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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.

Although fungicidal properties of phosphite have been recognized, its use as a fertilizer-P is still being debated. The objective of this study was to evaluate the effect of foliar-applied phosphit...

Nutrient management can reduce crop yield gaps, but available literature is mostly restricted to studies limited in time, geography, or in the number of nutrients evaluated. Our objective was to synthesize long-term experiments evaluating wheat (Triticum aestivum L.) yield and grain-N concentration (GNC) response to N, P, and K fertilizer rates and their interactions. We used data from three long-term (1966–2016) experiments conducted in Oklahoma (USA) comprising 155 site-years for yield (n = 8035) and 90 site-years for GNC (n = 4580). The last year of the experiments was the baseline to de-trend yield and GNC data. We first explored relationships between grain yield and GNC, grain N removal, apparent recovery of applied N in the grain (N recovery), and N-use efficiency (NUE) as affected by the presence and rate of N, P, and K across the entire dataset. Then, we subdivided the dataset into yield-environments based on the different data quartiles, and analyzed it using descriptive statistics, multi-level modeling, differences from the control, and conditional inference trees. Our main findings were: i) wheat yield was negatively related to GNC, but positively associated with N removal, N recovery, and NUE. ii) The co-application of P and, to a lesser extent, K, increased N removal and NUE but decreased GNC. iii) The proportion of variability in yield and GNC explained by fertilizer management increased with an increase in yield-environment. iv) Wheat yield response to N and to P were typically quadratic, although response to P was restricted to high yielding environments. v) Wheat GNC increased linearly with increases in N rate, but decreased with increases in P and K rate. vi) Conditional inference trees suggested that the co-application of P and K improved yields but decreased GNC. The co-application of P and K can increased wheat yield, N removal, and NUE, but the increases in yield were greater than those in N removal, thus decreasing GNC.

Soil acidification limits wheat (Triticum aestivum L.) yields and continues to intensify due to N application and crop harvesting. Applying agricultural limestone (aglime) is the most common remedy for soil acidity but requires a substantial investment. The banding of phosphorus (Banding P) with wheat seed is an alternative temporary solution with lower cash cost than aglime application. However, P2O5 fertilizer costs have increased, and Banding P treatment cannot prevent soil pH reduction. This study compares the net present value (NPV) of aglime and Banding P treatments over varied planning horizons for wheat production in acidic soil updating the work of Kaitibie et al. (2002). For sensitivity analysis, two wheat yield goals, two wheat prices, and two aglime prices were considered. Partial budgeting is used based on estimates from past agronomic research. Banding P treatment was always preferred with a 1‐yr planning horizon and was never preferred with a planning horizon of more than 3 yr. Due to increased P2O5 fertilizer price since 2002, the planning horizons where Banding P treatment now has higher NPV than aglime are shorter than those found by Kaitibie et al.

The relationship between yield potential and N response in long-term cereal production is not well known. The objective of this study was to evaluate the relationship between yield potential (yield level) and N responsiveness in long-term winter wheat (Triticum aestivum L.) and maize (Zea mays L.) field experiments in Stillwater, OK (53 yr), Altus, OK (two trials, 45 yr each), Arlington, WI (49 yr), Shelton, NE (11 yr), Nashua, IA (32 yr), and Kanawha, IA (26 yr). Nitrogen responsiveness or the response index (RI) was determined by dividing the actual grain yield from high N rate plots by the yield from either the 0-N fertilizer check (RI 0-N) or medium N rate plots (RI mid-N). Linear relationships between maximum yield, RI 0-N, RI mid-N, and year were thus examined. For the seven long-term trials comprising 261 yr of site data, yield and N responsiveness were not related whether or not a medium N rate or the check plot (0-N) was used to determine RI. Because yield level and N responsiveness are independent, and both impact N demand, using both should assist in formulating more accurate fertilizer N recommendations.

