Mid-Season Recovery from Nitrogen Stress in Winter Wheat

ABSTRACT

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.     

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

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.     

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.     

Effect of row spacing,growth stage,and nitrogen rate on spectral irradiance in winter wheat

Soil reflectance affects spectral irradiance measurements taken in winter wheat at early stages of growth when percent cover is low. The objective of this study was to determine the critical percent vegetation coverage needed for forage nitrogen (N) uptake calibration with indirect spectral irradiance measurements. Two field experiments were conducted at Tipton and Perkins, OK in October 1996. The effect of row spacing (15.2, 19.0, 25.4, and 30.5 cm) and growth stage (Feekes 4 and 5) under various N fertilizer rates (0, 56, 112, and 168 kg N ha^‐1) on spectral irradiance measurements from wheat was evaluated. The normalized difference vegetative index (NDVI) was used to characterize wheat canopy irradiance. In general, NDVI decreased with increasing row spacing and increased with N fertilizer rate at Feekes growth stage 4. Row spacing and N rate were independent of each other since no significant interaction was found. High correlation (r=0.81–0.98) was observed between NDVI and vegetation coverage. Percent vegetation coverage was a good predictor of the other dependent variables including forage dry matter, and total N uptake, which could indirectly be determined using NDVI. The coefficients of variation (CV's) from NDVI values decreased with increasing vegetation coverage suggesting that less variable NDVI values (CV less than 10%) might be obtained from plots where vegetation coverage exceeds 50%.     

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.     

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.     

Corn nitrogen management using NDVI and SPAD sensor-based data under conventional vs. reduced tillage systems

Present analyses to calculate nitrogen fertilizer recommendations are time consuming and costly. Therefore, a field study determining the efficiency of SPAD and NDVI meters to calculate soil N deficiency and guide fertilizer application timing and rate was completed. Reduced vs. conventional tillage at various N application rates was studied. Regardless of tillage system, both NDVI and SPAD were able to detect N deficiency at early growth stages, however, SPAD measurements better reflected plant N status regarding N application rates. A modified Michaelis-Menten model was used to illustrate the relationship between N rates and grain yield, as well as grain N content and leaf N content, and both showed acceptable goodness of fit. Grain yield under reduced tillage was significantly higher than that of conventional tillage. The combination of leaf nitrogen, SPAD, and NDVI data may become a tool to manage corn field nitrogen status and predict grain yield.     

施氮量对冬小麦氮素吸收、转运及产量的影响

2004至2005年在田间条件下,研究了施氮量0、105、2103、15.kg/hm2对冬小麦氮素吸收、累积、转运、产量及氮肥利用率的影响。结果表明,施用氮肥可显著提高冬小麦的子粒、秸秆产量及成熟期地上部总吸氮量,但过量施用氮肥对子粒和秸秆增产不显著;各施氮处理的氮肥利用率在34.2%～38.3%之间,随施氮量增加而略有降低。植株中氮素含量随生育期的延长而降低,氮素累积量总体呈增加趋势。施氮量对冬小麦氮素吸收有显著影响,同一生育时期,氮素含量和累积量都随着施氮量增加而提高。施氮可显著地促进氮素在子粒中累积,其中69%～87%的氮素是靠营养体的转运而来的。施氮量影响氮素的转运效率,随施氮量增加,转运效率降低。本试验条件下,冬小麦的合理施氮量应控制在105～210.kg/hm2之间。     

Mid-Season Prediction of Wheat-Grain Yield Potential Using Plant,Soil, and Sensor Measurements

ABSTRACT

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-season NDVI, chlorophyll content, plant height, and total N uptake to be good predictors of final winter wheat grain yield.     

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.     

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.     

NITROGEN FERTILIZER MANAGEMENT FOR IMPROVED GRAIN QUALITY AND YIELD IN WINTER WHEAT IN OKLAHOMA

From 2002 to date, a long-term field experiment has been conducted at Lake Carl Blackwell, Oklahoma, with different rates and times of nitrogen (N) fertilizer application to determine their effect on grain yield, protein and N uptake of winter wheat. Trend analysis for N rates (0, 50, 100, 150 and 200 kg N ha^?1) and orthogonal contrasts for different application times (pre-plant, top-dressed in February and March) were performed. With increasing fertilizer N, wheat grain yield and protein content increased from 2110 kg ha^?1 to 6783 kg ha^?1 and from 8.96 to 17.19%, respectively. For grain yield, protein, and N use efficiency, split applications of N fertilizer were much more efficient than applying all N pre-plant. Large differences in grain yields were noted for different years at the same N rate (range exceeded 5.0 Mg ha^?1) and that illustrated the need for making within-year-specific N rate recommendations.     

