Changes in soil C and N distribution assessed by natural δ13C and δ15N abundance in a chronosequence of sugarcane crops managed with pre-harvest burning in a Cerrado area of Goiás, Brazil

Abstract

Pre-harvest sugarcane straw burning affects the dynamics of soil chemistry and δ13C and δ15N abundance, but further studies are needed to understand the long-term effects of this practice on the degradation of chemical attributes of soil and sugarcane production. The present study evaluates chemical modifications of soil and natural δ13C and δ15N abundance in sugarcane crops managed with pre-harvest straw burning for 1, 5, 10 and 20 years. For comparison purposes, soil covered with natural Cerrado vegetation and forage grass (pasture) were also evaluated. After chemical characterization of the areas studied, according to Embrapa (1997) total organic carbon (TOC), bulk density (Bd) and natural δ15N and δ13C abundance were determined in soil samples, and carbon stocks calculated from TOC values. In general, the pasture area had the highest δ13C and δ15N content, the Cerrado vegetation area had the lowest values for these elements and sugarcane crops exhibited intermediary levels. Areas subjected to sugarcane field burning for a shorter period had the highest Ca and Mg and lowest P and K content. Sugarcane crops managed with straw burning for 1 and 5 years produced lower carbon stocks in the top soil layer (0–10cm) than sugarcane crops with 10 and 20 years, pasture and Cerrado areas. The replacement of natural Cerrado vegetation by sugarcane crops changed δ13C profile, likely because sugarcane is a C4 plant, which has a specific carbon accumulation pattern. Areas cropped with sugarcane for 1, 10 and 20 years and subjected to different types of soil use after replacement of the original Cerrado vegetation had the highest δ15N values, indicating accelerated mineralization of soil organic matter.