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The influence of soil pH and soil cation exchange capacity on ammonia volatilization from surface applied ammoniacal nitrogen has been reported in previous studies. Since the hydrolysis of ureacontaining N fertilizers causes an increase in alkalinity, a soil's inherent H+ buffering capacity (defined as the soil's total acidity, comprised of exchangeable acidity plus non‐exchangeable, titratable acidity), should exert a dominant influence on the maximum soil pH at the site of urea fertilizer application. The objective of this study was to demonstrate the importance of a soil's H+ buffering capacity in affecting NH3 volatilization from surface‐applied urea. The H+ buffering capacity of two soils was increased by adding hydroxy‐Al polymers to one soil, and weak and strong acid cation exchange resins to the other soil. Care was taken to keep cation exchange capacity and initial pH close to the same on amended and unamended (control) soils. Urea was surface‐applied to amended and unamended soils and ammonia volatilization and soil surface pH were measured. The increase of H+ buffering capacity of soils was found to reduce soil surface pH and NH3 volatilization after application of urea. It is concluded from this work that H+ buffering capacity of a soil is a better indicator of NH3 loss potential than a soil's initial pH.

Discharge and N content of surface water flowing from four Karst watersheds on Konza Prairie Research Natural Area, Kansas, managed with different burn frequencies, were monitored from 1986 to 1992. The goal was to establish the influence of natural processes (climate, fire, and bison grazing) on N transport and concentration in streams. Streams were characterized by variable flow, under conditions that included an extreme flood and a drought during which all channels were dry for over a year. The estimated groundwater/stream water discharge ratio varied between 0.15 to 6.41. Annual N transport by streams, averaged across all watersheds and years, was 0.16 kg N ha−1 yr−1. Annual N transport per unit area also increased as the watershed area increased and as precipitation increased. Total annual transport of N from the prairie via streams ranged from 0.01 to 6.0% of the N input from precipitation. Nitrate and total N concentrations in surface water decreased (P < 0.001, r values ranged from 0.14–0.26) as length of time since last fire increased. Increased watershed area was correlated negatively (P < 0.0001) to stream water concentrations of NO−3N and total N (r values = −0.43 and −0.20, respectively). Low N concentration is typical of these streams, with NH+4‐N concentrations below 1.0 µg L−1, NO−3‐N ranging from below 1.4 to 392 µg L−1, and total N from 3.0 to 714 µg L−1. These data provide an important baseline for evaluating N transport and stream water quality from unfertilized grasslands.

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