This research was conducted to investigate the potentials of normalized difference vegetation index (NDVI), a Soil-Plant Analyses Development (SPAD) chlorophyll meter, and leaf nitrogen (N) concentration [% dry matter (DM)] for rapid determination of N status in potted geraniums (Pelargonium ×hortorum). Two F1 cultivars were chosen to represent a dark-green leaf cultivar, Horizon Deep Red, and a light-green leaf cultivar, Horizon Tangerine, and were grown in a soilless culture system. All standard 6-inch (15.24-cm) pots filled with a medium received an initial top-dress application of 5 g controlled-release fertilizer (15N–9P–12K), then plants were supplemented with additional N in the form of urea at 0, 50, 100, or 200 mg·L−1 N every few days to produce plants ranging from N-deficient to N-sufficient. The NDVI readings of individual plants from a NDVI pocket sensor developed by Oklahoma State University were collected weekly until the flowering stage. Data on flower traits, including number of pedicels (NOP), number of full umbels per pot (NOFU), total number of flowers per pot (TNF), number of flowers per pedicel (NOF), and inflorescences diameter (IFD), were collected 3 months after initial fertilizer treatment. After measuring flower traits, pedicels were removed from each pot, and SPAD value, NDVI, and leaf N concentration (g·kg−1 DM) were measured simultaneously. Cultivar and N rate significantly affected all but two flower and one N status parameters studied. The coefficient of determination R2 showed that NOP, NOFU, and TNF traits were more related to the N rates and the status parameters studied for ‘Horizon Tangerine’ than for ‘Horizon Deep Red’. For the latter cultivar, NOP and TNF traits were highly related to NDVI and SPAD values than N rates and leaf N content parameters. Correlation analysis indicated that the NDVI readings (R2 = 0.848 and 0.917) and SPAD values (R2 = 0.861 and 0.950) were significantly related to leaf N content (g·kg−1 DM) between cultivars. However, sensitivity of the NDVI and chlorophyll values to N application rate in geranium was slightly less than leaf N content. Strong correlations (R2 = 0.974 and 0.979, respectively) between NDVI and SPAD values were found within cultivars. The results demonstrated NDVI and SPAD values can be used to estimate N status in geranium. Because the pocket NDVI sensor will be cheaper than the SPAD unit, it has an advantage in determining N content in potted ornamentals.

This study was conducted to formulate an in-season nitrogen (N) fertilization optimization algorithm (NFOA) to estimate midseason N rates that maximize corn (Zea mays L.) growth and minimize fertilizer inputs. Treatments included: a zero kg N ha−1; three treatments of 134 kg N ha−1 fixed rate applied in split, preplant, or sidedress; two treatments of 67 kg N ha−1 fixed rate preplant or sidedress applied; three NFOA-based midseason N rates (RI-NFOA, RICV-NFOA, flat-RICV-NFOA) with (67 kg N ha−1) and without preplant N; and two resolutions (0.34 and 2.32 m2) tested for RICV-NFOA only. With the 67 kg N ha−1 preplant application, midseason RI-NFOA-based N rates resulted in an N use efficiency (NUE) of 65% while the 134 kg N ha−1 fixed rate split applied had 56% NUE. Using the RICV-NFOA, NUE and net returns to N fertilizer were higher when spatial variability was treated at 2.32 m2 resolution.

Midseason fertilizer N recommendations in corn (Zea mays L.) and wheat (Triticum aestivum L.) are not consistent from one region to the next. Preplant soil testing, yield goals, economic optimums, chlorophyll meters, and optical sensor-based yield prediction models are limited regionally. The objective of this paper is to introduce an applied approach for applying preplant N fertilizer in automated gradients used for determining midseason N rates based on plant response. This approach assumes that midseason biomass estimated using normalized difference vegetation index (NDVI) sensor readings is directly related to corn and wheat grain yield, and that delaying applied N until midseason (eight-leaf stage in corn and Feekes 5 in winter wheat) can result in near-maximum yields. The ramped calibration strip (RCS) applicator applies 16 different incremental N rates (3-to 6-m intervals), over 45 to 90 m (number of rates, intervals, and distances can be adjusted depending on the crop). Because the RCS is superimposed on the farmer practice, producers can examine plant responsiveness over the range of rates to determine the optimum topdress N rate. The point where midseason growth differences no longer exist is the topdress N rate. Recording distance is required as you walk the RCS since distance is associated with an incremental N rate. Where adequate but not excessive preplant N is available, the ramp interpolated rate provides an applied method to determine how much midseason N should be applied to achieve the maximum yields based on growth response evidenced within the RCS.

Crop management strategies that improve Nitrogen Use Efficiency (NUE) increase profits while reducing the detrimental effects on the environment associated with fertilizer nitrogen (N) loss. Effective N management should include several critical factors that are very interrelated. A study was conducted at the Panhandle Research and Extension Center, Goodwell, OK to evaluate the effects of multiple nitrogen management practices including N rate, source, time of application, methods of fertilizer and residue incorporation over a long period of time on grain yield, N uptake and NUE in irrigated corn. Fourteen treatments were evaluated in a randomized complete block design with three replicates. Results of data analyzed on the individual year and averages of all years showed that grain yield and N uptake were improved with N rates and N management practices compared to checks. Both N recovery and efficiency of use were high for the 118 kg N ha− 1 rate.

