N And P Accumulation Status In Greenhouse And Their Leaching Regulated By Straw

In order to clarify the current situation of soil N and P accumulation states in greenhouse,this study investigated the N and P input status of greenhouse vegetables production in Quwo county,east of the loess plateau.The distribution characteristics of nitrate-N,Olsen-P and P extracted by calcium chloride（Ca Cl2-P）in soil profiles of vegetables with different planting years were explored,and their interactions was analyzed.By means of soil column simulation indoor,the contributions of organic fertilizer on N and P leaching,under conditions of different soil fertility,were evaluated and regulation of straw on N and P leaching was studied.（1）The input of N,P and K for greenhouse vegetable production had been investigated with different cultivation years,including in 1,7,10,13 and16-year.It was found that the inputs of N,P and K were so high as6088.3,2705.4 and 3287.2 kg·hm^-2 annually,respectively for new built greenhouse;which was 2 to 4 times the amount of fertilizer applied in old sheds.It should be highlighted that 80⁹0% of N and P was applied before transplanting;which resulted that the NO3--N concentration was higher than30.00 mg·kg-1 for 0²00 cm soil profile ever planting after one year.Its leaching was enhanced with the increase of cultivation year.NO3--N concentration in 0⁶0 cm and 180²00 cm reached 110²03 mg·kg-1 and 60mg·kg-1 respectively,after 16-year cultivation.The concentrations of Olsen-P and Ca Cl2-P in 0²0 cm soil layer were so high as 138.0 and 2.7 mg·kg-1,respectively,after one year cultivation.Afterward the concentrations of Olsen-P and Ca Cl2-P reached to 300 mg·kg-1and 7.6 mg·kg-1 respectively,in the 0²0 cm soil layer.Ca Cl2-P is strongly regarded to be related to P leaching.Change points of soil Olsen-P,which can be used to predict P loss,was 46.7 mg·kg-1.（2）Three events of soil column leaching test were carried out for three fertility soil levels,which were low soil fertility（L）,medium soilfertility（M）and high soil fertility（H）.The amount of water for leaching was equivalent to the irrigation amount used by farmers in greenhouses production.The results showed that soil fertility significantly affected N and P leaching.The highest N concentration of eluent was found at the first leaching event,and the total nitrogen（TN）concentrations of eluents for L,M and H were 5.87,7.32 and 183.6 mg·L-1,respectively.The concentration of TN in the following two events were obviously diminished.Compared with total phosphorus（TP）concentration of the second and third leaching under conditions of L and M,TP concentration of eluent for the first event was lower.However,at the first leaching H caused the highest TP content in the eluent.This may implies that,in practice,the first irrigation for H can produce a obvious effect on phosphorus leaching.The application of organic manure promoted TN leaching in the first eluent;whereas it had little effect on the P leaching,which may be related to the lower application of organic fertilizer in this experiment.（3）Soil column simulation was explored to study the regulation of straw on soil N and P leaching.In the experiment,the amount of straw equivalent to 7.5,15 and 22.5 t·hm^-2 were added.The leaching test was conducted three-week after the straw was mixed with the soil.It was observed that the TN concentration of leaching in the first leaching event increased obviously when straw was added,which may be related to the high temperature environment and it promoted N mineralization from straw.There was no effect on the phosphorus leaching capacity when the straw weight was 7.5 t·hm^-2,but the P leaching capacity was significantly reduced when the straw weight was 15 and 22.5 t·hm^-2.