Submitted to: Journal of Applied Animal Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/20/2007
Publication Date: 10/1/2007
Citation: Bailey, C.R., Daniels, L.B., Coblentz, W.K., Kegley, E.B., Mcbeth, L.J., Turner, J.E., Wistuba, T.J., Rosenkrans, C. 2007. Evaluation of Soft Red Winter Wheat Forage Yield, Nutritive Value and Tetany Hazard as Influenced by Sampling Date and Nitrogen Fertilization. Journal of Applied Animal Research. 32:1-6. Interpretive Summary: Many studies have described the nutritive value of winter-annual grasses in the Southern Great Plains and in the southeastern U.S., but few of these studies have evaluated soft-red winter wheat, which is grown annually on about 500,000 ha in Arkansas. While winter wheat is known to exhibit excellent quality characteristics and support rapid weight gains on stocker cattle, it also has been shown to elicit grass tetany (hypomagnesemia), a problem that usually occurs in older, high-producing cows in early lactation. The objectives of this study were to evaluate the effects of nitrogen fertilization and sampling date on the yield, nutritive value, and potential for tetany in soft-red winter wheat. In this study, fertilization with nitrogen during the fall increased concentrations of crude protein within the forage, but had only minimal effects of forage yield or concentrations of most nutritional indices. Concentrations of forage magnesium remained below requirements for lactating beef cows across all sampling dates and nitrogen fertilization levels, while potassium concentrations were 3.5 to 8.5 x the requirement for these same animals. Since incidence of tetany is often increased by high forage concentrations of potassium and crude protein, additional supplementation of magnesium may be warranted for post-partum cows grazing wheat pastures in Arkansas.
Technical Abstract: A study was conducted from December through March using a completely randomized design to evaluate yield, nutritive value, and tetany hazard of soft red winter wheat forage as influenced by nitrogen (N) fertilization rate and date of sampling. Dry matter (DM) yield, forage DM, crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), in vitro dry matter disappearance (IVDMD), organic matter (OM), calcium (Ca), magnesium (Mg), and potassium (K) were evaluated.Nitrogen fertilization had no effect (P>0.05) on forage yield, OM, ADF, NDF, IVDMD, Ca, or Mg. Forage DM (P<0.01) decreased while CP (P<0.01) and K (P<0.05) increased linearly with increasing levels of N fertilization. Date of sampling exhibited linear, quadratic, cubic and quartic effects (P<0.01) on concentrations of forage CP, DM, IVDMD, ADF, NDF, and K. With respect to sampling date, linear (P<0.01) and quadratic effects were observed for DM yield, but only linear effects were noted for OM (P<0.01). Calcium responded to sampling date with linear and cubic (P<0.01) patterns, while Mg exhibited linear (P<0.01), quadratic (P<0.01), and cubic (P=0.02) effects. No N x sampling date interactions were observed. Increasing levels of N enhanced concentrations of CP and decreased DM content, but had no effect on yield or other forage quality parameters. However, sampling date affected forage quality by decreasing concentrations of CP and IVDMD, while increasing concentrations of ADF and NDF.