Modeling Water Potential of Rye Cover Crop Residue on the Soil Surface.

Cover crop residues can provide significant amounts of nitrogen (N) to the subsequent crop, so estimating their N release is important to determine credits for N fertilizer applications. Simulation models may be useful to estimate N release, but they require input of the main factors controlling decomposition such as residue temperature and water potential. For conventional tillage, where residues are incorporated into the soil, temperature and water potential of the residues can be approximated by measuring temperature and water potential of the soil with currently available sensors. For conservation tillage, where residues are left on the soil surface, temperature of the residue can be measured with available sensors, but sensors for continuously measuring residue water potential are not currently available. Thus, developing a method to estimate water potential from variables commonly measured by weather stations (air temperature, air relative humidity, soil water potential) would be useful to obtain inputs for simulation models. To that effect, during two months after applying rye residue on the soil surface we measured residue water potential (with a dewpoint potential meter), as well as air temperature, air relative humidity, and soil water content (with standard weather station sensors). In addition, we conducted a laboratory study to evaluate the drying and rewetting of the residue as affected by air relative humidity. The collected data were used to develop simple algorithms to estimate residue water potential.