Nitrogen Management Strategies for Winter Wheat Yield and Grain Protein Improvement in Southeastern Colorado

There is an increasing demand for high quality wheat as the baking industry requires adequate protein levels for their products. Frequently, wheat with higher grain protein is marketed at a premium, and price deductions are incurred for low protein wheat. Protein premiums and penalties have increased the interest among wheat growers in producing high quality wheat that meets the market standard and increases profits.

Protein content is highly dependent on environmental factors, such as precipitation and temperature, genetic potential of cultivars, and management decisions. The most important management practice affecting grain protein content and yield is the rate and timing of nitrogen (N) fertilizer application. Because recent research studies show that variety selection has a big impact on fertilizer decisions, matching N rate and application timing with a variety should be considered. Efficient use of available N from soil and fertilizer is critical for economic wheat production.


Justification

There is an increasing demand for high quality wheat as the baking industry requires adequate protein levels for their products. Frequently, wheat with higher grain protein is marketed at a premium, and price deductions are incurred for low protein wheat. Protein premiums and penalties have increased the interest among wheat growers in producing high quality wheat that meets the market standard and increases profits.
Protein content is highly dependent on environmental factors, such as precipitation and temperature, genetic potential of cultivars, and management decisions. The most important management practice affecting grain protein content and yield is the rate and timing of nitrogen (N) fertilizer application. Because recent research studies show that variety selection has a big impact on fertilizer decisions, matching N rate and application timing with a variety should be considered. Efficient use of available N from soil and fertilizer is critical for economic wheat production.
Wheat producers have two options for applying N fertilizer: (i) as a single application where all N is applied pre-plant or at planting or (ii) as a split application where a small amount of N is applied pre-plant or at planting, followed by a late-winter or early spring topdressing. Dryland winter wheat growers are often reluctant to invest in fertilizer before they assess the condition of the crop in the spring. Split N applications provide increased management flexibility by allowing farmers to adjust N rates according to crop and environmental conditions. By providing N to meet the changing demands of a growing crop, producers can potentially increase nitrogen use efficiency. Increasing grain protein with a split application may provide a demonstrable means to produce high protein content wheat in a sustainable and cost-effective way.
Since the availability of N mid-season is environmentally dependent, the common practice of soil testing before planting is not suitable for detecting N deficiencies late season. Field analysis procedures (tiller counts) and chemical analysis of soil and plant tissue are effective for monitoring N status during the growing season. The main problem with these methods is the time required for sampling, analysis, and recommendations of rates to meet the demands of the growing crop. Delaying N applications may reduce yield potential and protein responses. Chlorophyll meters and spectral sensors (such as GreenSeeker) have been used to assess the N status and N fertilizer needs in several crops, including wheat. Chlorophyll readings have been positively correlated to grain yield, leaf N, and soil NH₄-N and NO₃-N. The speed of data collection and ease of operation make chlorophyll meters an ideal N-management tool.
With the increasing adoption of higher-yielding varieties, it is important to revise current N management practices and recommended rates to meet yield and protein goals. This research will enable dryland wheat growers to produce high-yielding wheat with acceptable protein content and optimum marketability.


Objectives

1. Develop N management strategies for optimum yield and protein content for dryland wheat production.
2. Compare yield and grain protein responses of red and white wheat varieties to contrasting N rates and application timing.
3. Determine if flag leaf N content, chlorophyll readings and GreenSeeker sensor measurements are reliable predictors of yield and protein content in response to N rates and application timing.
4. Evaluate the agronomic and economic performance of predicted N rates using the chlorophyll meter and GreenSeeker relative to N rates chosen by wheat producers.
5. Develop a comprehensive dryland winter wheat best N management guide for producers, extension agents and agricultural consultants.

Methodology
1.
The proposed research project will be conducted in two locations in southern Colorado for three consecutive years (2013-2015). The sites will be located on private farms in Prowers and Kiowa counties and will be managed as a partnership between Colorado State University Extension and the cooperating producers. Expenses related to fertilizers and seed will be paid from the grant. Equipment will be provided by the cooperating producers. The production system will be a no-till wheat-fallow system. The winter wheat variety Byrd, released by CSU in 2011, will be utilized as a high yielding hard red for these studies. For an adapted, high yielding hard white variety, we can utilize either Snowmass (released in 2009) or CO07W245 (released in 2012) depending on market factors and input from CWRF.
The experimental design will be a randomized complete block with a split-split plot arrangement and three replications at each location. The main plots (2 acres each) will be wheat variety. Subplots (1 acre) will be application timing (pre-jointing and boot), while the sub-subplots (0.25 acre) will be N rates. Treatments will include an unfertilized control (0 lb/A) and low, medium and high N rates (40, 80, and 120 lb N/ A). Pre-plant composite soil samples will be collected to determine nutrient recommendations for P, K, and micronutrients.
Chlorophyll readings will be made with a Minolta Chlorophyll meter SPAD-502 at four different growth stages (pre-jointing, jointing, boot, and head emergence). A total of 30 readings will be taken approximately halfway between the tip and the base of the last fully developed leaf from each sub-subplot. Normalized Difference Vegetation Index (NDVI) readings will be taken using the GreenSeeker Handheld Crop Sensor at pre-jointing, jointing, boot, and head emergence. Thirty GreenSeeker sensor measurements will be taken over the wheat canopy at 24” – 48” height at each treatment. Then leaves will be collected, dried and ground to determine total leaf N content by Carlo-Erba NA dry combustion analyzer.
Grain will be harvested from 0.2 acre per plot. Yield will be adjusted to 12% moisture. Total N uptake (total N concentration times aboveground dry matter), N uptake efficiency [(N uptake in fertilized plot – N uptake in the control treatment) / applied N fertilizer], and N use-efficiency (yield per unit N applied) will be calculated. Relative chlorophyll and GreenSeeker readings will be calculated as the ratio between treatment mean readings and the highest mean readings. Cate-Nelson graphs will be used to measure the applicability and reliability of chlorophyll and GreenSeeker readings as predictors of whether a wheat crop would respond to N fertilizer. Nitrogen fertilizer needs for maximum yield and grain protein will be calculated by the difference between the mean chlorophyll and GreenSeeker measurements from an area with 0 N lb/A and enriched N strips (40, 80 and 120 lb/A). End-use quality will be estimated in the CSU Wheat Quality Laboratory using approved methods (American Society of Cereal Chemists) for grain protein and ash content (via NIR spectroscopy), and kernel physical properties (weight, diameter, and hardness via Single Kernel Characterization System). Data will be analyzed using an analysis of variance and the least significant difference (LSD) method. Total N, N uptake, N use efficiency and relative chlorophyll and GreenSeeker readings will be correlated and regressed against yield and protein content.
The educational materials and outreach plan to be developed under this project are inter-related. Annual field days will take place simultaneously with the Wheat Field Days. At field days, attendees will receive progress reports. Due to the significant involvement of Extension faculty, traditional materials such as Fact Sheets and Technical Bulletins will be produced. These materials are CSU Extension trademarks and utilized widely in Colorado as printed and website resources.