Agronomic, economic, and environmental assessment of site-specific fertilizer management of Brazilian sugarcane fields
Introduction
Currently, Brazil is the world's largest sugarcane producer and one of the world's largest ethanol producers. In 2019, Brazil produced 620 million t of sugarcane in a cultivated area of 10.1 million hectares (Companhia Nacional do Abastecimento (CONAB), 2020). To meet the growing demands for renewable energy, estimates indicate that ethanol production will need to nearly double in Brazil by 2030, from the current 28 to 54 billion litres (Empresa de Pesquisa Energética (EPE), 2018). One approach for achieving sustainable sugarcane expansion will be by increasing agricultural yield. However, in the last decade sugarcane yield in the Brazilian industry stabilized in 76.1 Mg ha−1 (Companhia Nacional do Abastecimento (CONAB), 2020), behind the >100 Mg ha−1 obtained by high-technology producers and much lower than the potential sugarcane yield of 200 Mg ha−1 in Southern Brazil (Monteiro and Sentelhas, 2014).
Under tropical conditions, soil fertility is one of the main limitations for growth of most crops (Fageria and Baligar, 2003). Tropical soils present high levels of toxic aluminium, low pH, low cation exchange capacity and low contents of available nutrients (Marques Jr et al., 2015; Fontes and Alleoni, 2006). Because of this, application of soil amendments such as lime and gypsum are required to improve conditions of root growth (Caires et al., 2008; Caires et al., 2011). Due to its deep rooting capacity, sugarcane responds positively to the adequate contents of nutrients not only in the surface soil layer but also in deep soil layers (Landell et al., 2003). Not surprisingly, soils with adequate base saturation and low aluminium contents in the subsoil provide the highest sugarcane yields (Copersucar, 1997; Maule et al., 2001). As a consequence, a considerable ratio of the production cost of sugarcane is associated with the use of soil amendments and fertilizers (Cantarella and Rossetto, 2010). The increase in average yields or profitability by better inputs usage of sugarcane in Brazil will require the adoption of best management practices and new technologies such as precision agriculture (PA), which allow the site-specific management of soil fertility.
PA incorporates management practices to increase productivity, profitability and improving environmental stewardship of agricultural areas. The benefits are achieved by site-specific management of soil fertility, considering the spatial variability of soil attributes. Employing PA best practices to site-specific management of soil amendments and crop agrochemicals may enhance sustainable production through increases in profitability, productivity, crop quality, on-farm quality of life, food safety and rural development (Zamykal and Everingham, 2009). The application of PA in the sugarcane industry represents an essential tool for site-specific fertilizers management, mainly because sugarcane is third in fertilizer consumption among Brazilian crops, after soybean and corn (Cantarella and Rossetto, 2010). Sugarcane is a high-yielding crop that requires significant amounts of plant nutrients because mineral elements comprise 3–5% of its dry matter. Sugarcane accumulates, per 100 Mg of stalks produced, 100–154 kg N; 15–25 kg P2O5; 77–232 kg K2O; and 14–49 kg S (van Raij et al., 1997; Franco et al., 2007). That amount of nutrients might be replaced every year to allow sustainable production with no degradation of soil fertility over the years (Trivelin and Franco, 2011), especially considering the semi-perennial behaviour of sugarcane cultivation in which the yield of the coming season is dependent of the management adopted previously (Vitti et al., 2007).
The leading technologies available for PA users are yield monitors, remote and proximal sensing, and global navigation satellite systems (GNSS). However, applying these technologies to site-specific management of soil fertility is much more advanced for cereals than for sugarcane cultivation (Kanke et al. Bonomi et al., 2016). A survey conducted in 2008 revealed that aside from intensive activity at a few sugarcane mills and independent growers, there was practically no PA activity in the Brazilian sugarcane industry (Silva et al., 2011), and this scenario is possibly valid currently. The literature is still scarce on the benefits provided by the adoption of PA technologies to the sugarcane industry in Brazil, particularly the economic-environmental benefits of site-specific management of fertilizers, where some studies outside from Brazil reported the benefits of sensing technologies adoption for the sugarcane industry in nitrogen site-specific management (Lofton et al., 2012). The majority of studies are focused on the variable rate application of nitrogen (Kank et al., 2016; Lofton et al., 2012), mainly by proximal sensors (Amaral et al., 2017). Long-term studies with PA technologies are available for citrus (Colaço and Molin, 2017) and cereal crops (Robertson et al., 2007; Yost et al., 2016), but are lacking for sugarcane.
