Effects of Soil pH on Wheat Grain Yield and Quality

The effects of planting wheat in permanent beds with fertilization on grain yield and quality need to be better understood. An experiment was conducted at five sites during 2008 and 2009. The objective was to estimate the effects on wheat (Triticum aestivum L.) grain yield and quality of two granular forms of nitrogen (N) (urea and ammonium sulfate, AS) split applied at planting and tillering, and three sprays (urea, AS, and a fungicide) at anthesis. The granular N source affected yield, spike number, and rheological parameters depending upon the soil reaction. Dough resistance/extensibility ratio (P/L) was associated with the normalized difference vegetative index (NDVI) readings collected during tillering before the granular N application. Fungicide spray at anthesis improved yield and grain physical quality evaluated as thousand-grain weight (TGW), test weight, and hardness. Grain protein concentration (GPC) appeared to be mainly affected by environmental factors rather than fertilization practices.     

Utilizing Existing Sensor Technology to Predict Spring Wheat Grain Nitrogen Concentration

Optimum grain nitrogen (N) concentration and yield in spring wheat (Triticum aestivum L.) can be problematic without proper N fertilizer management. Sensor-based technologies have been used for application of fertilizers and also to predict yield in wheat, although little has been done in the prediction of grain N. Field studies were conducted in South Dakota in 2006 (Gettysburg, Bath, and Cresbard) and 2007 (Gettysburg, Aurora, Leola, and Artas). There were five N treatments (0, 56, 112, 168, and 224 kg N ha^?1) applied pre-plant with a second N application applied foliar at anthesis. Sensor readings were taken at growth stages Feekes 10, anthesis, and postfoliar application using the GreenSeeker Hand Held optical sensor. Grain samples were taken at maturity and analyzed for total N. Using similar information collected in 2003 and 2005, a critical normalized difference vegetation index (NDVI) value was determined using the Cate–Nelson procedure. The critical NDVI value needed to ensure optimum grain N was 0.70. In 2006 and 2007, the plots that received an application of N at anthesis had higher grain N than the plots not receiving N. There was also a significant response between applied N and grain yield. The results show that with further studies, the Greenseeker could be used to apply N to maximize yield and grain N in a precise and accurate manner.     

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.     

Effect of nitrogen rate on plant nitrogen loss in winter wheat varieties 1

Gaseous nitrogen (N) loss from winter wheat (Triticum aestivum L.) plants has been identified, but has not been simultaneously evaluated for several genotypes grown under different N fertility. Two field experiments were initiated in 1993 and 1994 at the Agronomy Research Station in Stillwater and Perkins to estimate plant N loss from several cultivars as a function of N applied and to characterize nitrogen use efficiency (NUE). A total of five cultivars were evaluated at preplant N rates ranging from 30 to 180 kg·ha^‐1. Nitrogen loss was estimated as the difference between total forage N accumulated at anthesis and the total (grain + straw) N at harvest. Forage, grain, straw yield, N uptake, and N loss increased with increasing N applied at both Stillwater and Perkins. Significant differences were observed among varieties for yield, N uptake, N loss, and components of NUE in forage, grain, straw, and grain + straw. Estimates of N loss over this two‐year period ranged from 4.0 to 27.9 kg·ha^‐1 (7.7 to 59.4% of total forage N at anthesis). Most N losses occurred between anthesis and 14 days post‐anthesis. Avoiding excess N application would reduce N loss and increase NUE in winter wheat varieties. Varieties with high harvest index (grain yield/total biomass) and low forage yield had low plant N loss. Estimates of plant loss suggest N balance studies should consider this variable before assuming that unaccounted N was lost to leaching and denitrification.     

