Background In the Great Plains, nitrogen (N) is usually applied before or shortly after wheat is planted. If conditions are overly dry, low soil moisture availability may result in reduced yields. Yields might also be reduced if too much N is applied to water stressed areas. Remote sensing can be used to identify areas that require additional N.

 Use of Data IKONOS imagery was obtained on July 14th, 2001 (Fig. 1) and June 11th, 2002 (Fig. 2) for wheat fields located east of Pierre, SD. False color images for both dates were prepared using IKONOS bands 4 (near infrared), 3 (red) and 2 (green). In a false color image, healthy plant vegetation appears darker or brighter red. Wheat symptomatic of N deficiency is typically yellow and may be stunted.

In 2001, research was conducted to test the feasibility of using remote sensing to identify N deficiency in wheat. Experimental check strips were left with no N application. Areas where N was not applied are evident in the footslope area of the image , but not in the backslope (Figure 1). These data suggest that at the time of image acquisition (July 14th, 2001), wheat growing in the footslope area was N stressed while in the backslope/summit area unfertilized plantswere not N stressed.

In 2002, the study was repeated. Reflectance differences between wheat fertilized with different N rates were not detected Figure 2). The lack of N response was attributed to the drought conditions. This study showed that under drought conditions, additional nitrogen applications do not make a difference.

 Economic and Environmental Benefits Imagery may be used to detect N deficiencies in wheat (Figure 1). Under low water conditions, plant growth may be slow, crop reflectance in fertilized and unfertilized treatments may be similar and plants most likely will not respond to N. Remote sensing may identify N deficient areas of the landscape. In these areas, it may be possible to increase yield by adding N.