Yield monitors, an essential technology widely used in cereal crops, are still rarely used in commercial sugarcane fields in Brazil. Examples of applications come mainly from academia, with the first studies performed by Magalhães and Cerri (2007). The main studies in the literature do not report the environmental and economic benefits of long-term PA adoption for sugarcane production, so studies demonstrating the economic, environmental and yield benefits to growers and society may help boost PA technologies' adoption the sugarcane industry. Therefore, the objective of this study was to verify the benefits of adopting variable rate application of soil amendments and fertilizers, based on intense soil sampling and yield monitoring. Our hypothesis is that soil properties are amenable to site-specific management and a precision agriculture approach to manage soil fertility's spatial variability in a sustainable way. Specifically, we evaluated the spatial variability of organic matter (OM), pH, phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), cation exchange capacity (CEC), base saturation (BS), sulphur (S), boron (B), copper (Cu), Iron (Fe), manganese (Mn) and zinc (Zn) with a site-specific fertilizer management of lime, nitrogen (N), phosphpurus (P) and potassium (K). We assessed the agronomic, economic, and environmental indicators related to site-specific management in a sugarcane field in Brazil. We used data obtained in four years of field experimentation conducted in the principal sugarcane-producing region of the world.
Section snippets
Materials and methods
To assess the effectiveness of site-specific management of soil fertility, two fields were chosen in the most representative region of sugarcane cultivation in Brazil, according to agroecological zoning (Manzatto et al., 2009). The experiment was set up in 2010 in Serra Azul, São Paulo State, Brazil (21°16′36.94“ S; 47°18’31.31” W), belonging to the Pedra Sugar Mill. The fields are located in neighbour's areas (~100 m of distance), presenting similar soil type, landscape and historical of
Temporal stability and descriptive statistics of soil properties
As expected, the calculated mean of all soil attributes assessed in field A increased after soil fertilization for the applied macro and micronutrients and decreased or remained nearly the same in the following year as nutrients were extracted by the plants; except for P and K, the nutrients were not replaced between successive sugarcane crop seasons (Table 3 and Fig. 4). Before sugarcane cultivation, except for P and S, the soil elements showed concentrations than the amounts considered
Discussion
Fertilizer application replenished the content of nutrients in the soil during sugarcane establishment. In the first year of cultivation, pH values reached the desirable range reported by Malavolta (1979). Plant nutrients become highly available under low-acidity conditions, with the ideal range for sugarcane being between 5.5 and 6.0 (van Raij et al., 1997). The amount of lime applied was calculated to achieve base saturation of 60% (van Raij et al., 1997), but the mean BS over the
Conclusion
The present study demonstrated that site-specific fertilizer management can be a useful tool for the sugarcane industry. Implementing appropriate fertilizer management of lime and NPK practices helps equilibrate and stabilize the content of nutrients in the soil, allowing profitable sugarcane yields. In this study, soil fertility declines for K over the growing cycles, indicating that fine-tuning the recommendation of sugarcane fertilization is required. The lack of temporal stability in
Declaration of Competing Interest
None.
Acknowledgements
The authors are grateful to the São Paulo Research Foundation (FAPESP) for their financial support (grant process: 2018/10225-3, 2015/01587-0, 2014/14965-0, 2013/50942-2 and 2011/02817-9) and the Pedra Sugar Mill for the field resources provided. We thank to the LNBR/CNPEM - Brazilian Biorenewables National Laboratory during the use of the Virtual Sugarcane Biorefinery open-access facility.
References (61)
- et al.
A computational environment to support research in sugarcane agriculture
Comput. Electron. Agric.
(2016) - et al.
Yield monitoring of sugar cane
Biosyst. Eng.
(2007) - et al.
Effects of long-term N fertilizer-induced acidification and liming on micronutrients in soil and in bromegrass hay
Soil Tillage Res.
(1998) - et al.
Soil nitrogen availability indices as predictors of sugarcanenitrogen requirements.
European Journal of Agronomy
(2017) - et al.
High soil penetration resistance reduces sugarcane root system development
Soil Tillage Res.
(2011) - et al.
Methods and procedures for automatic collection and management of data acquired from on-the-go sensors with application to on-the-go soil sensors
Comput. Electron. Agric.
(2012) - et al.
Potential of apparent soil electrical conductivity to describe the soil pH and improve lime application in a clayey soil
Soil Tillage Res.
(2018) - et al.
Site-specific assessment of spatial and temporal variability of sugarcane yield related to soil attributes
Geoderma
(2019) - et al.
Growth and yield of sugarcane as a function of phosphorus doses and forms of application
Rev. Brasil. Engenharia Agrícola e Ambiental
(2016) - et al.
Spatial dependence degree and sampling neighborhood influence on interpolation process for fertilizer prescription maps
Engenharia Agrícola
(2019)