CORN ROOT DISTRIBUTION BETWEEN AMMONIUM FERTILIZED AND UNFERTILIZED SOIL

Earlier research has shown that in a phosphorus (P) placement experiment the amount of increase in root proliferation in the fertilized volume, F, depended on the ratio of the available soil P levels in F and the unfertilized volume, U. The objective of this research was to determine the effect of the level of nitrogen (N) in F, and U on root proliferation in F. The research was conducted using the same procedures as were used for P. Com (Zea mays L.) was grown in pots of soil where 20% of the soil was fertilized with N at 10 rates and three replications using ammonium sulfate [(NH4)2SO4]. All the soil was treated with nitrification inhibitor to reduce nitrification of ammonium (NH4+) since nitrate (NO3-) would diffuse to the unfertilized volume much more rapidly than NH4. The fertilized volume was separated with plastic screen and the root growth in this volume was compared with root growth in a comparable volume of unfertilized soil that was also separated with plastic screen. After 10 days of growth in the pots, the plants were harvested and the root length in F and U of each pot measured. As rate of N in F increased, root length in F increased and in U decreased. This differs from the results with P where root length in U did not vary with rate of P used in F. Root weight in both F and U decreased as N in F increased. An increase in root length and root surface area in F was due to the increase in fine root production as N in F increased. A relation was obtained between the ratio of soil N in F and U, CsiF/CsiU and the ratio of root length in F and U, RLF/RLU. It was similar to what occurred in a study with P. Hence, knowledge of the effect of adding N to a specific soil volume will affect root proliferation in relation to the ratio of soil N level in F and U. This information can be used for predicting N uptake as related to N placement.