No abstract

Optical sensors have grown in popularity for estimating plant health, and they form the basis of midseason yield estimations and nitrogen (N) fertilizer recommendations, such as the Oklahoma State University (OSU) nitrogen fertilization optimization algorithm (NFOA). That algorithm uses measurements of normalized difference vegetative index (NDVI), yet not all producers have access to the sensors required to make these measurements. In contrast, most producers have access to smartphones, which can measure fractional green canopy cover (FGCC) using the Canopeo app, but the usefulness of these measurements for midseason yield estimations remains untested. Our objectives were to (1) quantify the relationship between NDVI and FGCC, (2) assess the potential for using FGCC values in place of NDVI values in the current OSU Yield Prediction Model, and (3) compare the performance of NDVI and FGCC-based yield prediction models from the collected dataset. This project, implemented on 13 winter wheat sites over the 2019-2020 growing season, used a range of nitrogen (N) rates (0, 34, 67, 101, and 134 kg N ha−1) to provide different levels of yield. Our results indicated that while NDVI and FGCC are highly correlated (r2 = 0.76), FGCC is not suitable for direct insertion into the current yield prediction model. However, a yield prediction model derived from FGCC provided similar estimates of yield compared to NDVI (Nash Sutcliffe Efficiency = −3.3). This new FGCC-based model will give more producers access to sensor-based yield prediction and N rate recommendations.

Placement of fertilizer in the seed furrow to increase nutrient availability is a common practice in row-crop production. While in-furrow application of fertilizer is widely utilized in the production of winter wheat (Triticum aestivum L.), there is a lack of work evaluating new formulations and nutrient combinations that are available. The objective of this study was to quantify the effects of in-furrow fertilizer products and combinations of products on winter wheat grain yield, nitrogen and mineral concentrations. Trials were conducted across five site-years in central Oklahoma using 11 fertilizer formulations placed in-furrow at the time of planting. In locations that soil test phosphorus (STP) levels or potassium were above sufficiency, the use of in-furrow fertilizers did not improve yield over the control. Inconsistency of response was noted at locations where STP levels were below the critical threshold. While one location showed no response to the addition of P regardless of source, two other locations had significant yield responses from three or more P-containing fertilizers. The addition of both sulphur and zinc resulted in increased yield over the base product at one low STP location. Nutrient concentrations were also influenced in nutrient-limited soils; however, no trends in response were present. Based upon the results of this study, the application of in-furrow fertilizer has the potential to increase winter wheat grain yield and nutrient concentration, when soil nutrients are limiting. As expected the addition of fertilizer when soil test levels are at or above a sufficiency did not increase grain yield.

Nutrient stratification of no-till managed soil can affect soil test analysis levels of plant-available phosphorus (P). Research has suggested sampling to different depths due to soil acidity, but little work has been conducted to investigate any change to sampling recommendations for immobile nutrients. The objective of this study was to determine the soil sampling depth that had the greatest relationship with yield response to fertilizer-P. The depths sampled in this study were 0-5, 0-10, 0-15, 10-30, 5-10, 5-15, 10-15, and 15-30 cm. The results indicated that the top 15 cm of a soil profile had the greatest amount of Mehlich 3 extractable P (M3P) available and that the 5-to-10 and 5-to-15-cm depths had the highest correlation with relative yield. Soil depths outside of the proposed root zone of winter wheat (Triticum aestivum L.) (15-30 cm) had the lowest correlation with yield response. INTRODUCTIONNutrient stratification can affect soil test analysis levels of plant-available phosphorus (P). Increased nutrient stratification occurs in areas where no-till managed soils are not constantly being inverted by tillage practices. Stratification of nutrients has been well documented in notill scenarios (Hansel et al., 2017;Howard et al., 1999;Souza, 2020;Wright et al., 2007). This begs researchers to question if altering current soil sampling strategies could lead to more accurate representation of plant-available nutrients.Research has suggested different depths for sampling for soil acidity for more accurate liming recommendations. Reeves and Liebig (2016) suggested a depth of 7.6 cm for soil pH, as most acidification due to fertilizer inputs occurs Abbreviations: M3P, Mehlich 3 extractable phosphorus.

In the central Great Plains, winter wheat is used for over-winter grazing for cattle and sheep until the late spring months, when livestock are moved to grass pasture. As the popularity of summer cover crops increases, interest in their use in forage production systems increases as well. There is specific interest in the opportunity to increase productivity by the inclusion of a crop grown in the fallow season of winter wheat fields. The intensification of systems in a resource (water and/or nitrogen) limited region could decrease winter wheat forage production influencing a system’s ability to sustain continuous forage production. Nitrogen (N) management could be effective in mitigating negative impacts on winter wheat. The objective of this study is to evaluate the influence of different summer forage crop species and different N management strategies in a multi-year continuous winter wheat forage production system in the central Grain Plains. Increased production of dry matter and crude protein was observed by implementing summer forage crops into a winter wheat forage system. A deleterious effect of summer crops compared to traditional fallow periods was observed but mitigated by the split application of N even compared to the same rate applied at pre-plant.