Abstract
Core Ideas Early season N deficiencies in corn are hard to recognize, or they appear later in the season, and are too late to correct the deficiency. Indicator crop growing over the winter and early spring cycle makes perfect sense in terms of being able to detect N deficiencies earlier in the growing season. Indicator crop concept could apply to other cereals and potentially cover crops. Use of optical reflectance sensors has proven to determine optimum N fertilizer requirements and direct in‐season N fertilizer applications. However, corn (Zea mays L.) producer adoption of this technology has been slow due to limited time to determine N deficiencies and apply N fertilizer in‐season. A study was established in north‐central Oklahoma to investigate the N fertilizer response of winter wheat (Triticum aestivum L.) and spring barley (Hordeum vulgare L.) as indicator crops with N fertilizer applied at sufficient (168 kg N ha−1) and zero N rates and to estimate optimal early season N fertilizer application rates of the subsequent corn crop. In the spring, corn was planted adjacent to the indicator crops and harvested to determine the agronomic optimum N rates at 100 and 95% of optimum yield and response of N fertilizer at harvest (RIHarvest). In‐season response of the indicator crops was determined using the normalized difference vegetative index (RINDVI) and was used to provide input values to calculate the algorithm N recommendations of the corn crop. Data analysis determined that positive relationships, though not significant, were observed between RIHarvest and RINDVI at Feekes 5/6 and 7 in wheat and Feekes growth stage 5 of barley. Significant relationships between optimum N rates and algorithm N recommendations were observed; however, the slopes of the relationships were negative, which was not to be expected. The potential of indicator crops to predict the early season response of corn to N fertilizer is unique and could help refine N management strategies.
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