Wade Everett Thomason

Switchgrass Response to Harvest Frequency and Time and Rate of Applied Nitrogen

Abstract Switchgrass (Panicum virgatum L.) is currently being evaluated as a raw material for producing fuel, chemicals, and electricity. Switchgrass biomass is bound by the growing environment that includes fertility. More information is needed on sustainable switchgrass production as influenced by nitrogen fertility and harvest management. Field experiments were initiated at Chickasha and Perkins, OK in 1996 and 1998, respectively to evaluate switchgrass response to applied nitrogen (N) at rates of 0, 112, 224, 448, and 896 kg ha−1. In addition, harvest frequency and time of N application were evaluated. Yield maximums and the greatest N, potassium (K), phosphorus (P), and sulfur (S) uptake values were achieved with 448 kg N ha−1 applied all in April and harvested three times. In fact, harvest frequency was the most important factor affecting yields over the course of these studies with average dry matter yields of 16.3, 14.7, and 12.9 Mg ha−1 yr−1 for three, two, and one harvest yr−1, respectively. No significant change in soil organic carbon was detected over time. Although dry matter yields were found to decline with time, total N uptake did not. Forage N concentration was found to be greater in later years, thus increasing production costs. While yields were highest (18.0 Mg ha−1) with 448 kg N ha−1 applied all in April and three harvests, applying 0 N and harvesting three times produced almost as much total biomass (16.9 Mg ha−1). This limited response to N is possibly explained by the evolution of switchgrass under low N conditions. Increasing forage concentrations of K, magnesium (Mg), P, and S were noted with increasing yields, indicating a potential for response to these nutrients. #Contribution from the Oklahoma Agricultural Experiment Station.

NITROGEN FERTILIZATION OPTIMIZATION ALGORITHM BASED ON IN-SEASON ESTIMATES OF YIELD AND PLANT NITROGEN UPTAKE

Current methods of determining nitrogen (N) fertilization rates in winter wheat (Triticum aestivum L.) are based on farmer projected yield goals and fixed N removal rates per unit of grain produced. This work reports on an alternative method of determining fertilizer N rates using estimates of early-season plant N uptake and potential yield determined from in-season spectral measurements collected between January and April. Reflectance measurements under daytime lighting in the red and near infrared regions of the spectra were used to compute the normalized difference vegetation index (NDVI). Using a modified daytime lighting reflectance sensor, early-season plant N uptake between Feekes physiological growth stages 4 (leaf sheaths lengthen) through 6 (first node of stem visible) was found to be highly correlated with NDVI. Further analyses showed that dividing the NDVI sensor measurements between Feekes growth stages 4 and 6, by the days from planting to sensing date was highly correlated with final grain yield. This in-season estimate of yield (INSEY) was subsequently used to compute the potential N that could be removed in the grain. In-season N fertilization needs were then considered to be equal to the amount of predicted grain N uptake (potential yield times grain N) minus predicted early-season plant N uptake (at the time of sensing), divided by an efficiency factor of 0.70. This method of determining in-season fertilizer need has been shown to decrease large area N rates while also increasing wheat grain yields when each 1m2 area was sensed and treated independently.

PRODUCTION SYSTEM TECHNIQUES TO INCREASE NITROGEN USE EFFICIENCY IN WINTER WHEAT

ABSTRACT Most current research on winter wheat (Triticum aestivum L.) focuses on increasing yields of either grain or plant biomass. Increased production costs and environmental awareness will promote the development of methods to increase the efficiency of applied nutrients. Nitrogen (N) is often the most limiting nutrient for cereal grain production and represents one of the highest input costs in agricultural systems. This study was conducted to evaluate the effects of several short-term practices on nitrogen use efficiency (NUE) in winter wheat at three locations in Oklahoma. The variables evaluated included variety, nitrogen source, nitrogen timing, nitrogen rate, production system (forage only vs. grain only and a combination of the two), resolution of nitrogen application based on in-season estimated yield (INSEY), and application of a late-season senescence delaying chemical and late-season KH2PO4. Results indicate that many approaches can be taken to increase NUE in wheat production systems. Averaged over 9 site yrs, the highest NUE was for forage-only production systems (66% for “Jagger” and 52% for “2174”) far higher than grain-only production systems (26% for “Jagger” and 37% for “2174”). The combination of a 3-way split application using sensor measurements and 1 m2 application resolution produced the highest average grain-only NUE at 81% for 2174 and 48% for Jagger compared with 29% NUE for pre-plant applied N. The most critical components of NUE from this study appear to be production system, variety, N fertilizer timing, and INSEY based topdress N applications.

