Effects of different sugarcane leaf biochar application rates on sugarcane yield and nutrient uptake and utilization

【Objective】The effects of different sugarcane leaf biochar application rates on sugarcane yield and nitrogen， phosphorus and potassium nutrient uptake and utilization were studied in order to provide a basis for scientific application of sugarcane leaf biochar to promote sugarcane growth and achieve high nutrient utilization. 【Method】Field experiment and pot experiment were conducted in 2021-2022 by using ¹⁵N isotope tracer technique. Guiliu 05136 and Guitang 42 were used as test varieties. Four treatments were set up：CK（control，no sugarcane leaf biochar application），T1（sugarcane leaf biochar，2.7 t/ha），T2（sugarcane leaf biochar，5.4 t/ha）and T3（sugarcane leaf biochar，10.8 t/ha）. The yield，nitrogen， phosphorus and potassium content and accumulation rate of stems and leaves during the harvest period of sugarcane were analyzed. Moreover，fertilizer nitrogen uptake and nitrogen use efficiency were also studied. 【Result】Compared with CK，the application of different amounts of sugarcane leaf biochar had no significant effect on leaf yield（P>0.05，the same below），but increased stem yield to different degrees，and with the increase of sugarcane leaf biochar application， stem yield showed a trend of first increase and then decrease，and reached the highest level in T2 treatment，which showed a significant difference（P<0.05，the same below）. There were no significant changes in nitrogen and phosphorus content in stems and leaves，and nitrogen and phosphorus uptake accumulation rate in aboveground. However， T2 treatment significantly increased the phosphorus accumulation rate of sugarcane leaf in field trail， and the nitrogen， phosphorus accumulation rate of stem in pot trail in 2022. The application of sugarcane leaf biochar increased potassium content in stems by 31.3%-38.2% in 2021 and 10.5%-29.5% in 2022，respectively in field trial， where T2 treatment was equivalent to T1 treatment and significantly higher than T3 treatment in 2022. The application of sugarcane leaf biochar had no significant effect on the potassium content of stems，leaves and tail in pot trial. Biochar application increased the accumulation of potassium absorption in the stem and aboveground in the field， and increased by 18.2%-45.6% in stems and by 13.5%-32.8% in aboveground，and the highest was found in T2 treatment. However，no significant differences was found in physiological use efficiency of nitrogen and phosphorus. The physiological utilization efficiency of potassium was significantly reduced by 14.7%-23.1%（2021） and 6.0%-19.5%（2022）in field trial. The tracer of 15N isotope further showed that stem had the highest nitrogen fertilizer uptake，accounting for 46.5%-54.2% of the total nitrogen uptake，while leaves and tails had the equivalent nitrogen uptake，accounting for 23.3%-27.5% and 22.6%-28.0% of the total nitrogen uptake respectively. There was no significant difference in nitrogen fertilizer absorption in leaves and tails under different sugarcane leaf biochar application rates，but T2 treatment significantly increased the stem nitrogen fertilizer uptake by 36.5%-37.5% and the nitrogen use efficiency by 18.1%-24.2% compared with other treatments. 【Conclusion】In this study，the nitrogen and phosphorus uptake under sugarcane leaf biochar with different dosage is different in different years， but it is beneficial to improve the sugarcane yield and the potassium uptake of stems. At the same time，5.4 t/ha sugarcane leaf biochar treatment not only has the highest stem yield and potassium uptake in stems，but also significantly promotes the uptake of nitrogen fertilizer in stems and improves the nitrogen use efficiency，so it can be used as the recommended suitable application rate.