Effects Of Nitrogen Fertilizer Management Model On Nitrogen Residue And Utilization In Greenhouse Vegetable Soil

Excessive nitrogen (N) fertilization input has resulted in deteriorated crop yield and quality, lowefficiency of N use, soil quality degeneration and serious environmental problems, etc. Field plot trailsthat aiming to resolve the problems were carried out in Guan Lu village (GL) and Dong Liu Ying village(DLY) of Shouguang, Shandong Province, the famous greenhouse vegetable production base in northernChina. Based on the results of the effects of different N fertilizer management models on soil quality,utilization and fate of N and the statistical analysis of Gray Relational Analysis, an optimum N fertilizermanagement model was selected. To understand the mechanism of N fertilizer recovery rates underfarmer's common practices and optimum N fertilizer management model, the micro-plot experimentwith¹5N tracing technique was utilized to investigate the fate and utilization on chemical and organic Nfertilizer. The main findings were as follows:(1) Based on the statistical data of literatures and the farm's survey in Shouguang, theconventional chemical and organic N were1000and1200kg/ha, respectively. N surplus was analyzedaccording to "black box method" under conventional N fertilizer model. The results showed N loss wasvery serious in greenhouse vegetable system.(2) Soil fertility such as total N, organic matter, available P and K were high in the0-20cmsurface layers and accumulation increasing with increasing length of period of vegetable production.There were no significant differences on soil urease and invertase abilities among different N fertilizermanagement models. Compared with conventional N fertilizer model, reducing30%-50%N fertilizercombined with some measurements could preserve soil fertility in greenhouse vegetable. Soil salinityoccured in the topsoil layer (0-20cm) of greenhouse, significantly increasing with increasing Nfertilizer application and length of period of vegetable production (P<0.05). Soil electrical conductivity(EC) values were highly significantly and positively correlated with NO₃^--N concentrations, indicatingthat the excess NO₃^--N accumulations were an important factor contributing to soil salinity.Compared with conventional N fertilizer management model, soil EC value significantly lower in N5model (P<0.05). The results indicated that reducing50%chemical N fertilizer combined with straw anddrip irrigation had significant impact on soil salinization inhibition. NO₃^--N accumulation was the mainsoil mineral N residue form. NO₃^--N accumulation in0-100cm soil profile was significantly increasedwith the increasing of N rate. NO₃^--N mainly accumulated in0-20cm soil depth in GL. Over-applied Nfertilizer under conventional N fertilizer management model resulted in more NO₃^--N accumulated in60-100cm soil profile in DLY. The average NO₃^--N accumulation amounts in0-100cm soil profileunder conventional N fertilizer management model were higher than other N fertilizer models.Reducing50%N fertilizer combined with straw and drip irrigation significantly decreased soil NO3–-Naccumulation.(3) The highest N fertilizer rate and irrigation (conventional N fertilizer model) not only lowered Nagronomic efficiency, N recovery and N physiologic efficiency, but also failed to improve tomato yieldand quality, thus reducing outputs and profit for farmers and wasting N fertilizer. High crop yields, quality and N use efficiency could be achieved with reducing30%-50%N fertilizer application, butsome measurements should be combined with it.(4) Gray Relational Analysis indicated that the best comprehensive evaluation was achieved by50%reduction of the conventional N chemical fertilizer input combined with adjustment of the C/Nratio and water–fertilizer coupling (N5model) and the worst comprehensive evaluation wasconventional N fertilizer model (N1). So N5model was selected as the optimum N fertilizermanagement model. The micro-plot experiment with¹5N tracing technique showed that¹5N recoveryderived from chemical N fertilizer was significantly higher than¹5N recovery derived organic Nfertilizer under N1and N5models. NO₃^--N was the main chemical N residue form, but organic-boundwas the main organic N residue form.¹5N loss derived from chemical N fertilizer was significantlyhigher than¹5N recovery derived organic N fertilizer. Increasing N rate decreased crop recovery butincreased soil N recovery. Compared with N1model,¹5N recovery under optimizing N application wassignificantly improved, whatever¹5N derived from chemical or organic N fertilizer (P<0.05). Otherwise,¹5N residue and loss derived from chemical N fertilizer were significantly decreased under N5model(P<0.05). A great deal of manure was used for the high benefit of greenhouse vegetable cropping system,which led to more organic N residue and loss. There was no significantly difference between N1and N5model.The present study showed that environmental protection and high crop yields could be achievedwith a50%reduction of the conventional N chemical fertilizer input combined with adjustment of theC/N ratio and fertigation. These combined approaches represent a practical approach for reducingexcess N input while maintaining the sustainability of greenhouse-based intensive vegetable systems.