Effects of soil type and soil chemical composition on nutrient content of annual ryegrass for beef and dairy cow nutrition

Annual ryegrass (Lolium multiflorum Lam.) is an important crop grown on approximately 1.1 million hectares in the southeastern United States. Used primarily for winter grazing, ryegrass has considerable yield variation among production areas, possibly due to differences in ryegrass response to the range of soil properties encountered in Louisiana. The objectives of this research were: (i) to evaluate variation in soil nutrient status among a range of soil series; and (ii) to compare yield, mineral uptake, and livestock nutritional value of annual ryegrass grown on these soils. Two replicated greenhouse studies were conducted to evaluate two cultivars of annual ryegrass, Gulf and Rio, grown in seven distinct soils collected from throughout Louisiana. Soils were unamended and received no additional fertilizer during the studies. Each study was harvested twice for yield and nutrient uptake determinations. Plant tissue samples were analyzed for potassium (K), calcium (Ca), iron (Fe), magnesium (Mg), manganese (Mn), zinc (Zn), and copper (Cu) concentrations using atomic absorption spectrophotometry. There were no cultivar differences or cultivar by soil interactions for yield or nutrient uptake. Yield and nutrient uptake of K, Ca, and Mn, were affected by the soil used. None of the soils produced ryegrass with sufficient Ca to meet the requirements of a dairy cow (Bos taurus), even though several of the soils had adequate to high soil test levels of Ca. All of the soils produced ryegrass with adequate Mg for beef cows (B. taurus; Bos indicus), but only half provided adequate Mg for dairy cows, All soils produced forage that met the beef cow Zn requirement, but only six provided adequate Zn for dairy cattle. All soils produced ryegrass with enough Mn to meet the requirements of both beef and dairy cattle, but there were large variations among the forages grown on the seven soils. These results indicate that mineral supplementation for beef cattle fed ryegrass grown on these soils might not be essential, but mineral supplementation for dairy cattle would be necessary.