Effects Of Biochar On Distribution Of Organic Carbon And Nitrogen In Soil Aggregates In Semiarid Farmland

The Loess Plateau of northwest China is an important dryland agricultural area and has a great yield-increasing potential with abundant light and land resources; however, lower fertility and limited precipitation often limited primary production and sustainable development in the areas. Biochar is a carbon rich material with dense porosity, high specific surface area and high bio-chemical stability. Recently, biochar has gained much attention as a soil amendment, however, variable biochar properties may interact differently in soils of varying texture over interaction period. So the field trial was needed to corroborate the effect and optimise application of biochar. The objective of this study was carried out to investigated the effects of biochar addition on the distribution of soil aggregates carbon and nitrogen in the rainfed farmland. Biochar was added to a maize field at four rates(CK: 0 t·hm-2, C1: 10 t·hm-2, C2: 20 t·hm-2 and C3: 30 t·hm-2) one year before. The soil samples were collected from three different profiles(0~10 cm, 10~20 cm and 20~30 cm) in the next two consecutive years. Soil samples were fractionated into different aggregate sizes(>2 mm, 2~0.25 mm, 0.25~0.053 mm and <0.053 mm) using the wet sieving method, and then the contents of soil organic carbon and total nitrogen in different water-stable aggregates were measured. Correlations of contents of total organic carbon(TOC) and dissolved organic carbon(DOC), microbial biomass carbon(MBC) and readily oxidized organic carbon(ROOC) were also analyzed. and to It aimed at providing certain scientific basis for comprehensive understanding of soil eco-environmental effect of biochar on promoting semiarid farmland soil qualities and agricultural application by quantifying aggregate characteristics and distributions of soil carbon and total nitrogen following the application of biochar over 2 to 3 years, and by investigating its inter-annual variation characteristics. The main results are as follows:1. Biochar had effects on the aggregate distribution characteristics of soil in semiarid farmland; however, which varied with biochar application rates and experimental periods.(1) Biochar significantly decreased the contents of >2 mm water-stable aggregate in the 10~20 cm and 20~30 cm soil layers before sowing and after harvest in 2013; while effects of biocharonthecontentsoftheotheraggregateswerenotsignificantorhadnoobviousregularity.(2)contentsofeachwater-stableaggregatessizeindifferenttreatmentsinthe0~10cmsoillayerhadnosignificantdifferencebeforesowingandafterharvestin2014;andcontentsof2~0.25mmand0.25~0.053mmaggregatesindifferenttreatmentsinthe10~20cmand20~30cmsoillayersbeforesowingfollowedthetrend:c3,c2>c1>ck,yetthedifferenceamongtreatmentsdecreasedafterharvest.(3)biocharsignificantlyaffectedthegeometricmeandiameter(gmd),meanweightdiameter(mwd)andthecontentsof>0.25mmwater-stableaggregatesindifferentsoillayersbeforesowingin2013;whilegmdwasnotsignificantlyaffectedineachsoillayerafterharvestin2013,beforesowingandafterharvestin2014.thecontentsof>0.25mmwater-stableaggregatesinsoilincreasedwiththeyearforwardofbiocharapplication.2.biocharsignificantlyincreasedthecontentsofsocandtnindifferentaggregatessizesinsemiaridfarmland,butbiocharshowedcertaintemporalandspatialdifferencesonthecontributionratesofsocandtnindifferentaggregatesizes.(1)thecontentsofsocindifferentaggregatesizesinthe0~10cmand10~20cmsoillayersofdifferentbiochartreatmentsshowedaconsistentregularity:c3,c2>c1>ck;whilethecontributingratesin>0.25 mmaggregatesdecreasedasawhole.(2)biocharadditionincreasedthecontentsoftnindifferentaggregatesizesineachsoillayerwiththetrend:c3>c2>c1>ck.atendencytoincreasethecontributingratesoftnin2~0.25 mm,0.25~0.053mmand<0.053 mmaggregateswasobserved.3.biocharincreasedthecontentsofsocindifferentsoillayersofsemiaridfarmlandontheloessplateau,yettheeffectsofbiocharonthecomponentsofactiveorganiccarbonrelatedtoexperimentalperiods.(1)ingeneral,biocharincreasedthecontentsofsocindifferentsoillayersofsemiaridfarmlandontheloessplateau,andthecontentsofsocincreasedsignificantlyinthe0~10cmsoillayerofeachtreatment.(2)thecontentsofdoc,mbcandroocincreasedwithbiocharapplicationrateindifferentsoillayersin2013,significantlypositivecorrelatingwithtoccontents;however,acontrarytendencywasobservedin2014.