Hydropedological Processes and the Variability in Nitrogen Availability for Corn.

Hydropedological processes affect soil water and nutrient transport and cycling. This study evaluated the impact of hydropedological properties on soil N availability and plant N uptake at three functional units identified in a ridge-valley agricultural landscape. Unit A was in a depressional area consisting of fine textured deep (>1.0 m) soils (Hagerstown series). Unit B was on a sloping area (15% slope) with fine textured shallow (<0.5 m) soils (Opequon series). Unit C was located near an intermittent stream with medium textured deep (>3.0 m) soils (Melvin series). Two N treatments (NH₄NO₃) were applied to corn (Zea Mays L.) at planting (0 and 135 kg ha^-1). Soil samples were collected from Ap1 and Ap2 horizons to represent corn growing stages of six mature leaves (V6), tasseling (VT), and physiological maturity (PM) and following major precipitation events. Whole plant samples were collect at V6, VT, and PM. Unit A had the greatest biomass throughout the growing season, while Unit C had the least. The greatest difference in N uptake between the two N treatments was observed the highest in Unit A (46-170 kg N ha^-1), and the least in Unit C (7-63 kg N ha^-1), with Unit B falling in between (32-107 kg N ha^-1). This suggested the N application in Unit A was more effectively taken up by corn, and the conditions in the other two units were more subject to N loses. Hydropedological differences among the three units explain this observation. High clay contents and deep soil in Unit A resulted in greater water and fertilizer retention, thus greater N use efficiency, while coarser soil texture in Unit C has weaker water and fertilizer holding capacity. Steep slope and shallow soil in Unit B facilitated surface and subsurface N movement and thus greater potential for N lose.