密度对沿淮晚播小麦产量形成及品质性状的影响

目前晚播小麦的面积不断增加,为明确沿淮地区晚播小麦的适宜种植密度,采用裂区试验设计,于2013—2015年在不同晚播条件下(11月5日、11月15日、11月25日),设置3个种植密度(300万株·hm-2、450万株·hm-2、600万株·hm-2),分析种植密度对玉米茬晚播小麦产量形成及品质性状的影响。结果表明:播期推迟导致小麦生育期滞后,主要影响拔节期前营养生长期的长短;密度对生育进程无显著影响。随播期推迟,小麦开花期和成熟期的干物质积累量下降,花前贮存同化物的转运量和花后同化物的积累量下降,花后同化物对籽粒贡献率明显增加;穗数、穗粒数和千粒重均有所下降,进而产量显著下降;蛋白质含量、湿面筋含量和沉淀值上升。播期对分蘖穗干物质积累与运转及产量构成因素的影响均大于主茎穗。与11月5日播期相比,11月25日播期下开花期干物质积累量、成熟期营养器官积累量、籽粒干重、花前营养器官贮存同化物的转运量及其对籽粒的贡献率在主茎穗中分别下降13.37%、9.96%、9.04%、25.37%和17.07%,在分蘖穗中分别下降55.71%、54.34%、51.80%、59.70%和22.70%。同一播期条件下,随着种植密度的增加,小麦开花期和成熟期的干物质积累量上升,花前贮存同化物的转运量减少,花后同化物的积累量及其对籽粒贡献率增加;穗数增加,千粒重降低;蛋白质含量和湿面筋含量上升,沉淀值下降。与主茎穗相比,密度对分蘖穗干物质积累与运转及产量构成因素的影响更大。与300万株·hm-2密度相比,600万株·hm-2密度下单穗粒重、穗粒数和千粒重在主茎穗中分别下降17.90%、13.60%和4.76%,在分蘖穗中分别下降20.17%、14.46%和6.23%。可见,适当增加密度有利于增加晚播小麦产量并改善晚播小麦品质性状,本研究中11月15日、11月25日两晚播条件下适宜密度分别为450万株·hm-2、600万株·hm-2。     

种植密度对冬小麦氮素吸收利用和分配的影响

为了探讨实现冬小麦籽粒产量与氮素利用效率协同提高的途径,为制定高产、高效栽培管理措施提供理论依据,在大田条件下,以大穗型小麦品种"泰农18"和中穗型小麦品种"山农15"为试验材料,根据品种特性分别设置4个种植密度("泰农18":135万苗.hm 2、270万苗.hm 2、405万苗.hm 2和540万苗.hm 2;"山农15":172.5万苗.hm 2、345万苗.hm 2、517.5万苗.hm 2和690万苗.hm 2),研究了种植密度对籽粒产量、氮素吸收积累和运转分配、氮素利用效率以及土壤中硝态氮、铵态氮和无机态氮总积累量的影响。研究结果表明,随种植密度增加,两种穗型冬小麦品种成熟期植株氮素积累量、籽粒产量、氮肥吸收利用效率和氮肥偏生产力均表现为先增加后降低,籽粒氮积累量、氮素收获指数和籽粒氮含量下降,花前营养器官氮素转运量和对籽粒氮的贡献率升高。随种植密度的增加,"泰农18"的氮素利用效率随密度的增大先增大后减小,"山农15"随密度的增大而减小。土壤中硝态氮、铵态氮和无机态氮总积累量随密度增加而降低。在本试验条件下,"泰农18"和"山农15"兼顾高产和高效利用氮素的适宜种植密度分别为270万苗.hm 2和345万苗.hm 2。     

Modern wheat cultivars have greater root nitrogen uptake efficiency than old cultivars

