Sustainable Nitrogen Management in Sugarcane Production

Abstract

Nitrogen is one of the most essential macro-nutrients that improve crop growth, development, quality, and productivity of sugarcane. However, nitrogen fertilization in sugarcane yield has serious constraints. Leaching, runoff, and fixation losses of nitrogen increase production costs, decrease nitrogen use efficiency and crop productivity, and cause environmental pollution. On the contrary, agronomic management practices are pivotal for sustainable nitrogen management in sugarcane fields. Sustainable nitrogen management in sugarcane is possible by applying the integrated approaches of field management and crop production. For this, the optimum rate of nitrogen fertilizer applied via the best method at a crucial time of the crop growth stage significantly lowered the nitrogen losses and improved the crop productivity and nitrogen use efficiency. Legume intercropping provides promising results for controlling nitrogen leaching losses from sugarcane fields. Using urease inhibitors and controlled-release fertilizers is also a pivotal approach to decreasing nitrogen losses. Furthermore, introducing nitrogen-efficient sugarcane genotypes and nanomaterials in agriculture improved farmers’ economics and environmental safety.

1. Introduction

Sugarcane is a tropical perennial grass that belongs to the Saccharum genus and Gramineae family. It has two wild (S. spontaneum and S. robustum) and four domesticated (S. officinarum, S. edule, S. barberi, and S. sinense) species that are a rich source of sucrose with less fiber than wild species [1, 2]. The elongation and expansion of the sugarcane stalk provide an optimum space for sucrose storage [3]. Sugarcane is commercially grown asexually by planting stalk cuttings called setts. The secondary shoot emerges to produce tillers of sugarcane. In the second year, the underground stool buds and root primordia that remain in the soil regrow into a new ratoon crop [4].

Sugarcane is a vital cash crop grown in tropical and subtropical regions globally [5]. Sugarcane is mainly cultivated for making sugar, whereas byproducts of sugarcane and the sugar industry (bagasse, molasses, filter mud, and ash) are also economically significant [6, 7]. Bagasse is used in paper manufacturing, animal feed industry, and as a raw material for bioenergy production [8]. In contrast, molasses is a thick, black, and uncrystallized liquid produced from cane juice while manufacturing raw sugar [9]. It is used in alcoholic beverage distillation and as animal supplements [10, 11].

Furthermore, press mud, ash, molasses, and vinasse (a byproduct of ethanol production) are also rich sources of mineral nutrients (N, P, K, Ca, Mg) and are used as organic fertilizers [12]. Sugarcane is cultivated in subcontinents of Africa, America, and Asia. Furthermore, Brazil, China, Mexico, Thailand, Pakistan, India, Australia, and the United States produce more than 80% of global sugarcane production. Whereas, Brazil, Thailand, and Australia are the topmost raw sugar suppliers in the world [2]. Moreover, the increasing global population has increased food demand and renewable energy production. The versatile use of sugarcane has secured a central position in determining the economic status of agricultural countries worldwide.

Nitrogen is one of the macronutrients necessary to increase the crop growth. The efficient use of nitrogen is the key to ensuring crop productivity and to augment farmer’s economics. Less nitrogen use efficiency (NUE) has significant deleterious effects, including less crop growth, increased plant susceptibility to various biotic and abiotic stresses, and a potential source of environmental pollution. Further, the NUE in sugarcane was reported less than 50% globally [13]. Nitrogen losses that occur via ammonia volatilization, nitrate leaching, and N₂O emissions are leading causes of reduced NUE in sugarcane [14]. Moreover, denitrification caused a 25% loss of applied N fertilizer in the atmosphere [2, 15]. Many researchers indicated severe environmental issues and potential economic losses due to less NUE in sugarcane farming [16].

The increased economic benefit can be achieved by switching the sugarcane industry from yield maximization to profit optimization [17]. It is possible through sustainable nitrogen management in sugarcane fields [18, 19]. Various strategies could be adopted for sustainable nitrogen management in sugarcane production [19]. Before, we shed light on different nitrogen sources, the critical process of their losses, and their environmental consequences.

