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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.

The process of improving crop management inputs by use of remote sensing devices is a new technology. This study presents the use of the normalized-difference vegetative index (NDVI) combined with ...

We combined field studies to regional soil databases with the objective of presenting a protocol to forecast regional gains in winter wheat (Triticum aestivum L.) forage and grain yield and revenue, from liming or selecting a variety tolerant to acidic soils. First, we developed forage and grain yield response curves to soil pH using a variety by soil pH study conducted during 3 yr (2013–2015) at two Oklahoma locations. Second, we used a database of soil pH samples representing 93% of the wheat growing region of the state (n = 11,905) coupled with 15-yr average county yield and harvested area to estimate potential gains for grain-only and dual-purpose scenarios. Relative grain yield maximized at soil pH of 5.8 for sensitive varieties and 4.8 for tolerant varieties. Forage yield maximized at soil pH of 6.0 for sensitive varieties and 5.5 for tolerant varieties. About 35% of the region had pH limiting to dual-purpose and 28% to grain-only production. Liming could improve grain-only statewide yield in 0.14 Mg ha–¹ and revenue in US$19 ha–¹, and adoption of tolerant varieties could increase yield in 0.11 Mg ha–¹ and revenue in $10 ha–¹. Liming could improve dual-purpose revenue in $37 ha–¹ and variety selection in $28 ha–¹ due to improved yield and forage. Potential additional statewide wheat production resulting from variety selection is 53,800 Mg and from liming 82,500 Mg. Our protocol can be used to aid development of agricultural policies and research prioritization at regional levels where acidic soils are prevalent.

Unfavorable weather conditions and lack of appropriate farm machinery often delay N application. This results in nitrogen (N) deficiency during the vegetative and early reproductive growth stages of winter wheat. The objective of this study was to evaluate the impact of N application timings (from tillering to flag leaf growth stages) on winter wheat grain yield and protein. The study was conducted across 12 site–years in Oklahoma, US. The treatments included a non-fertilized check, a pre-plant application of 100 kg N ha−1, and ten in-season application timings at 100 kg of N ha−1. The in-season treatment applications were initiated at the point when an N deficiency was visually identified by comparing the pre-plant treatment to the non-fertilized check. The treatments were applied in a progressive order every seven growing degree days (GDD > 0 °C) until a cumulative GDD of 63 was reached after visual deficiency (DAVD). All in-season treatments increased grain yield and protein as compared to the non-fertilized check, showing that N was a yield-limiting factor. The nitrogen applications made post Feekes 8 decreased grain yield when compared to pre-plant applications. Across this data set, that timing corresponded to a range of 21 to 63DAVD. The results suggested that forgoing N application until the growth stage Feekes 7, even when the visual N deficiency was highly apparent before that stage, had no negative impact on the yield, and it even increased the yield as compared to the pre-plant application in some cases. The plant developmental stage at which the N application takes place is more critical than the level of N deficiency. Our results show that N fertilizer applications should be made posteriorly to the crop dormancy to maximize both yield and protein, and that plants can recover from N deficiency when applications are made until the late-vegetative phase (Feekes 7). This document shows that winter wheat producers have a much wider N application window than traditionally believed.

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.

Subsurface drip irrigation (SDI) is a micro-irrigation system that could be adopted by producers in the semi-arid regions around the world for efficient use of water. Yet, several crop management issues related to SDI system need to be addressed to assess the feasibility of SDI. One such issue is the impact of crop row placement on crop performance, irrigation water use efficiency and yield under SDI. A study was conducted in the Southern U.S. Great Plains, in which drip tape laterals were buried 30 cm deep at 153 cm spacing, with two crop rows planted at 76 cm spacing, and irrigated with one tape. Corn (Zea mays L.) and grain sorghum (Sorghum bicolor L.) rows were offset from equidistance from the drip tape by 0, 8, 15, 23, and 38 cm using high precision guidance system (real time kinematics). This resulted in 5 treatments and 4 replications. This treatment structure was imposed on three irrigation (high, medium and low) regimes. Analysis of Variance showed no interaction between offset treatments and irrigation or year in corn and grain sorghum yields. The row offset did not impact the overall yield as the yield loss in row farther from the tape was compensated by the increased yield in row moved closer to the tape. The yield distribution ranged from 50% in both rows for 0 cm offset to 59% in row closer to the tape for 38 cm offset. The findings of this study suggests that while driver accuracy is important to maintain equal yields in neighboring crop rows, the overall yields are affected more by irrigation and climatic conditions and not by the row offsets with respect to SDI tape. This data suggests that SDI can be successful regardless of access to high precision guidance systems.

