DISSOLUTION OF ROCK PHOSPHATE IN SILAGE LEACHATE

Following a favourable crop response to rock phosphate (RP) in a long term fertility trial in DeKalb, IL, an experiment was designed to diss olve RP in silage leachate on the premise that silage has a pH of 4.0 to 4.2 and that once drained of its leachate, it can be used for anima l feed. Two types of RP, Brown Sugar RP and Ruhm's RP, having 30% P2O5 were dissolved in pure organic acids similar to those present in sila ge leachates. The amount of dissolved phosphorus (P) from RP in organi c acids increased with organic acid:RP ratio. The highest amount of P dissolution was found with butyric acid. Thus, butyric acid with Brown Sugar RP, 2519, 1500, and 710 mu g P/g RP were dissolved at 800, 400, and 200 acid:RP ratio, respectively; with Ruhm's RP the values were 3 900, 1988, and 835, mu g P/g RP, respectively. After dissolution of th e two types of RP in the acids, there was an increase in solution pH o f 1 to 2 units. Of the three types of silage leachates used, grass sil age leachate had the highest acidity and calcium (Ca) concentration fo llowed by high moisture and low moisture corn silage leachates, respec tively. Soluble P concentration was five times higher in high moisture corn and grass leachates than in low moisture corn silage leachate. T here was a decrease in acidity, Ca, and P content with the number of s uccessive leachings. In low moisture corn silage leachate, 13.9 and 3. 05 mg P/g Brown Sugar RP and 14.4 and 3.05 mg P/g Ruhm's RP were solub ilized in the 1st and 2nd leaching, respectively. The study shows that corn low moisture silage leachate can dissolve RP efficiently and tha t it is a good, promising, and environmentally safe method for RP diss olution.