Organic Sugarcane in Brazilian Savannah: Soil Physical Properties Related to Water Storage and Carbon.

Our objective was to study the effectiveness of organic agriculture techniques in sugarcane production over soil water holding capacity and total soil carbon. The study was conducted in a sugarcane-cultivated area, over an Oxisol, located in Goianesia, Goias State, Brazil (15°10'S and 49°15'W, 640 m altitude). The annual average rainfall was 1,500 mm and the mean annual temperature 24.4°C. Each experimental unit consisted of 100m x 100m square plots. Different areas were assessed for representing a chronosequence of organic farming: as time zero (Org.0) a 10 year-old plantation in conventional system was considered; (Org.2) plantation cultivated in organic system for two years; (Org.10) plantation cultivated in organic system for ten and, (Org10SR): plantation cultivated in organic system for 10 years without renovation. Undisturbed soil samples were taken at 0-10, 20-30 and 40-50 cm. The experimental design was completely randomized, with five replications and six treatments, and each organic area received 60 mm vinasse annually. Total soil carbon (TC), soil texture, bulk density, macro, micro and total porosity, saturated hydraulic conductivity (SHC) and soil water retention curve were measured. Data were analyzed using Scott-Knott test (P<0.05). Org10 promoted a decrease in bulk density compared to Org0, and increased TC. Macroporosity in Org10 was 15% higher than others, in all evaluated layers. Microporosity did not suffer any effect of the treatments. Org10 increased total porosity compared to Org0. The treatments had no effect over hydraulic conductivity until 40cm depth, but below this depth, Org10 and Org10SR presented higher SHC. Soil water retention was highest in the Org10SR for all soil layers. Org10 proved be the best system to improve soil physical properties and increase TC after the conventional production system in this Oxisol. The higher adoption time of this kind of management, the more relevant will be beneficial changes in the soil physical properties, as well as increases in total carbon.