Sorghum leaves more residue with a higher decomposition rate than maize

Crop residue is an important component of the sustainability of agricultural production systems, and field comparative studies of residue decomposition across species and management practices are rare. Maize and sorghum are summer cereal options that compete for their acreage and are known to have contrasting harvest index. Our objective was to explore changes in residue amount, quality (assessed by residue total soluble carbohydrate concentration and C/N ratio), and decomposition rate of both crops. Our hypothesis was that sorghum leaves higher amounts of residue than maize after harvest, with decomposition rate differences among crops being negligible because the environmental context effect is a major component. We conducted field experiments in a temperate environment with maize and sorghum planted simultaneously. Sorghum crops were on average across conditions out-yielded by maize by 2.6 Mg ha⁻¹, and left on average 2.2 Mg ha⁻¹ more residue at harvest than maize. Sorghum residue decomposed at a significantly higher rate than maize (-4.6 vs −2.6 days⁻¹ for sorghum and maize, respectively; p < 0.001). This is because the sorghum residue has a higher concentration of total soluble carbohydrates and a lower C/N ratio compared to maize. These residue quality traits were significantly affected by crop management. As a result of the differing rates of decomposition, both crops had similar amounts of residue after 90 days of fallow. Our findings highlight the importance of considering species and management variations in both the quantity and quality of crop residues when assessing their impact on soil fertility and carbon cycling, as these factors influence decomposition rates.