Sensor based nitrogen (N) management technology has helped to improve fertilizer recommendations for various crops. The objective of this study was to estimate the in-season yield potential (YP0) of grain sorghum (Sorghum bicolor L. Moench) using a hand held optical sensor. This experiment was conducted with four levels of N (50, 100, 150 and 200 kg ha−1) and three application timing (Preplant, topdress and split) arranged in a randomized complete block design with three replications at three locations, in Oklahoma in 2004 and 2005. Sensor readings were taken using red (650 ± 10 nm) and green (550 ± 12.5 nm) sensors at sorghum growth stages 2, 3, 5, 6 and 7. Results from statistical analysis have shown that 75 and 77% of the variation in sorghum grain yield was explained by red and green Normalized Difference Vegetation Index (NDVI), respectively at growth stage 3. Similarly, grain N content was correlated to both green and red (coefficient of determination, r2 = 0.61) NDVI readings at growth sta...

Response to fertilizer is a function of several factors including weather, soil condition, previous year yield level, and the actual amount of fertilizer applied. The main objectives of this paper were to evaluate if cumulative precipitation (PPT), growing degree days (GDD), soil moisture (SM) and fertilizer can explain variability in long-term grain yield and fertilizer response index (RI); to assess if demand for N fertilizer is greater the ensuing year given low or high yield levels in the previous year; and to evaluate if rainfall distribution coupled with the previous year grain yield level and RI of winter wheat (Triticum aestivum L.) improves the predictability of ensuing year RI. Data from two long-term experiments located at Stillwater and Lahoma, OK were used in this report. The experimental design was a randomized complete block with four replications. Twelve (Stillwater) and thirteen (Lahoma) treatments that consisted of annual application of N, P and K inorganic fertilizers were included although selected treatments were used to address the objectives. Soil moisture at 75 cm depth was a better predictor of both grain yield (R 2 = 0.35) and RI (R 2 = 0.66) at Stillwater while SM at the 60 cm depth was significantly correlated to grain yield (R 2 = 0.39) at Lahoma. For years where the previous year yield was low, the ensuing year had a low RI while in many years where the previous yield was high; the ensuing year had a high RI in both experiments. The practical significance of these findings is that producers could theoretically adjust preplant or in-season topdress N fertilizer rates by considering the previous year yield level and the degree of response to N.

Field average based recommendations have been a common practice for recommending the major crop nutrients nitrogen (N) and phosphorus (P). The problem is yield will not be the same from year to year with application of the same amount of recommended rate of fertilizer. The objectives of this study were to demonstrate how recommendations generated using nutrient response experiments were dynamic; and to assess the relative contribution of temporal variability, N and P fertilizers on winter wheat grain yield and N concentration. Twelve factorial combinations of four N (0, 56, 112, and 168 kg ha−1) and three P (0, 14.5, and 29 kg P ha−1) rates were evaluated in a randomized complete block design with three replications at Perkins, Oklahoma. To address the first objective, ANOVA and orthogonal polynomial contrasts were used. To address the second objective, a ten predictor variable multiple linear regression model with two quantitative variables and their interaction (N, P and N×P) and seven-year var...

Foliar applications of fertilizer phosphorus (P) could improve use efficiency by minimizing soil applications. Nine experiments were conducted in 2002 and 2003 to determine foliar P rates and appropriate growth stages for application. Treatments comprised of 10 factorial combinations of three foliar P application timings and four rates of foliar P. Foliar application times were V4 (collar of fourth leaf visible), V8 (collar of eighth leaf visible), and VT (last branch of the tassel completely visible but silks not yet emerged) corn growth stages. Foliar P rates were 0, 2, 4, and 8 kg ha−1. Foliar P applied at the VT growth stage improved grain and forage P concentration, which was reflected in increased grain yield in some of the experiments. A foliar P rate of 8 kg ha−1 improved yield to some extent and forage and grain P concentration more than the smaller rates. The results suggest that foliar P could be used as an efficient P‐management tool in corn when applied at the appropriate growth stag...

As research intensifies on developing precision agricultural practices for corn (Zea mays L.) production, an important component will be to identify the scale at which these practices should be implemented. We hypothesized that optical sensing can be used to measure individual corn plant biomass and N uptake. A 3-yr study was conducted at three locations in Oklahoma. Optical sensor readings of normalized difference vegetation index (NDVI) and plant height measurements were collected on individual corn plants at various growth stages ranging from V8 (collar of eighth leaf unfolded) to VT (last branch of the tassel is completely visible) and correlated with individual plant biomass, forage yield per unit area occupied by the plant, and N uptake of that plant. Individual plant height measurement, collected before reproductive growth, was a good predictor of plant biomass across the six site years of the study (r 2 = 0.81). The index of NDVI X plant height provided the highest correlation with by-plant forage yield on an area basis. Optical sensor and plant height measurements collected at the V8 to V10 (collar of 10th leaf unfolded) growth stage can distinguish individual plants and provide information as to their biomass accumulation and N uptake. This research demonstrates that by-plant information can be collected and used to direct high resolution N applications. The index, NDVI X plant height, may be used to refine midseason fertilizer N rates based on expected N removal and by-plant measurements at or before V10.

