate of autotrophic nitrification and dissimilation reduction with the increase of continuous cropping years and the application of organic fertilizer instead of chemical fertilizer.The rates of heterotrophic nitrification and nitrate nitrogen assimilation were both zero.In order to further understand the influence mechanism of different fertilization measures on soil nitrogen transformation under the continuous cropping system of greenhouse vegetable cultivation,we sampled the soil of tomato planting plots with different fertilization measures in the same continuous cropping year at the flowering and harvesting stages respectively,and analyzed the effect of fertilization measures on soil nitrogen transformation of greenhouse tomato at different growth stages.The results are as follows:(1)Fertilization can significantly reduce soil pH value at different growth stages of tomato,and the pH value reduction effect of fertilizer application is more significant than organic fertilizer application.Fertilization could significantly increase the soil total nitrogen content,and the effect of organic fertilizer on total nitrogen content was significantly higher than chemical fertilizer during tomato harvest.The soil ammonium nitrogen content did not change significantly under different treatments at different growth stages of tomatoes,and the nitrate nitrogen content was also not affected by fertilization measures at tomato harvest stage,but the application of chemical fertilizer significantly increased the nitrate nitrogen content at flowering stage.At different growth stages of tomato,soil microbial biomass carbon and nitrogen content was significantly reduced by applying chemical fertilizers,while they were significantly increased by applying organic fertilizers.The soil total PLFAs,fungi and bacteria were significantly reduced by application of chemical fertilizer.Application of organic fertilizer can significantly increase soil total number of PLFAs,fungi and bacteria.(2)Tomato have different nutrient requirements at different growth stages,so the effects of different fertilization treatments on the nitrogen conversion rate of tomato soils in different growth stages are different.During the flowering period of tomato,fertilization generally improves the soil compared with no fertilizer treatment The conversion rate of nitrogen in the medium,and the effect of chemical fertilizer is higher than that of organic fertilizer,and during the tomato harvest period,fertilization generally reduces the nitrogen conversion rate in the soil,and the reduction effect of chemical fertilizer is also more significant than organic fertilizer.(3)Whether it is in the flowering or harvesting period of tomato,compared with no fertilization,the application of fertilizer will significantly increase the total carbon and total nitrogen content of the shoots of the plant,the total nitrogen content of the roots,the plant biomass,N absorption and N utilization efficiency,and the effect of increasing organic fertilizer is significantly higher than that of chemical fertilizer.In conclusion,this study describes the effect mechanism of different continuous cropping years and fertilization measures on soil nitrogen conversion process under facility vegetable cultivation,and explores whether the use of organic fertilizer instead of chemical fertilizer is beneficial to the turnover of nitrogen in the soil and alleviates the continuous cropping obstacles in the soil.This research is of great significance to maintain high productivity and sustainable development of greenhouse vegetable cultivation.