Nitrogen management is crucially important in shallow-rooted vegetable production systems characterized by high input, high output and high environmental risk. Catch crops can be used as a biological N management tool to recover residual soil mineral N by prolonging growing season during the fallow period. The objectives of the experiment were (1) to study effects of different summer catch crops on vegetable-planted soil inorganic N residue and leaching, and (2) to screen desirable summer catch crops based on shoot and root growth of catch crops and N leaching in soils of greenhouse vegetable cropping system.
To collect the leachate more easily, the method of simulated soil column was used in the study. 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 biomass and N uptake of shoot and root, root length, root length density and the specific root length were measured to clarify effects of different catch crops in soil inorganic N residue and leaching.
Higher shoot biomass, root biomass and root length density of sticky corn and oat treatments were found compared with pea and amaranth treatments. Higher N uptake was shown in sticky corn, oat and pea treatments in comparison to amaranth. Compared with fallow treatment, catch crop planting could efficiently reduce soil inorganic N residue at harvest in all 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 treatment, inorganic N leaching could be reduced by 100%, 96%, 82% and 58% with sticky corn, oat, pea and amaranth treatments, respectively. Correlation analysis indicated that there was a 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, which indicated N leaching might be influenced by synergistic effect between aboveground and root system of catch crops. In addition, it was difficult to reflect the relationship between root growth and N leaching by only using static root parameters. In conclusion, sticky corn and oat were more desirable summer catch crops in greenhouse vegetable cropping system than pea and amaranth in the study.