Information is limited on using winter legumes as a source of nitrogen (N) inter-cropped with switchgrass in the southern Great Plains of the United States. The objectives of this study were to evaluate N contribution of several winter legumes to switchgrass, and to determine the influence of winter legumes on biofuel quality and soil fertility status. Field experiments were conducted at two locations in Oklahoma in which six winter legumes and four rates of N fertilizer were studied over a three-year period. Winter legumes did not increase switchgrass forage yield, cellulose, lignin, and hemicellulose concentrations at any location. Soil organic matter (OM), nitrate-N (NO3-N), soil test phosphorus (P), soil test potassium (K), and soil pH remained unchanged. In contrast, applying inorganic N only increased switchgrass yield. This study demonstrated that southern Great Plains may not be conducive to utilizing legumes as the primary N source for switchgrass.

The GreenSeeker™ optical sensor is used as a management decision aid in many crops across the world. This sensor measures the normalized difference vegetative index (NDVI). It has been observed that when the by-plot coefficients of variation (CV) from the GreenSeeker™ sensor NDVI readings in winter wheat (Triticum aestivum L.) was incorporated into the midseason calculation of the response index (RI), RI at harvest was better predicted than with NDVI alone. This study further evaluated the use of CV's collected from both small 1.48 m2 and large 17.0 m2 areas. Trials consisted of 3 seeding rates by 4 nitrogen rates. Results from this study showed that CV from NDVI readings and plant population were negatively correlated. Improved prediction of RI by utilizing CV was not found. It was however observed that when CV's were less than 5.0 and NDVI values were greater than 0.80 the RI was less than 1.2.

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.

