Phosphorus solubilization in the rhizosphere and its possible importance to determine phosphate plant availability in soil. A review with main emphasis on German results

Limited fertilization adapted to plant demand is of high economical and ecological relevance. This requires a reliable analysis of plant available P, based on knowledge of phosphorus dynamics in soils and P mobilization by plants. On chernozem-like soils, as well as under dry conditions, the double-lactate (DL) phosphate extraction methods apparently do not adequately reflect the P uptake ability of plants. This paper summarizes rhizosphere processes that affect P availability partly by reference of selected own experiments. Root exudates increased the double-lactate (DL) extractable P amount of soils in sterile and non sterile cultures. Microbial colonisation increased both the exudate amount and the specific ability of exudates to solubilize P. In spite of rapid exudate turnover, DL-P solubility was increased. Sugars released from P-deficient plants increased the P solubilizing ability of a bacterial strain (Enterobacter radicincitans), perhaps by changing bacterial acid production. Root exudates solubilized more P from soil than lactate extracts did. An investigation of physiological processes in the rhizosphere could contribute to a better understanding of nutrient availability and perhaps lead to the development of extraction methods that better reflect the availability of soil phosphorus to plants. Connecting field experiments with basic studies offers the opportunity to better understand plant nutritional processes to realize an effective and sustainable agriculture.