Sugarcane is one of the important economic crops of Thailand. It’s a raw material in the cane and sugar industry, and animal feeds and is also used as an energy crop for ethanol production. Sugarcane leaf burning was the common management for sugarcane harvesting process which was related to dust and small particles which affects and impacts both the environment and human health. Burning also leads to loss of plant nutrients, soil organic matter which eventually leads to loss of soil fertility. The utilization of bio-products from microorganisms including living cells and enzymes leads to acceleration of sugarcane trash decomposition especially leaf degradation. The result indicated that both microbial cells and enzymes affected plant nutrient accumulated in soil especially total N and Humic acid content. The utilization of microbial cells and microbial enzymes for sugarcane trash management could be an alternative to avoid the burning process and improve soil fertility. This information can be integrated with fertilizer management for sugarcane production.
Keywords: sugarcane trash, soil fertility, biodegradation
Sugarcane is one of the important economic crops of Thailand. It’s a raw material in the cane and sugar industry, animal feeds and used as an energy crop for ethanol production. The remaining fiber after process can be used as fuel to generate electricity for the factory. Thailand is the 3rd largest sugarcane producers in the world after Brazil and India (USDA, 2016). The cultivating area of sugarcane in Thailand is more than 100 million rai in 2020 and increased by around 2.44% in 2021 (Office of Agricultural Economics. 2018). From large cultivation area, it’s estimated that 1 rai (1 rai = 0.16 ha.) of sugarcane planting area will have sugarcane trash after harvest which is approximately 0.63-1.51 ton/rai. Therefore, it will be up to 6.16 million tons each year.
The grower always burnt sugarcane trash before and after harvesting as conventional field management to avoid the harvesting barrier. The heat from burnt sugarcane trash resulted in 97-99% nitrogen loss which is equal to 40,656 tons nitrogen loss/year. Furthermore, the burning process led to reduction of sugarcane yield quality due to reducing of sugar content, loss of plant nutrients and organic matter in soil which were easily lost by heat. Burning trash generates the air pollution problem and smoke dust (Razafimbelo et al., 2006) that is harmful to human health. The small particle dust is smaller than 2.5 micrometers called “PM 2.5” generated from trash burnt was found to be a cause of respiratory disease, lung cancer and the other health problems in humans.
The effective microorganisms and microbial enzymes, especially cellulase can accelerate the decomposition of sugarcane trash. They were considered as alteratives instead of trash burnt. During decomposition, plant nutrients were released while some components such as lignin and other organic compounds were transformed to soil organic matter that will enhance fertility and carbon stock in the soil. The releasing of plant nutrients during decomposition process become the cause of nutrients available in the soil leading to a decrease in the use of chemical fertilizers. This process will be one guideline for sustainable sugarcane production.
Utilization of sugarcane trash and nutrient content
Sugarcane trash can be used as animal feeds. It contains 6.4% (dry weight) of protein. Fresh and dry leaves used as animal feeds are fermented with molasse, rice bran and urea to increase feed nutrition. However, when using sugarcane trash as animal feeds, it’s necessary to mix it with the other protein sources. Sugarcane trash is also used as renewable energy source by produce as fuel pellets from sugarcane leaves. The fuel pellets have density >1.0 kg/m3, moisture <10%, heat per unit 16.8 MJ/kg and contain 6% ash. The production of fuel pellets helps to increase the value added component of the trash and growers get more income from selling the trash material.
Plant nutrients in sugarcane trash
Sugarcane trash contains plant nutrients such as nitrogen, phosphorus and potassium 0.49%, 0.21% and 0.58%, respectively. When till into the soil, it will provide approximately 4.9-9.8, 2.1-4.2 and 5.8-11.6 kg/rai of Nitrogen, Phosphorus, and Potassium, respectively. Sugarcane trash is also used as mulching material to maintain moisture content in soil. However, plowing sugarcane trash into the soil was one of the management’s practices to prevent the occurrence of small particle dust and loss of plant nutrients in the soil from burning heat. Tilling sugarcane trash into the soil made the trash decomposition faster than trash mulching on soil surface. However, decomposition of sugarcane trash after tillage takes a long time due to high carbon and nitrogen ratio of the trash. It’s also affected the scramble of nutrients in the soil through the immobilization process. The sugarcane trash decomposition caused by the activity of soil microorganisms that naturally exist by producing extracellular enzymes involved in plant tissue decomposition to break down the complex structure of the trash. The organic component that is the constituent of sugarcane trash is decomposed into smaller bits enough to enter the microbial cell. Microorganisms obtain energy and essential elements from macromolecule decomposition to build new structure within the cells. However, some of those organic components will be converted into soil organic matter through polymerization or condensation process. The increase in soil organic matter was used to assess the soil fertility level. It helps to improve the physical, chemical, and biological properties of the soil, and carbon sequestration in the soil which were suitable for plant growth.
