CAHNRS > Washington Oilseed Cropping Systems > Soil Fertility

Soil Fertility

Canola plant.

All essential elements are required in order for canola plants to complete their life cycles. To maximize yield, adequate levels of all essential elements are required. Essential elements are categorized as either macronutrients or micronutrients. Plants require macronutrients in larger quantities than micronutrients. However, micronutrients are just as essential to plants completing their life cycle as micronutrients. The macronutrients of greatest regional importance to canola production are Nitrogen, Sulfur, and Phosphorous. Boron and zinc have been found to be deficient in the region.

Extension Publications

Cover of FS045E.

Canola Growth, Development and Fertility (FS045E)

The purpose of this guide is to summarize current information on canola growth and fertilizer requirements. Canola is a relatively new crop to the Pacific Northwest and little fertility research has been conducted in this region. The information contained in this guide is intended to serve as a reference until the results of ongoing, local research are available. Canola is distinct from wheat in terms of growth habit, nutrient uptake, and nutrient removal in the seed. According to published research and fertilizer recommendations, canola requires more nitrogen and sulfur than wheat to achieve the same yields. Soil test-based requirements for phosphorus and potassium are similar to wheat, but boron requirements are higher. Because canola plant residue is higher in nitrogen and phosphorus than wheat straw, cycling of nutrients from residue to the subsequent crop may be an important rotational benefit of canola.

Visit the Department of Crop and Soil Sciences site to see all the CSS Field Day Abstracts.

  • Pan, W. 2015. The Roots of Soil Fertility. Invited Leo M. Walsh Soil Fertility Distinguished Lectureship, recorded at ASA-SSSA-CSSA meetings, Minneapolis, MN. December 16, 2015.
  • Madsen, I.J., M.E. Reese, T.L. Beard, T.M. Maaz, L.E. Port, M.L. Nunez, J.C. Huettenmoser, and W.L. Pan. 2015. Subsoil Accessibility and Nutrient Availability in Three Rainfall Zones in the Inland Pacific Northwest. Climate Change and Cereal Production in Semi-Arid Regions of the World. REACCH International Conference. Minneapolis, MN.
  • Madsen I., W. Pan, and R. Bolton. Detecting Moisture Change in Fertilizer Microsites through Soil Color-Moisture Calibrations. Soil Science Society of America Annual Meeting. November 16-18. Minneapolis, MN. 2015. ASA/SSSA/CSSA Online Program; SSSA Division: Nutrient Management & Soil & Plant Analysis. ASA/SSSA/CSSA Annual Conference; 11/15-18/2015; Minneapolis MN.
  • Koenig, R. 2012. Oilseed Fertility Management. It’s Not Your Father’s Wheat. Oral presentation in Pacific Northwest Oilseed Crop Adaptation session. Northwest Bioenergy Research Symposium. Seattle, WA. Nov. 13, 2012.
  • Pan, W., A. Hammac, T. McClellan, I. Madsen, L. Graves, K. Sowers, and L. Young. 2012. Oilseed Root Characteristics: Implications for Water and Nutrient Management. Poster presentation at Northwest Bioenergy Research Symposium. Seattle, WA. Nov. 13, 2012.

Nitrogen in Canola

Nitrogen (N) is frequently one of the most limiting nutrients in canola production systems in the Washington. Nitrogen is taken up by plants as either ammonium (NH4+) and nitrate (NO3–). Ammonium is generally considered immobile and does not leach deep into the soil profile whereas nitrate is generally considered mobile and can leach with in the soil profile. Due to the variation in mobility ammonium samples are only taken in the surface soils whereas nitrate samples are taken to a depth of 4-6’. Nitrogen deficiencies show up as yellowing on the oldest leaves. While some level of nitrogen correction can be made during the growing season it is preferable to develop a strong nutrient management plan prior to the growing season.

Phosphorus in Canola

Phosphorus (P) is a structural component of DNA, RNA, and cell membranes in living organisms. Phosphorous has limited mobility in the soil and in acidic or alkaline soils, P can become strongly absorbed to soil particles thereby reducing the availability of P to the plant roots. Plants have developed a variety of strategies to improve P availability. Phosphorous may be a limiting nutrient in canola production. However, in the majority of P research studies conducted in Washington it was found that P replacement strategies common in wheat production were adequate for supplying canola P needs. Anecdotal evidence indicates that soil test P can be increased through the frequent use of canola in rotation.

Sulfur in Canola

Sulfur–like N–is an essential element for plant growth and frequently a limiting factor in agricultural systems. Sulfur is taken up by plants as the anion sulfate (SO4–). In wet years, SO4– may leach deep into the soil profile. When developing a canola nutrient management plan, soil samples for SO4– should be taken to a depth of 3-5’. In the canola plant S is an immobile nutrient which means deficiency symptoms will most likely show up on new leaves. Frequently, S deficiency symptoms do not show up until the plant has initiated bolting. S deficiency is characterized by cupped and purple leaves on the stem.

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Samantha Crow
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