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How Do I Access Available Phosphorus

Jan 21, 2011

Question: I have soil tests showing very low levels of phosphorus using the bray 1 method and very high levels with the bray 2 method. Will the phosphorus become available later? What do I need to do to free it up?                                   

Answer: P1 measures phosphorus that is readily available to plants. P2 measures readily available phosphorus plus a part of the active reserve phosphorus in the soil. A P1:P2 ratio less than 0.5 could indicate tie-up issues. It could also be due to a history of rock phosphate use, which is not very plant available. The high P2 will not become readily available for plant uptake. There are several things you can do to reduce the negative effect of a P1:P2 ratio of less than 0.5. Apply phosphorus in the spring just prior to crop use instead of making fall applications. Consider fertilizing every year instead of every two years. A banded application of phosphorus would also be preferred. In addition, there most likely would be a high response to starter fertilizer for corn. Also, the response to sulfur and zinc use should be good. 
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