Fertilizer P Uptake Determined by Soil P Fractionation and Phosphatase Activity

The aim of this study was to determine if three cereal crops differed in their behavior to take up soil and fertilizer P, with emphasis on the relationship between phosphatase activity and P fractionation. We used a vertical rhizobox experiment with wheat, oat, and barley sown on Chilean Andisol (Barros Arana Series) with low P availability under greenhouse conditions. Plants were fertilized with the equivalent of 100 kg P ha of triple superphosphate (TSP) or rock phosphate (RP). Plant biomass was determined for each of the three cereal plant species. Additionally, phosphatase (P-ase) activity in roots, soil in presence of roots (soil+R), and soil in absence of roots (soil−R) after 60-day growth were evaluated, and soil P fractionation was determined using the Hedley procedure. Fertilizer increased both P uptake and biomass production, particularly in shoots. The P uptake efficiency (∆P uptake between fertilized and unfertilized treatment/P input) was low (4.6%) and similar for both fertilizers for oat, but RP was more efficient for wheat (> 30%) and even more so for barley (nearly threefold), due the higher shoot P concentration of RP fertilized plants, which could be attributable to a major P-ase activity in plants fertilized with RP. Despite, fertilizer P was most clearly identified in labile inorganic soil fractions with Olsen P being greater after TSP addition than RP. In particular, plants showed contrasting soil+R P-ase activity inducing differences in soil+R P speciation, increasing labile NaHCO-P and NaOH-P fractions with TSP. Strong relationships were found between the sum of labile P fractions and P uptake. We conclude that slower release of RP has a positive impact on P-ase activity and leads to better fertilizer efficiency than TSP, especially for barley.