Soil contains both organic and inorganic (ammonium, nitrate, nitrite, and nitrous oxide) forms of nitrogen. By-products of the sugar industry are a source of organic N used in sugarcane fields [6, 20], though it has comparatively slow N release that subsequently affects the sugarcane growth [21]. Further, Legume intercropping is a sustainable source of mineral N. For example, soybeans and cowpeas used as intercrop in sugarcane fields have comparatively fewer N losses [22, 23]. Moreover, the rhizobium activity in legume-sugarcane intercropping provides approximately 50-60% of symbiotically fixed atmospheric N for the use of sugarcane [24]. Thus, the total requirement of N for the sugarcane field could be decreased without compromising the sugarcane yield [23, 25, 26]. Approximately 90% of the total organic soil N is converted into inorganic form through mineralization [2].

Contrary, inorganic source of nitrogen is the most often used nitrogenous fertilizer for sugarcane [27]. Usually, a mixture of inorganic fertilizers is given at sowing or according to crop growth stages. Furthermore, the ratoon crop has a different fertilizer requirement than first-year-sown sugarcane cropping [28]. Schroeder et al. [29] reported the increasing trend of liquid N fertilizer application to sugarcane fields. However, the type of N fertilizer used frequently depends upon cost, whereas researchers reported no difference in cane yield with different forms of nitrogen application [27]. However, studies demonstrated that the inorganic nitrogen source has numerous environmental losses that lower crop productivity [14].

Ammonium (NH₄⁺) and nitrate (NO₃⁻) are the most abundant forms of inorganic N, which is readily absorbed by plant roots [30]. Positively charged ammonium ions are stored in exchangeable form on the negatively charged surface of clay particles and organic materials [31, 32]. As a result, the ammonium form of N is comparatively immobile in soil and less susceptible to leaching and denitrification losses [14]. However, high volatilization losses occur from the ammonium form of nitrogen [33, 34] and NO₃⁻ is considered highly mobile in soil solution and susceptible to leaching losses [35, 36].

2. Processes of nitrogen losses

A specific kind of bacterial strain present in the soil is responsible for nitrogen loss [37]. Further, these bacteria cause immobilization of nitrogen, which undergoes leaching, seepage, runoff, volatilization, and denitrification [38]. Amongst these, ammonia (NH₃) volatilization and denitrification significantly increased the nitrogen losses from agricultural fields [39]. Research studies demonstrated that 30–70% of N losses occur through NH₃ volatilization [40]. A small fraction of water molecules, such as dew droplets, irregular rain, and condensed vaporized moisture from soils, contribute to releasing NH₃ gas from urea granules [41, 42]. The capacity of sugarcane crops to absorb ammonium ions decreased due to the increased activity of urease catalyst present in crop roots [2]. Urease catalysts boost hydrolysis activity and enhance the volatilization of ammonia gas, resulting in nitrogen losses in the environment [43]. On the other hand, nitrate ions (NO₃⁻) are susceptible to leaching losses [38]. Less organic matter and clay particles declined the capacity to retain NO₃ in soil, enabling it to move freely with water in the soil [44]. Heavy precipitation or surface irrigation helps NO₃ leach below the root zone [45]. In addition, [46] reported the critical role of soil type in determining the leaching rate, i.e., well-aerated and coarse-textured soil have high leaching losses [47]. In sugarcane crops, nitrate leaching losses are high due to the high water delta of sugarcane crops [42, 48, 49]. Additionally, the flooded condition enhances the denitrification (NO₃⁻ → NO₂⁻ → NO→N₂O → N₂) of applied nitrogen, which is also reported with elevated percentages of nitrogen losses from sugarcane fields [42, 48]. High temperature during sugarcane growing season and less organic matter substantially increased the N₂ emissions [50]. Research studies indicate that around 6.7% of the total nitrogen losses come from N₂O emissions [49, 51]. Meanwhile, [38] stated that 12.3 kg of applied N (150 kg N/ha) was lost in an environment in N₂O-N. Many researchers have reported severe environmental constraints about nitrous oxide emissions from sugarcane fields [27, 50, 52].

