A no-till (NT) production system has potential to reduce soil erosion, fossil fuel consumption, and greenhouse gas emissions compared with a conventional till (CT) system. Nitrogen fertilization (four to six N rates) and tillage system (CT and NT) effects on irrigated, continuous corn (Zea mays L.) yields were evaluated for 5 yr on a clay loam soil to determine the viability of the NT system and N needs for optimum yield. Corn in both NT and CT systems responded similarly to available N supply. Grain yields were significantly increased by N fertilization in both tillage systems, with a 16% higher average maximum yield in the CT than in the NT system. Grain yields were near maximum with an available N (soil 1 fertilizer N) level of 276 and 268 kg N ha 21 in the CT and NT systems, respectively. Nitrogen fertilizer use efficiency (NFUE) averaged 43% over N rates and years for both systems. Total N required to produce 1 Mg of grain at maximum yield averaged 19 and 20 kg N Mg 21 grain for the CT and NT systems, respectively. Corn residue increased with increasing N rate with no difference in residue production between tillage systems. The lower grain yield with NT probably resulted from the slow early spring development and delayed tasseling compared with the CT system as a result of cooler spring soil temperatures in the NT system. No-till, irrigated, continuous corn production has potential for replacing CT systems in the central Great Plains area, but with reduced yield potential. Current N fertilizer recommendations for CT corn based on yield goal may need to be modified for NT to account for the lower yield potential and slightly higher N requirement.

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Farm managers are becoming increasingly aware of the spatial variability in crop production with the growing availability of yield monitors. Often this variability can be related to differences in soil properties (e.g., texture, organic matter, salinity levels, and nutrient status) within the field. To develop management approaches to address this variability, high spatial resolution soil property maps are often needed. Some soil properties have been related directly to a soil spectral response, or inferred based on remotely sensed measurements of crop canopies, including soil texture, nitrogen level, organic matter content, and salinity status. While many studies have obtained promising results, several interfering factors can limit approaches solely based on spectral response, including tillage conditions and crop residue. A number of different ground-based sensors have been used to rapidly assess soil properties "on the go" (e.g., sensor mounted on a tractor and data mapped with coincident position information) and the data from these sensors compliment image-based data. On-the-go sensors have been developed to rapidly map soil organic matter content, electrical conductivity, nitrate content, and compaction. Model and statistical methods show promise to integrate these groundand image-based data sources to maximize the information from each source for soil property mapping.

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