Background Potassium deficiencies maybe observed in coarse textured soils and where erosion has removed the topsoil. Potassium (K) deficiencies may reduce yields and profitability.

In the last few years, areas of K deficiency have been observed in the UMAC region. K deficiency may result from several factors. One factor is that K removal by crops can exceeds K additions. The amount of K removed from the soil by corn and soybeans averages 0.29 lbs/bu and 1.40 lbs/bu, respectively. In a two-year corn/soybean rotation, over 125lbs K20/acre can be removed from the soil. These removal rates cannot be maintained. If K is not replenished in the soil through natural weathering processes of minerals or by adding fertilizer, K will become deficient. Remote sensing can be used to identify K deficiencies in fields.

Potassium is a mobile nutrient within a plant. When K deficiency appears in plants, symptoms usually occur on older leaves first because K is translocated from the older leaves to the younger leaves. When K is deficient, the tips and edges of the older leaves start to turn yellow (chlorosis) (Figure 1). Eventually the leaf margins will die (necrosis) and turn brown.

 Use of Data IKONOS imagery was obtained on July 3rd, 2002 for a farm in east central South Dakota. A false color image was prepared using IKONOS bands 4 (near infrared), 2 (red) and 1(blue). In a false color image, healthy plant vegetation appears darker or brighter red. Upon investigation of the imagery by the farmer, areas in cornfields did not appear as healthy as other areas (Figure 2) and plants in this area has symptoms similar to these shown in Fig. 1. This land manager suspected that these areas might be low in soil K.

 Economic and Environmental Benefits The remote sensed image brought home the extensiveness of the problem and that K management needs to be investigated more closely. Economic benefits from the imagery include solving the K deficiency problem in this and other fields resulting in higher yields. The farmer plans to use this information to improve potassium management in his fields. Reducing K deficiencies may also improve N use efficiency, reduce NO3 leaching to ground water and reduce wind and water erosion.