Effects And Mechanisms Of Different Summer Catch Crops Planting On Soil Nitrogen Leaching In Greenhouse Vegetable Cropping System

Nitrate leaching which caused by excessive application of nitrogen is a common problem in intensive vegetable production area. Catch crops planted according to soil nitrogen status can be an effective way to reduce nitrate accumulation in vegetable soil and nitrate leaching in groundwater, which can be used as a biological N management tool to recover residual soil mineral N by prolonging growing season during the fallow period. Four crops were selected as summer catch crops. They were:sticky corn, amaranth, oat and pea. Fallow treatment was also established as control in the study. The objectives of the experiment were (1) to analysis the effects of different catch crops on soil inorganic nitrogen residues, leachate N concentrations, denitrification, and (2) to reveal the mechanism of catch crops on reducing inorganic nitrogen leaching, also (3) to found appropriate catch crop species and selected indicators which are suitable for cultivation of vegetable production systems. The experiment was conducted at Yuzhong campus of Lanzhou university by using soil column to simulate soil profile of vegetable.The result indicated higher shoot biomass, root biomass and root length density with sticky corn and oat treatments were found compared with pea and amaranth treatments. Higher N uptake was showed with sticky corn, oat and pea treatments in contrast to amaranth. Compared with fallow treatments, catch crops planting could efficiently reduce the soil inorganic N residue at harvest at 0-60 cm soil layers. The ranking of soil inorganic N residue left by catch crops was: amaranth and oat> pea> sticky corn. Inorganic N leaching could also be significantly reduced by catch crop planting. Compared with fallow treatments, inorganic N leaching could be reduced by 100%,96%,82% and 58% with sticky corn, oat, pea and amaranth treatments, respectively. The correlation analysis indicated there was significant positive relationship between specific root length and aboveground N uptake of catch crops. There was no strict and regular relationship between each root parameter of catch crop and soil inorganic N residue and leaching. The residual inorganic nitrogen of sticky corn was low, which may lead to lack of N source of denitrification; Though a high nitrate content of fallow treatment, cumulative emission of N2O was no difference to sticky corn, possibly because of the lack of C source. Soil microbial C, N concentrations were higher than that of fallow treatment, which agreed with their high CO2 emissions; With the increase of soil depth, soil microbial C, N content of sticky corn and fallow treatments were decreased. In conclusion, sticky corn and oat were more desirable summer catch crops in greenhouse vegetable cropping system than pea and amaranth in the study.