Rates of Nitrate Uptake with Sudangrass and Microbial Reduction in a Field

Removal of nitrate from a field soil by sudangrass ( Sorghum sudanense ) and by conversion by microorganisms are accounted for with the aid of a convective dispersion equation with a sink term. Rates of nitrate disappearance from the soil showed sharp increases associated with irrigation or rainfall and seemed to decrease exponentially with soil moisture potential. Leaching displayed similar increases which subsided three to four days after irrigation. Plant uptake accounted for about 50% of added nitrate, organic matter and residual nitrate for about 34%, leaching for another 4%, and the balance was unaccounted for. While a nitrate balance showed a percentage distribution of nitrate in a soil‐plant system, rate measurement revealed a time‐dependent function for the plant uptake of nitrate in the system which is essential for stochastic or mechanistic model studies.