Influence of fertilization, irrigation, and stage and height of cutting on yield and composition of Kentucky bluegrass (Poa pratensis L.)

A field study pertaining to the influence of fertilization, irrigation, and stage and height of cutting on the yield and composition of bluegrass has been in progress at Madison, Wis., for 7 years, 1928 to 1934, inclusive. Approximately 80 plats were involved in this investigation, but for convenience of presentation results from only 10 typical and representative plats are presented in this paper. The results are summarized as follows: 1. Nitrogen in an available form and water were found to be the two most important limiting growth factors under the conditions of these experiments. Mineral fertilization alone gave only small increases in yield. Nitrogen used in conjunction with mineral fertilization and irrigation consistently doubled, and in some instances trebled, the yield of grass. Water alone, during the period of 1930 to 1934 doubled yields. Nitrogen alone did not give maximum increases unless it was supported by mineral fertilization. 2. When the grass was cut to ground level (as closely as is possible with a lawn mower) higher seasonal yields were obtained than when it was cut at a higher level (1 1/2 inches). In 1934, grass cut to ground level produced 9,656 pounds of oven-dried grass per acre as compared to 8,205 pounds, which is the average of grass from plats 1, 2, 3, and 4 cut at 1 1/2 inch level during the same period. 3. Grass cut when 8 to 10 inches high to ground level gave only slightly greater increases in yield than that cut when 4 to 5 inches high to ground level. Only 5.3% increase in yield favoring the taller growing grass was recorded in 1933 and 1934. 4. When moisture is not a limiting factor of growth, the P2O5 content of grass cut regularly is lowest during the early spring, attains a maximum in July and August, and drops slightly in the fall. There is a uniform rise in CaO content from spring to fall. 5. Grass cut when 8 to 10 inches high was found to be appreciably lower in P2O5 and CaO content than grass cut when 4 to 5 inches high. 6. Nitrogen fertilization lowered the CaO and P2O5 content of the grass. Phosphate fertilization increased the phosphorus content of the grass to an appreciable extent. 7. Grass of high nitrogen content is produced only where frequent applications of nitrogen are made throughout the growing season. The percentage nitrogen content of the herbage was found to vary directly with the amount of nitrogen fertilizer applied. 8. The nitrogen content of herbage may be increased by the application cation of phosphorus and potash to the soil. 9. The nitrogen content of herbage decreases as the plant approaches maturity. 10. The crude protein produced per acre was found to vary directly with the amount of nitrogen fertilizer applied. The plat given 1,160 pounds of ammonium sulfate per acre produced 4.44 times more crude protein than did the plat which was not fertilized with nitrogen. 11. The percentage of non-protein, water-soluble nitrogen was found to vary directly with the amount of nitrogen fertilizer applied. Of the total nitrogen on the plat given 1,160 pounds of ammonium sulfate per acre, 25.8% was in a non-protein, water-soluble form, whereas 21.9% of the total nitrogen on the plat given mineral fertilizationzation but no nitrogen was in this form. 12. The percentage of true protein was found to vary directly according to the rate of application of ammonium sulfate. 13. The recovery of fertilizer nitrogen, when moisture was not a limiting factor of growth, was high, ranging in 1934, as is evident from a review of the data, from 39.5 to 121.7%, or an average of 87.6% for all plats receiving nitrogen.