Humic acid coated P fertilizers to improve phosphorus use efficiency in calcareous soils

Phosphorus mobility and availability in soil are mainly governed by both soil and fertilizers proprieties including soil P-sorption capacity, soil organic matter content, soil pH and P fertilizer solubility. Although, the application of considerable P fertilizer rates in calcareous soils, containing high levels of calcium carbonate, P availability and uptake are extremely affected, which limit crop production in several cropping systems around the world. One approach to enhance P use efficiency and its agronomic benefits is to use humic substances (HS). In this regard, our study aims to assess the impact of P granular fertilizers coated with HS, on plant growth, mineral nutrition and P use efficiency. Two pot experiments were carried out at the OCP R&D Center using di-ammonium phosphate (DAP) coated with 0.5% of HS (extracted from leonardite) and applied at recommended doses on maize and tomato crops grown under sandy calcareous soil conditions (pH 8.0). As results, coating DAP with HS improved maize and tomato shoot dry weight by 6.2% and 16.8 % respectively, compared to uncoated DAP. Likewise, root dry weight (17% and 30%) and leaf chlorophyll content (+5%) were enhanced by HS coating. In addition, the use of HS improved greatly P uptake by 15% and 13% in both maize and tomato plants, which can have a benefic impact on P use efficiency. Under current calcareous soil conditions, the results showed also that HS improved nitrogen, potassium, iron and zinc plant uptake.