Effect Of Combined Application Of N Fertilizer And Manure On Humus Composition Contents And Characteristics In Greenhouse

With the rapid development of greenhouse vegetable production,the problem of excessive fertilizer application in greenhouse is very serious.Composition and component ratio of soil humus are important indicators for assessing soil organic carbon quality,and also have important influences on soil structure and quality.Therefore,it is of great significance to rational fertilization in facilitated vegetable production to study effect of application of nitrogen?N?fertilizer and manure on composition contents,composition and profile distribution of soil humus under greenhouse.For this study a field fertilization experiment was conducted in a greenhouse growing tomato for five consecutive years.The experiment was designed to have four treatments?N0,N1,N2 and N3?of applying merely N fertilizer at a rate of.0,187.5,375.0,and 562.5 kg·hm^-2,respectively,and four?MN0,MN1,MN2 and MN3?combined application of N fertilizer and manure that is,each of the four N treatments coupled with organic manure(M:75 000 kg·hm^-2).The carbon?C?and N contents and their characteristics of soil humus composition under different N application and combined application of N fertilizer and manure were studied.The relationship between soil humus composition and tomato yield were analyzed.The effects of combined application of N fertilizer and manure on the contents and characteristics of humus composition were discussed.The main conclusions from the study were as follows:?1?Combined application of N fertilizer and manure could increased the contents of total organic carbon?TOC?,total nitrogen?TN?,water soluble organic carbon?WSOC?and water soluble nitrogen?WSN?in soil,and the contents of TOC,TN,WSOC and WSN increased significantly in 0?20 cm soil layer,but there was no significant difference between different N application levels.The contents of TOC,TN and WSOC generally decreased with soil depth.?2?Combined application of N fertilizer and manure could increased significantly the C and N contents of loosely combined humic acid?HA₁?,loosely combined fulvic acid?FA₁?,stably combined humic acid?HA₂?and humin?HM?in 0?20 cm soil layer?P<0.05?,and HA₁-C content was significant difference between different N application levels.The C and N contents of HA₂,stably combined fulvic acid?FA₂?and HM generally decreased with soil depth.The C contents of HA₁and FA₁increased first and then decreased with soil depth,while the N contents decreased first,then increased and then decreased with soil depth.?3?Combined application of N fertilizer and manure increased the C/N ratio of HA₁,FA₁and HA₂,and the HA/FA?humic acid to fulvic acid?and PQ value?the proportion of humic acid in extractable humus?of soil humus were increased,and the E₄/E₆?the ratio of absorbance of humic acid or fulvic acid at 465 nm and 665 nm wavelengths?and?log K?the difference between logarithmic of absorbance of humic acid or fulvic acid at 400 nm and 600 nm wavelengths?of humic acid?HA?were reduced,the E₄/E₆and?log K of fulvic acid?FA?were increased.In general,combined application of N fertilizer and manure promoted the formation of HA and FA composition with higher activity,and made the structure of HA tend to be complicated,and the structure of FA tend to be simplified.?4?Compared with N0,N1,N2 and N3 treatments,tomato yield increased by 7.32%,12.85%and 1.46%respectively in MN0,MN1 and MN2 treatments,but decreased by 3.23%in MN3 treatment.There was no significant difference in tomato yield in the soil relative to treatment.Compared with the single application of N fertilizer?N1?,the yield of tomato increased the most when N application was 187.5 kg·hm^-2?N1?and 75 000 kg·hm^-2manure.As mentioned above,under the conditions of tomato cultivation in the greenhouse,combined application of N fertilizer and manure for five consecutive years not only significantly increases the amount of TOC in the 0?20 cm soil layer,but also helps FA transform to HA,promotes formation and accumulation of HA,especially HA₁,and consequently improves quality of the soil organic carbon significantly.It is,therefore,concluded that combined application of 187.5 kg·hm^-2N fertilizer and 75 000 kg·hm^-2manure is the best option to improve quantity and quality of TOC,and achieve higher yields.