Indirect measures of plant nutrients

Abstract Indirect, non‐destructive sensor‐based methods of plant and soil analyses could replace many of the wet chemistry testing methods that are in place today. Over 140 years have past since Justus von Liebig first employed soil testing in 1850. Today, simultaneous analyses of moisture, organic carbon (C), and total nitrogen (N) in plants and soils using non‐destructive near infrared reflectance spectrophotometry are possible. Recent work has targeted indirect measurements of the nutrient status in soils using spectral radiance data collected from growing crop canopies. The use of spectral measurements from plant canopies has heen driven, in part, by newer variable rate technologies which apply nutrients to prescribed areas. More recent work has documented significant soil variabiliry on a 1 m2 scale. Because of this, indirect measures are necessary to avoid the cost of chemical analyses (10,000 samples requiredper hectare) and to avoid on‐the‐go chemistry. Also, in order for application technologies ...

Plant Density and Hybrid Impacts on Corn Grain and Forage Yield and Nutrient Uptake

ABSTRACT Corn (Zea mays L.) production recommendations should be periodically evaluated to ensure that production practices remain in step with genetic improvements. Since most of the recent increases in corn grain yield are due to planting at higher densities and not to increased per-plant yield, this study was undertaken to measure the effects of plant density and hybrid on corn forage and grain yield and on nutrient uptake. Plant density (4.9, 6.2, 7.4, and 8.6 seeds m−2) and hybrid relative maturity (RM) [early (108 day RM); medium (114 day RM); and late (118 day RM)] combinations were evaluated over five site-years under irrigated and non-irrigated conditions. The interaction of hybrid with plant density was never significant for grain, stem, or leaf biomass. The latest RM hybrid out-yielded the medium and early hybrids by 550 and 1864 kg ha−1, respectively. Grain yield was highest at 8.6 plants m−2. Total stem yield was also greatest at the highest plant density but by only 340 kg ha−1 more than at 7.4 seeds m−2. Based on grain yield response over sites, the estimated optimum density was 7.6 seeds m−2, which is 0.7 seeds m−2 higher than the current recommendation at this average yield level (11.5 Mg ha−1). Grain nitrogen (N), phosphorus (P), and potassium (K) uptakes were highest for the medium RM hybrid. Nutrient uptake levels varied by planting density, with the lowest levels observed at the lowest and highest plant densities. At 4.9 seeds m−2, the reduced uptake is explained by lower biomass yields. At the 8.6 seeds m−2 rate, N and K levels may have been lower due to dilution.

Forage and Grain Yield Response to Applied Sulfur in Winter Wheat as Influenced by Source and Rate

ABSTRACT Recently, environmental quality issues related to sulfur (S) have made it necessary to reduce its release into the atmosphere in wet or dry forms, which in turn might influence the S requirement of crops. It is anticipated that by 2020, S deposition will decrease by up to 30% in eastern portions of Oklahoma and by 15% throughout the remainder of the state. This change calls for frequent monitoring and evaluation of S nutrition in wheat and other crops. Experiments were conducted at Hennessey and Perkins research stations for a period of seven years starting in the fall of 1996, with the objective of assessing the effect of different levels of elemental and sulfate-S fertilizers on the grain and forage yields of winter wheat in Oklahoma. The experimental design was a randomized complete block with three replications. Four S rates, 0, 56, 112, and 224 kg S ha− 1, were applied to the plots from 1996 to 2002 as CaSO4. Another two rates, 56 and 112 kg S ha− 1, were included in the trials beginning in 1998 using 92% elemental S. Gypsum, as a source of S for winter wheat, resulted in a greater yield than did elemental S in cases where S fertilizer sources were deemed significant. In six of 14 trials from 1996 to 2002, applied S as CaSO4 significantly increased wheat-grain yields. Observing significant grain and forage yield increases due to applied S was important, but the response was sporadic and unpredictable from one year to the next.

