Effects Of Biochar And Straw On Soil Respiration And Aggregation

Soil respiration is the primary path by which CO2 fixed by land plants and from soil organic matter(SOM)decomposition by soil microbes return to the atmosphere.It is also known as carbon mineralization.Soil aggregates are groups of soil particles that bind to each other more strongly than to adjacent particles.Aggregate stability refers to the ability of soil aggregates to resist disintegration when disruptive forces associated with tillage and water or wind erosion are applied.Wet aggregate stability suggests how well a soil can resist raindrop impact and water erosion.Many researches have been done on the impacts of low temperature biochar on soil respiration and aggregation but little studies have been done in comparing the effects of biochar on carbon mineralization between low organic matter and high organic matter mollisols.It is also observed that there is a knowledge gap in the influence of biochar and straw on some soil physical(Bulk density,total porosity,water holding capacity)properties over a short period of time.This study aimed at;addressing the aforementioned knowledge gap by determining the effects of low and high biochar application rates as well as corn straw on microbial soil respiration,nitrogen mineralization,microbial biomass carbon and microbial biomass nitrogen from soil;determining the influence of biochar,straw and manure on soil organic carbon,microbial biomass carbon,soil aggregation,aggregate size distribution,aggregate mean weight diameter and some selected soil physical properties;determining the influence of biochar,straw and poultry manure on growth and yield of corn.Two trials were conducted between November,2014 and December,2016 at Northeast Agricultural University,Harbin,China.The first was an incubation experiment to determine the influence of three different levels(0.5%,1%,and 2%)of biochar and straw(1%)on carbon mineralization,nitrogen mineralization,microbial biomass and total nitrogen(TN)from two mollisols of different levels of organic matter;high(HOM)and low(LOM).The incubation experiment consisted of eight treatments(CK-soil,B1-soil + 0.5%biochar,B2-soil + 1%biochar,B3-soil + 2%biochar S-soil + straw,SB1-soil + straw + 0.5%biochar,SB2-soil + straw + 1%biochar,SB3-soil + straw + 2%biochar).The treatments were further categorized into two groups;Sole biochar(CK,B1,B2,B3)and straw(S,SB1,SB2,SB3).The second was a field experiment with a randomized complete block design set out to determine the influence of biochar(B1 = 1%and B2 = 5 0/%),poultry manure and corn straw on soil aggregation,soil mean weight diameter,total organic carbon in soil aggregates,soil organic carbon,microbial biomass carbon,pH and soil physical(soil bulk density,total porosity and water holding capacity)properties at four soil depths(0-10 cm,10-20 cm,20-30 cm,30-40 cm).Biochar(BI)was applied at the rate of 12,500 kg.ha-1 while biochar(B2)was applied at the rate of 62,500 kg.ha-1.Application rate for manure was 25,000 kg.ha-1 while that of corn straw was 15,000 kg.ha-1 Corn yield was also determined after harvesting.The seven treatments(CK-soil,S-straw,Bl-1%biochar,B2-5%biochar,SB1-soil + 1%biochar,SB2-soil + 2%biochar and M-manure)were replicated four times.The size of each plot was 20 m2(5m × 4m).Overall,soil respiration rate was reduced by biochar additions.Soil respiration in high organic matter soil was higher than that of low organic matter soil throughout the incubation period.Treatments with straw-biochar combinations recorded higher respiration rates than sole biochar treatments.Higher biochar application rates(2%)led to a further decline in soil respiration.For nitrogen mineralization,NO3--N was reduced by the addition of biochar and straw combinatons in both high organic matter and low organic matter soils(HOM and LOM).CK produced the highest NO3--N throughout the incubation period.For NH4+-N,staw-biochar combinations recorded the highest N-mineralization.Total nitrogen was increased by biochar and straw additions;B2(soil + 1%BC)and SB3(SB3;soil + straw + 2%BC)recorded the highest total nitrogen values during the incubation period.Biochar and straw additions also increased soil microbial biomass carbon and soil microbial biomass nitrogen in HOM and LOM soils used for the experiment.For the field trial,sole biochar treatments(B1 and B2)and corn straw(S)recorded the greatest influence on soil mean weight diameter(MWD).Manure addition had the greatest influence on microaggregate formation while B1 and B2 recorded the greatest contribution to macroaggregate formation.Lowest total organic carbon(TOC)values were recorded in the silt + clay aggregate fractions(<0.053 mm).Soil bulk density increased with depth throughout the experiment but a decrease in soil bulk density among the treatments with respect to CK was observed.Soil total porosity decreased with soil depth,and the treatments increased soil total porosity with respect to CK.Treatments S,B2 and M had the greatest influence on soil water holding capacity(WHC)at the top soil(0-10 cm).A raise in soil pH and soil microbial biomass carbon was recorded by all the treatments when compared to CK while B2 and SB1 had the greatest influence on soil organic carbon.For yield parameters,SB2 had the greatest effect on cob length while SB1 produced the highest number of cobs per m2.Poultry manure had the greatest effect on weight of 100 grains and cob weight.