A Preliminary Study On Combined Application Of Biochar And Nitrogen Fertility Of Typical Upland Red Soil

This study examined the promotion effect of combined application of biochar and nitrogen fertilizer on soil basic fertility based on the typical upland red soil in Jiangxi province. The variations of chemical properties such as organic carbon, total nitrogen, ammonium, nitrate and pH, physical properties such as bulk density, total porosity, saturated hydraulic conductivity and water-stable aggregates, and crop (rapeseed and sweet potato) production were determined after the application of biochar (0,2.5,5,10,20,30,40t/ha) and nitrogen fertilizer(60,90,120kg/ha), which provided reference bases for the improvement of soil fertility and crop production in typical upland red soil.The results were as follows:(1) The saturated hydraulic conductivity of undisturbed soil in typical upland red soil region ranged from1.44×10-3to3.45×10-3cm/s, decreasing with the increase of soil depth. Available water content varied from0.083to0.124cm3/cm3with the maximum value in plough layer from the soil moisture characteristic curves. The soil bulk density and porosity were the main factors that affected hydraulic characteristics. The combination of geostatistics and classical statistics was made to evaluate the spatial variabilities of soil nutrients in upland red soil. The variation coefficients of soil nutrients were different in both surface (0-15cm) and subsurface (15-30cm) layers. Available phosphorus (AP), ammonium nitrogen (AN) and nitrate nitrogen (NN) exhibited moderate spatial variation while the other nutrients had weak variability. SOM and CEC of surface soil were described separately by gaussian and spherical models, the others by index models. The spatial distribution maps drawn with the method of Kriging interpolation showed that SOM and CEC were distributed in irregular patches while TN and NN presented strip and block distribution. The above results provided scientific data for understanding soil physical properties and soil nutrients, guiding menthods for soil improvement in red soil area.(2) The soil bulk densities all decreased in some degrees after the application of biochar and nitrogen fertilizer. With the increment of biochar application rate, bulk density decreased gradually, and total porosity and saturated hydraulic conductivity increased more or less.(3) The soil water stable aggregates had significant improvements after biochar applied to soil. When the amount of biochar amendment was40t/ha (C6treatment), the soil water stable aggregates (>2mm and>0.25mm)had a remarkable increase than other treatments. In the rapeseed harvest season, Mean weight diameter (MWD) increased by28.02%comparing to CK with the application rate of biochar being40t/ha (C6treatment). In addition, the SOC, TN and C/N in all fractions of aggregates also increased after biochar applied to upland red soil.(4) The soil organic carbon (SOC) at the depth of0-30cm increased by38.07%after combined application of biochar and nitrogen fertilizer. The increment of SOC contents in surface layer was higher than that in subsurface layer, with C6N3(biochar:40t/ha; N fertilizer:120kg/ha) and C6N2(biochar:40t/ha; N fertilizer:90kg/ha) treatments being the most effective. Total nitrogen (TN) under different treatments increased in some degrees and the differences were significant among all treatments (p<0.05). The increase amplitude of TN contents in surface layer was higher than that in subsurface layer, with C6N3treatment having the best performance. Compared with CK, the C6N3treatment increased TN content by58.49%. AN and NN also improved to a certain extent, but there were no notable differences among all treatments. Compared to CK treatment, the C6N3treatment increased NN content by31.79%.The pH of soil rose from4-72-4.99to4.81-5.22after treatments and the differences were significant among treatments (p<0.05), reflecting the improvement of soil acidity in typical upland red soil.(5) The biochar amendment enhanced the yields of rapeseed and sweet potato in varied degrees, and there were significant differences among the treatments(p<0.05). Compared with the control, the yields of rapeseed and sweet potato increased by2.90%-58.30%and11.24%-124.90%, respectively, with the largest increment occurring in C6N3treatment. The largest contribution rate of biochar and nitrogen fertilizer to yields of rapeseed and sweet potato was C6N1treatment.