EFFECT OF RATE AND TIME OF NITROGEN AND INTERVAL OF PHOSPHORUS AND POTASSIUM FERTILIZATION ON HERBAGE PRODUCTION ON PERMANENT PASTURE

Abstract

In two 3-year cycles of a field experiment annual N treatments were superimposed on mineral treatments applied annually and triennially to a permanent pasture sward.Applications of P and K were reflected by changes in exchangeable K and acid-soluble plus adsorbed P. There was somewhat greater penetration of K than of P and soil levels of both were generally lowest where rate of N application was highest.Yields varied from year to year but tended to be more uniform with annual than with triennial mineral treatments. In the 6-year period average yields for all 0-, P-, K-, and P–K-treated plots were approximately 1.3, 1.6, 1.5, and 2.0 tons per acre of dry matter. Time of nitrogen application had little influence on total yield but seasonal distribution of herbage was much more uniform with nitrogen applied in summer than in spring. Soil moisture, which was a major factor in the response obtained with nitrogen applied in summer, was limiting during the late summer in two of the three years measured.Percentages of P and K in grass reflected the mineral treatments which had much less influence on botanical composition and species foliage cover than N. This element suppressed legumes, increased grass, and markedly influenced the K level in grass.