Optimizing Water and Nitrogen Use for Sustainable Wheat Production

View the project final report

• 2016 annual report

Commodities

• Agronomic: wheat

Practices

• Crop Production: irrigation, nutrient cycling, application rate management
• Production Systems: general crop production

Water and nitrogen (N) are two key components for most cropping systems. Sustainability of crop production in semi-arid and arid regions of the Western U.S. is threatened by limited water availability, which results in increasing competition from urban development, environmental restrictions, and energy production sector. Altered geographic distribution, intensity, and frequency of extreme climate events (such as heat and drought), and the recently approved water rights will continue to present challenges for agricultural producers in terms of water resource use and socio-economic stability. This phenomenon is compounded by the inefficient use of precious irrigated water due to the lack of solid scientific knowledge and clearly demonstrated methodologies for water and nutrient conservation. Nitrogen fertilizer is the principal (and the most costly) nutrient input, yet its use efficiency is only about 40 -50% in most U.S. agricultural operations. Thus, 50-60% of N fertilizer applied to cropland is not used by the crops and is lost to the environment. Low N use efficiency (pounds of N applied per bushel of crop produced) is resulting from a loss of applied N from the soil - plant system via various pathways including gaseous plant emission, denitrification, leaching, surface runoff and volatilization. An increase of N use efficiency in cereal production, by just 10 %, would translate into savings of U.S. $5 billion annually  and substantial improvement in environmental quality. Improving N use efficiency in cereal crops is a challenging task that encompasses the ability to accurately estimate a crop's need for N and developing nutrient management practices that would provide the best return from fertilizer application. Wheat is an integral crop for Western U.S., where it is grown as a main cash crop or as a vital rotational crop in combination with other high-value crops such as vegetables. There is an urgent need to develop more efficient nutrient management strategies in order to maximize wheat grain yields and enhance grain quality. Advanced crop canopy sensors utilize the optical characteristics of plants and their associated vitality and health properties. The newly emerged hyperspectral remote sensing entails acquiring images in narrow and continuous spectral bands. These sensors are very useful for detection of specific characteristics and differences in vegetation. The recent technologies such as high-resolution multispectral sensors, hyperspectral digital cameras, spectroradiometers, and other optical sensors could play an important role in managing nutrients within the crop production systems. The specific portion of the electromagnetic spectrum -  i.e. narrow bands - have shown significant improvement in accuracy of discrimination capabilities among various types of plant stresses. Accurate and timely information regarding both water and N status obtained with remote sensors can be of tremendous help for irrigation and fertilization decision making. The proposed study aims to demonstrate that sensor-based technologies, utilized in combination with traditional practices such as soil testing and evapotranspiration (ET) monitoring, can substantially improve the management of N and water use. This study will serve as an initial step in developing robust practical sensor-based water and N management methodology for a variety of key crops grown in semi-arid regions. This project will enable us to identify the most valuable environmental and plant measurements for developing such a methodology. Agronomy Advisory Committee and Fertilizer Tax Advisory Committee are two key stakeholder groups in Idaho and Montana, respectively, advising University research and extension faculty. These two groups, as well as Idaho Wheat Commission, Idaho Barley Commission, Idaho Bean Commission, and Montana Wheat and Barley Commission, have highly supported this collaborative project. Addressing sustainability of crop production and food security in the context of continuously rising fertilizer costs and water limiting environment has been identified as the primary objective by many of these stakeholder groups. In close collaboration with wheat producers, we choose to conduct the field studies in Southern Idaho (where wheat is grown as a primary rotational component in cropping systems dominated by potatoes, sugar beets and seed crops)  and Northwestern Montana (where exceptionally high yield and exceptional quality wheat is a primary cash crop). The project incorporates research and education focused on: 1) conducting field studies for determining the minimum N and water requirements for optimum wheat grain yield and quality, 2) developing a sensor-based system for identifying - and distinguishing between - N and water stresses, 3) developing an empirical model for predicting wheat yield and protein content in varying water x N interactions,  4) developing water and N use recommendations for growers based on developed model, and 5) delivering extensive educational outreach programs (workshops, field demonstrations, scholarly and educational materials) focused on water and nutrient conservation and utilization of sensor-based technologies. Expected outcomes: 1) developing grower recommendations derived from scientifically sound and robust model based on locally obtained data; and 2) improved grower understanding of how sensor-based methodologies can be successfully utilized for improving the efficiency of water and nutrient use.

Specific objectives and how we intend to achieve them:

Objective 1.    Determine the minimum N and water requirements for optimum wheat grain yield and quality.

• Response of wheat grain yield, grain test weight and grain protein content will be evaluated in four N environments (0, 50, 100, and 200 lb N/a) in combination with three water regimes (100%, 75%, 50% ET).
• Combination of minimum N and water levels at which no significant increase in wheat grain yield and quality is observed will be identified.
• Wheat plant height, leaf area, biomass production, chlorophyll content, tissue N content, and plant spectral reflectance will be monitored throughout the growing season to enhance our understanding of which plant physiological parameters are most helpful in predicting yield and quality mid-season.

Objective 2.    Develop a sensor-based system for identifying - and distinguishing between - N and water stress.

• Canopy spectral reflectance measurements will be collected with an Analytical Spectral Radiometer Device (ASD) from wheat grown in varying N x water environments discussed in Objective 1.
• ASD provides uniform data collection across the entire solar irradiance spectrum (350 nm - 2500 nm).
• This device will enable us to identify specific wavelengths that correspond to water and N stress and will help us to distinguish the two types of stress.

Objective 3.    Develop an empirical model for predicting wheat grain yield and protein content in varying water x N environments.

• Sensor-based indices derived from wheat spectral reflectance data and physiological parameters (detailed in Objective 1) will be statistically accessed and correlated with wheat grain yield and quality.

The relationship between the indices and parameters that explain the most variation in wheat yield and quality will be used to develop a model.

Objective 4.    Produce grower recommendations based on the developed model

• The sensor-based model will be used to develop practical grower recommendations for N fertilization and irrigation management to optimize wheat grain yield and quality.
• Specific water and N savings obtained with utilization of the model will be calculated.

Objective 5.    Improve grower adoption of efficient water and N application practices and enhance grower understanding of sensor-based technologies.

• We will deliver hands-on workshops on utilization of crop sensors, seminars on water and nutrient use efficiency and field days for demonstrating wheat response to various N x water environments and model utilization.
• Growers' attitude, knowledge and adoption will be measured using Western Region Sustainable Agriculture Research & Education Program Outreach Survey (Appendix E).