The availability of nitrogen (N) contained in crop residues for a following crop may vary with cultivar, depending on root traits and the interaction between roots and soil. We used a pot experiment to investigate the effects of six spring wheat (Triticum aestivum L.) cultivars (three old varieties introduced before mid last century and three modern varieties) and N fertilization on the ability of wheat to acquire N from maize (Zea mays L.) straw added to soil. Wheat was grown in a soil where ¹⁵N‐labeled maize straw had been incorporated with or without N fertilization. Higher grain yield in three modern and one old cultivar was ascribed to preferred allocation of photosynthate to aboveground plant parts and from vegetative organs to grains. Root biomass, root length density and root surface area were all smaller in modern than in old cultivars at both anthesis and maturity. Root mean diameter was generally similar between modern and old cultivars at anthesis but was greater in modern than in old cultivars at maturity. There were cultivar differences in N uptake from incorporated maize straw and the other N sources (soil and fertilizer). However, these differences were not related to variation in the measured root parameters among the six cultivars. At anthesis, total N uptake efficiencies by roots (total N uptake per root weight or root length) were greater in modern than in old cultivars within each fertilization level. At maturity, averaged over fertilization levels, the total N uptake efficiencies by roots were 292?336 mg N g^?1 roots or 3.2?4.0 mg N m^?1 roots for three modern cultivars, in contrast to 132?213 mg N g^?1 roots or 0.93?1.6 mg N m^?1 roots for three old cultivars. Fertilization enhanced the utilization of N from maize straw by all cultivars, but root N uptake efficiencies were less affected. We concluded that modern spring wheat cultivars had higher root N uptake efficiency than old cultivars.     

On‐farm comparison of variable rates of nitrogen with uniform application to maize on canopy reflectance,soil nitrate,and grain yield

Recent development in canopy optical‐sensing technology provides the opportunity to apply fertilizer variably at the field scale according to spatial variation in plant growth. A field experiment was conducted in Ottawa, Canada, for two consecutive years to determine the effect of fertilizer nitrogen (N) input at variable‐ vs. uniform‐application strategies at the V6–V8 growth stage, on soil mineral N, canopy reflectance, and grain yield of maize (Zea mays L.). The variable N rates were calculated using an algorithm derived from readings of average normalized difference vegetation index (NDVI) of about 0.8 m × 4.6 m, and N fertilizer was then applied to individual patches of the same size of NDVI readings (0.8 m × 4.6 m) within a plot (2184 m²). Canopy reflectance, expressed as NDVI, was monitored with a hand‐held spectrometer, twice weekly before tasseling and once a week thereafter until physiological maturity. Soil mineral N (0–30 cm depth) was analyzed at the V6 and VT growth stages. Our data show that both variable and uniform‐application strategies for N side‐dressings based on canopy‐reflectance mapping data required less amount of N fertilizer (with an average rate of 80 kg N ha^–1 as side‐dressing in addition to 30 kg N ha^–1 applied at planting), and produced grain yields similar to and higher nitrogen‐use efficiency (NUE) than the preplant fully fertilized (180 kg N ha^–1) treatment. No difference was observed in either grain yield or NUE between the variable‐ and uniform‐application strategies. Compared to unfertilized or fully fertilized treatments, the enhancements in grain yield and NUE of the variable‐rate strategy originated from the later N input as side‐dressing rather than the variation in N rates. The variable‐rate strategy resulted in less spatial variations in soil mineral N at the VT growth stage and greater spatial variations in grain yield at harvest than the uniform‐rate strategy. Both variable‐ and uniform‐application strategies reduced spatial variations in soil mineral N at the VT stage and grain yield compared to the unfertilized treatment. The variable‐rate strategy resulted in more sampling points with high soil mineral N than the uniform‐rate strategy at the VT stage.     

