Field-scale watershed evaluations on deep-loess soils: III. Rainfall and feitilizer N use efficiencies

ABSTRACT:

Water is often the most limiting crop production factor, but it also can cause nutrient runoff and leaching losses. The objectives of this report were to (1) compare water use efficiency for the production of continuous corn (Zea mays L.) on long-term conventional-till and ridge-till watersheds in western Iowa, and (2) relate water use to fertilizer N use efficiency. Information on crop yield, rainfall, buseflow, runoff, and soil water content was collected over a period of 23 yr. Potential evaporation was calculated from microclimate data. Using these data, water use efficiency was computed Nitrogen use efficiency was estimated using crop removal and fertilizer application data. There were no significant differences in seasonal rainfall or estimated water loss between the two watershed, but water use efficiency for ridge-tillage (22.8 kg ha⁻¹ mm⁻¹ yr^−l or 517 lb ac⁻¹ in⁻¹ yr⁻¹) was significantly greater than for conventional tillage (20.3 kg ha⁻¹ mm⁻¹ yr⁻¹ or 460 lb ac⁻¹ in⁻¹ yr⁻¹). The estimated N removal by crop harvest accounted for 48 and 59% of the applied N. Ridge-till reduced runoff;. increased infiltration, and reduced water loss due to greater residue; therefare, greater water use efficiency was observed The ridge-till field bad less residual NO₃-N in the root zone for subsequent leaching but higher N concentrations in the baseflow since average N fertilization rates exceeded average crop removal by 68 kg ha⁻¹ yr⁻¹., This interaction demonstrates the importance of balancing both N and water use efficiencies to achieve a sustainable production system.