Sugarcane water footprint under different management practices in Brazil: Tietê/Jacaré watershed assessment

The objective of this study was to perform a thorough evaluation of the water footprint in the Tietê-Jacaré Watershed, analyzing its overall situation, and formulating a constructive reduction response in the water footprint by using vinasse for fertigation. Cane yields from five sugarcane crops under two water regimes (rainfed and full irrigation by subsurface drip irrigation), combined with two N fertilization rates (zero and 150 kg ha−1 year−1), were used for water footprint estimation. The water footprint scenario considered the vinasse potential for fertigation, partially replacing the average Tietê-Jacaré Watershed water deficit, and limiting its application rate in 300 m3 ha−1. On average, the green, blue and grey water footprint found were 145, 38 and 18 m3 Mg−1, respectively; lower values when compared to other sugarcane-producing countries. The larger fraction of green against blue water footprint confirms the importance of rainfall in the Tietê-Jacaré Watershed. Nevertheless, the yield increase through fertigation practices promotes better use of the water resources showing that there is a potential for yield optimization in areas where reasonable rainfall occurs. Considering the vinasse fertigation replacing part of the necessary water volume required to implement subsurface drip irrigation on all the 9750 sugarcane hectares, the increase in rural water withdrawal due to full irrigation was only 17%, against an increase of 47% in sugarcane yield. Hence, in regions without water availability issues and with great land-use pressure, the yield intensification promoted by subsurface drip irrigation might be a way to release crop land areas.