Phosphorus Partitioning and Phosphatase Activity Along Topographic Gradients of an Agricultural Watershed Cropped with Corn and Soybean

ABSTRACT

While chemical partitioning of soil P is a key factor in determining its potential bioavailability and susceptibility to runoff, phosphatase activity provides another approach for characterizing soil P. This study evaluated the changes in sequentially determined P fractions and phosphatase (acid and alkaline phosphomonoesterase [PME], phosphodiesterase [PDE]) activity along topographic gradients of an agricultural watershed cropped with corn and soybean. Analysis of variance showed a significant (p < 0.05) crop effect on H₂O, NaOH, NaHCO₃, and H₂SO₄ extracted P while all P pools were not affected by slope position or crop and topographic positions interaction. Alkaline and phospho-diesterase activities as indicated by p-nitrophenol concentration were affected very strongly by topographic positions. Overall P accumulation and phosphatase activity was higher at the depression where water accumulates. Further studies in phosphorus partitioning and phosphatase activity along topographic gradients of an agricultural watershed and climates similar to those in this study will be necessary to generate useful information for a judicious application of inorganic fertilizers to sustain agricultural production.

KEYWORDS:

• Phosphorus partitioning
• acid and alkaline phosphomonoesterase
• phosphodiesterase
• topographic gradients
• agricultural watersheds
• corn and soybean