关键词: 甘蔗, 蔗叶利用, 土壤养分, 溶解性有机碳氮, 微生物生物量碳氮

Abstract:

The sugarcane industry in the Yunnan Province plays an important role in the local economy. As the second largest producer of sugarcane in China, its healthy development is of significant economic importance. However, the problems of soil fertility decline and sugarcane yield reduction caused by continuous cultivation have become increasingly prominent. Meanwhile, the low utilization rate of the large amount of sugarcane leaves produced after harvest and traditional burning treatments has caused serious environmental pollution. Therefore, exploring effective ways to utilize sugarcane leaf resources and achieve the dual goals of soil improvement, sugarcane quality, and yield enhancement is of great theoretical and practical value. Addition of exogenous substances is considered an effective way to improve soil quality and promote crop growth. Therefore, this study investigated the effects of three different forms of cane leaf additives (sugarcane leaf-derived biochar, sugarcane leaf ash, and crushed sugarcane leaf) on the soil physicochemical properties, active organic carbon and nitrogen fractions, microbial community composition, and the growth and quality of sugarcane. The study was conducted over a one-year period in a barrel planted in Kaiyuan City, Yunnan Province. The objective of this study was to provide a scientific foundation for the effective utilization of sugarcane leaf resources and sustainable development of the sugarcane industry. The experimental design employed a completely randomized block group design, incorporating four distinct treatments: control check (CK), sugarcane leaf-derived biochar treatment (SLBC), sugarcane leaf ash treatment (SLA), and crushed sugarcane leaf treatment (SL), with three replicates for each treatment. The experiment was conducted under uniform conditions of water and fertilizer. At the tillering stage of sugarcane, a mixture of potassium dihydrogen phosphate and urea fertilizer was applied. The results showed that all three sugarcane leaf additives significantly improved the basic nutrient status of the soil; however, their mechanisms and effects were significantly different. Among them, sugarcane leaf-derived biochar was the most effective in increasing soil organic matter (SOM) and available nitrogen (AN), with increases of 60.3% and 85.1%, respectively, compared with CK. In addition, amendment with sugarcane leaf-derived biochar significantly increased the contents of soil dissolved organic carbon (DOC) and dissolved organic nitrogen (DON), indicating that it could effectively promote the accumulation of active carbon and nitrogen components in the soil. In contrast, the addition of crushed sugarcane leaves had a relatively weak effect on soil nutrient improvement. Although it significantly increased the SOM content at the beginning of the experiment, its effect gradually weakened owing to the lack of physical protection. Sugarcane leaf ash contributed the least to the soil carbon pool because of the substantial loss of organic carbon during combustion. Moreover, the DOC/DON ratios were significantly reduced after all treatments, with the addition of sugarcane leaf ash exhibiting the greatest reduction effect. Notably, sugarcane leaf-derived biochar significantly reduced soil total phosphorus (TP) content but increased the utilization rate of available phosphorus (AP), which may be related to its promotion of the activity of specific microbial communities, such as the orders Xylariales and Rhodobacterales. In terms of soil microbial biomass carbon (MBC) and nitrogen (MBN), SLBC treatment significantly increased soil MBC by 60.3% compared to CK, and the increase in the MBC/MBN ratio indicated that it was more conducive to the colonization of fungal communities. This was mainly due to the porous structure of biochar, which provides a good habitat for microorganisms, and the slow release of soluble organic matter, which maintains the continuous activity of microorganisms. Although SL also increased MBC, the increase was relatively low (29.5%) and lacked the ability to retain nutrients in the long term. The SLA showed a significant decrease in microbial activity over the later stages of the experiment because of the lack of a continuous carbon source. Correlation analysis further showed that soil carbon and nitrogen components were significantly positively correlated with the relative content of chlorophyll in sugarcane leaves (SPAD) (p<0.05), but weakly negatively correlated with soil pH and TP. This relationship indicated that increasing carbon- and nitrogen-rich substances has a positive impact on sugarcane growth, but attention should be paid to the appropriate application of phosphorus and the regulation of soil pH. Analysis of sugarcane agronomic traits revealed that the three treatments did not significantly increase the plant height, stem diameter, or fresh weight of sugarcane; however, the sugarcane leaf-derived biochar and crushed sugarcane leaf treatments significantly increased the SPAD value and juice Brix of sugarcane leaves by 26.1% and more than 10%, respectively. This finding indicates that sugarcane leaf biochar and crushed cane leaves have the potential to enhance sugarcane quality by improving the leaf photosynthetic efficiency and sugar accumulation. However, the sugarcane leaf-derived biochar treatment resulted in a 25% reduction in fresh weight of sugarcane, which may be related to the fact that the initial adjustment of soil pH by biochar inhibited the growth of sugarcane seedlings in the short-term experiment. Conversely, the application of crushed cane leaves resulted in more balanced performance in terms of maintaining sugarcane yield and quality. This study revealed the mechanisms underlying the effects of different exogenous forms of sugarcane leaf additives on soil improvement and sugarcane growth. Sugarcane leaf-derived biochar, with its stable aromatic structure and porous characteristics, has significant advantages in enhancing soil carbon and nitrogen components and microbial activity. However, its short-term inhibitory effect on sugarcane yield needs to be further verified through long-term experiments. Conversely, crushed sugarcane leaves are more suitable for short-term soil amendment because of their rapid decomposition and nutrient release characteristics. The effects of sugarcane leaf ash are relatively limited because of the easy loss of nutrients. Overall, the application of sugarcane leaf-derived biochar in combination with crushed sugarcane leaves may synergistically enhance short-term benefits and long-term soil health during actual production. Future research should further explore the optimal ratio and application methods of sugarcane leaf-derived biochar and crushed sugarcane leaves and verify their long-term effects through field experiments to promote the efficient utilization of sugarcane leaf resources and green and sustainable development of the sugarcane industry.

Key words: sugarcane, sugarcane leaf utilization, soil nutrients, dissolved organic carbon and nitrogen, microbial biomass carbon and nitrogen