Surface Runoff Losses of Soluble Nitrogen and Phosphorus Under Two Systems of Soil Management

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Abstract
Evaluation of surface runoff losses of soluble nitrogen (NO3‐N, NH4‐N) and phosphorus (inorganic P) was initiated due to recent concerns about the discharge of plant nutrients from the agricultural sector. The annual loss of these two elements from field plots, as derived from natural rainfall, was determined. The influence of a crop rotation, soil management practice and fertilizer rates of the previous 15 years was studied. Corn (Zea mays L.), beans (Phaseolus vulgaris L.), and wheat (Triticum aestivum L.) were combined factorially with two rates of fertilization (high and moderate) and two soil management practices (good vs. poor). Well‐managed soils produced the least surface runoff losses of N and P. Ammoniacial N losses were not significantly associated with crop, fertility level, or management practice. Values ranged from 0.14 to 1.30 kg/ha per year. Surface losses of nitrate N and inorganic P were directly influenced by crop, fertility level, and soil management. These losses ranged from 0.39–29.23 and 0.04–0.49 kg/ha per year, respectively. Heavy fall fertilization of N on wheat prior to intense rains on poorly managed soils produced the largest loss of nitrate N. Except for heavy fall fertilization of N on poorly managed soils, the total yearly accumulative N discharge in surface runoff did not exceed the amount delivered in rainfall as measured during a 10‐month period. Phosphorus losses exceeded that amount contained in rainfall.
Funding Information
  • U.S. Environmental Protection Agency (WP-01493-011 and 13020 DBP)

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