Carbon balance in sugarcane areas under different tillage systems

Soil tillage for sugarcane production has a significant impact on greenhouse gas (GHG) emissions and soil carbon (C) stocks. However, the short- and long-term effects of different soil tillage methods in sugarcane systems on C footprints are still poorly studied. We conducted a field experiment in a sugarcane system to evaluate the effects of conventional tillage (CT), chiseling (CHI), no tillage (NT), and compacted no-till (NTC) on nitrous oxide (N2O) and methane (CH4) emissions and stalk yields in the cane plant cycle and on soil C changes in the short term (3 years) in a Brazilian subtropical climate. Furthermore, we used the DayCent model to predict soil C dynamics for the next 30 years under green harvest management in scenarios with 0, 50 and 75% straw removal and to estimate the C savings of different soil tillage methods. Soil C stocks were determined before the treatments were applied and 1, 2 and 3 years after planting sugarcane. GHG sampling was performed only 1 year during the sugarcane plant cycle. Soil tillage did not significantly affect sugarcane stalk yield. The CH4 fluxes ranged from − 58.2 to − 3.6 μg CH4 m−2 h−1, and annual emissions did not differ between soil tillage systems. The N2O fluxes after soil tillage for sugarcane ranged from 3.8 to 2279 μg N2O m−2 h−1, and the highest annual emissions were observed in NTC. The conversion from grain production system to sugarcane production resulted in an initial decrease in soil C stocks, with C losses in the 0–20-cm layer over 3 years varying from 0.26 to 2.12 Mg C ha−1. The simulated data for the period 2016–2046 indicated recovery of C stocks in all soil tillage systems, with accumulation rates varying from 0.01 to 0.10 Mg C ha−1 year−1. Regardless of the soil tillage system, straw removal decreased the soil C stocks. The time interval for recovery of the initial C stocks ranged from 10 to 20 years, depending on the intensity of straw removal and soil tillage. Soil C losses and GHG emissions reduced the potential C savings of sugarcane ethanol. The CO2eq emissions observed during soil tillage and the sugarcane growing cycle should be quantified and included in the C savings estimates of biofuel production systems.