Nitrogen Application in Winter Wheat Grown in Mediterranean Conditions: Effects on Nitrogen Uptake,Utilization Efficiency,and Soil Nitrogen Deficit

ABSTRACT

Nitrogen (N) is one of the most growth restricting nutrients in cereal grain and represents one of the highest input costs in agricultural systems; therefore, environmental and economic considerations require the effective use of N fertilizer in plant production. This study was conducted for three years to better understand wheat plant response to optimize N fertilizer and how to reduce the risk of ground water pollution.

Two of the most important durum wheat cultivars in Southern Italy and four N fertilization levels (0, 60, 120, and 180 kg N ha^{? 1}, indicated as N0, N60, N120, and N180, respectively) were compared in this experiment. During plant growth, fresh and dry matter, plant nutritional state (SPAD readings and stem nitrate content), and N uptake were determined. At harvest, plant N content, N uptake, grain yield, yield components and quality were determined, allowing the calculation of the pre- and postanthesis N uptake and the N utilization efficiency indices. Furthermore, at the beginning and at the end of each year, soil mineral N was measured to calculate mineral N deficit in the soil.

The results indicated that the treatment with 120 kg N ha^{? 1} of fertilizer ensures a good balance between yield and N utilization. In fact, N180 and N120 showed similar yield (3.01 and 3.07 t ha^{? 1}, respectively) and protein content (13.7 and 13.5 %). Meanwhile, throughout the three-year experiment, N180 presented the highest final mineral N content in the soil at the end of the cropping cycles, increasing the amount of N available for leaching. The N120 treatment showed the same values of N utilization indices as compared to N180, indicating that further doses of N fertilizer did not increase wheat N utilization. Plant N status shows that it is possible to modify the N fertilization to reach its optimum level during plant growth, in accordance with variable weather conditions, and consequently the plants requirements. The mean treatments of the preanthesis N uptake were about 67.5% of the total N uptake, and it was significantly and positively correlated with wheat yield. On the contrary, the postanthesis N uptake showed positive correlation with grain protein content, confirming the importance of late N supply in grains quality. The variation of weather conditions affected winter wheat yield, quality, N utilization and plant N status, but any difference throughout years was found between N180 and N120, confirming that higher N rate did not influence wheat growth, yield, and N uptake.     

灌溉条件下施氮水平对土壤 作物系统中肥料氮素去向的影响

本试验利用１５Ｎ示踪技术，研究３种施氮水平（适宜施氮量Ｎ１０∶１５０ｋｇＮ·ｈａ－１，低于适宜施氮量的５０％Ｎ０５∶７５ｋｇＮ·ｈａ－１，高于适宜施氮量的５０％Ｎ１５∶２２５ｋｇＮ·ｈａ－１）对灌溉冬小麦氮素利用、去向及作物产量的影响。结果表明：在灌溉条件下，３种施氮水平（Ｎ０５，Ｎ１０，Ｎ１５）的冬小麦氮素利用效率分别为３８５％、３２３％和２２４％，以Ｎ０５水平为最高。Ｎ１０施氮水平获得了最高的作物产量（６８０×１０３ｋｇ籽粒·ｈａ－１，１４７×１０３ｋｇ生物量·ｈａ－１），Ｎ０５水平同Ｎ１０水平相比，在产量上没有显著性差异；而Ｎ１５水平因施氮过量造成籽粒产量明显下降，与不施肥相比，差异不显著。在深层条施（５～８ｍｍ）条件下，仍有３０２％～３６７％的化学氮素通过各种途径而损失。在Ｎ１５水平中，施用氮素的４６％仍存在于０～５０ｃｍ土层中，远远高于其它两种施肥水平。土壤残留态的无机氮素含量以Ｎ１５施氮水平为最高     

砂姜黑土强筋小麦施肥技术研究

通过田间试验研究了施用不同肥料和不同施肥方法等对强筋小麦养分吸收和产量品质的影响。结果表明:在氮肥用量相同时,氮肥后移小麦产量和品质均好于全部基施(习惯施肥)处理;高氮和硫酸铵处理能提高强筋小麦的品质。磷酸二铵提高小麦产量效果好于过磷酸钙,而对子粒品质影响则过磷酸钙好于磷酸二铵;高量磷肥虽然不能进一步提高小麦产量,但能改善小麦的品质。增施有机肥和钾肥可促进小麦对N、P、K养分的吸收,显著提高小麦产量和品质,是砂姜黑土区优质高产强筋小麦重要施肥技术。锌肥能提高小麦产量和品质,含硫肥料有改善小麦品质的作用。试验表明,在砂姜黑土上,施用有机肥,稳定磷肥用量,加大氮、钾肥用量,配施锌肥和硫肥,分期施用氮肥(追肥量占总氮量比例在40%以上)有利于强筋小麦的优质高产。     

