SOLUTE MOVEMENT IN UNCROPPED RIDGE-TILLED SOIL UNDER NATURAL RAINFALL

Authors: Jaynes, Dan; SWAN, JAMES - IOWA STATE UNIVERSITY

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Reducing off-site movement of fertilizer derived nitrate is a high priority of agricultural research. Improving nitrogen fertilizer application methods may help reduce the required fertilizer application rates and reduce off-site movement of nitrate. Ridge tillage, where corn is planted into soil ridges that are several inches high, and plant residues from previous year's crops accumulate in the furrows between the ridges, has proven to be a viable system for reducing water runoff and sediment erosion from corn fields. We proposed that the ridge - furrow configuration resulting from ridge tillage could also be used to reduce off-site movement of nitrate from fertilizer by injecting the fertilizer directly into the ridges. Using inert chemical tracers to simulate the movement of fertilizer derived nitrate, we demonstrated that tracers injected into the ridges experienced less leaching deep into the soil than tracers injected into the furrows. Less deep leaching helps prevent the movement of agrichemicals such as nitrate into underlying ground water and keeps the nitrate up in the root zone where it serves as a nutrient for growing plants. These studies suggest that ridge-injection of nitrogen fertilizer may be an economical and environmentally friendly practice for corn production in ridge tillage systems.

Technical Abstract: Reducing off-site movement of fertilizer derived nitrate is a high priority of agricultural research. Injection of N fertilizers within the ridge of ridge tillage systems rather than within the furrow or broadcast uniformly on the surface has shown promise in reducing nitrate leaching in short-term rainfall simulation studies. This study measured leaching patterns over the growing season under natural rainfall of tracers injected into different ridge positions in established ridge-tilled plots located in Boone and Treynor, IA. After corn (Zea mays L.) planting in 1992, mobile tracers were injected as pseudo-line sources 10 mm below the soil surface in ridge top, ridge shoulder, and furrow positions with a point injector. Corn seedlings were removed by hand after germination so that tracer movement could be followed without the added complexity of root and canopy interactions. Movement of tracers was measured by triplicate soil sampling gto a maximum depth of 1.22 m four times after tracer application. Sample collection spanned a period of 102 days and 282 mm of cumulative precipitation after tracer application at the Boone site and 97 days and 314 mm of precipitation at the Treynor site. All tracers showed downward movement over time. Furrow applied tracer had generally lower mass recovered and markedly lower concentrations in the soil profile than tracers applied to ridge top and shoulder positions. There was no consistent difference in mass recoveries between ridge top and ridge shoulder placed tracers. Tracer movement was essentially vertical with furrow placed tracer exhibiting the most lateral spreading. Fertilizer injection within the ridge of a ridge tillage system shows promise for reducing leaching and increasing nutrient availability to plants.