An economic analysis of cattle weight gain response to nitrogen fertilization and irrigation on WW-B. Dahl bluestem
Dudensing, Jeffrey D'Wayne
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The objective of this research was to estimate total stocker steer gains ha-1 at various levels of nitrogen fertilization and irrigation application on WW-B. Dahl Old World bluestem. In order to do this, forage mass and quality responses to nitrogen (N) and irrigation (I) had to be determined. The data for this study were obtained from two independent studies conducted from 2001 to 2003 at Texas Tech University. Stata statistical software was used to obtain coefficients for the effects of accumulated growing degree days (AGDD), N, I, precipitation, and maturity on forage mass and quality. Quality assessments were based on acid detergent fiber (ADF), neutral detergent fiber (NDF), and crude protein (CP). Panel data with fixed effects was the most appropriate statistical model. Statistical tests confirmed that the model was corrected specified. From the forage mass and quality values, the National Research Council’s Nutrient Requirements of Beef Cattle 2002 equations were used to estimate total stocker steer gain ha-1. In estimating total stocker steer gains, a monthly utilization of 70% of forage mass was assumed. Estimated average daily gains were validated with previous research. The results agreed with the findings of Mitchell et al. that GDD could be used to estimate forage mass and quality. However, N, I, precipitation and maturity can be incorporated into Mitchell’s model to increase the understanding of forage mass and quality. By using these regressions and incorporating them into the NRC equations, the response to variable rates of N and I was evident in stocker steer gains. Three initial steer weights (181 kg, 227 kg, and 272 kg) were used to capture the effect on gains. Results indicated that individual steer gains were higher with low irrigation and high nitrogen fertilization levels. Total cattle gains were maximized with high irrigation and high nitrogen levels.