Fifteen years of soil organic carbon field measurements in rainfed and irrigated cropland soils across Brazil's Cerrado reveal mixed trends

We present soil organic carbon (SOC) data collected from 2010 to 2025 across 146 rainfed and 34 irrigated cropland plots in sandy soils in Western Bahia, a heavily cultivated area in Brazil's Cerrado. Rainfed fields are cropped once annually, while irrigated fields are cultivated twice yearly. Data from 143 plots were gathered from the 0-20 cm layer between 2010 and 2018, and data from 40 plots from 0-100 cm were collected between 2017 and 2025. All plots had native vegetation cleared prior to 1990. The analysis reveals two distinct patterns: rainfed soils appear stable, with no significant carbon changes in both the 0-20 and 0-100 cm layers. Conversely, irrigated soils increased by 2.6% per year (p=0.066) from 2010 to 2018, but declined by -5.75% per year (p<10^-5) from 2017 to 2025. In 2018, irrigated fields had higher SOC levels (p=0.034) than rainfed fields, but by 2025, the difference was not significant (p=0.423). Both systems showed no significant difference from the original Cerrado ecosystem (p=0.269 and 0.455, respectively, based on 2018 data). It seems that rainfed soils have reached a long-term equilibrium similar to that of the native Cerrado. The trend in irrigated soils, however, remains puzzling, showing fluctuations from increases to decreases. A combination of high water availability and increased temperatures may have contributed to the decline in SOC in recent years.