Crop Rotation and Nitrogen Management in a Shallow Soil at Central Montana.

Most soils at central Montana have shallow profiles. Fertilizer N applied in the fall and N mineralized from crop residues could be subjected to leaching by overwinter recharge water to groundwater. Crop rotation and N application studies were conducted at the Central Agricultural Research Center near Moccasin, MT to investigate soil N dynamics and crop N uptake. Changes of bromide tracer and nitrate concentrations in soil profiles demonstrated the leaching process of fall applied N during the winter. Throughout the winter seasons, pea residues consistently released more mineral N than spring wheat residues. The increased N concentration from pea residues in the soil profile may result in more N leaching. However, winter wheat planted into pea stubble received a much greater yield than that planted into spring wheat stubble. Furthermore, surface applied N fertilizer on pea stubble is more available to crops than on spring wheat stubble.