| According to the problems of soil nutrient imbalance, leaching of nitrogen andphosphorus and agriculture non-point source pollution duing to excessive fertilizerapplication in vegetable greenhouses, the study was conducted in the soils ofoveryearing cucumber greenhouses (Soil texture along the profile of greenhouse1islooser than that in greenhouse2) with high amount of fertilizer application. At first,the field survey was carried out to investigate the situation of fertilizers applicationand variation of physico-chemical properties of soils in cucumber greenhouses fordifferent cultivating years. After that the plot experiments were set up to explore thedistribution and accumulation characteristics of nitrate in soil profile, the nitratedynamics in soil solution of root zone (at35-40cm of soil layer) and non-root zone(95-100cm of soil layer) and leaching solution collected from soil at the depth of100cm for different fertilizer applications (T1: no fertilizer application; T2: recommendedfertilizer application; T3: recommended fertilizer application+30%chemical nitrogen;T4: recommended fertilizer application+30%organic nitrogen; T5: conventionalfertilizer application) in two types of cucumber greenhouses. In addition, dynamics oftotal phosphorus, TOC (total organic carbon) and water soluble potassium were alsostudied in soil solution and leaching solution. It would provide academic base forincreasing utilization rate of fertilizer and decreasing the soil and water environmentalpollution duing to nutrients leaching, and it would also provide data base for ensuringthe high yield, high efficiency, high quality, safety and environment protection incucumber production.(1) It is normal to apply too much fertilizer in greenhouse fields with cucumber atpresent. The physico-chemical properties should be changed due to excessivefertilization with increase of cultivating years. The results of investigation showedthat total fertilizer rate had reached1641kg N/hm2,1302kg P2O5/hm2,2047kgK2O/hm2in cucumber growth regions, and the percentage of chemical fertilizer was67.1%,37.0%,59.5%for nitrogen, phosphorus and potassium, respectively. Afterfertilizer application following this rule for many years, the soil physico-chemicalproperties have been changed. Soil pH declined significantly for both topsoil (0-20 cm) and deep-layer soils (20-40cm) with increase of cultivating years, accounting for16.8%and12.8%respectively. However, the contents of organic matter in soilenhanced significantly with increase of cultivating years and the highest amplitudewere356%and197%. EC values in top-layer soils ranged from0.15ms/cm to1.21ms/cm and were stable in cucumber greenhouse for1-10cultivating years. Soil ECvalues increased markedly with increase of cultivating years when cucumbergreenhouses has been built for more than10years, and there was a quadraticpolynomial correlation between EC and cultivating years was very remarkable(r=0.546**, n=30). Moreover, there were significantly positive correlations betweenthe levels of available nitrogen, phosphorus, potassium and cultivating years (N:r=0.742**, r=0.491**; P: r=0.583**, r=0.536**; K: r=0.483**, r=0.483**; n=30).Available Fe, Zn concentrations in topsoil and cultivating years had also significantcorrelation(r=0.450*, r=0.396*, n=30). It was indicated that there were acidification,salinization and nutrients accumulation in cucumber greenhouse soil of this area.(2) The plot experiment was set up in two cucumber greenhouses with different soiltextures. The result showed that reducing50%N rate would not decrease thecucumber yields in two greenhouses compared to conventional fertilization treatment.The ratios of input to output for treatments of reducing fertilizer applications (T2, T3,T4) were2.28-3.56times as high as that of conventional fertilization treatment.According to both cucumber yield and economic benefit, T4treatment was theoptimum fertilization management in greenhouse1, while T2treatment in greenhouse2.(3) After cucumber harvest, for greenhouse1, the amounts of nitrate accumulated insoil layer of100cm was4853kg/hm2for conventional fertilization treatment, whichwas significant higher than those of treatments of reducing fertilizer applications (T2,T3, T4)(1587-1877kg/hm2)(P<0.05); For greenhouse2, the nitrate accumulation insoil layer of100cm was1281kg/hm2for conventional fertilization treatment, whilethose of reducing fertizizer applications (T2, T3, T4) were854-1212kg/hm2, therewas no significant difference among the four treatments. For the analysis of the nitrateconcentrations characteristic in soil solution of root zone and non-root zone, it showedthat nitrate concentrations in soil solution of root zone ranged at9.21-256mg/L forgreenhouse1, and7.45-202mg/L for greenhouse2, respectively. Moreover, the nitrateconcentration in soil solution of root zone for conventional fertilization treatment(121-256mg/L) was significant higher than those of reducing fertilizer applications(18.5-116mg/L) in greenhouse1. In addition, the nitrate concentrations in soilsolution of non-root zone for two greenhouses were17.1-219mg/L for greenhouse1,and15.9-274mg/L for greenhouse2, respectively. During the cucumber growth period,the amounts of (NH4++NO3-)-N leaching were72.8,66.2kg/hm2for greenhouse1and 2, respectively. The NO3--N was the predominant species in leaching solution. Thenitrate leaching amount of T4treatment was the lowest compared to other in thesetwo different greenhouses. Compared to the treatment of conventional fertilization,the amounts of NO3--N leaching decreased by47.1%in greenhouse1and68.1%ingreenhouse2for T4treatment, respectively.(4) The concentrations of phosphorus in soil solution of root zone and non-root zonefor both of the two greenhouses were low. P concentration in soil solution from rootzone ranged from0.57mg/L to3.71mg/L in greenhouse1and ranged from0.37mg/Lto5.89mg/L in greenhouse2, while P concentrations in soil solution from non-rootzone ranged at0.06-2.02mg/L in greenhouse1and0.17-4.55mg/L in greenhouse2.The average P concentrations in leaching solution were as1.83mg/L and1.46mg/Lin two greenhouses during the cucumber growth period, respectively. The P amountsin leaching solution were1.49kg/hm2and2.46kg/hm2in two greenhouses,respectively. The P amount in leaching solution was65.1%higher in greenhouse2than that in greenhouse1.(5) For greenhouse1, the concentrations of TOC in soil solution of root zone(21.5-35.0mg/L) and non-root zone (16.7-23.7mg/L) for conventional fertilizationtreatment were higher than those of reducing fertilizer applications (root zone:12.1-25.9mg/L; non-root zone:8.54-17.6mg/L); for greenhouse2, the TOCconcentrations in soil solution ranged at17.5-44.4mg/L for root zone and10.5-27.2mg/L for non-root zone, respectively. The average concentrations of TOC in leachingsolution were15.9mg/L and22.7mg/L in two greenhouses respectively; the amountsof TOC leaching were76.9kg/hm2and143kg/hm2in two greenhouses respectively,and the amount of TOC leaching was22.9%higher in greenhouse2than that ingreenhouse1.(6) For greenhouse1, the concentration of potassium in soil solution of root zone andnon-root zone ranged at36.2-114mg/L and20.8-105mg/L respectively. Thepotassium concentration in soil solution of non-rhizosphere for conventionalfertilization treatment (60.3-105mg/L) was significant higher than that of treatmentsof reducing fertilizer applications (21.0-60.5mg/L). For greenhouse2, the potassiumconcentration in soil solution of root zone and non-root zone ranged at57.9-139mg/L,9.33-80.6mg/L, respectively. During the cucumber growth period, the averageconcentration of potassium in leaching solution was49.5,29.5mg/L respectively intwo greenhouses; the amount of potassium leaching was61.2,49.8kg/hm2respectively, the amount of potassium leaching was22.9%higher in greenhouse1thanthat in greenhouse2. |
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