Combined effect of silicon and nitrogen doses applied to planting furrows on sugar, biomass and energy water productivity of sugarcane (Saccharum spp.)

Brazil has the largest cultivated area for sugarcane in the world, with a predominance of rain-fed production systems (64%) and marginal areas that are subject to frequent water deficits. The remaining 36% under cultivation is equipped with irrigation systems; however, a significant portion of these irrigation systems (76%) is dedicated to crop maintenance. Their primary purpose is to provide water for initial plant maintenance during planting and regrowth of ratoons, which helps to alleviate drought stress caused by water scarcity during dry periods. The remaining 24% of the irrigated sugarcane production areas use deficit and full irrigation strategies to partially (50%) and fully (100%) meet the plants' water demands, respectively. Therefore, a large part of the cultivated area for sugarcane in Brazil is subject to a water deficit at one or more stages of the crop's development cycle, which can retard plant growth, nutrient use and productivity. One potential strategy for mitigating these harmful effects is the application of silicon (Si) in the furrow at planting, which can also increase crop water productivity (WPc). The objective of this research was to determine the effects of different applications of Si and nitrogen (N) on WPc, in terms of sugar (SWPc), biomass (BWPc) and energy (ENWPc) for sugarcane crop. The research was conducted at the University of São Paulo (USP/ESALQ), Piracicaba, São Paulo State, Brazil. The experimental design involved randomized blocks, with four blocks and 12 treatments. The treatments consisted of three applications of Si, 175, 350 and 525 kg·ha−1 and four N treatments of 15, 30, 60 and 90 kg·ha−1. Biometric responses, effects on juice quality, and indices related to yield and WPc were determined. The water consumption and agricultural yield (AY) of sugarcane were clearly influenced by the treatments. The lowest water consumption was obtained with the 15Nx350Si treatment, 561 mm per year. The treatment with the highest AY value was 60Nx350Si (162.3 Mg·ha−1). The SWPc, BWPc and ENWPc of the sugarcane crop were affected by the different application rates of N and Si. In general, the highest average WPc values were obtained with the 15Nx350Si treatment (SWPc=2.6 kg·m−3, BWPc=10 kg·m−3 and ENWPc=224.5 MJ·m−3). The different N and Si treatments did not significantly affect biometric variables (except for fresh biomass and leaf area) or juice quality; therefore, Si application did not compromise the quality of the end-product.