Field-average based recommendations have been a common practice for nitrogen (N) rate recommendations. The problem is that, even when the same amount of N fertilizer is applied at the recommended rate, yields differ from year to year, the result being poor use efficiency. Reduced fertilizer use efficiency can result in unnecessary costs to producers, especially with a likely price of US$ 1·10 per kilogram of N fertilizer anticipated within the next few years, largely due to rising oil and natural gas prices. It has been estimated that by the year 2025 the consumption of N fertilizer will increase by 60–90%, with two-thirds of this being applied in the developing world. In light of this, methods that increase N use efficiency and profitability of farms, while reducing environmental impact, are no longer simply commendable but required in developing countries. The present review assesses the temporal variability in winter wheat with respect to N nutrition and presents improved methods, including the calibration stamp (CS), N-rich strips (NRS) and ramped calibration strips (RCS) to overcome this variability. These methods can be used either as visual tools or along with NDVI handheld sensors for accuracy. Unlike the CS and NRS, the RCS method is designed to include more pre-plant N rates in strips to improve top-dress N estimation. Hypotheses as backgrounds to these methods have been developed and tested in the USA and Mexico. However, the simplicity of these technologies suggests that many farmers in both developed and developing countries can readily apply them.

Soil acidity has become a major yield-limiting factor in cropping systems of the Southern Great Plains, in which winter wheat (Triticum aestivumL.) is the predominant crop. Sunflower (Helianthus annuusL.) is a strong rotational crop with winter wheat due to its draught and heat tolerance. However, the effects of low soil pH on sunflower productivity have not been explored. The objective of this study was to determine the critical soil pH and aluminum concentration (AlKCl) for sunflower. Sunflower was grown in a randomized complete block design with three replications of a pH gradient ranging from 4.0 to 7.0 at three locations with varying soil types. Soil pH was altered using aluminum sulfate (Al2(SO4)3) and hydrated lime (Ca(OH)2). Plant height, vigor, and survivability were all negatively affected by soil acidity. Sunflower yield was reduced by 10% at or below soil pH 4.7 to 5.3 dependent upon location and soil type. Levels ofAlKClabove 6.35 mg kg−1reduced seed yield by 10% or greater. We concluded that sunflower may serve as a better rotational crop with winter wheat under acidic conditions when compared to other adaptable crops.

Grain sorghum (Sorghum bicolorL.) has become a popular rotation crop in the Great Plains. The transition from conventional tillage to no-tillage production systems has led to an increase in the need for crop rotations. Some of the soils of the Great Plains are acidic, and there is concern that grain sorghum production may be limited when grown on acidic soils. The objective of this study was to evaluate the effect of soil pH for grain sorghum production. Potassium chloride-exchangeable aluminum was also analyzed to determine grain sorghum’s sensitivity to soil aluminum (Al) concentration. The relationship between relative yield and soil pH was investigated at Lahoma, Perkins, and Haskell, Oklahoma, USA with soil pH treatments ranging from 4.0–7.0. Soil pH was altered using aluminum sulfate or hydrated lime. Soil acidity reduced grain sorghum yield, resulting in a 10% reduction in yield at soil pH 5.42. Potassium chloride-exchangeable aluminum levels above 18 mg kg−1resulted in yield reductions of 10% or greater. Liming should be considered to increase soil pH if it is below these critical levels where grain sorghum will be produced.

Long-term experiments play a vital role in revealing dynamic soil and weather processes that directly influence sustainable crop production and ecosystem health. The objective of this review paper is to present one of the oldest long-term continuous winter wheat (Triticum aestivum L.) experiments, the Magruder Plots, and their contribution to the scientific community regarding questions of yield response to amendments, yield stability, percentage organic matter (OM) lost over time, soil nutrient status, microbial activity, weed population, and information on the economic return from winter wheat production. Alexander C. Magruder initiated the experiment in 1892 and is in progress to date. The original plot was started to evaluate wheat production on native prairie soils without fertilization. After 6 yr the principal investigator split the initial plot into two and fertilized one half with cattle manure. The experiment was then modified to include 10 treatments in 1930 by Dr. Horace J. Harper to answer several soil fertility related questions. Since 1947, six treatments have remained intact that evaluate simple combinations of manure, and inorganic N, P, K, and lime. Following 114 yr of continuous winter wheat production under conventional tillage, the check plot that has never received any fertilizer addition continues to produce wheat grain yields of >1 Mg ha -1 . Despite the decline in soil organic matter from 4 to 1% during this time period, wheat grain yields continue to show slight increases with time, likely due to improved genetics. While continuous wheat without rotation is not recommended, this 114-yr study documents the feasibility.