Effect of fertilization on the nitrogen, calcium, and phosphorus contents of pasture herbage

Observations were made over a period of 6 years of a series of plots on a mixed pasture sod top-dressed without incorporation with various combinations of dolomitic limestone and fused phosphate. The more desirable pasture plants, Kentucky bluegrass, white clover, and lespedeza, increased and the weeds decreased as a result of the use of either of these fertilizing agents. Either or both of the treatments increased the yields of dry matter and the percentage of nitrogen in the dry matter. None of the treatment combinations changed the carotene content to a significant extent. The application of phosphate to the soil increased the percentage of Ca in the herbage in the last 4 years of the experiment but not in first 2, and the limestone had little effect on the Ca content. The P content of the vegetation was little affected by the limestone, but was increased when phosphatic fertilizers were applied. The percentages of N and Ca have decreased steadily during the 6 years of observations, but the P percentage has remained relatively constant. The yields of dry matter have been very responsive to meteorological conditions and have not exhibited any time trends either upwards or downwards. There has been no definite evidence of luxury consumption of N, Ca or P. The percentages of N and Ca in the dry matter have been higher when greater yields were obtained, but this may have been due to an increase in metabolic tissue in the more vigorously growing vegetation rather than to an excess storage. The P content of the herbage was virtually independent of the yields. It is concluded that the herbage from any of these plots, including the unfertilized controls, probably contained enough macronutrients, except P, to meet the needs of cattle, provided that it be eaten in sufficient amount to supply the energy requirement. The P was adequate in the vegetation from all plots that received phosphatic fertilization but was suboptimum for growing beef calves in the forage from the nonphosphated plots. The effects of the fertilizer treatments on the composition of the herbage has varied from year to year, and there has been a downward trend in the Ca and P content over the experimental period. The relation between the total yield of dry matter and its Ca content changed rather abruptly after the third year, and there has been little evidence of luxury consumption by these plants. While the causes of these results are largely unexplained, they are undoubtedly the resultant of the interaction of many chemical, physical, and biological forces. Until our knowledge of these forces and their interrelationships is much more complete, it seems unsafe to draw sweeping conclusions in respect to the effect of fertilization on the nutritive value of plants.