The Influence Of Summer Catch Crop On Soil Nitrogen Transformation And Leaching In Greenhouse Vegetables

Excessive fertilizer?inorganic and organic?input and irrigation often result in serious nutrient accumulation in the soils of greenhouse,which can significantly affect continuous crop production and lead to low nutrient use efficiency.In this study,the effects of fertigation,summer catch crop and residue management on the leaching of dissolved total nitrogen?DTN?were investigated with lysimeters in typical vegetable greenhouse in North China.Previously,organic biological nitrification inhibitor?BNI?was found in the root exudates of sorghum.Hence,in this study,sorghum was planted as a summer catch crop to investigate the effects on nitrogen transformation and microbial properties,in comparison to sweet corn as control.The results showed that:?1?Compared with conventional practice?CN?,the recommended fertigation practice?RN,RN+WS,and RN+CC?based on fertigation did not significantly influence fruit yield,but reduced N,P,and K inputs and irrigation by 44-57%,45-64%,33-52%and 49%,respectively,from 2011 WS season to 2013 AW season.In addition,the apparent surplus of NPK was also significantly decreased by fertigation compared to conventional practice.The fertigation technique decreased soil soluble total nitrogen?STN?content from 2426 N hm^-2 to 1596 kg N hm^-2 after 6 growing seasons.The soluble organic nitrogen?SON?accumulation was among 514-923 kg N hm^-2,suggesting the important role of SON in soil N cycle.Compared to the recommended fertigation practice?RN?,catch crops planting?RN+CC?and straw incorporation?RN+WS?significantly enhanced N turnover and increased SON accumulation in 0-180 cm soil layer by 409 and 201 kg N hm^-2,respectively due to increased C inputs.The SON/STN was also increased to 28%,30%and 34%in the RN,RN+WS and RN+CC treatments;whereas the SON/STN in the CN treatment was the lowest?25%?.The peak of SON in soil came out one month after fertilization,which was later than soluble inorganic nitrogen?SIN?by about two weeks.?2?Compared to the conventional practice of furrow irrigation and summer fallow,fertigation during planting of the main crop and planting of subsequent catch crop in the summer significantly reduced the dissolved total nitrogen?DTN?and the dissolved organic nitrogen?DON?leaching by 365 kg N hm^-2 and 110 kg N hm^-2,respectively.Compared to summer fallow period,the catch crop significantly increased the ratio of DON/DTN in leachates.Approximately 46%and 69%of the total N in the roots and in the shoots of sweet corn were detected in the leachates collected in the succeeding cucumber growing season,accounting for 8%and 62%of the total amount of N in the leachate,respectively.These results suggested that fertigation and planting summer catch crop could significantly reduce N leaching from intensive greenhouse vegetable production in China.?3?This study also demonstrated that the sorghum?variety Jinza 12?as a catch crop was more efficient than sweet corn for reducing nitrogen accumulation in the soil.Meanwhile,soil NH4+-N content was highest in the treatment with Jiliang 2 after urea application,which might be related to the biological nitrification inhibitors?BNI?released by the root of sorghum.In conclusion,sorghum as catch crop can significantly reduce nitrogen loss through nitrogen uptake and nitrification inhibition.?4?Sorghum planting could significantly increase the yield of next crop,maintain high level of ammonium-form nitrogen and lower soil nitrifying potential than fallowing treatment.Sorghum planting decreased aMoA gene copy number of ammonia-oxidizing bacteria?AVB??from 9.07×108 to 1.20×108g-1 dry soil?and ammonia-oxidizing archaeon?AOA??from 1.80×109 to 7.59R108 g-1 dry soil?.Sorghum planting significantly influenced the relative abundances of the 16S RNA genes of AOB and AOA at genus level.Compared with fallowing treatment,both sorghum and sweet corn planting increased the proportion of Crenarchaeote for AOA,in which Candidatus Nitrososphaera was the dominant population.The proportion of Candidatus Nitrososphaera and Nitrososphaeraceae in 0-30 cm soil layer and Nitrososphaeraceae other in 30-60 cm soil layer were significantly lower with sorghum planting.For AOB,Nitrosomonadaceae other was the dominant population,however,the community structures of AOB were not affect with sorghum.It implied that sorghum as catch crop could significantly reduce the soil nitrate content and increase the ammonium nitrogen content through the inhibition of soil nitrification process,thereby reducing nitrate leaching in protected vegetable field.