Leaching characteristics and nutrient supplying potentials of selected P and K fertilizer sources

Putting greens on golf courses are typically constructed of sand root-zone mixes having very low CEC and few or no Al and Fe hydroxyoxide coatings. As a consequence of these properties, the retention of potassium (K) and phos phorus (P) by USCA-specification putting-greens is limited. A new commercia l source of P and K may aid in the maintenance of adequate P and K levels i n greens. A glasshouse study was conducted using FloraDwarf bermudagrass (C ynodon dactylon (L.) Pers. Cynodon transvaalensis Burtt Davy) on lysimeters (15 cm diameter and 45 cm depth) to characterize the leaching and nutrient supplying potential of several commercial P and K sources. Phosphorus and K treatments were applied to an established bermudagrass stand at 225 and 2 60 mg per lysimeter, respectively, in a randomized complete block design wi th three replications. Clippings and leachates were collected biweekly over a 12-wk period and analyzed for P and K. Clippings were dried at 70 degree s C for 48 hr and weighed for dry matter estimation. Lysimeters were mainta ined at or near gravimetric water content and leached every 4 wk using an a dditional 1/2 pore volume of water. Potassium sources did not differ in the ir influence on bermudagrass growth, except for potassium sulfate, but larg e differences in quantity of K leached during the first and second leaching event were noted. Monopotassium phosphate (MKP) and a liquid 0-20-20 ferti lizer leached the largest quantity of K, and the coated K sources the least . Regardless of K source, more than 80% of the K leached during the first t hree leaching events. Relatively large differences in P leaching characteri stics were noted among the P sources, with MKP and ammonium polyphosphate ( APP) contributing the largest quantity of P to the leachate and concentrate d superphosphate (CSP) and 0-20-20 fertilizer the least. Quantities of P an d K leached did not correlate with dry matter or nutrient uptake, Total rec overy ranged between 43 and 93% for P and 82 and 104% for K. Because of the low cation and anion retention properties of putting green root-zone mixes , large differences in K leaching among the various K sources are not expec ted but, due to inherent solubility, leaching differences among the P sourc es appear to exist.