Legume growth and straw retention in sugarcane fields: Effects on crop yield, C and N storage in the central-south Brazil

Abstract

Large amounts of straw are remained in the sugarcane fields after the crop to be mechanically harvested. Straw is pointed out as a feedstock to attend high bioenergy production demand. However, either indiscriminate straw removal or high amount of straw kept on the field may impair several soil functions and thereafter decreases plant tillering and crop yield. Better nutrients cycling and soil physical protection due to Leguminosae species grown within the sugarcane renewal period may offset implications of straw managements across the crop cycles. Thus, does Crotalaria sp. grow within the sugarcane renewal period can offset the undesirable implications of unsustainable straw management on soil and crop yield? To address this research question, a two-year experiment was carried out in Quirinópolis, Chapadão do Céu, Iracemápolis and Quatá, first two sites are in Goiás state, while the other sites are in São Paulo state, Brazil. Soil and plant parameters under straw retention rates (i.e., 0%, 50% and 100% of straw retention) were assessed. This management was coupled with fallow (F) and Crotalaria sp. (CR) grown within the sugarcane renewal period. Soil parameters evaluated included, carbon (C) and nitrogen (N) stocks, while stalk yield was plant parameters assessed. The straw retention implications on soil and plant were site-specific. Carbon and N stocks in the upper 0.4 m soil layer were, respectively, 3.5 and 3.1 time higher at the fine-textured soil than the stocks of those elements at the coarse-textured soil. Regardless of Crotalaria sp. grown, stalk yield increased (ranged from 3 to 16 Mg ha−1) under total straw retention rate for most sites, while in the coolest site 50% and 100% straw retention reduced stalk yield in 13 and 14 Mg ha−1, respectively. In addition, Crotalaria sp. grown within the sugarcane renewal period does not seem able to avoid reduction on soil N availability due to straw retention along the ratoon cycles. Overall, straw removal for bioenergy should be judiciously performed, according to local edaphoclimatic conditions.