3. Consequence of nitrogen losses

Nitrogen losses from sugarcane fields have detrimental effects on crop growth, and net income return and pollute the environment [53]. However, the extent of N losses was elevated from moist tropics [2]. Advanced agricultural countries have developed a “water quality monitoring program” to identify the N leaching percentage into groundwater [54]. However, leaching losses from single field sources (sugarcane fields) still have ambiguity for researchers [54, 55].

The emission of nitrogen in gaseous form during the denitrification process is a significant contributor to air pollution. N₂O is a prominent greenhouse gas with a global warming potential 298 times greater than carbon oxide [56, 57, 58]. The release of NO and N₂O into the atmosphere is crucial in creating nitric acid, a key component of acid rain [59]. The leached nitrate below the root zone removes other cations, i.e., calcium (Ca), magnesium (Mg), and potassium (K), and replaces the hydrogen (H) ions which turn the soil acidic [60, 61]. Groundwater pollution increases with increased concentration of NO₃⁻ after leaching, and groundwater becomes unfit for drinking purposes [61].

Furthermore, the increased N losses also decrease the profitability of sugarcane farming [62]. Chai et al. [63] stated that nitrogenous fertilizers increased 30% of total expenses in sugarcane cultivation, and higher N losses decrease the farmer’s income [64]. Therefore, high N losses from sugarcane fields resulted in less nitrogen use efficiency, significant economic losses, and severe environmental concerns [35, 65]. Various strategies could be followed to augment nitrogen utilization and lower the risk of increased nitrogen losses.

4. Importance of sustainability in nitrogen management

Nitrogenous fertilizer application decreases food security challenges [66]. However, these fertilizers are the major precursor of nitrogen pollution, a significant threat to environmental sustainability [67]. Nitrogen losses augment climate change, which results in the deterioration of soil, water, and air quality and loss of biodiversity. Investigation indicated that billions of dollars have been spent in various sectors responsible for environmental deterioration worldwide [68]. Amongst these sectors, agriculture plays a vital role as the high use of nitrogen in agricultural fields (sugarcane, rice) has a significant proportion of nitrogen losses in the environment [66].

Further, the UN shared serious concerns about global environmental deterioration and focused on sustainable nitrogen management [69]. In addition, the sustainable nitrogen management index (SNMI) indicates the relationship between crop yields produced and the extent of environmental pollution [70]. Meanwhile, the environmental performance index (EPI) uses SNMI to indicate the score of environmental damage (Table 1) [70].

Country	Rank	EPI score	10 years change
Ukraine	1	79.5	18.3
United States of America	6	71.9	−4
Austria	12	68	−0.9
Canada	13	67.3	−0.3
Brazil	17	65	1.2
Saudi Arabia	18	64.3	39.8
Germany	25	61.9	−3.4
Russia	26	60.5	8.6
New Zealand	31	57.5	3.8
Turkey	32	57.4	4.5
United Kingdom	37	54.3	−7.6
Greece	43	52.6	−6.6
Afghanistan	48	51	0.9
Oman	50	50.6	35.2
Bangladesh	54	49.9	5.9
China	55	49.5	2.7
Pakistan	104	35.1	1.3
Israel	106	34.9	−2.4
India	108	34.7	2.4
Iran	113	33.8	−7.1
Sri Lanka	115	33.2	3.1

Table 1.

Countrywide performance on sustainable nitrogen management index.

Source: https://epi.yale.edu/epi-results/2020/component/snm [Accessed: January 25, 2024]; EPI ≤ 0 = worst conditions about SNMI.

5. Advanced approaches for sustainable nitrogen management in sugarcane production

Researchers have reported nitrogen losses in specific countries like Europe [71], Pakistan [72], and India [73]. They also suggested that integrating agronomy, plant breeding genetics, and allied sciences could help improve nitrogen use efficiency and hinder nitrogen losses. Moreover, a prestigious book publishing agency like IntechOpen can hasten this development with regular calls for “Sustainable nitrogen management” submissions. Raghuram et al. [66] suggested the integration of agronomic management approaches to enhance the NUE of any crop. Besides the basic and conventional approaches (investigating the soil fertility status, reduced tillage, etc.), some advanced management approaches that could help sustain N management in sugarcane fields are given below.

