Dept. of Crop and Soil Sciences

Nutrient Cycling & Rhizosphere Ecology

The goal of our program in Nutrient Cycling and Rhizosphere Ecology is to further the understanding of soil-plant relationships as related to mineral nutrition, crop productivity and long-term sustainability of agroecosystems. We are addressing nutrient management issues facing agriculture (especially in Washington State) by improving nutrient use efficiency, optimizing crop productivity and quality while enhancing environmental quality and soil productivity.


Research topics:

Nitrogen Cycling and Use

Nitrogen is a primary factor in plant productivity and environmental impact of agricultural systems. We have characterized N cycling, plant N nutrition and defined best management practices for improving N efficiency in numerous systems including dryland cereals, irrigated potatoes and even golf greens. We have also developed a unique approach to evaluating N use efficiency and its soil and plant components. In addition, Manure Nutrient Balancer (MNB) is a decision support model we developed to determine agronomic rates of land-applied manure based on N, P and K inputs, soil conditions, manure characteristics, application methods and crop requirements.

Root Physiology, Morphology and Monitoring Tools

Assessments of nutrient cycling and rhizosphere ecology requires reliable tools for quantifying and modeling root system development and function. We have been at the forefront in developing approaches for 1) digital analysis of a) harvested, washed root samples and b) intact root systems, using simple scanning equipment and 2) modeling root system relationships between root age and nutrient uptake. We have then applied these techniques to examine the ecological and management implications of cropping systems on root development.


The overall goal of this interdisciplinary collaboration between WSU, UW and other partners is to stimulate an integration of the Pacific Northwest paper and agricultural industries for improving their environmental and economic sustainability. Phase I of this project was initiated to explore the potential for using crop residues (primarily wheat straw) as a supplemental source of fiber in papermaking and also utilize the straw pulping waste to produce a fertilizer/soil amendment for recycling nutrients and organic matter to enhance soil productivity and quality. Current research objectives will be to determine optimal straw pulping, fiber blending and black liquor processing for producing corrugated medium, linerboard and fertilizer amendments appropriate for U.S. paper and agricultural industrial scales.

Straw utilization alternatives to field-burning are needed to improve the sustainability of wheat and Kentucky bluegrass seed production in the Pacific Northwest (PNW). Increasing restrictions on post-harvest residue straw burning have resulted from public concerns over air quality. Management systems that minimize reliance on burning are needed. Straw removal can improve bluegrass seed production and no-till direct seeded cereal based systems, but viable economic outlets for the harvested straw are limited, resulting in the accumulation of unused stacks of straw by producers. At the same time, a major challenge to fiber-based manufacturing industries of the 21st century is the optimized utilization of plant/crop based renewable resources. Current studies are being designed to assess crop straw sources for ethanol and industrial chemical production. Related site:

Cover Cropping

Cover crops can be used in irrigated systems of the Columbia Plateau for soil protection, reducing nitrate leaching, and addressing pest management problems. Our earlier research suggested that vigorous and well-established cover crops can provide ample soil coverage and recycle sufficient N to reduce fertilizer requirements enough to pay for the management of the cover crop. Cover crop options have been identified for different situations related to planting windows afforded by varying harvest dates, N recovery goals, and pest issues. Cover crops can be used as green manures, grazed by livestock, or harvested as forage. A diversity of crop species have been evaluated for growth, N accumulation and soil surface coverage and fitted to growing degree models. Variations in climate and soils in the Columbia Plateau warranted an examination of climatic variations that require site specific cover crop management options within the region. In addition, it has been unclear as to the extent of current use of winter cover crops. GIS and remote sensing techniques may provide a valuable tool for evaluating current use, needs and future improvements in cover crop adoption.

Precision Nutrient Management

Precision Farming has been called the greatest technological advancement in agriculture since the invention of the tractor. That may be a bit premature, but the concept is exciting and the technologies are now available to experiment with some radical changes in the way we manage farm fields. The idea is to manage chemical inputs, tillage, seeding rates and crop selection site-specifically to account for the soil and microclimatic variations that influence crop growth and yield within a field. This represents a dramatic departure from more traditional uniform management of whole fields, which ignores changes in soil and growing conditions across a variable topography.

It is predicted that site-specific management will improve the efficiency of cropping systems, improve yield and quality while reducing environmental impact due to chemical and soil losses. However, we need to improve our understanding and our methods of assessment, analysis, data integration and management, predictive tools to provide reasonable recommendations that are applicable on a site-specific basis. Soil Scientists and Agronomists have a lot of work ahead of them! Recently available tools such as global positioning, geographic information systems, remote sensing, portable field monitors, yield monitors and variable rate applicators promise to reshape the way we manage our cropping systems.




Dr. WIlliam L. Pan
Professor / Scientist

Dept. of Crop and Soil Sciences
201 Johnson Hall
PO Box 646420
Pullman, WA 99164-6420

Phone: (509)335-3475
Fax: (509)335-8674


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Dept. of Crop and Soil Sciences, PO Box 646420, Washington State University, Pullman WA 99164-6420, 509-335-3475, Contact Us