Availability of banded triple superphosphate with urea and phosphorus use efficiency by corn

Phosphorus fixation results in low P use efficiency in acid soils. Increase in soil pH through urea hydrolysis may improve P availability and use effi ciency. Growth chamber and field experiments were conducted to evaluate eff ects of urea on triple superphosphate (TSP) transformation and P use effici ency. A Ste. Rosalie clay (Typic Humaquept), an Ormstown silty clay loam (T ypic Humaquept) and a Chicot sandy clay loam (Typic Hapludalf) were used in the growth chamber experiment with three rates of N (0, 200 and 400 mg N k g(-1)), two N sources, either urea or NH4 NO3, based on 87 mg P kg(-1) soil . In the field, three rates of urea (0, 60 and 120 kg N ha(-1)) and two rat es of TSP (26 and 52 kg P ha(-1)) were compared on a Ste. Rosalie clay and an Ormstown silty clay loam. Compacted or blended mixtures of urea-TSP with different ratios of N:P were used in the field experiment. In the growth c hamber experiment, soil pH and dissolved organic carbon (DOC) concentration was increased by added urea, and Mehlich (3) and water extractable P thus increased with increased urea. Soil pH, DOC and available P levels were not significantly affected by added NH4 NO3. Phosphorus uptake increased with added N, either urea or NH4 NO3, but P concentration increased only with ad dition of urea. In the field, soil Mehlich (3)-P at day 20, P uptake and us e efficiency, corn yields increased when urea was applied with TSP. Compact ed mixtures of urea-TSP increased P uptake and use efficiency, corn yields in comparison with blended mixtures. The beneficial effects of banded urea with TSP on P availability and P use efficiency were primarily attributed t o urea hydrolysis, subsequent pH increase and organic matter dissolution as well as synergistic effect of N and P. These results indicate that compact ion of urea plus TSP may offer a significant advantage over blended mixture s.