Late nitrogen application increased protein concentration but not baking quality of wheat

Late application of nitrogen (N) fertilizers at heading or anthesis is usually performed to produce wheat (Triticum aestivum L.) with high bread‐making quality. However, increasing energy costs and ecological problems due to N losses call for efficient and simplified N fertilization strategies. This study aimed to investigate the effect of late N fertilization on grain protein quality and thus baking quality and to evaluate if similar wheat quality can be maintained without late N application. Field experiments with two winter wheat cultivars differing in quality groups were conducted. The fertilization treatments comprised a rate of 220 kg N ha^?1 applied in two or three doses (referred to as split N application), and 260 kg N ha^?1 applied in four doses (additional late N fertilization) with different N fertilizer types. The results show that although split N application had no effect on grain protein concentration (GPC), it affected N partitioning in the grain, increasing mainly the concentration and proportion of the glutenin fraction. As a result, baking quality was improved by split N application. Late N fertilization enhanced GPC and the relative abundance of certain high molecular weight glutenin subunits (HMW‐GS). However, it had no effect on N partitioning in the grain and did not further improve baking quality. No obvious differences were found between N fertilizer types on grain yield and quality. The N fertilization effect was more pronounced on the wheat cultivar whose baking quality was more dependent on protein concentration. In evaluating baking quality of wheat flour, gliadin and glutenin proportions were better correlated with loaf volume than the overall protein concentration.     

OPTIMUM FIELD ELEMENT SIZE FOR MAXIMUM YIELDS IN WINTER WHEAT,USING VARIABLE NITROGEN RATES

The resolution at which variability in soil test and yield parameters exist is fundamental to the efficient use of real-time sensor-based variable rate technology. This study was conducted to determine the optimum field element size for maximum yields in winter wheat (Triticum aestivum L.), using variable nitrogen (N) rates based on sensor readings. The effect of applying N at four different resolutions (0.84, 3.34, 13.38, and 53.51 m²) on grain yield, N uptake and efficiency of use was investigated at Haskell, Hennessey, Perkins, and Tipton, Oklahoma. At Feekes growth stage 5 an optical sensor developed at Oklahoma State University measured red (670 ± 6 nm) and near-infrared (NIR, 780 ± 6 nm) reflectance in each subplot. A normalized-difference-vegetative-index (NDVI) was calculated from the sensor measurements. Nitrogen was applied based on a NDVI–N rate calibration. Nitrogen rate, yield, N uptake, and efficiency of use responses to treatment resolution and applied N fertilizer differed in the 3 years of this experiment. In the first year, no significant influence of resolution on N rate, yield, N uptake, or efficiency of use was observed, likely a result of a late freeze that drastically reduced yields. In the second year of the experiment, there was a trend for a lower N rate and a higher efficiency of use for the 0.84 m² resolution. In the third year of this study, there was a trend for a higher yield and a higher efficiency of use for the 53.51 m² resolution at both sites. In general, the finer resolutions tended to have increased efficiency of use in high yielding environments (>2300 kg ha^?1), and decreased yields in low yielding environments. This study indicates that application of prescribed fertilizer rates based on spatial variability at resolutions finer than 53.51 m² could lead to increased yields, decreased grower costs, and decreased environmental impact of excess fertilizers.     

Optical Sensor‐Based Algorithm for Crop Nitrogen Fertilization

Abstract

Nitrogen (N) fertilization for cereal crop production does not follow any kind of generalized methodology that guarantees maximum nitrogen use efficiency (NUE). The objective of this work was to amalgamate some of the current concepts for N management in cereal production into an applied algorithm. This work at Oklahoma State University from 1992 to present has focused primarily on the use of optical sensors in red and near infrared bands for predicting yield, and using that information in an algorithm to estimate fertilizer requirements. The current algorithm, “WheatN.1.0,” may be separated into several discreet components: 1) mid‐season prediction of grain yield, determined by dividing the normalized difference vegetative index (NDVI) by the number of days from planting to sensing (estimate of biomass produced per day on the specific date when sensor readings are collected); 2) estimating temporally dependent responsiveness to applied N by placing non‐N‐limiting strips in production fields each year, and comparing these to the farmer practice (response index); and 3) determining the spatial variability within each 0.4 m² area using the coefficient of variation (CV) from NDVI readings. These components are then integrated into a functional algorithm to estimate application rate whereby N removal is estimated based on the predicted yield potential for each 0.4 m² area and adjusted for the seasonally dependent responsiveness to applied N. This work shows that yield potential prediction equations for winter wheat can be reliably established with only 2 years of field data. Furthermore, basing mid‐season N fertilizer rates on predicted yield potential and a response index can increase NUE by over 15% in winter wheat when compared to conventional methods. Using our optical sensor‐based algorithm that employs yield prediction and N responsiveness by location (0.4 m² resolution) can increase yields and decrease environmental contamination due to excessive N fertilization.     

