Rhizosphere Acidification Increases Phosphorus Recovery of Black Locust: II. Model Predictions and Measured Recovery

Abstract

Abstract Phosphorus fertilization is often inefficient, with low recovery. In the central hardwood region of the USA, inexpensive fertilizers may be economical if recovery can be increased. Rhizosphere acidification was studied as a means of increasing P recovery from rock PO 4 . Total quantities of P in 90‐d‐old locust ( Robinia pseudoacacia L.) seedlings were predicted using a previously evaluated rhizosphere acidification model and pH‐affected supply and uptake rates. Six forest soils were fertilized with 0 or 50 mg kg −1 of P, using three rock PO 4 sources of varying solubility. Locust seedlings were planted and grown for 90 d. To test model predictions, plants were harvested and assayed for total P content. Results showed good correlation between predicted contents and measured contents ( r 2 = 0.72‐0.98). Additionally, rhizosphere acidification greatly increased P recovery from rock PO 4 in these soils. Predicted P recovery was 40 to 300% greater with acidification than without. These results indicate that legume rhizosphere acidification may be a means of increasing P cycling in central hardwood forests and plantations. Here, soils may be neutral or slightly acid, and interplanting legumes will increase N and P availability to crop trees.