Farm406

farm406 32 areas are often yellow (similar to nitrogen deficiency, yet less uniform) or even pink. The roots are thickened and necrotic (brown) with a club or "witch's broom" appearance similar to nematode damage. See photos for specifics. Substantial yield losses occur at pH levels below 4.5. The most sensitive cereal crops appear to be barley and durum, followed by spring wheat. Legumes can develop nitrogen deficiency in low pH areas before they exhibit aluminum toxicity because nitrogen fixation is reduced below about pH 6. Producers and their advisers are encouraged to look at pH in their standard 0 to 6-inch soil tests reports. If the pH is consistently above 7.5, it's unlikely the field has a problem. If pH is between 6 and 7.5, a judgment by the crop adviser or producer will need to be made if additional soil sampling or scouting is worthwhile. If soil pH is below 6.0, scout for yellow seedlings, and roots that are necrotic, thickened and/or clubbed. To verify symptoms are caused by low pH, a 0 to 3-inch soil sample can be analyzed for pH, either with a field pH stick, probe, color strips, or lab analysis. Also sample the zone at the edge of poor growth areas because the potential is there for problem areas to grow in size. Even if aluminum toxicity symptoms are not found, soil sampling diverse topographic positions in fields is encouraged because areas where pH is less than 6 should be managed differently to prevent further acidification. The best management approach to slow acidification is to reduce nitrogen-fertilizer inputs to cropping systems, and use that nitrogen more efficiently. This means inclusion of legumes and other crops that use less nitrogen fertilization. For example, perennial forage has been shown to result in a pH that is 0.5 units higher than continuous spring wheat after five years. Nitrogen fertilizer management must maximize nitrogen use efficiency with practices such as split- applications and variable rates. In areas where low pH is already affecting plant growth, producers may select species and varieties of common crops that are more adapted to low pH soils. In fields where low pH is causing crop failure, liming, as done in many other parts of the country as standard practice, may be necessary. Our most alarming finding is that we have found soil pH dropped one pH unit over 14 years after applying nitrogen fertilizer at recommended rates to a field site with an initial soil pH greater than 7. This implies that even a neutral to alkaline soil can become acidified over time by nitrogen fertilization. For additional information go to http:// landresources.montana.edu/soilfertility/acidif/index. html or contact Clain Jones (clainj@montana.edu, 406-994-6076), Jane Holzer (msca@3rivers.net, 406-278-3071), or Dale Krause (kconsulting@ itstriangle.com, 406-622-5627). Stunted growth and club roots from Al toxicity. Courtesy Rick Engel Yellowing leaves from Al toxicity. Courtesy CIMMYT.org Healthy and stunted field pea roots. Used by permission from Alan Robson and UWA Publishing.

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