Evaluation Of Catched Vegetables Suitable For Protected Vegetable Fields In Guangdong And Their Effects On Nitrogen And Phosphorus Leaching

Excessive applications of chemical nitrogen（N）and phosphorus（P）fertilizers to intensive vegetable soils lead to severe N and P leaching losses,which become a serious agronomy and environmental problem.Plantation of catch crops,which can absorb the surplus soil N and P,during the fallow period,is an effective method to reduce leaching losses of N and P.In the current work,we conducted field trails at two sites with plastic-shed greenhouse vegetable productions systems（two vegetable production base at Sanshui of Foshan,and Xingning of Meizhou,respectively,Guangdong area.Firstly,we observed the comprehensive effects of six leafy vegetables（including four local prevalent varieties of edible amaranth,pepper leaves and radish seedlings）as catch crops on the p H,available N and total P concentrations of leachate（by lysimeter method）,and the available soil nutrients after leafy vegetables were harvested,also the yield and selected qualities of subsequent crops in Sanshui.At the same time,the economic and environmental benefits of four amaranth（eg.,Danhongxian,Taihongxian,Naning Xian,and Baijiancuixian）as catch crops were confirmed by the field plot trail conducted in Xingning.By the current work,we hypothesized that there are optimal leafy vegetables as catch crops that with triple effects of agronomy,environmental and economic benefits.The main results are as follows:1）Plantation of the six leafy vegetables as catch crops during the summer fallow period of the intensive vegetable soils in Sanshui,produced economic benefits of36,800-54,900 yuan/hm²;All six leafy vegetables as catch crops effectively decreased the N and P leaching losses from soils.Of which,the decrease efficiencies of catch treatments on ammonium N,nitrate N and total P were 31.2～67%,35.5～53.7%and 30.1～50.7%,respectively;After leafy vegetables were harvested in Sanshui,it was found that the content of available P in the soils of six catch crop treatments were27.1～65.1%higher than that of the control treatment.In addition,the average soil organic matter content increased by average 19.7%under leafy vegetable plots.There was no significant changes about the total N and total P of soils between the catch treatments and the control treatment.These results suggested that leafy vegetables as catch crops did not deplete the soil N and P.Compared with the lettuce harvested from the control treatment,there were no significant differences about the yield,N and P absorptions,and quality of the lettuce,the subsequent primary vegetable.2)Consistently,the same amaranths planted in Xingning as catch crops produced extra economic benefits with 32,200 to 42,300 yuan/hm².At the same time,cultivation of amaranth reduced the concentrations of ammonium nitrogen,nitrate nitrogen and total P in the leachate by was 31.2～49.5%,35.5～37.5%,and 30.1～43.6%,respectively,compared the fallow treatment.Compared with the control treatment,the available N and P contents in the soils with catch crops did not reduce.Interestingly,and the concentration of available P increased by 31.9～68.1%after amaranth were planted during the fallow period.Therefore,it is demonstrated that leafy vegetables as catch crop is feasible to increase farmers’income,reduce N and leaching losses from vegetable fields,while not affect the yield and quality of primary vegetables.3)In conclusion,Danhongxian can be preferred as an optimal leafy vegetable,which had the highest reduction efficiency on soil N and P leaching losses（e.g.,NO₃-N,35.5～53.7%,total P 30.1～50.7%）and the largest economic benefits（32200～54 900 yuan/hm²）)and did not affect the soil fertility and thereby the production and quality of the succeeding primary vegetable.This conclusion has been demonstrated by the experimental data obtained from two field plot-scaled experiments in the Pearl River Delta region,South China.