Furrow diking and N management for dryland wheat production in permanent raised beds

The permanent bed planting system for wheat (Triticum aestivum L.) production has recently received additional attention. Studies using hard red spring wheat (cultivar Nahuatl F2000) were conducted at two locations in central Mexico. The studies included the installation of three furrow diking treatments, two granular N timing treatments and three foliar N rates applied at the end of anthesis. The objective was to evaluate the effect of these factors on wheat grain yield, yield components and grain N in a wheat–maize (Zea maize L.) rotation with residues of both crops left as stubble. Results indicated that diking in alternate furrows increased both grain yield and the final number of spikes per m². The split application of N fertilizer enhanced the number of spikes per m² and grain N uptake, but the effect on grain yield was inconsistent. Similarly, grain protein increased with the foliar application of 6 kg N ha^?1, depending upon the maximum temperature within the 10 days following anthesis. The normalized difference vegetative index (NDVI) readings collected at four growth stages were generally higher for the split N application than for the basal N application at planting. Grain N uptake was associated to NDVI readings collected after anthesis.     

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.     

PERFORMANCE OF DUALEX IN SPRING WHEAT FOR CROP NITROGEN STATUS ASSESSMENT,YIELD PREDICTION AND ESTIMATION OF SOIL NITRATE CONTENT

Dualex and SPAD are devices developed for the purpose of testing crop nitrogen (N) status. These instruments were used in a wheat experiment in order to compare their respective performance in assessing leaf nitrogen (N) concentration, response to N topdressing application, soil nitrate (NO₃)-N levels and in predicting grain yield. The experiment included different N rates in 2005 and 2006 in the Montérégie region of Quebec, Canada. Dualex readings correlated negatively with SPAD readings, leaf N concentration, soil NO₃-N content and wheat grain yield. SPAD alone and the ratio of SPAD to Dualex measurements (Chl/Phen) were linearly related to N application rate but no effect of N application rate was found for individual Dualex parameters. However, both SPAD and Dualex readings were affected by year effects. The Dualex was also capable of indirect evaluation of in-season soil NO₃-N accumulation and the prediction of wheat yield, but more so as Chl/Phen.     

EFFECT OF DELAYED NITROGEN FERTILIZATION ON MAIZE (ZEA MAYS L.) GRAIN YIELDS AND NITROGEN USE EFFICIENCY

Maize grain yield potential can be estimated mid-season using NDVI at the V8 growth stage, thus affording delayed sidedress nitrogen (N) application. Several combinations of preplant and sidedress N at various growth stages were evaluated. Maize grain yields were maximized with 90 kg N ha-1 preplant followed by 90 kg N ha-1 sidedress at V6 or V10 (8 of 9 site-years). Delaying N application until V10 growth stage when preplant N was applied did not result in lower yields. Mid-season N supplies fertilizer at the time when crop need and N uptake are at a maximum, and thus facilitates more efficient N use. Lowest nitrogen use efficiencies (NUE) were observed with higher N rates and when all N was applied preplant. Highest NUE's were achieved with 45 kg N ha-1 preplant followed by 45 kg N ha-1 sidedress applied at V6 growth stage (8 of 9 site-years) and at V10 (6 of 9 site-years).     

By-Plant Prediction of Corn (Zea mays L.) Grain Yield using Height and Stalk Diameter

Methods for determining midseason nitrogen (N) rates in corn have used the parameter normalized difference vegetation index (NDVI) and, in some cases, plant height. The objective of this study was to analyze the relationship of stalk diameter along with predictors of yield, including NDVI and plant height with grain yield. Five site-years of data were analyzed, where several rows of corn plants were selected, and yield from plants within the row was recorded individually. Measurements of stalk diameter, plant height, and NDVI were taken from growth stages V8–VT. Using a value of stalk diameter × plant height gave the best correlation with grain yield (r² = 0.34, 0.55, 0.67; V8, V10, V12, growth stages respectively). This work showed that stalk diameter × plant height was positively correlated with by-plant corn grain yields, and this parameter could be used for refining midseason fertilizer N rates for growth stages V8–V12.