In-Season Prediction of Nitrogen Use Efficiency and Grain Protein in Winter Wheat (Triticum aestivum L.)

In a 3-year study, grain yield, nitrogen use efficiency (NUE), and grain protein (GP) were evaluated as a function of rate and timing of nitrogen (N) fertilizer application. Linear models that included preplant N, normalized difference vegetation index (NDVI), cumulative rainfall, and average air temperature from planting to sensing (T-avg) were evaluated to predict NUE and GP in winter wheat. GreenSeeker readings were collected at Feekes (F) 3, 4, 5, and 7 growth stages. Combined with rainfall and/or T-avg, NDVI alone was not correlated with NUE. However, NDVI and rainfall explained 45% (r² = 0.45) of the variability in GP at F7 growth stage. Preplant N, NDVI, rainfall and growing degree days (GDD) combined explained 76% (r² = 0.76) of the variability in GP at F3. Mid-season climatic data improved the prediction of GP and should therefore be considered for refining fertilizer recommendations when GP levels are expected to be low.     

Alleviation of drought stress in winter wheat by late foliar application of zinc,boron, and manganese

In many regions, drought during flowering and grain‐filling inhibits micronutrient acquisition by roots resulting in yield losses and low micronutrient concentrations in cereal grains. A field and a greenhouse experiment were conducted to study the effect of foliar applications of zinc (Zn), boron (B), and manganese (Mn) at late growth stages of winter wheat (Triticum aestivum L.) grown with or without drought stress from booting to maturity. Foliar applications of Zn, B, and Mn did not affect grain yield in the absence of drought. However, under drought, foliar application of Zn and B in the field increased grain yield (15% and 19%, respectively) as well as raising grain Zn and B concentration, while Zn and Mn sprays in the greenhouse increased grain yield (13% and 10%, respectively), and also increased grain Zn and Mn concentrations. Furthermore, under drought stress both in the field and greenhouse experiment the rate of photosynthesis, pollen viability, number of fertile spikes, number of grains per spike, and particularly water‐use efficiency (WUE) were increased by late foliar application of micronutrients. These results indicate that by increasing WUE foliar application of Zn, B, and Mn at booting to anthesis can reduce the harmful effects of drought stress that often occur during the late stages of winter wheat production. These findings therefore are of high relevance for farmers' practice, the extension service, and fertilizer industry.     

Effect of zinc application methods on apparent utilization efficiency of zinc and potassium fertilizers under rice-wheat rotation

Apparent utilization of zinc (Zn) and potassium (K) fertilizers was examined in rice (Oryza sativa L.)-wheat (Triticum aestivum L.) using combinations of no K; soil applied K levels and no Zn; soil and foliar applied Zn. Application of 33.2 kg K ha^?1 in rice and 24.9 kg K ha^?1 in wheat along with foliar spray of 2 kg Zn ha^?1 at 30 and 60 days gave the highest mean grain yields. Foliar application of zinc increased Zn concentration in flag leaves, grain, and straw of rice and wheat and K concentration in flag leaves of rice and straw of wheat significantly. Potassium application increased Zn concentration in rice grain and straw and K concentration in wheat straw significantly. Zinc and K increased the uptake of each other in grain; straw and total uptake by both crops significantly. Zinc fertilizer enhanced the utilization of soil K. Potassium fertilizer enhanced the utilization of applied Zn.     

