Phenology and Establishment of Winter Rye Cover Crop Under Iowa Conditions.

Phenology and Establishment of Winter Rye Cover Crop Under Iowa Conditions.

Guillermo Marcillo¹, Fernando Miguez¹ and Thomas C. Kaspar²,

¹ Agronomy Department, Iowa State University, Ames, IA,

²USDA-ARS National Laboratory for Agriculture and the Environment, Ames, IA

Despite the undeniable contribution of cover crops to row cropping systems, knowledge gaps remain and adoption of the practice in the US Midwest still faces challenges. An adequate characterization of cover crop phenology would inform farmers for better farm scheduling, and provide a more accurate description of crop events needed by simulation models of crop growth. To increase the current knowledge about rye phenology, our goals for this project are: 1) Monitor in-field progression of vegetative pheno-phases of rye cover crop within a typical corn-soybean rotation, and, 2) Describe quantitatively the tillering habits and leaf progression of a cereal rye cover crop (Secale cereale sp.) established under Iowa conditions. Cover crop phenology between fall-2015 and spring-2016 was recorded weekly, distinguishing 3 vegetative phases: seedling, tillering, and jointing (zadoks system, 1981). We counted tillers per plant, estimated plant populations (plant.m^-2), and measured fractional green canopy cover (%) through photograph and image processing analysis (www.canopeoapp.com), of a rye cover crop, broadcast-seeded at two different dates (September 11, and September 19, 2015), over No-till plots in 2 central Iowa locations. Preliminary results show no significant differences for vegetative development at the two locations during the 2015-2016 season, with rye cover crop reaching the jointing stage (zadoks 32) before spring termination. Furthermore, vegetative development between tillering and jointing (zadoks 20 - zadoks 30) increased linearly with thermal time (cumulative degree days) beyond a 0 ^o C base temperature. Although final tiller counts and final leaf numbers were not significantly different, green canopy cover and plant populations were significantly different at the two locations, with increasing rye populations seemingly associated with higher green cover. Phenology of rye cover crop terminated at the jointing stage within a corn-soybean rotation responds to thermal accumulation, and is expected to follow typical patterns of tiller and leaf production reported for other grain cereals. Future work involves evaluating results for fall-2016/spring-2017 period, and simulate cover crop growth via process based models that account for site-specific responses to environmental conditions (e.g. temperature, photoperiod).