Effects Of Combined Application Of Biochar And Nitrogen Fertility On Physical And Chemical Properties And Crop Yield Of Typical Upland Red Soil

This study examined the effect of combined application of biochar and nitrogen fertilizer on soil fertility improvement and crop yield based on the typical upland red soil in a long time in Jiangxi province. The variations of physical properties such as bulk density, total porosity, saturated hydraulic conductivity and water characteristic curve, chemical properties such as organic carbon, phosphorus, CEC and pH, and the change of crop (rapeseed and sweet potato) yield between two seasons were determined after the application of biochar (0,2.5 t/ha,5 t/ha,10 t/ha,20 t/ha,30 t/ha, 40 t/ha) and nitrogen fertilizer(60 kg/ha,90 kg/ha,120 kg/ha), and the effects of biochar on the ammonium nitrogen and nitrate nitrogen leaching in red soil were studied by the method of laboratory simulation which provided reference bases for the improvement of soil ffertility and crop production in typical upland red soil.The results were as follows:(1) The soil bulk densities all decreased in some treatments, total porosity and saturated hydraulic conductivity increased more or less after the application of biochar and nitrogen fertilizer. With the change of time, saturated hydraulic conductivity in 0-15 cm and 15-30 cm soil layer were improved more apparent with the increasing amount of applied biochar. By studying the hydraulic characteristics of the soil, the available water content had a significant increase with the increment of biochar application. The available water content was higher in 15-30 cm soil layer than in 0-15 cm in upland red soil.(2) The soil organic carbon (SOC),CEC and available phosphorus content in the depth of 0-30 cm increased after combined application of biochar and nitrogen fertilizer. The SOC and available phosphorus content in 0-15cm soil layer was higher than in 15-30 cm soil layer. But the CEC content was on the contrary. The soil acidity had an increase with the increment of biochar application in upland red soil. There was a significant correlation among available phosphorus and the pH, and organic carbon after the biochar was applied. Biochar not only has obvious effects on soil pH and the SOC content, but also improve the soil phosphorus content.(3) The effects of biochar on the ammonium nitrogen and nitrate nitrogen leaching in red soil were studied with the soil column leaching method. The leaching rate was significantly decreased with the increase of biochar. Breaking through curves of ammonium nitrogen and nitrate nitrogen had the same trend in the CK, C2, C3, C4, C5 and C6. The cumulative loss rate of ammonium nitrogen decreased by 22.00%, 38.33%,34.51%,34.91%,29.83%,28.28% and 20.03% respectively. The nitrate nitrogen decreased by 98.86%,96.49%,94.23%,90.21%,86.15% and 83.46% correspondingly. The peak values of ammonium nitrogen's relative concentration (C/Co) were 0.12,0.12,0.11,0.10,0.09 and 0.09 respectively, and that of nitrate nitrogen were 0.36,0.35,0.34,0.33,0.32 and 0.32. The cumulative loss rate of ammonium nitrogen and nitrate nitrogen and the peak values of the ammonium nitrogen have and nitrate nitrogen's relative concentrations were both negatively and very significantly correlated with their corresponding soil organic carbon, CEC and biochar application amounts. The peak values of nitrate nitrogen had significant positive correlation with soil bulk density. The breakthrough curves of each treatment were prolonged obviously. The more amounts of biochar were applied, the more obviously breakthrough curves were prolonged. It can be found from the analysis of the NO3--N breakthrough curves that bulk density, organic carbon, total porosity, CEC of the soil were affected with biochar application, resulting in changes of all the curves. When the CXTFIT 2.0 model is used to simulate the penetrating process, the simulation value and the actual investigated value of the breakthrough curves were positively correlated with the correlative coefficient being over 0.8497. Therefore, the CXTFIT 2.0 model could predict the nitrate-N transport and relative infiltrations. These results could provide scientific data for the effect of nitrate-N on groundwater body after biochar incorporation into the soil.(4) The biochar amendment enhanced the yields of rapeseed and sweet potato significantly. The largest increment occurred in C6N3 treatment. With the increase of biochar, the yields of rapeseed and sweet potato were higher at the same level of nitrogen fertilizer. With the increase of nitrogen fertilizer, the yields of rapeseed and sweet potato were higher at the same level of biocar amount. The contribution of biochar to sweet potato yield WAs higher than to rapeseed yield. The rate of nitrogen fertilizer contribution to rapeseed yield was higher than the rate of biochar contribution to sweet potato yield.