| The comprehensive impacts of biochar on soil physical and chemical properties,soil nutrient properties and soil microbiological properties in upland red soil for longer periods need further evaluation.Therefore,this study determined the effects of biochar combined with nitrogen fertilizer on soil physicochemical properties,soil nutrient properties,soil microbial biomass carbon,soil microbial biomass nitrogen,soil basal respiration and the horizontal transport of NO3--N in typical upland red soil in Jiangxi province following three consecutive crop rotation.The field experiment was conducted with a 7×4 factorial design at biochar rates of 0,2.5,5,10,20,30 and 40 t/ha(designated as C0,C1,C2,C3,C4,C5 and C6 correspondingly)and nitrogen fertilizer rates of 0,60,90 and 120 kg N/ha(designated as N0,N1,N2 and N3 correspondingly).The results were as follows:(1)Biochar improved the physicochemical properties of upland red soil within 3 to 5 years.Soil pH,soil porosity,and saturated hydraulic conductivity increased and soil bulk density decreased with increasing biochar amount.However,at each nitrogen application level,only the C6 treatment was significantly higher than the CO treatment in all field years.The effect of biochar on soil pH was gradually weakened,and this trend is most pronounced in the treatment of the highest nitrogen fertilizer application(120 kg/ha).In the fourth season of sweet potato harvest,soil bulk density was significant decreased in the C5N2 and C6N2 treatments compared with C0N2 treatment.In the fifth season of sweet potato harvest,the saturated hydraulic conductivity was significant increased in the C5N2 and C6N2 treatments.But the soil porosity had a significant increase only in the C6N2 treatment compared with the C0N2 treatment.In the forth season of tuber bulking,the content of<0.25 mm water-stable aggregates decreased and the content of>1 mm water-stable aggregates increased with the increase of biochar application in the 0-15 cm and 15-30 cm soil layer.Under the higher biochar application treatment,the MWD in the 0-15cm soil layer had a significant increase.(2)The content of soil organic carbon significantly increased by 38%-75%in the C6N2 treatment compared with the C0N2 treatment in all field years.Biochar had a positive effect on siol total nitrogen,nitrate-N,ammonium-N and soil available phosphorus,but the effect was gradually reduced with the application time of biochar prolong.The soil total nitrogen in the fourth season of sweet potato harvest reduced by 19.57%and 20.65%compared with the forth season of tuber bulking in the C6N2 and C5N2 treatment.In the fouth tuber bulking and sweet potato harvest season the soil nitrate-N and ammonium-N significantly increased in C6N2 treatment compared with the C0N2 treatment.Soil available phosphorus significantly increased in the C6N2 treatment with the C0N2 treatment in the forth tuber bulking season and the forth rape seedling stage.(3)The experimental results indicated that soil microbial biomass C was increased,but the soil microbial biomass N and the carbon-to-nitrogen ratio was decreased with biochar application.In the third sweet potato harvest season,the contents of soil microbial biomass C and soil microbial biomass N were increased by 18.22?122.74%and 20.86?312.91%respectively and the carbon-to-nitrogen ratio was decreased by 18.11?51.56%with biochar combined with nitrogen fertilizers application.In the forth sweet potato harvest season,compared with the C0N2 treatment,applying biochar at the rate of 40t/ha significantly decreased soil microbial biomass carbon-to-nitrogen ratio by 7.97,increased soil microbial biomass C,N by 43.3%and 162.6%,respectively.But applying biochar had no significant effect on soil basal respiration.In conclusion,biochar application tended to improve soil properties and soil biological properties in a long time.(4)The horizontal transport velocity and concentration of NO3-N were both significantly affected by biochar addition.In addition,the horizontal transport velocity and concentration of NO3--N were increased when the application rate of biochar is less than 30 t·hm-2.However,when the application rate of biochar is more than 30 t·hm-2,the horizontal transport velocity and concentration of NO3--N declined while the soil NO3--N utilization improved as the amount of biochar increased,These results provide a scientific data for predicting the effect of biochar application on NO3--N in upland red soil. |
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