IMPACT OF WATER AND NUTRIENT MANAGEMENT ON THE NUTRITIONAL QUALITY OF WHEAT

Field experiments were conducted in 2002–03 and 2003–04 growing seasons to determine wheat response to four irrigation regimes applied at different growth stages and four nitrogen levels of 0, 50, 100, and 150 kg nitrogen (N) ha^?1. The experiment was conducted at the research area of the Department of Crop Physiology, University of Agriculture, Faisalabad, Pakistan. Recommended wheat variety “Inqlab-91” was used as the experimental crop. Both irrigation and nitrogen application have positive effects on grain yield increase. The grain crude protein decreased with increasing number of irrigations whereas in contrast, nitrogen application significantly improved grain crude protein at all irrigation levels. Grain phosphorus (P) and potassium (K) percentage increased with the application of irrigation and nitrogen. Grain yield, number of spikes m^?2, grains spike^?1 and grain weight responses were greater at the higher N rates. Mean grain yield in four, three and two irrigation treatments compared with that in one irrigation treatment increased 47, 23, and 9% during 2002–03 and 91, 84, and 23% in 2003–04, respectively. Water deficit reduced spikes m^?2. In both years, the average reduction in spikes m^?2 at maximum irrigation deficit (one irrigation) at all N levels was 24%. Similar reduction occurred in grains spike^?1 where water deficit decreased this component on an average of 36%.     

Type and placement of zinc fertilizer impacts cadmium content of harvested durum wheat grain

Due to potential international marketing concerns, North Dakota durum wheat (Triticum turgidum L. Desf.) producers require strategies that limit cadmium (Cd) in harvested grain. These trials were conducted in order to determine the impact of type and placement of zinc (Zn) fertilizer on harvested grain seed Cd levels and to determine the best timing of foliar Zn-ethylenediaminetetraacetic acid (EDTA). Foliar Zn-EDTA applied at Feekes 10 growth stage had the lowest grain Cd of 0.97 mg kg^?1 when evaluating different fertilizer sources and application timings. Application of 22.4 kg ha^?1 potassium chloride with the seed at planting resulted in the highest grain Cd of 0.151 mg kg^?1 and might be a concern when environmental conditions are conducive for Cd uptake from soil. Stepwise linear regression determined that soil pH and chloride explained 96% of the variability of grain Cd. Applying 1.1 kg Zn ha^?1 as foliar Zn-EDTA in combination with 33 kg nitrogen ha^?1 at Feekes 10.54 growth stage resulted in significantly lower grain Cd, and significantly higher grain Zn, iron, and protein content. Treatments that significantly lowered grain Cd did not decrease grain yield, test weight, or protein content. The treatments that most reduced grain Cd resulted in the most benefits from a production, marketing, and nutritional standpoint and represents an agronomic approach to biofortification of durum wheat.     

Wheat Yield Differences between Two Cropping Systems in Permanent Raised-Beds as Affected by Components of Nitrogen Use Efficiency

Permanent raised-bed is an alternative planting system for wheat (Triticum aestivum L.) in rain-fed areas. However, this system in monoculture conditions produces lower yields compared with wheat in rotation. Our objective was to estimate these yield differences as affected by nitrogen (N) use efficiency (NUE). Wheat in monoculture and in rotation with maize (Zea mays L.) was evaluated for eight years (2002–2009) with four N rates (0, 40, 80 or 120 kg ha^?1). Yield response to N in monoculture was consistently lower than for wheat in rotation. Yield reduction in monoculture at low and high N rate was 81 and 99% attributed to NUE out of which 70 and 82% was due to the uptake efficiency (UPE) and 30 and 19% to the utilization efficiency (UTE), respectively. Total N uptake proved to be the parameter that needs to be improved to enhance wheat yield in monoculture.