Nitrogen (N) deficiencies can significantly reduce plant growth as well as flower quantity and quality. However, excessive N application leads to increased production costs and may cause water contamination as a result of runoff. Ground-based remote sensing of plant chlorophyll content offers the possibility to rapidly and inexpensively estimate crop N status. The objective of this study was to test the reliability of three different Normalized Difference Vegetation Index (NDVI) measuring methods and SoilPlant Analyses Development (SPAD) chlorophyll meter values as indicators of geranium (Pelargonium ·hortorum L.H. Bailey) N status. Two potted geranium cultivars, Rocky Mountain White and Rocky Mountain Dark Red, were supplied with N at 0, 50, 100, and 200 mg L levels, respectively. NDVI readings were measured at 45 cm above the canopy or media of individual plants or 45 cm above the canopy of a group of plants (four plants treated with the same N rate were placed together). Significant correlations existed between indirect chlorophyll content measurements of SPAD values and NDVI readings regardless of four-pot group or single-pot measurements with N application rates and leaf N concentration. Using a cross-validation technique in discriminant analysis, 70.8% to 79.2% of sample cases were correctly categorized to the corresponding N statuses including very deficient, deficient, and sufficient. Therefore, ground-based, non-destructive measurements of a chlorophyll meter and pocket NDVI unit were able to indicate N status. Considering that flower color can interfere with NDVI measurements, the chlorophyll meter may better determine N content when flowers are present. Geraniums (Pelargonium spp.) are considered one of the most valuable potted plants produced in the United States with an estimated wholesale value of over $100 million in 2010 for both seed and vegetatively produced plants (U.S. Department of Agriculture, 2010). Geraniums are typically grown under greenhouse conditions during winter and spring to respond to the high demand of spring commercial markets. Nitrogen use efficiency is of great concern in floriculture production under greenhouse conditions. Nitrogen fertilization requirements and plant tissue analysis standards for geraniums are available (Biamonte et al., 1993; Dole and Wilkins, 2005; Kofranek and Lunt, 1969; Krug et al., 2010; Mills and Jones, 1997; Price et al., 1997). However, monitoring N status based on leaf sampling and foliar analysis is timeconsuming and expensive. Because N is a major nutrient affecting plant chlorophyll content (Moorby and Besford, 1983), measuring chlorophyll concentration can be a useful index to assess the growth status and leaf N level of a plant (Seemann et al., 1987). Ground-based remote sensing of plant chlorophyll content and concentration offers the possibility of rapidly estimating crop N status and plant quality. For several horticultural crops, leaf N and chlorophyll concentration were found to be strongly correlated using a SPAD chlorophyll meter (Neilsen et al., 1995; Shaahan et al., 1999; Vos and Bom, 1993; Wang et al., 2004; Westerveld et al., 2003; Zanin and Sambo, 2006). In addition, the NDVI index is commonly used to differentiate plant properties such as chlorophyll, biomass, and plant nutrition (Raun et al., 1998). Use of an NDVI index is widely accepted in large-scale agronomic field production and some horticultural crops (Baghzouz et al., 2007; Bell et al., 2004; Carrillo, 2006; Clay et al., 2006; Eitel et al., 2008; El-Shikha et al., 2007; Penuelas et al., 1994; Xiong et al., 2007) but has limited reports for greenhouse settings. Based on assessing variability of reflectance measurements on plant growth and physiological conditions, using a statistical approach to extract useful information could be used to improve crop performance (Parihar et al., 2003). Discriminant analysis, a multivariate statistical classification model technique, is a powerful tool for selecting the predictor variables that allow the discrimination between different group levels and for classifying cases into different groups with a better than chance accuracy (Fernandez, 2010). It has been used successfully to separate N and water stresses in Helianthus annuus L. (Penuelas et al., 1994), evaluate N status in Triticum aestivum L. (Filella et al., 1995), assess water and N stresses in Zea mays L. (Karimi et al., 2005a, 2005b; Strachan et al., 2002), and evaluate N and potassium deficiencies in Olea europaea L. orchards (Gomez-Casero et al., 2007). To our knowledge, there is no report about the detection of N status in potted geraniums to predict N fertilization needs using discriminant analysis. In a previous experiment, Wang et al. (2012) found that NDVI and SPAD values can be used to reflect N status in geranium, and that cultivar and N rate can significantly affect flower quantity and quality. The objective of this study was to test the reliability of three NDVI measurements and SPAD values as indicators of geranium N status. Through assigning the aforementioned NDVI and SPAD values to predefined N levels based on leaf N content, we also conducted discriminant analysis with the purpose of integrating information as a tool to classify different N statuses. Materials and Methods Plant material and growth conditions. On 13 Dec. 2010, plugs (four to eight leaves) of two commercial geranium (Pelargonium ·hortorum L.H. Bailey) cultivars, Rocky Mountain White and Rocky Mountain Dark Red, were obtained from Park Seed Co. (Greenwood, SC). Plugs were transplanted into standard (15.2-cm diameter and 1.35-L volume) pots with 0.35 kg Sun GR MetroMix media (Sun Gro Horticulture, Bellevue, WA) 4 weeks later. Both cultivars belong to the light-green leaves-type geraniums Received for publication 20 Oct. 2011. We express our thanks to Mr. Stephen Stanphill for technical support in this research. We thank Dr. Janet Cole and Dr. Eric Stafne for kindly revising this manuscript before submission. We express our deep gratitude to the constructive advice from the three anonymous reviewers and Sun Gro Horticulture for the media donation. Mention of trade name or commercial products is solely for the purpose of providing specific information and does not imply recommendation or endorsement by Oklahoma State University. Approved for publication by the director, Oklahoma Agricultural Experiment Station. To whom reprint requests should be addressed; e-mail bruce.dunn@okstate.edu. HORTSCIENCE VOL. 47(3) MARCH 2012 343 CROP PRODUCTION

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.

