Evaluation of Agronomic Effectiveness of Activated Phosphate Rock.

Unlike water soluble phosphorus (P) fertilizers, most phosphate rocks (PRs) are non-reactive in agricultural soils, particularly in neutral to alkaline soils. One innovative and practical approach to enhancing PR agronomic efficiency is “activation” of the PRs with water soluble P (WSP) fertilizers. In greenhouse studies unreactive PR was activated with a modest amount of WSP at a ratio 20% WSP to 80% PR (4:1 PR/WSP ratio = “0.2 Activation”) and evaluated on three soils with varying acidity/alkalinity level (Hiwassee loam – 5.49, Greenville loam – 6.80, and Sumter – 7.57).  Rice and soybeans were used as test crops during the spring/summer seasons, and wheat during the winter season. P uptake was determined at three growth stages (4 weeks after planting, anthesis, and grain filling). At maturity, the crops were harvested to determine grain and biomass yields, grain and straw P contents, and to calculate the relative agronomic effectiveness (RAE) of the P sources. Irrespective of the soil, crop and planting season, significant improvement in the agronomic effectiveness of the “activated” PR was observed, with an average RAE value greater than 80%. The combined results suggests that, combination of a modest amount of WSP with PR could be a cost effective means of enhancing P availability in PRs without the soil pH constraint on the agronomic effectiveness of PRs. Further studies will evaluate the effectiveness of the “activated” PRs under field conditions.