Abbreviations: NUE: nitrogen use efficiency; UPE: uptake efficiency; UTE: utilization efficiency; Ns: nitrogen supply; NDVI: normalized difference vegetation index     

Utilization of Existing Technology to Evaluate Spring Wheat Growth and Nitrogen Nutrition in South Dakota

Abstract

Sensor‐based technologies for in‐season application of nitrogen (N) to winter wheat (Triticum aestivum L.) have been developed and are in use in the southern Great Plains. Questions arise about the suitability of this technology for spring wheat production in the northern Great Plains. A field experiment was established in Brookings, SD, to evaluate the GreenSeeker Hand Held optical sensor (NTech Industries, Ukiah, CA) for predicting in‐season N status on three spring wheat cultivars (Ingot, Oxen, and Walworth) across five N treatments. Nitrogen rates were 0, 34, 68, 102, and 136 kg N ha^?1 applied preplant as ammonium nitrate. Sensor readings and plant biomass samples were collected at Feekes 6 and Feekes 10 growth stages. The sensor measures reflectance in the red and near infrared (NIR) regions of the electromagnetic spectrum. A normalized difference vegetation index (NDVI) was calculated. The ability of the sensor readings to predict biomass, plant N concentration, and plant N uptake for each sampling date was determined. In general, biomass, plant N concentration, and N uptake increased with increasing N rate for both sampling dates. Readings collected at Feekes 6 and Feekes 10 showed a significant relationship with plant biomass, N concentration, and N uptake for all varieties. Plant N uptake and NDVI resulted in a higher regression coefficients compared to biomass and plant N concentration for all varieties. Results suggest that existing sensor‐based variable nitrogen technology developed for winter wheat could be utilized in the northern Great Plains for estimating in‐season N need for spring wheat.     

Zinc bioavailability and nitrogen concentration in grains of wheat crop sprayed with zinc sulfate,ammonium sulfate,ammonium chloride,and urea

Abstract

It is still unclear if different sources of nitrogen (N) can variably influence grain accumulation of zinc (Zn), N, and phytate. We tested foliar treatments of 0 or 0.25% Zn as zinc sulfate in combination with 0 or 1% N as ammonium chloride, ammonium sulfate or urea sprayed on field-grown-wheat (Triticum aestivum L.) foliage at anthesis and 10 days later. Leaf burning caused by ammonium chloride significantly decreased grain yield. Grain N concentration was the highest in the urea +0.25% Zn treatment. Foliar N application influenced grain Zn concentration only if Zn was included in the spray. Grain phytate concentration was significantly decreased by both N and Zn sprays. Estimated Zn bioavailability in grains was the highest at 0.25% Zn and was not influenced by the N sources. Based on grain yield, grain N concentration, and Zn bioavailability in grains, foliar application of Zn?+?urea is an optimal strategy.     

Winter wheat fertilizer nitrogen use efficiency in grain and forage production systems

Abstract

Nitrogen use efficiency (NUE) is known to be less than fifty percent in winter wheat grain production systems. This study was conducted to determine potential differences in NUE when winter wheat (Triticum aestivum L.) is grown strictly for forage or grain. The effects of different nitrogen rates on plant N concentrations at different growth stages and on grain yield were investigated in two existing long‐term winter wheat experiments near Stillwater (Experiment 222) and Lahoma (Experiment 502), OK. At both locations in all years, total N uptake was greater when wheat forage was harvested twice (Feekes 6 and flowering) compared to total N uptake when wheat was grown only for grain. Percent N content immediately following flowering was much lower compared to percent N in the forage harvested prior to flowering, indicating relatively large losses of N after flowering. Averaged over locations and years, at the 90 kg N ha^?1 rate, wheat produced for forage had much higher NUE (82%) compared with grain production systems (30%). While gaseous N loss was not measured in this trial, the higher NUE values found in the forage production systems were attributed to harvesting prior to anthesis and the time when plant N losses are known to be greater.