Recovery of Fixed Ammonium by Corn in Greenhouse Studies

Abstract

AbstractThe availability of native fixed NH4 and applied NH4 fixed in the Ap and B1 horizons of a Dodge silt loam was investigated. In addition, the effect of freezing on the fixation of applied NH4 was studied. By applying K and N to either the same or separate layers of soil in green‐house pots it was also possible to evaluate the effect of K on the release of fixed NH4. When NH4 and K were applied in the same layer of soil, the Ap and Bl horizons fixed 5 and 15% of the added NH4, respectively. An additional 5% of the added NH4 was fixed in each horizon when the soil was frozen after applying NH4. However, when NH4 and K were applied to separate layers of soil, negligible amounts of NH4 were fixed. Highly significant correlations between exchangeable K in the moist soil after cropping and the amount of applied NH4 fixed as measured by differential N uptake showed that the level of exchangeable K in the soil controlled the release of fixed NH4 to the crop. Correlations between two methods of measuring fixation of applied NH4, namely, differential N uptake and analysis of the soil after cropping, were highly significant.These studies also indicated that about 15% (0.12 me. per 100 g.) of the native fixed NH4 in the Bl horizon was released when the level of exchangeable K in the soil was very low. However, very little native fixed NH4 was released from the Ap horizon, presumably because sufficient K remained in the soil of this horizon to block release of fixed NH4. These studies indicate that even under the most advantageous conditions very little of the native fixed NH4 is available to crops.