Although nitrogen use efficiency (NUE) of small grains is well documented at 33% worldwide, there has been little research relating NUE to yield factors. This study examined the relationship between NUE and the response index at harvest (RIHARVEST) of winter wheat (Triticum aestivum L.). Yield data from a long-term fertility study established at Lahoma, Oklahoma in 1971 was used to explore the relationship. In this report, six nitrogen (N) rates at non-limiting levels of P and K were evaluated. Regression analysis showed a positive relationship between NUE and RIHARVEST for all years across all N rates (r2 = 0.37). But this relationship was improved (r2 = 0.45) when both RINDVI and RIHARVEST were included in the model. The linear relationship between NUE and RIHARVEST was significantly improved, when yield data and corresponding NUE were separated according to the annually applied fixed N rate. As the N rate increased the resulting slope of the relationship between NUE and RI was reduced. These a...

This study was conducted to determine the scale at which spatial variability should be treated using an in-season nitrogen fertilization optimization algorithm (NFOA). Treatments included variable nitrogen (N) rate applications at three resolutions (0.84, 13.4, and 26.8 m2), two treatments of 90 kg N ha−1 fixed rate applied preplant or midseason, and a check plot. Treatments were arranged in a completely randomized design with three replications established at two locations for three years. On average, the NFOA-based N rates achieved a higher N use efficiency (NUE) of 41% compared with only 33% of the 90 kg N ha−1 fixed rate applied midseason. The highest NUE among the NFOA-based N rate treatments was 56% at 13.4 m2 resolution. These benefits were attributed to a large reduction in NFOA-based N rate recommendations. Determining midseason N rate requirements using NFOA at 13.4 m2 resolution resulted in increased NUE and net return to N fertilizer.

Identifying the optimum resolution where differences in corn (Zea mays L.) grain yields are detectable could theoretically improve nitrogen (N) management, thereby resulting in economic and environmental benefits for producers and the public at large. The objective of this study was to determine the optimum resolution for prediction of corn grain yield using indirect sensor measurements. Corn rows, 15–30 m long, were randomly selected at three locations where the exact location of each plant was determined. In 2005 and 2006, four of eight rows at each location were fertilized with 150 kg N ha−1 as urea ammonium nitrate (28% N). A GreenSeeker™ optical sensor was used to determine average Normalized Difference Vegetation Index (NDVI) across a range of plants and over fixed distances (20, 40, 45.7, 60, 80, 91.4, 100, 120, 140, 160, 180, 200, 220, and 240 cm). Individual corn plants were harvested and grain yield was determined. Correlation of corn grain yield versus NDVI was evaluated over both increasing di...

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.

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 . 1M g ha 21 . 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.

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...

Nitrogen use efficiency (NUE) in cereal grain production is estimated to be 33% throughout the world, and can be lower when N is applied in single, pre-plant applications compared with split N applications. This study was conducted to evaluate tillage system and anhydrous ammonia (AA) application methods on yield, N uptake, and NUE in hard red winter wheat (Triticum aestivum L.), using a narrow (10 cm) nozzle spacing on a V-blade (Noble or sweep blade) applicator and wide (46 cm) nozzle spacing on a knife applicator. Over the four-year period evaluated, conventional tillage was significantly higher in grain yield in five of eight site years over no-till. However, no-till was significantly higher in grain yield at Lahoma in 2003 where the highest overall grain yield was observed. Mixed results were evaluated in NUE for tillage; four site years of no significant differences between tillage systems and the other four site years split evenly between conventional-till and no-till. The V-blade improved...

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...

Bed planted wheat systems offer a new alternative for the traditional wheat producer to provide opportunities for crop rotation, more efficient use of water, and new techniques of nutrient management. This study was conducted to determine if planting winter wheat (Triticum aestivum L.) in Oklahoma on raised beds can maintain grain yields while providing more options in the cropping system. Experiments were conducted at Hennessey and Lake Carl Blackwell, Oklahoma in 2000–2001 and 2001–2002 cropping seasons. The experiments consisted of a factorial combination of two planting systems (bed and conventional), four winter wheat varieties (‘Custer’, Jaggar', ‘Intrada’ and ‘2174’), and three nitrogen (N) rates (0, 67, and 134 kg ha− 1). The experimental design was a randomized complete block with three replications. Grain yield was not statistically different between the bed and conventional planting systems for three of four site years. However, there was a trend for the conventional wheat production s...

