| In recent years, biochar is increasingly widely used in agriculture as a soil amendmentand controlled-release carriers to fertilizer. In order to boost the study and utilization ofbiochar in agriculture, a field experiment and a laboratory simulation experiment wereconducted to study the influence of biochar application rates on soil quality. The researchcomparatively observed the effects of biochar application rates on soil physical and chemicalproperties, soil biological activities, nutrient concentrations and crops above-ground biomassin a field trial using a winter wheat and summer maize rotation system under temperateconditions in loess soil, Shaanxi province, China. The correlation between soil biologicalactivities and soil physical and chemical properties was studied after different amount ofbiochar applied. The results showed that:1. Applying biochar effectively reduced the cumulative the leaching amount of NH4+-Nand NO3--N in the leachate compared with the control, which distinctively decreased by41%and18.6%respectively under the application rate of80t·hm-2. The leaching loss of NO3--Noccurred predominantly in the first three times, the leaching amount of which accounted for97.3to98.8%of the total in the leachate. The biochar application of80t·hm-2significantlyenhanced retention time of NO3--N in soil to retard its leaching loss. In the whole leachingprocess, NO3--N was main form of the leaching of nitrogen. Its accumulative leaching amountaccounted for97.3to98.14%of the total NO3--N and NH4+-N.2. The application of biochar increased indistinctively the soil water content and the soiltotal porosity after the crops harvest. However, the soil bulk density decreased with theincrease of biochar, and tended to be larger after corn harvest than after wheat harvest. Aftercorn and wheat harvest, the soil bulk density of80t·hm-2decreased by10.56%and9.02%compared to the control treatment. The biochar application increased the pH distinctively.Amendment with biochar increased soil base saturation percentage after both crops harvest by44.94to84.72%and44.11to94.29%. Only the soil cation exchange capacity (CEC) of80t·hm-2after wheat harvest increased by9.25%compared to the control treatment. Organiccarbon concentrations increased as the biochar application rate increased. The increases,which ranged from53.82to263.65%, tended to be larger after corn harvest than that rangedfrom30.19to150.94%after wheat harvest. 3. The soil total N, total K, NO3--N and available K concentrations after crops harvestand the total P contents after wheat harvest increased as the biochar application rate increased.The application of biochar increased indistinctively the above ground biomass production andyield of both crops. But the harvest index decreased significantly by32.25%and9.13%aftercorn and wheat harvest. The N and P contents of corn crop and wheat seeds increasedsignificantly. However, the P contents of corn seeds and wheat crop and K contents of cornand wheat seeds decreased.4. Compared to the control treatment, biochar application significantly increased theurease and catalase activities after crops harvest, and the alkali phosphatease activities aftermaize harvest. The soil enzymes index was distinctively increased after both crops harvest by77.27to163.64%and20.93to118.6%, respectively. Whilst, the quantities of three type soilmicrobes markedly increased as the biochar application rate increased, and the increasestended to be larger after corn harvest than that after wheat harvest.5. The amendment of biochar improved soil microbial biomass carbon (MBC) inseedling stage, wintering period and green stage. And it also improved soil microbial biomassnitrogen (MBN) in corn maturity, green stage and jointing stage. The maximum biocharapplication rate (80t·hm-2) resulted in the most significant effect. But it decreased the soilmicrobial biomass carbon and nitrogen ratio (MBC/MBN) in corn maturity, green stage andjointing stage. Dynamic changes showed that the MBC and MBN were the lowest in thewintering period, the highest in the jointing stage, which was in accordance with the vigorousgrowth period of the crop. Biochar amendment also was found to significantly decrease theseasonal fluctuation of MBC and MBC/MBN, and increase the seasonal fluctuation of MBN,with the growth rate, which ranged from0.1to25.7%, increasing as biochar increased.6. The results of correlation analysis showed that soil biological activities were negativecorrelated with soil bulk density except invertase activity and MBC. There existed significantcorrelations between urease and catalase activity, MBN, the quantities of microbes and soilfertility factors. Path Analysis showed that urease and MBN mainly enacted a directcoefficient to soil fertility, while the catalase activity mainly enacted an indirect effect.According to the results of Principal Components Analysis, soil fertility can be described bymicrobe factor, enzyme activity factor, and available phosphorus factor. Soils after maizeharvest had higher comprehensive score than that after wheat harvest. The comprehensivescore of different treatments increased as the application rate increased, which indicated thathigh rate of biochar would have a more significant effect on improving soil fertility. |
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