Productivity and Nutritive Quality of Johnsongrass as Influenced by Interseeded Ladino Clover and Fertilization with Commercial Fertilizer or Broiler Litter

Abstract

Johnsongrass (Sorghum halepense) is a warm-season perennial forage grown throughout the southeastern US. It was a very popular forage for cattle grazing during the early 20th Century; however, it currently is not utilized widely for grazing, but instead managed primarily as a noxious weed in row crops. Previous research has reported Johnsongrass to be a high-producing, medium-quality forage that can be grazed or used as a hay crop. Over the last several decades, the poultry industry has expanded greatly in Alabama, especially in the Sand Mountain region. Broiler litter is an excellent organic fertilizer because of its low moisture content and high organic matter and nutrient content. However, after many years of repeated land application, high concentrations of some nutrients may accumulate in soil and become a potential liability to environmental quality, animal welfare and human health. Therefore, locating alternative areas in the state for land-application of broiler litter is warranted, and the Black Belt region of Alabama is of special interest in this regard because of its soils that are often of low fertility and historically have not been amended with broiler litter. The current experiment utilized twenty-four 18-m2 forage plots seeded with either Johnsongrass or a Johnsongrass-clover mixture. Three fertilizer source treatments were utilized, including commercial fertilizer (CF; ammonium nitrate and diammonium phosphate mixture), non-compacted broiler litter (BL-N) and compacted broiler litter (BL-C). Both broiler-litter treatments were applied on the basis of soil-test P and supplemented with ammonium nitrate to meet crop N requirement. Plots were harvested 2 times per year over the course of a 2-year experiment. Yield and forage quality data were analyzed using mixed-model procedures in which year was treated as a random effect and harvest as a repeated measure. Results of this study indicate that DM yield and foliar concentrations of CP, NDF, ADF, lignin, Ca, P, Mg, Al, Cu and Fe were not affected by fertilizer-source treatments. However, hemicellulose and Zn concentrations were 8% lower (P = 0.0526) in forages fertilized with CF than broiler-litter treatments. Johnsongrass-clover contained 6% more CP (P = 0.0753) and 6% more hemicellulose (P = 0.0854) than Johnsongrass. Compacted broiler litter supported forage productivity and nutritive quality similar to those of forage fertilized with BL-N. Broiler litter applied on the basis of soil-test P and supplemented with ammonium nitrate was comparable to CF for supporting productivity and nutritive quality of Johnsongrass and Johnsongrass-clover forages grown on Black Belt soils.