Nitrogen Gradients and Nitrification Associated with Decomposing Corn Plants and Barley Straw in Soil

Ammonia, nitrite, and nitrate concentrations and pH were measured in 5‐mm increments of soil over a 50‐mm distance from decomposing layers of corn plants ( Zea mays L.) and barley straw ( Hordeum vulgare L.) that contained from 1.00 to 2.10% N. During 16 days of incubation, corn plants containing 2.05% N produced an ammonia concentration of 1.3 meq/100 g of soil in the layer near the plant material and inhibited nitrification. At 1.78% N the maximum ammonia concentration was approximately 0.55 meq/100 g of soil and nitrification proceeded almost without inhibition. At 1.27% N, a nitrogen deficiency existed and nitrate moved from the soil into the plant material. Similar gradients of a lesser magnitude were found in soil near decomposing layers of barley straw. Plant materials with the higher N contents increased adjacent soil pH, whereas those with lower N contents had less influence.