Modeling Rye and Hairy Vetch Residue Decomposition as a Function of Degree‐Days and Decomposition‐Days

Temperature and precipitation affect crop residue decomposition rate. Degree‐days (DGD) and decomposition‐days (DCD) are used to account for the effect of temperature and precipitation, but little information is available about winter cover crop (WCC) residue decomposition as a function of DCD or DGD. This study was conducted to model the decomposition of rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth) residues and the subsequent release of C and N under field conditions using DGD and DCD. Rye and hairy vetch WCCs were planted during the fall either in monoculture or biculture and killed before corn (Zea mays L.) planting. Grab samples of WCC residues were taken six times during the corn growing season. A single‐pool exponential decay function was used to model biomass decomposition and C and N release. Most decay models showed coefficients of determination (r2) larger than 0.7. Both DGD and DCD were equally effective as time scales. Winter cover crops differed in their initial biomass and C content and in their biomass decomposition and C and N release rates. At corn V6 stage, 33 and 75% of the initial N content had been released from rye and hairy vetch residues, respectively. At the end of the growing season, hairy vetch had almost completely decomposed while 5% of the initial biomass of rye remained undecomposed. Decomposition dynamics of hairy vetch residue indicate that it is a potential source of N while decomposition dynamics of rye indicate that it is more useful in soil conservation.