Sugarcane trash management and soil fertility
The recommended Nitrogen fertilizer for sugarcane is generally 100–200 kg N/ha/year, and this is based on the traditional system of management. Harvest residues are burnt and the soil continues to be cultivated every year. Sugarcane trash contains around 60% of the total above-ground plant Nitrogen (Chapman et al. 1994). When it is burnt, more than 70% of the Carbon and Nitrogen are lost to the atmosphere (Mitchell et al. 2000). Consequently, with retention of trash, Nitrogen and Carbon may be accumulating in the soil. Many researchers studied on the utilization of sugarcane trash management in various conditions. Sugarcane trash management strategy consisted of control without management, mulching and their incorporation into the soil. It was found that sugarcane trash that has been incorporated into the soil led to fastest sugarcane trash degradation and highest accumulation of Nitrogen in soil up to 0.015 kg/rai. Incorporation of sugarcane trash into the soil gave an advantage for faster decomposition because the trash directly gets into contact with the soil that further accelerates the decomposition process. Leaving the remaining trash as mulching material on the soil surface led to the increase of total Nitrogen in soil. Nitrogen form of nitrate was higher than the form of ammonium. The total Nitrogen in soil tended to increase followed the mulching period. Trash management without burning also reduced the amount of chemical fertilizers needed while there was an increase in organic Carbon, soil organic matter and plant nutrients in the soil. Sugarcane trash also plays an important role on the soil’s biological properties since it was a food source of soil microbes that stimulated biological activities in the soil as well as the improvement of the soil’s physical properties. (Office of Cane and Sugar Board, 2015; Robertson and Thorburn, 2007). Sugarcane trash management, in combination with plant nutrient management, especially Nitrogen fertilizer in low fertility soil resulted to the increase in production yield, soil fertility and carbon sequestration (Tan,1995).
Utilization of microorganisms and microbial enzymes to accelerate sugarcane trash decomposition
Biodegradation was considered as the alternative way for trash management to avoid trash burning. Beary et al. (2002) studied the utilization of mix-culture of fungi and bacteria for sugarcane trash biodegradation after harvesting. The mix-culture consisted of Ceriporiopsis subvermispora and Cellulomonas sp. which were selected from their abilities on cellulose degradation and Azospirillum brasilense, a free-living Nitrogen fixing bacteria. The application of mix-culture microorganisms and 0.3% of molasses led to differences in decomposition rate, population number of bacteria and fungi, pH, Nitrogen content and available Phosphorus in the soil when compared to the control treatment and single culture. The result indicated that the utilization of mix-culture can accelerate sugarcane trash decomposition after it is harvested. Mohan et al., (2011) also found that the application of effective microorganisms can make the decomposition rate of sugarcane trash faster. The overall research indicated the importance of sugarcane trash management for cane production and soil fertility. Some researchers focused on the role of soil microorganisms on decomposition rate of sugarcane trash. In Thailand, there are no microbial products for accelerating the decomposition rate of sugarcane trash. Most of the decomposition naturally occurred and took a long time. Guevera and Zambrano (2006) isolated the microorganisms from various sources such as agricultural materials and sugarcane residues for the decomposition of sugarcane trash. Nine microbial isolates had cellulase activity that accelerated sugarcane trash decomposition and were identified as Bacillus subtilis, Streptomyces sp. and Cellulomonas sp. The main objectives of our study were to determine the rate of sugarcane trash decomposition and its acceleration by effective microorganisms and its cellulase enzyme, as well as the effect of acceleration of decomposition on soil fertility to use as an alternative to reduce sugarcane trash burnt.
