Multiple studies have shown that on alkaline soil, rock phosphate effectiveness is maximized when applied with an acidic agent like ammonium sulphate or other acidic agents like, composts, sulphur, humates, other acid fertilizers such as MAP and/or phosphate solubilizing bacteria.
A recent study showed that blending rock phosphate with a relatively small amount of ammonium sulphate (21 – 0 – 0 – 24) outperformed Di Ammonium Phosphate (DAP), in terms of chickpea biomass yield when the two phosphorous sources were applied at the same rate even on alkaline soil (pH 8.0).
The phosphorous was applied at 60 kg/ha and two different levels of ammonium sulphate (16 kg of N/ha and 32 kg of N/ha) were used. The experiment also tested the rock phosphate blended with ammonium nitrate at the same two rates. In the experiment, the biomass increase of the DAP was 6.85% over the control whereas the rock phosphate and ammonium sulphate was 19.3% over the control at the lower ammonium rate and slightly higher at 21.9% increase over the control at the higher rate.
The rock phosphate with ammonium nitrate at the lower rate performed similar to the DAP whereas at the higher level saw a lower increase.
Mahesh Ganesa Pillai, Sumedh Sudhir Beknalkar and Saket Sanjaya Kashettiwar. AGRONOMIC EFFICIENCY OF ROCK PHOSPHATE IN FINE SIZE WITH AMMONIUM SULPHATE AND AMMONIUM NITRATE. Int J. of App.Lf. Sci., Vol. 1(1), 62-65; 2014.