Predicting early season nitrogen rates of corn using indicator crops

Abstract

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 diff erence 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.