Study On Soil Nitrogen Accumulation Transformation And Reduction Potential In Urban Intensive Facility Greenhouses

As a highly intensive urban agricultural model,facility agriculture,with its long cultivation cycle,highly intensive management,and excessive fertilizer inputs,leads to large changes in the soil ecosystem and risks of soil succession barriers such as acidification,secondary salinization,and nutrient imbalance,which restrict the sustainable development of facility agriculture and threaten the security of the regional ecological environment.This paper was based on the research object of continuous crop facility greenhouses in Daxing,Beijing,by means of field investigation,data collection and laboratory test analysis.To investigate the characteristics of soil physicochemical properties and nitrogen apparent balance in the facility greenhouse under long-term single-crop continuous crop pattern;Exploring soil nitrogen accumulation transformation patterns in facility greenhouse profiles based on indoor incubation experiments and first-level kinetic simulations;The evaluation of environmental risk of soil nitrogen surplus and environmental risk of nitrogen leaching in facility greenhouses was carried out to define the risk of soil nitrogen security,reveal the recommended amount of nitrogen application for watermelon in different planting years with the help of comprehensive soil fertility index,and calculate the potential of nitrogen fertilizer reduction for farmers of continuous crop facility greenhouses.The main research findings were obtained as follows:（1）The organic matter,effective phosphorus,fast-acting potassium and total nitrogen content of the soil in the study area showed an"inverted U-shaped"pattern of change with the increase of planting years.And the penetration resistance of soil increased with the depth of soil layer from 0 to 20 cm,and gradually stabilized after more than 20cm,and the average penetration resistance of soil tended to decrease with the increase of planting years.Moreover,soil p H,EC and bulk density varied from 8.03 to 8.20,210.67to 650.33 us·cm^-1 and 1.48 to 1.59 g·cm^-3,respectively.Soil p H and bulk density decreased with increasing planting years,and soil EC showed an increasing trend.（2）Soil biodiversity of facility greenhouses with planting years>20 a was lower than that of grain fields and open fields.In addition,there was a trend of decreasing soil microbial diversity in the facility greenhouses with increasing growing years.In terms of soil microbial phyla in the study area,Proteobacteria were the dominant phylum,accounting for 21.73%to 22.66%of the relative soil abundance.And as far as soil microbial phyla were concerned,Alphaproteobacteria accounted for an absolute predominance of 8.78-17.27%.（3）The level of nitrogen fertilizer input varied widely in the research areas,and nitrogen was in a long-term surplus.Fertilizer input types for facility greenhouses and open-air vegetable fields were mainly organic fertilizers,while grain fields were mainly chemical fertilizers;The nitrogen input to the facility greenhouses of different planting years ranged from 406.08 to 609.74 kg·hm^-2,and the total nitrogen input tended to decrease with the increase of planting years;The nitrogen surplus in the greenhouses of different planting years ranged from 1 to 5 a(534.86 kg·hm^-2),6 to 10 a(488.35 kg·hm^-2),11 to 20 a(355.64 kg·hm^-2)and>20 a(311.90 kg·hm^-2),and the nitrogen utilization rate ranged from 12.28%to 21.81%.The nitrogen utilization ranged from 12.28%to21.81%,and showed an inverted"U"shape trend with increasing planting years,followed by a decrease.（4）The total nitrogen and accumulated mineral nitrogen in the soil of facility greenhouses existed in surface aggregation,and the nitrogen conversion capacity of facility greenhouses differed in different planting years.The soil nitrogen accumulation in the profile from the largest to the smallest was for facilities with planting years>20 a,11 to 20 a,6 to 10 a and 1 to 5 a,respectively;The variation of accumulated mineral nitrogen in facility greenhouses ranged from 68.73～92.48 mg·kg^-1 and the variation of mineralization potential（N₀）ranged from 74.76 to 122.39 mg·kg^-1 at different growing years.Moreover,the accumulated nitrogen mineralization and nitrogen supply capacity of the soil in the facility greenhouse increased with the planting years from 1 to 20 a,and a decreasing trend was observed after planting years>20 a.（5）The recommended fertilizer application rate for watermelon in different planting years ranged from 48.52 to 97.60 kg·hm^-2,with an increasing trend followed by a decreasing trend with increasing planting years.And the range of N fertilizer reduction potential in the research area was 78.54%to 92.04%relative to the actual amount of inputs,and the range of minimum N fertilizer reduction potential under environmentally safe conditions was 69.22%to 79.50%.The results of the study provide farmers with scientific and reasonable potential for nitrogen fertilizer reduction in terms of economic benefits and ecological tolerable range.Figure[30]Table[23]Reference[124]...