Two experiments were conducted in 2003 – 2005 at Hennessey and Lake Carl Blackwell, Oklahoma, to determine the effect of row configuration in bed and flat planting systems in dryland winter wheat. In the bed and flat systems, 8 and 12 treatments were evaluated that included a factorial combination of 2-varieties (“Jagalene” and “2174”), 2-N rates (0 and 100 kg ha−1) and row configurations. The row configurations were 2- and 3-row on a 75 cm bed. With 2- and 3-row per bed, 30 and 15 cm row spacing were used, respectively. In addition the traditional configuration of a solid stand with 15 cm row spacing was evaluated in the flat system. In four of six site years, bed wheat (either 2- or 3-row per bed) resulted in yields equal to flat planted wheat (15 cm row spacing). No differences in wheat grain yield were found when planting either 2- or 3-row per bed, or on the flat. However, both 2- and 3-row per bed resulted in increased yields when compared to 2- and 3-row configurations without beds. This s...

Improving crop management inputs with remote sensing devices is an emerging technology. This study documented the progression of the normalized difference vegetative index (NDVI) during the life cycle of corn (Zea mays L.), evaluated the spatial variability of corn growth in terms of the CV (calculated from NDVI readings), and documented the relationships between NDVI,CV (calculated from NDVI), and grain and biomass yields and plant density. Four rows, 30 m in length, from two locations during 2 yr were randomly selected for this study. An optical sensor was used to collect NDVI readings at multiple growth stages during the life cycle of corn. The NDVI increased with progression of vegetative growth stages until V10, where a plateau was encountered, followed by a decline in NDVI after the VT growth stage. Coefficient of variation data from the NDVI readings revealed two dominant peaks during the life cycle of corn, one between the V6 and V8 growth stages and the second during the late reproductive growth stages. The CV data illustrated that the greatest variation expressed by corn during the vegetative growth stages was between the V6 and V8 growth stages. The highest correlation of NDVI with corn grain yield was found at the V7 to V9 growth stages; likewise, CV and plant density were also more highly correlated from V7 to V9. The CV from NDVI readings was highly correlated with grain and biomass yields at all growth stages.

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.

Non-destructive biomass estimation of vegetation has been performed via remote sensing as well as physical measurements. An effective method for estimating biomass must have accuracy comparable to the accepted standard of destructive removal. Estimation or measurement of height is commonly employed to create a relationship between height and mass. This study examined several types of ground-based mobile sensing strategies for forage biomass estimation. Forage production experiments consisting of alfalfa (Medicago sativa L.), bermudagrass [Cynodon dactylon (L.) Pers.], and wheat (Triticum aestivum L.) were employed to examine sensor biomass estimation (laser, ultrasonic, and spectral) as compared to physical measurements (plate meter and meter stick) and the traditional harvest method (clipping). Predictive models were constructed via partial least squares regression and modeled estimates were compared to the physically measured biomass. Least significant difference separated mean estimates were examined to evaluate differences in the physical measurements and sensor estimates for canopy height and biomass. Differences between methods were minimal (average percent error of 11.2% for difference between predicted values versus machine and quadrat harvested biomass values (1.64 and 4.91 t·ha−1, respectively), except at the lowest measured biomass (average percent error of 89% for harvester and quad harvested biomass &lt, 0.79 t·ha−1) and greatest measured biomass (average percent error of 18% for harvester and quad harvested biomass &gt, 6.4 t·ha−1). These data suggest that using mobile sensor-based biomass estimation models could be an effective alternative to the traditional clipping method for rapid, accurate in-field biomass estimation.

The use of by-plot coefficient of variation (CV) has not been evaluated in precision agricultural work. This study evaluated the relationship between CVs determined from normalized-difference vegetative index (NDVI) sensor readings, plant population, and sensing direction on NDVI values. Randomly selected plots, measuring 1 m2 (2003) and 3 m2 (2004), were established for this study. Plots in 2004 were divided into three 1 m2 subplots with, 0 and 120 kg ha−1 fall-applied N, and 80 kg ha−1 topdress nitrogen (N). Sensor reading of subplots were taken at Feekes 5 and 7 using the Green Seeker hand-held sensor. Results showed that the relationship between vegetative RI (RINDVI) and harvest RI (RIHarvest) improved with increasing CV values. The prediction of RIHarvest was improved when CV was integrated into the RINDVI calculation. RIHarvest can be better predicted with RINDVI when the CV of spectral radiance measurements is used in the RINDVI equation.

