Fertilizer-use efficiency of different inorganic polyphosphate sources: effects on soil P availability and plant P acquisition during early growth of corn

Polyphosphate-based fertilizers are worldwide in use, and their effect on crop yield is often reported to be similar to orthophosphate products, although some studies showed higher yields with polyphosphate applications. However, information on how these fertilizers may influence plant P acquisition is very limited. A pot experiment was carried out under controlled conditions with corn (Zea mays L.) growing on a sandy soil (pH 4.9) and a silty-loam soil (pH 6.9) differing in P-sorption properties. The objective was to evaluate phosphorus fertilizer-use efficiency (PFUE) of several polyphosphate (poly-P) compounds (pyrophosphate [PP], tripolyphosphate [TP], and trimetaphosphate [TMP]) using orthophosphate (OP) as a reference. Focus was put on evaluating plant parameters involved in plant P acquisition, i.e., root length and P uptake per unit of root length. Furthermore, soil P availability was characterized by measuring ortho-P and poly-P concentrations in soil solution as well as in CAL (calcium-acetate-lactate) extracts. The P availability was differentially influenced by the different P sources and the different soils. In the silty-loam soil, the application of poly-P resulted in higher ortho-P concentrations in soil solution. In the same soil, CAL-extractable ortho-P was similar for all P sources, whereas in the sandy soil, this parameter was higher after OP application. In the silty-loam soil, poly-P concentrations were very low in soil solution or in CAL extracts, whereas in the sandy soil, poly-P concentrations were significantly higher. Phosphorus fertilizer-use efficiency was significantly higher for poly-P treatments in the silty-loam soil and were related to a higher root length since no differences in the P uptake per unit of root length among poly-P and OP treatments were found. However, in the sandy soil, no differences in PFUE between OP and poly-P treatments were observed. Therefore, PFUE of poly-P compounds could be explained by better root growth, thereby improving plant P acquisition.