Potassium content of Puerto Rican soils as related to sugarcane growing

The potash-bearing minerals, the total potash content in some profiles, the available potash range, and the mean available potash extracted by 1-percent citric acid and by dwarf sorghum (hegari) in pot tests, are reported here for Puerto Rican soil groups. In soils in which feldspars were present, the mean available potash extracted by the sorghum and by citric acid was equivalent to 747 and 376 pounds of K2O per acre, respectively. The sorghum extracted about twice as much potash. In soils from which feldspars were absent, the mean available potash extracted by the sorghum and by citric acid was equivalent to 440 and 365 pounds of K2O per acre, respectively. Chemical methods are therefore not always reliable to determine the potash that plants absorb from the soil. Tests of the response of sugarcane in Puerto Rico to the application of potash fertilizers generally have been limited to a few soils. Optimum sugarcane yields of P.O.J. 2878 were obtained in the first five consecutive crops, in an acid soil of Puerto Rico, with a minimum applicacation of 90 pounds of K2O per crop per year. The sixth and later sugarcane crops, and the 9-crop mean yield, responded significantly to the application of potash in excess of 90 pounds of K2O per acre. No significant yield response was obtained with M. 336 grown in sand lysimeters with four increment levels varying from 19 to 253 pounds of K2O per acre, respectively. No significant correlation was obtained either between cane yields and the K contents of the cane leaves at different stages of growth. The 3-month cane leaves varied from 1.54 to 2.94 percent of K, with the minimum and maximum applications of potash, respectively.