Drastic increases in the cost of N fertilizer and increased public scrutiny have encouraged development and implementation of improved N management practices. This study evaluated the relationship between corn (Zea mays L.) grain yield and early season normalized difference vegetation index (NDVI) sensor readings using the GreenSeeker sensor. The relationships between grain yield and several predictor variables were determined using linear and nonlinear regression analysis. Categorizing NDVI measurement by leaf stage indicated that growth stagewas criticalfor predictinggrain yield potential. Poor exponential relationships existed between NDVI from early sensor measurements (V6–V7 leaf stage) and grain yield. By the V8 stage, a strong relationship (R 2 5 0.77) was achieved between NDVI and grain yield. Later sensor measurements (V9 and later) failed to distinguish variation in green biomass as a result of canopy closure. Normalizing the NDVI with GDD (growing degree days) did not significantly improve yield potential prediction (R 2 5 0.73), but broadened the yield potential prediction equation to include temperature and allowed for adaptation into various climates. Sensor measurements at the range of 800 to 1000 GDD resulted in a significant exponential relationship between grain yield and NDVI (R 2 5 0.76) similar to the V8 leaf stage categorization. Categorizing NDVI by GDD (800–1000 GDD) extended the sensing time by two additional leaf stages (V7–V9) to allow a practical window of opportunity for sidedress N applications. This study showed that yield potential in corn could be accurately predicted in season with NDVI measured with the GreenSeeker sensor.

The components that define cereal-grain yield potential have not been well defined. The objective of this study was to collect many differing biological measurements from a long-term winter wheat (Triticum aestivum L.) study in an attempt to better define yield potential. Four treatments were sampled that annually received 0, 45, 90, and 135 kg N ha−1 at fixed rates of phosphorus (P) (30 kg ha−1) and potassium (K) (37 kg ha−1). Mid-season measurements of leaf color, chlorophyll, normalized difference vegetative index (NDVI), plant height, canopy temperature, tiller density, plant density, soil moisture, soil NH4-N, NO3-N, organic carbon (C), total nitrogen (N), pH, and N mineralization potential were collected. In addition, soil texture and bulk density were determined to characterize each plot. Correlations and multiple linear-regression analyses were used to determine those variables that can predict final winter wheat grain yield. Both the correlation and regression analyses suggested mid-seas...

Although spring-applied nitrogen (N) has been shown to be most efficient, the technique of delaying all N applications until mid-season, and the resultant effect on maximum yields, has not been thoroughly evaluated. This experiment was conducted to determine if potential yield reductions from early-season N stress can be corrected using in-season N applications. Data from three experimental sites and two growing seasons (six site-year combinations) were used to evaluate three preplant N rates (0, 45, and 90 kg ha−1) and a range of in-season topdress N rates. Topdress N amounts were determined using a GreenSeeker hand-held sensor and an algorithm developed at Oklahoma State University. Even when early-season N stress was present (0-N preplant), N-applied topdress at Feekes 5 resulted in maximum or near-maximum yields in four of six site-year combinations when compared with other treatments receiving both preplant and topdress N. *Contribution from the Oklahoma Agricultural Experiment Station.

resulting in an estimated 1066 kg ha 1 (17 bu ac 1 ) Corn ( Zea mays L.) grain yields are known to vary from plant to yieldlossover354commercialfields.LauerandRankinplant, but the extent of this variability across a range of environments (2004) and Liu et al. (2004) had differing results, notinghas not been evaluated. This study was initiated to evaluate by-plant that PSV did not significantly alter grain yields in Wis- corn grain yield variability over a range of production environments consin and Ontario, Canada, respectively. Nafziger et and to establish the relationships among mean grain yield, standard al. (1991) noted that uneven emergence of corn can deviation, coefficient of variation, and yield range. A total of forty- occur when soils are dry at the time of planting and six 8- to 30-m corn transects were harvested by plant in Argentina, could lead to decreased grain yields. It is generally ac- Mexico, Iowa, Nebraska, Ohio, Virginia, and Oklahoma from 2002 cepted that when adjacent plants differ by more than

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.