5.1 Rate of nitrogen application

Nitrogen management in sugarcane fields has undergone a series of changes to enhance nitrogen use efficiency since the 1960s [74]. Desalegn et al. [75] provided valuable recommendations to enhance cane productivity and maximize profitability with optimum nitrogen fertilizer rate for sugarcane crops. N application at a lower rate than the optimum concentration decreased sugarcane yield [13, 76], whereas excessive application does not provide any significant yield benefit [77] and increases N losses, resulting in higher production costs [27]. In addition, Friedl et al. [78] also suggested that the optimum nitrogen application rate ensures high crop productivity with reduced N2O and N2 emissions from sugarcane fields. In contrast, lower crop growth rate and yield were recorded with a reduced dose of N application [79]. Furthermore, many studies indicated that the optimal use of nitrogen helps in reducing the environmental losses of nitrogen [80] and it enhances the yield of other agronomic field crops [22, 81, 82, 83].

5.2 Method of nitrogen application

Nitrogen application also effectively influences crop productivity as the appropriate method of application reduces N emissions from agricultural fields and enhances N use efficiency [84]. Regardless of trash-management practices, subsurface application of nitrogen is recommended to lower nitrogen losses [2].

Applying N fertilizer to sugarcane involves band placement on either side of the sugarcane set, keeping it away from it, and banding the middle of the cane row prior to top dressing with soil [29]. Kamboj et al. [85] reported higher cane productivity using band placement of N fertilizer management. Similarly, Castro et al. [86] also noticed a significant effect of fertilizer application methods on sugarcane growth and yield-related traits. Moreover, subsurface fertilization in ratoons can be done by stool splitting with a single coulter or dual coulters beside the cane row to a depth of 70-100 mm [2]. Das and Mandal [87] suggested the modern fertilizer application through the splitting of two fertilizers concurrently. The most preferred subsurface application approach is stool splitting (three cane rows handled per pass instead of two) since it is easier and faster [87]. Singh et al. [88] stated that the sub-surface N application significantly improves cane production from ratoon crops.

On the contrary, the liquid N fertilization approach improves sugarcane yield compared with the broadcasting method [89]. Meanwhile, Padmanabhan et al. [90] found that drip irrigation of liquid nitrogen increases ratoon crop growth and yield. Moreover, many studies reported that optimum nitrogen delivery improves sugar recovery and brix percentage [91, 92, 93]. Appropriate nitrogen management is also vital for improving nitrogen use efficiency in sugarcane crops [94].

5.3 Time of nitrogen application

The application timing should correspond to the crop’s demand for nitrogen [2]. This is commonly accomplished by split-applying N in a sugarcane crop, wherein a low-concentration fertilizer is provided at sowing, and the remaining N dose is given by top dressing [95]. Early (i.e., immediately after harvest) or late application of nitrogen (i.e., when the crop becomes nitrogen deficient) significantly increases the risk of nitrogen loss to the environment, which decreases cane yield [76]. Therefore, split application of nitrogenous fertilizers in ratoon crops is recommended due to its potential to provide significant ecological benefits by reducing leaching emissions [96, 97]. However, a split application could not give the ultimate benefits in flooded soils [98].

5.4 Use of urease inhibitors

Broadcasting urease inhibitors in conjunction with urea potentially reduces the volatilization of NH₄ emissions, whereas the sub-surface placement method could not yield promising results [99]. Urease inhibitors decelerate nitrogen hydrolysis and substantially contribute to improving NUE [100]. Urease inhibitors effectively reduce the losses of NH₄ by volatilization [101]. The urease inhibitor application significantly reduces ammonia volatilization from the sugarcane field, ultimately improving sugarcane production [102]. Additionally, urease inhibitors augment soil fertility, NUE, and sugarcane yield [103, 104]. However, the efficiency of urease inhibitors diminishes due to insufficient rainfall and prolonged dry conditions [105].

