EFFECTS OF 25 YEARS OF N, P AND K FERTILIZATION ON YIELD, PERSISTENCE AND NUTRITIVE VALUE OF A TIMOTHY SWARD

Abstract

The effects of over 25 yr of levels of applied N, P and K on forage DM yield, crude protein content, in vitro digestibility (IVD), botanical composition and persistence of a timothy (Phleum pratense L.) sward were assessed in a long-term field experiment on an acidic Riverbank L. Ammonium nitrate (0, 90, 180, 270 kg N ha−1), superphosphate (0, 15, 29, 44 kg P ha−1) and muriate of potash (0, 47, 94, 141 kg K ha−1) were applied annually in all possible combinations to a timothy sward since 1960. In the first 3 yr of the experiment, only N and K were required for maximum yield and persistence of timothy. The requirement for applied P, however, increased with time; in the last 3 yr (1985–1987) of the trial, the highest level of applied P resulted in profitable forage DM yield increases. After 25 yr, the productivity of the timothy sward was dependent upon a balanced application of all three macronutrients; absence of any one nutrient resulted in little or no response to applications of the other nutrients. The long-term persistence of timothy was solely dependent on K fertilization. The proportion of bentgrass and bluegrass species declined with increasing levels of applied K while that of timothy increased. The change in botanical composition due to applied N and K significantly affected IVD and crude protein content.Key words: N, P, K, fertilization, yield, persistence, timothy