Sugarcane Production in Brazil: Effects of Water Regime on Biomass Accumulation and Partitioning.

Due to the growing demand for clean energy and the increasing land and production cost, Brazilian sugarcane production has expanded from the traditional production region - Brazil's southeast, to the Brazilian Savanna - the Cerrado region. Soil and weather conditions in the Cerrado area are less favorable and more challenging to sugarcane production than in the traditional areas. In the Cerrado region, little or no rain is common during five to six months in the dry season (May to Sept) submitting sugarcane to severe water stress during this period. Irrigation has been one of the strategies used to improve water use efficiency, and the sustainability of sugarcane production in the Cerrado area. Nevertheless, due to its relative recent production history in the area, little is known about sugarcane biomass production and partitioning values for different irrigation regimes in the Brazilian Cerrado. This information is crucial to parameterize sugarcane growth models and to support decisions on irrigation strategies and water resources management. This study evaluated the effects of different irrigation – water regimes - on the sugarcane biomass production and partitioning in the Brazilian Savanna. A split plot within a randomized complete-block design was established with the irrigation regime as the main plot, and the sugarcane variety as he split plot. Irrigation regime treatments were 0, 25, 50, 75 and 125% of crop evapotranspiration demand. The subplot treatments comprised of two sugarcane varieties viz. CTC 18 and RB96 6928. Fresh and dry mass of green leaves, dry leaves, shoots and stalks were measured at the end of sugarcane plant season.

Water regimes had a significant impact on fresh and dry mass of green and dry leaves and stalks. Higher irrigation regimes resulted in higher fresh and dry mass for both varieties. Differences in fresh mass were larger than in dry mass, which shows that improving irrigation regime for sugarcane, not only accumulates more dry mass, but also water within its tissue - cell turgor. As total fresh biomass, and total dry biomass, increased the amount of water in sugarcane stalks, and consequently, the amount of vinasse produced will also be increased. Vinasse is an important byproduct in the sugarcane industry, as it is used as a valuable nutrient and water amendment in the sugarcane fields.

Besides generating reference number to parameterize sugarcane growth models for the Brazilian Savanna under different irrigation regimes, this study showed that investments on irrigation technology could promote increases of total biomass production. Additionally, it was shown that irrigation increases the ratio of stalk to total biomass production - harvest index.