5.5 Use of controlled-release fertilizers

The recent growing technology adopted to lower nitrogen losses while improving crop production is based on controlled-release fertilizers (CRF). These fertilizers may be polymer-coated urea (PCU), nutrient-coated urea, and bioactive bacterium-coated urea. The use of CRF reduced the ammonia (NH3) and nitrous oxide (N₂O) emissions by 32.7% and 25.0%, respectively, compared to regular urea [106]. These fertilizers gave the utmost results in reducing nitrogen emissions in the 6.5-7.5 soil pH range [107]. In addition, Efretuei et al. [79] observed that the nitrogen release from coated urea enhanced the expression of genes related to catalysts involved in nitrogen intake and utilization, resulting in increased NUE of rice [108]. Similarly, biochar-coated urea significantly controlled nitrate leaching and improved NUE [109]. Mustafa et al. [110] reported promising results of CRF application in reducing nitrogen emissions and improving nitrogen use efficiency and sugarcane production. Sustainable nitrogen management with CRFs can contribute to achieving better sugarcane yield [111]. Conversely, Boschiero et al. [93] reported CRFs with non-significant effects on yield and quality attributes of sugarcane grown at peanut-harvested fields. Nevertheless, Wang et al. [48] determined that utilizing controlled-release polymer-coated urea reduced N₂O emissions by up to 30% in acidic sulfate fields, in contrast to regular urea.

5.6 Use of nitrogen-efficient sugarcane genotypes

Another viable approach for sustainable nitrogen management in sugarcane production is the intervention of nitrogen-efficient sugarcane cultivars. Higher nitrogen use efficiency is directly linked with eco-sustainability and crop profitability. Additionally, efficient utilization of nitrogen within the plants and better uptake of nitrogen from the soil determined the NUE of a crop [112]. Unfortunately, sugarcane verities are less efficient in nitrogen uptake [113]. Therefore, developing nitrogen-efficient cultivars through plant breeding approaches could break promising outcomes of improved NUE, better cane yield, and environmental sustainability [114]. Moreover, improving internal nitrogen use efficiency (iNUE) could improve biomass per unit of nitrogen [115, 116]. However, the limited availability of nitrogen-efficient sugarcane varieties directed the implementation of sustainable nitrogen management in sugarcane fields [117, 118, 119].

5.7 Use of nanoparticles

Nanotechnology has introduced new possibilities for sustainability in nitrogen fertilizer management [120]. Nanomaterials improved the nitrogen use efficiency and crop yield [121]. However, previous studies also mentioned following specific precautionary measures about the phytotoxic properties of nanoparticles [122, 123] as toxic nanomaterials caused cellular damage [123, 124, 125, 126]. However, the damage was insignificant in retaining the plant performance and crop yield [126, 127]. Furthermore, it is imperative to investigate the impact of nanoparticles infiltrating the food chain.

6. Conclusion and future perspectives

Less nitrogen use efficiency is fundamental to increased nitrogen losses, high input costs with low sugarcane production, and decreased net crop benefits globally. Furthermore, research investigations reported less NUE is a significant challenge to environmental safety. However, there is a need for sustainable nitrogen management in the sugarcane field. Research investigations showed various approaches to improve nitrogen use efficiency. However, integrated fertilizer management provides promising results with sustainability in nitrogen management. For this, agronomic management includes the optimum time of application with a balanced fertilizer rate to meet crop demand.

Additionally, using controlled-release fertilizers reduces nitrogen losses and improves NUE in field crops. In addition, introducing nitrogen-efficient sugarcane genotypes and using nanotechnology could also improve the NUE and develop sustainability in sugarcane production. Besides, further research should be carried out to investigate the safe use and introduction of nanoparticles in the food chain.

Acknowledgments

Our heartfelt gratitude goes out to everyone who has contributed to this book chapter, whether via their skill or unwavering encouragement. We hope to leave a lasting impression on the scientific community, and we look forward to continuing this adventure of research and discovery with you all. We are also grateful to this publishing group for their supportive policy to spread knowledge in the form of this book.