Irrigation effect on the contribution of aboveground plant litter to soil organic matter formation in agricultural systems

Abstract:

Due to a growing pressure on global water resources, conversion from irrigated to dryland cropping systems is increasing in many agricultural regions of the world. Irrigation increases crop production and soil moisture, and so the transition to dryland can impact many aspects of soil organic matter (SOM) dynamics. Irrigation may also affect the fate of aboveground litter as it decomposes and forms organic matter. In fact, irrigation can favor the leaching of dissolved organic matter, the physical transfer of litter fragments into the soil, and microbial decomposers activity. However, little is known about the effect of irrigation on these processes. Our objective was to study the impact of irrigation on aboveground litter decomposition and SOM formation. We incubated ¹³C- and ¹⁵N-labeled maize residue, at a rate equivalent to 486 g dry matter m^-2 and followed litter mass loss and SOM formation in irrigated and dryland maize managed under no-till conditions during the course of one year. We did not find a legacy effect of irrigation on litter decomposition during the winter, as litter mass recovery in Spring was similar in irrigated (84%) and dryland treatments (87%). Moreover, there were no significant treatment effects on the fraction of litter-derived carbon (C) or nitrogen (N) found in SOM. On average, 8.9 g m^-2 of litter-derived C (~ 4% of the added C) was recovered at 0-5 cm in the soil after six months, indicating low decomposition during winter. We did not find litter-derived C below 5 cm, but litter-derived N was present in all sampling depths. We will present these results and those from the final Fall harvest and discuss how potential reductions in irrigation availability may affect the fate of crop residues and SOM formation in maize fields under no-till conditions.