Effect of sugarcane trash accelerate on accumulation of plant nutrients and Humic acid in soil
The effective sugarcane trash degrading microorganisms were isolated from the soil and various sources such as compost, termite gut and termite mound together with an enrichment method in basal medium containing sugarcane leaves as a sole Carbon source. The pure isolates were tested on their abilities to degrade lignocellulosic compound in sugarcane trash by producing cellulase, xylanase and lignin degrading enzyme. The effective strains were selected based on cellulase production. It was found that most of microbial isolates can produce cellulase enzyme followed by xylanase while a few isolates can produce lignin degrading enzyme. Sugarcane trash was incubated in the soil with different living microbial cells and crude cellulase in the pots for 30 days.
The result indicated that the application of living cells and microbial enzymes to accelerate sugarcane trash decomposition did not have a significant effect on soil pH, EC and Potassium content in soil while N-mineralization, Phosphorus content, organic Carbon, Humic acid and decomposition were different. The maximum N-mineralization was found in control without acceleration while living cells and microbial enzymes gave the lower N-mineralization. It’s possible that living cells require Nitrogen to reduce C:N ratio of sugarcane trash. In contrast, microbial enzymes yielded higher available phosphorus than living cells and control. Humic acid content was used as representative of biochemical transformation of Carbon in organic matter like sugarcane trash to Humic substance, a stable organic Carbon. The formation of Humic substance would affect soil fertility and soil properties. It was found that the sugarcane trash decomposition which was accelerated by both living microbial cells and microbial enzymes gave more Humic acid content than the control. Furthermore, the percentage of organic Carbon (OC) and decomposition in both living cells and microbial enzymes were higher than the control treatment (Table1). This result indicated the possibility to accelerate sugarcane trash and can improve soil fertility from the increase of OC and Humic acid accumulation in the soil.
Key component of fertilizer management in sustainable sugarcane production
The key components of fertilizer management of sugarcane production include an effective system of trash management, appropriate cultivation practices, and a fertilization regime that replaces nutrients loss through crop harvesting (Follett et al. 1987). Sugarcane trash management by accelerating decomposition by microbial cells and microbial enzymes were done and considered as an upstream strategy to reduce environmental impact and loss of soil fertility. The success was necessary to combine the information to be integrated with soil database, fertilizer and farmer management, crop model, and effective technology for fertilization. So, our research team set up the fertilizer management for sustainable sugarcane production as follows:
- Utilization of sugarcane trash by accelerating decomposition to improve soil fertility.
- Isolation and selection of effective sugarcane trash degrading microbes, optimum condition for enzyme activities, N-mineralization rate, decomposition rate, status of plant nutrient and accumulation of organic Carbon in the soil.
- Development of soil data sets to apply with the Tailor-made fertilizer technology in sugarcane.
- Expand the board utilization of “Tailor- made fertilizer” recommendation that was limited for northeast sugarcane production (SimCane) to be applied for the production in the central area of Thailand. The soil data such as soil genesis, soil characteristic and area were implemented to the database to generate “Comparative soil series”.
- The development of site-specific nutrient management for sugarcane in the central area.
- Make the effective recommendation of site-specific fertilizer management to get the highest yield and more income. The information used for making decision system as a tool to select fertilizer management that is appropriate for soil fertility status.
- Using unmanned aerial vehicle (UAV)-based imagery to estimate top dressing Nitrogen in sugarcane production.
- Using an indirect method of the normalized difference vegetation index (NDVI) with an unmanned aerial vehicle to assess the Nitrogen level for application of make-up fertilizer promptly. It can be used to increase fertilizer efficiency.
Management of soil organic matter is critically important for sustaining the long-term productivity of cropped soils. Sugarcane trash can be used as nutrient sources for plant and remain as soil organic matter to retain “a better healthy soil” for sugarcane production. The decomposition process is accelerated by living cells or microbial enzymes which caused faster trash decomposition than it naturally occurs. This could be an incentive for growers to avoid trash burning. This management could set up a guideline to improve soil fertility and reduce environmental impact in sugarcane planting area. Furthermore, the information from an upstream trash management will be implemented with the soil database in specific area, “tailor-made-fertilizer recommendation” and crop model linked with analysis of NDVI for effective fertilizer management in sustainable sugarcane production. We are continuously finding a better way to increase yield, reduce costs and get better quality of sugarcane while at the same time keeping a “healthy soil” in agriculture.
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