Nitrogen And Earthworm Impacts On Clover And Maize Growth And Promoting Mechanism

In order to reduce the use of chemical nitrogen fertilizer,at the same time can still meet the demand for food,sustainable agricultural development has been received more and more attention.Earthworms can increase plant yield by promoting nitrogen mineralization,at the meantime,improving soil physical and chemical properties,soil microbial community and function.Effects of earthworm on different plants in different application level is poorly understood.This study set up three plants level(contrast,clover,corn),two nitrogen levels(0,240 kg ha-1)and two earthworm treatments(inoculated or not),to investigate earthworm impacts on soil properties,clover and maize growth under poor and rich nitrogen conditions.The results showed that:(1)Regardless of plant species and plants present or not,earthworms significantly improved soil aggregate structure,which increased the 2-0.25 mm aggregates,reduced the clay and sand content,especially under rich nitrogen conditions.Earthworms increased significantly mean weight diameter of aggregates under two nitrogen level of no plants and rich nitrogen conditions of planting clover.2)The changes of soil microbial community structure were mainly affected by plant species.The interactions between earthworms,nitrogen and plants were significant.Compared with soil bacteria,soil fungi was affected significant by earthworms,probably due to the disturbance and feeding from earthworm.3)Soil nematodes were mainly affected by plant species,similar to the change of soil microorganism.But nitrogen was also an important factor.The effect of earthworms weakened in nitrogen fertilizer applied to the plant system.It was worth noting that earthworms reduced significantly soil nematode abundance without nitrogen added under the condition of planting clover.Also the total nematode abundances were significantly lower under the absent of plants.4)The soil enzyme activity were mainly affected by plant species.At the same time,earthworms significantly increased the activity of total carbon,nitrogen and phosphorus enzymes,and also total enzyme.It was worth noting that,regardless of whether nitrogen fertilizer,earthworms decreased significantly the total enzyme activity under the maize system.5)Earthworms increased significantly maize aboveground and root biomass under the condition of not applying fertilizer,but had no significant effect on maize biomass under no nitrogen fertilizer conditions.The opposite was that,earthworms had no significant effect on clover biomass of without applying nitrogen,but decreased significantly clover biomass of nitrogen applied.In summary,earthworms could promote the growth of plants by increasing soil available nitrogen,and also by soil microbial community,depending on plant species.Understanding the relationships between earthworm,plant species and soil microorganism,is conducive to more fully understand the effects of earthworms on crop system,better development and management for sustainable agriculture.