Home & Garden: Test soil before you plant | PostIndependent.com

Home & Garden: Test soil before you plant

Curt Swift
Free Press Gardening Columnist

Fall is the time to have your soil tested in preparation for spring planting. Whether you intend to plant a new garden, orchard, lawn, lavender field, or field crop, a soil test can help your planting be a success.

Plus, collecting a soil sample is easy. Dig a hole and take a slice of the soil of the edge. Interpreting the results and making recommendations based on those results is the technical part.

During my final years working with Colorado State University, I interpreted and made recommendations specific to the plants being grown for over 700 soil-test reports. Now that I’m retired from that position, I continue to review and make recommendations based on soil-test reports. In some cases the recommendations are unfortunately made after the plants already suffered from assorted soil problems. A great example of this is the field of dying pinto beans in Montrose. Shortly after I identified the plants as dying from Fusarium root rot — a disease of beans and many other plants — a soil sample was collected and sent off for analysis. Beans should have never been planted in that field; the nitrogen level was much too high.

Beans have a symbiotic relationship with Rhizobacteria that form nodules on their roots. These bacteria convert nitrogen gas in the soil atmosphere to plant-available nitrogen. When soil already contains a high level of nitrogen, these nodules do not form and the bean plant is therefore unable to obtain the nitrogen it requires. While this may not make sense, the health and yield of beans and other legumes suffers when soil nitrogen exceeds a specific level.

The same problem can occur when fertilizing a grass/legume hay field. Nitrogen is not needed if the mix is 50-percent alfalfa or greater. The critical level for legumes differs for each crop whether it be beans, peas, red bud or honeylocust trees. Peas, which obtain 80 percent of their nitrogen from nitrogen-fixing bacteria, benefit from a small application of nitrogen based on a soil test. In addition to yield loss, these nitrogen-deficient plants are unable to produce the root protectants necessary to prevent invasion by soil-inhabiting root pathogens such as Fusarium.

A soil test prior to planting provides the information necessary to prevent yield loss. Even the non-nodule forming legumes such as Honeylocust have nitrogen-fixing bacteria, providing them with the required nitrogen. Researchers found these legumes have nitrogen-fixing bacteria in their root cells.

Get in touch with me at curtis.swift@alumni.colostate.edu if you have questions.

Free Press columnist Dr. Curtis E. Swift is a retired horticulture agent with the Colorado State University Extension. Reach him at Curtis.Swift@alumni.colostate.edu, 970-778-7866 or check out his blog at http://SwiftsGardeningBlog.blogspot.com. He owns Swift Horticultural Consulting and High Altitude Lavender.


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