Effects of Ammonium Nitrate and Potassium Sulfate Fertilization on Nitrogen and Sulfur Composition of Tall Fescue and Orchardgrass

In two experiments tall fescue (TF) and orchardgrass (OG) were fertilized in split applications on Julian days 107 and 135 with 0, 294, or 882 kg NH4N0₃/ha and 0 or 833 kg K2SO4/ha to determine the effect on TF and OG N and S components. Ammonium nitrate fertilization significantly increased total N, nonprotein N (NPN) and protein N (PN) concentrations in TF and OG. Nonprotein N (% of total’ N) was decreased (P<.001) in TF as level of NH4NO3 fertilization increased. Potassium sulfate fertilization did not alter concentration of N components of either grass except NPN concentration was reduced (P<.05) in TF. The NH4NO3 level x K2SO4 level interaction was nonsignificant for all N fractions. For each grass ammonium nitrate fertilization reduced total S and nonprotein S (NPS) and increased protein S (PS) concentrations significantly while K2SO4 fertilization increased all three S components significantly. The NH4NO3 level x K2SO4 level interactions were significant for all S fractions in TF and NPS and PS in OG. Total Nrtotal S, NPN:NPS and PN:PS ratios significantly increased with increasing level of NH4NO3 fertilization in TF and OG. Potassium sulfate application reduced total N:total S ratio significantly in both grasses as well as PN:PS ratio in TF. Herbage total N and NPN concentrations were positively (P<.001) correlated for TF (r =79) and OG (r =.70). Similarly, correlations between total S and NPS were r =.76 and r =.86 (P<.001) for TF and OG, respectively. Total N and total S concentrations were not related for either grass. These data indicate TF composition was altered by NH4NO3 and K2SO4 fertilization. Orchardgrass N and S fractions changed as levels of fertilizer NH4NO3 and K2SO4 were varied.