Characterizing cereal rye biomass and allometric relationships across a range of fall available nitrogen rates in the eastern United States

Cereal rye (Secale cereale L.) is widely grown due to its winter hardiness and adaptability to varied soil and environmental conditions. Fall and spring climate and available soil N drive biomass production. However, there is limited empirical information on the effects of these factors on cover crop performance. Farmers need early spring indicators of cereal rye performance to guide management. A 3-yr experiment was initiated to test and model the effects of climate and soil N fertility on cereal rye growth and allometric relationships in Pennsylvania, Maryland, and North Carolina under five-six fall fertilizer rates. We hypothesized that allometric relationships between early spring growth indicators can guide management decisions. Measurements included tillering, biomass, tissue N, and normalized difference vegetation index (NDVI) at Zadoks growth stages (GS) 25, 30, and 60. Nitrogen application increased biomass: maximum average biomass was 2853, 4844, and 9739 kg ha^–1, respectively, at GS25, GS30, and GS60. At GS25, biomass accounted for the greatest amount of model variation and better predicted GS60 biomass than shoot density and NDVI. Variance attributed solely to GS25 and GS30 biomass constituted 38.5 to 65.2% of total model variance. Models accurately predicted biomass and N accumulation 34 to 60% of the time. This study illustrates the difficulty in predicting late season biomass and N content based on early measurements. One extension of this research would be the development of a simple protocol to accurately sample cereal rye biomass at GS25 to estimate potential N accumulation and biomass at GS60.