RELATIONSHIP BETWEEN AMMONIUM AND NITRATE IN WHEAT PLANT TISSUE AND ESTIMATED NITROGEN LOSS

ABSTRACT Nitrogen (N) is one of the most important elements in the nutrition of higher plants and one of the most costly inputs in the production of winter wheat in the Great Plains. Nitrogen ranks second only to precipitation as the most frequent yield limiting factor, and even when N is not the yield limiting factor, wheat is less than 50% efficient at utilizing applied N fertilizer. If N supplied to the crop is not utilized efficiently, it may be lost from the cropping system to the surrounding environment. The objective of this study was to evaluate the relationship between NH4–N and NO3–N in wheat tissue and estimated plant N loss. Two experimental sites for this study were selected as subplots located within existing plots in two long-term winter wheat experiments at Stillwater (experiment 222) and Lahoma (experiment 502), Oklahoma. Wheat forage samples were collected at Feekes growth stage five (leaf sheath strongly erected) and Feekes growth stage 10.5 (flowering complete to top of ear). Samples were dried, ground, and analyzed for total N, NH4–N, and NO3–N. The relationship between total N, NH4–N, and NO3–N at both growth stages and estimated plant nitrogen loss (plant N uptake at flowering minus total N uptake in the grain plus straw) were evaluated. No relationship was found to exist between forage NH4–N and NO3–N and estimated plant N loss. Due to cool and moist climatic conditions during late spring in both years, estimated N losses were small from anthesis to maturity using the method described. Plant tissue NO3–N at Feekes five was correlated with total N accumulation in the plant at flowering and with grain N uptake at experiment 502 in both years.

Effect of growth stage and variety on spectral radiance in winter wheat.

Abstract Before sensor‐based variable rate technology (VRT) can be used to reduce nitrogen (N) fertilizer rates in winter wheat (Triticum aestivum L.) spectral radiance readings must be understood. One prominent issue is the impact of crop growth stage on spectral radiance readings, and the ensuing problem of relating databases gathered at different locations and different stages of growth. In order to evaluate the impact of growth stage on spectral radiance, sensor readings were taken from a winter wheat variety trial and two long‐term N and phosphorus (P) fertility trials. The normalized difference vegetative index was computed using red and near infrared (NIR) spectral radiance measurements [NDVI=(NIR‐red)/(NIR+red)]. TotalNuptake in winter wheat at Feekes growth stages 4, 5, 7, and 8 was highly correlated with NDVI. In the variety trial, non‐significant differences in ND VI readings were noticed between the five common genotypes (by growth stage) grown in this region. However, slopes from linear regression of total N uptake on NDVI were different at different stages of growth, which suggests the need for growth stage specific calibration. Freeze injury (altered tissue color) affected the relationship between total N uptake and NDVI, however, NDVI continued to be a good predictor of in‐season total N uptake in wheat even though cell blasting altered tissue color. This work showed that NDVI is a good predictor of biomass, but not necessarily total N concentration in plant tissue. The amount of variability in total N uptake as explained by NDVI increased with advancing growth stage (Feekes 4 to 7), largely due to an increased percentage of soil covered by vegetation.

Defining Useful Limits for Spectral Reflectance Measures in Corn

ABSTRACT Recent work has shown that spectral measurements from a corn (Zea mays L.) canopy can be used to reliably predict differences in growth and nutrient status. Most researchers have found that the accuracy of this assessment increases as the season progresses. In contrast, real differences upon which to base management decisions need to be measured as early in the season as possible due to the time restrictions associated with fertilizer and chemical application equipment and weather. The objectives of this research were to evaluate the relationship between Normalized Difference Vegetative Index (NDVI) measurements and corn biomass and grain yield and to define upper and lower limits for effectively using NDVI measurements to make in-season management decisions in corn. Forage biomass and grain yield from eight field studies conducted in the Coastal Plain of Virginia in 2005 were compared to indirect measures of spectral reflectance and leaf area index (LAI). The NDVI was well correlated with vegetative forage biomass (R2 = 0.81) and LAI (R2 = 0.90) within the range 0.27 to 0.82. This range in NDVI values corresponds to 166 to 485 cumulative growing degree days (GDD), and a resultant developmental window of V5 to V9 when NDVI measurement are most useful and appropriate for making in-season management decisions for corn production.

Managing Nitrogen and Sulfur Fertilization for Improved Bread Wheat Quality in Humid Environments

ABSTRACT A large proportion of the wheat (Triticum aestivum L.) milled and utilized by bakeries in the eastern United States is hard red winter wheat (HRWW). Potential for producing this higher value commodity in the eastern United States is dependent on availability of adapted HRWW cultivars that are competitive with soft red winter wheat (SRWW) cultivars and implementation of management systems to enhance end-use quality. The effects of late-season nitrogen (N) (0–45 kg of N/ha) applied at two growth stages (GS 45 and 54) and sulfur (S) (0–34 kg of S/ha) applied at GS 30 on grain, flour, and milling and breadbaking quality were evaluated. Three diverse wheat cultivars (Soissons, Heyne, and Renwood 3260) were studied in two to five environments. Application of S and late-season N had little effect on grain yield. But N consistently increased grain and flour protein as well as bread loaf volume. The magnitude and significance of response to N and S varied by location and cultivar. While S alone did not ha...