Effects Of Different Straw Biochar On Nutrient Adsorption,Leaching And Utilization

The climate of the Qinghai-Tibet Plateau is cold and cool,and it is difficult for straw to decompose when it directly returned to the field.If it is made into biochar to return to the field,which will conducive to improving the soil structure,reducing nutrient leaching,and improving the utilization rate of agricultural resources.Combining adsorption test,soil column test and pot test,to explore the effects of different biochar types and dosages on nitrogen and phosphorus nutrient adsorption,water infiltration and evaporation,nutrient leaching and utilization.The adsorption experiment studied the adsorption properties and mechanisms of biochar made of potato stalks,Lycium chinense Miller branches and rapeseed stalks at pyrolysis temperatures of 300,400,500,600 and 700°C on NH₄⁺-N,PO₄^3--P and NO₃^--N.After determining the optimal carbon-making temperature,soil column simulation was used to study the water infiltration and nutrient leaching of three types of biochar under different dosages.Further,the effects of different biochar dosages（1%,3%,5%）on soil fertility,cabbage growth and nutrient uptake were further explored through potting experiments.This study elucidates the water retention and fertilizer retention capacity,soil improvement effect and crop growth effect of different biochar species and dosages,which provides theoretical basis and technical support for the further promotion and application of straw carbonization and field return in the agricultural area of eastern Qinghai-Tibet Plateau.The main results obtained are as follows:（1）The adsorption performance of biochar on NH₄⁺-N,PO₄^3--P and NO₃^--N with the different pyrolysis temperature and different materials was quite different,among which the adsorption effect of biochar on NH₄⁺-N and PO₄^3--P was better,but the adsorption of NO₃^--N was poor.Potato stalk charcoal prepared had the largest adsorption of NH₄⁺-N and PO₄^3--P at 400°C,which was 3.92 and 3.96 mg·g^-1,respectively.The nutrient adsorption effect of biochar of different straw species is manifested as follows:potato stalk charcoal>rapeseed charcoal>Lycium chinense Miller branch charcoal.The Langmuir model and the quasi-secondary kinetic equation can better fit the adsorption process of NH₄⁺-N and PO₄^3--P by potato stalk charcoal.The adsorption of nutrients by biochar is a physical-chemical composite process,mainly based on the chemical adsorption of single-molecule layers.Potato stalk charcoal prepared at pyrolysis temperature of 400°C has the best nutrient adsorption performance.（2）With the increase of biochar consumption,the time for water infiltration increases,and the average infiltration rate of soil decreases.When biochar was added by 5%,the average soil infiltration rates of potato stalk charcoal,Lycium chinense Miller branch charcoal and rapeseed charcoal were reduced by 23.48%,15.65%and 41.74%respectively compared with CK.With the exception of 5%potato stalk charcoal,all other biochar treatments reduced the amount of water accumulated into filtration.The addition of biochar inhibited the pre-evaporation of the soil,and until the end of evaporation,the cumulative evaporation of potato stalk charcoal,Lycium chinense Mille branch charcoal and rapeseed charcoal was reduced by 8.50%-15.10%,8.86%-15.63%and 8.27%-12.96%respectively compared with CK.The Horton model can better simulate the infiltration process of soil water in each treatment,and R² is between 0.996-1.All biochar treatments reduced the amount of soil water leaching,the nutrient leaching was mainly NO₃^-,and the amount of NH₄⁺,NO₃^-and PO₄^3-was the least while adding to 5%potato stalk charcoal,which was 11.08%、15.12%and 10.32%lower than CK,respectively.From the perspective of increasing water infiltration,reducing water evaporation and reducing nutrient leaching effect,the water retention and fertilizer retention effect of adding 5%potato stalk charcoal is the best.（3）With the increase of biochar consumption,the quality and yield of dried cabbage increased,and when the amount of addition was 5%,the yield of cabbage reached the maximum,which was 64.60%higher than CK.When biochar is added 3%.,the root growth was the best,and the total root length,total root surface area and total root volume of Chinese cabbage were increased by 40.12%,70.03%and 19.96%compared with CK,respectively.When the amount of biochar was 5%,the nutrient uptake of N,P and K in Chinese cabbage was significantly increased,which was46.81%,41.38%and 85.42%higher than that of CK.When biochar was added by 5%,the soil full N,full P,available P,available K and organic matter were increased by23.16%,12.19%,19.08%,96.18%and 111.65%compared with CK,respectively,which had the best effect on the improvement of available potassium and organic matter.The addition of biochar significantly increased the composite index of soil fertility.When the amount of biochar is 5%,it has a good effect on plant growth,nutrient absorption and soil fertility.