FERTILIZER MANAGEMENT AND TILLAGE Soybean Responses to Potassium Placement and Tillage Alternatives following No-Till

ABSTRACT growing seasons when drought occurs, since soil K avail-ability and root growth and activity in the surface layerMore information is needed about optimum potassium (K) fertil-are more vulnerable to drought than those in subsurfaceizer placement for soybean [Glycine max (L.) Merr.] production in layers. In addition, crop residue deposit at the soil sur-no-till fields. This study was conducted at two locations in Ontario, Canada, from 1998 to 2000 to examine soybean responses to K place- face in no-till usually results in higher soil moisture and ment methods and tillage systems on soils with a 5- to 7-yr no-till lower soil temperature in the surface layer, which may history and medium to high soil-test K levels. Fertilizer K treatments reduce soil K availability and restrict root growth early (15-cm deep banding in fall, 7.5-cm shallow banding in spring, surface in the season (Barber, 1971; Fortin, 1993). The risks of broadcast in fall, and a zero K control) were compared in three reduction in plant K uptake by drought or low tempera-conservation tillage systems (fall zone-till, fall disk, and no-till). The ture become severe when soil K concentrations in sub-K fertilizer rate was 100 kg ha1 for all but the control treatment. surface layers are too low to optimize plant K uptake.Soybean row widths (76 or 38 cm) varied with tillage systems, and Subsurface placement of K fertilizer, therefore, maysoybean rows were positioned above K fertilizer bands if applicable. improve applied K availability and reduce soil K stratifi-Yield responses to K application occurred in the fall zone-till and cation in no-till systems. Because the land area of no-tillno-till systems on some medium- to high-testing soils. There was no significant leaf K or seed yield advantage to band placement compared soybean in North America has increased rapidly sinc