How Much Sugarcane Straw is Needed for Covering the Soil?

Burning sugarcane (Saccharum officinarum) prior to manual harvest has been gradually replaced by a mechanized, green harvesting system that returns large amounts of crop residue (straw) to the soil surface in Brazil. A portion of the residue is required to protect soil against erosion, but some may be available as a feedstock for bioelectricity and cellulosic ethanol. Since excessive straw removal will degrade soil resources, it is imperative to determine the amount of straw needed for soil protection and to incorporate that information into decision-support tools so that straw management is sustainable. Our objective was to determine the amount of sugarcane straw needed to completely cover the soil surface. Photographic image analysis was used to quantify surface soil cover under 0 to 21 Mg ha(-1) of straw. Photos of 1-m(2) areas where various quantities of straw were homogeneously distributed were taken at a resolution of 8 megapixels (3264 x 2448 pixels) and then processed with ImageJ 1.52a software to obtain soil cover fraction. Straw layer thickness was also measured to the nearest millimeter using a ruler mounted in a rectangular acrylic box (0.5 m(2), 0.15 m height) into which the equivalent of 1 to 21 Mg ha(-1) of straw was placed. Soil cover increased exponentially, reaching more than 90% with 3 Mg ha(-1) and full coverage with approximately 7 Mg ha(-1). Straw layer thickness increased linearly by 0.5 cm per Mg of straw left on the soil surface. Our findings will lead to more sustainable straw management practices that balance soil conservation and provision of feedstock for bioenergy production.