A fertile soil should be capable of supplying all the elements plants need for growth. Fertility is an essential component of soil health and productivity. Not only must nutrients be present in the soil, they need to be in a form the plant can use. Since these ionized forms of nutrients are soluble in water, plant roots can absorb them along with the water they take up. The rate at which nutrients become available is affected by weather, irrigation, soil type, pH, and fertilizer applications. Nutrients present in forms other than ions are not directly available to plants although they do represent reserves that can become available in the future.
Five different pools of soil nutrients can be found in soil. The “rocks and minerals” pool is also called parent material. This parent material can be a rich source of nutrients, but they release very slowly, generally over decades to hundreds of years depending on climate and rainfall. Organic matter is also a pool of nutrients that slow-release over just a few seasons. When cover crops, manure, compost, or organic fertilizers are added to the soil their nutrients are not immediately available to plants. The organic matter must first be broken down by microorganisms. As the organisms feed and die, nutrients release gradually into the ion form plants can take up.
Two other pools that concentrate nutrients are the surfaces of clay and humus particles. Because of their extremely small size, humus and clay particles have large amounts of surface area relative to their volume. Their surfaces have negative charges which make them very attractive to positive charged cations, which means clay-rich soils have a larger cation exchange capacity (CEC) than sandy soils. However, those with sandy soils can greatly increase their cation exchange capacity through the addition of organic matter and the creation of humus.
The fifth pool represents the nutrient pool immediately available for plant uptake: those nutrients currently in the soil solution, the mixture of water and nutrients in the soil. This pool is in equilibrium with the clay and humus nutrient pools. As nutrients are taken by plants from the soil solution, they are replaced by the nutrients adsorbed to the clay and humus particles. Increasing soil organic matter can increase cation exchange capacity, especially in sandier soils. Research continues on adequate crop nutrition in organic and sustainable systems.
Featured Fertility Publications
Collins,D. C. Miles, C. Cogger, R. Koenig. 2013. Pacific Northwest Extension Publication PNW646.
Collins, D. 2012. Washington State University Extension. EM050E.
Soil Scientist Doug Collins published an article on Readthedirt.org that explains his research on how and when soil nutrients are available to crops.
Steury, 2011. Article highlighting CSANR soil research in Washington State Magazine.
Mullinix, K. and Granatstein, D. 2011. Intl. J. Fruit Sci. 11:74-87.
The WSU Puyallup Research Center faculty have conducted extensive work on compost, manure and biosolids. This website provides information on yard waste and food waste composts, clopyralid, calculating bulk density, nutrient management for organic systems and compost facility operator training events. The site has links to the Compost Mix Calculator the Organic Fertilizer Calculator and Center research publications.
Recorded webinar (online presentation) from Jan 2011 by Craig Cogger, Crop and Soils Scientist and Extension Educator. This seminar discusses research and guidelines on soil amendment choices based on use, nitrogen availability, carbon sequestration potential, handling nutrient imbalances in organic amendments, and an update on herbicide issues in some composts.
Additional Fertility Publications
Video of keynote address by Chad Kruger at the 26th Annual BioCycle West Coast Conference April 2012.
This webinar highlights recent research by Rita Hummel of WSU on struvite as a phosphorus source for greenhouse production of bedding plants and vegetable starts. Her research includes struvite derived from municipal wastewater and dairy manure. Craig Cogger opened the webinar with a brief overview of the phosphorus challenge. After Rita’s presentation of greenhouse research results, Keith Bowers discussed struvite production as one phosphorus removal technology for wastewater at livestock, food processing, and public sewage treatment sites. The webinar closed with a brief summary by Craig and an open question period.
WSU scientist Lynne Carpenter-Boggs is working with an international group of scientists to help find bean varieties and microbial inoculates that will improve yields on the ancient soils that farms in many parts of Africa must contend with. Dr. Carpenter-Boggs took a Flip camera to Africa and shot some wonderful footage of farms, people and animals.
WSU scientists have conducted extensive research on Anaerobic Digestion (AD) as a technology for recovery of methane (energy), stable carbon, and nutrients from organic wastes such as manure, food processing wastes and the organic fraction of municipal solid wastes (OFMSW). Our research has evaluated the technical and economic performance of commercially available systems, developed improved AD reactors, and commercialized WSU patented nutrient recovery technology. This webinar, presented by CSANR director Chad Kruger and CSANR scientist Craig Frear, will provide an update on the latest results from the WSU Climate Friendly Farming Project’s AD research.
Beginning in 2002, organic amendments, cover crops, and soil quality have been investigated in our farming systems experiment. An interdisciplinary team is studying a range of issues important to smale scale, direct-market, and organic agriculture, including nutrient management, soil quality, weed management, economics, marketing, and on-farm research.
Article in Sustaining the Pacific Northwest Newsletter
TerAvest, D., J.L. Smith, L. Carpenter-Boggs, L. Hoagland, D. Granatstein, and J.P. Reganold. 2010. HortScience. 45:637-642.
Reeve, J.R., L. Carpenter-Boggs, J.P. Reganold, A.L. York, and W.F. Brinton. 2010. Bioresource Technology.
Organic Waste to Resources Research and Pilot Project Report. Brown, S., K. Kurtz, C. Cogger and A. Bary, March 2010. Ecology Publication Number 09-07-059. This study tested the benefits of compost and biosolids applications to soils. Benefits included increased C and N levels, improved soil bulk density, water holding capacity and crop yield.
Chapter 16 in Climate Friendly Farming: Improving the Carbon Footprint of Agriculture in the Pacific Northwest. Full report available at http://csanr.wsu.edu/pages/Climate_Friendly_Farming_Final_Report/.
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