Soil and water

Build your soil this fall

Our fall weather is quite unpredictable.

Hopefully we will recover from the recent snows and still have some time for fall yard work.

This last season, I didn’t plow my garden at all and it did very well. I did my usual activities of fertilizing, weeding, hilling my potatoes and applying good organic matter to the soil surface. I always had a part of my garden that I didn’t plow, but this year I didn’t even plow where I planted my potatoes.

Intermountain soils in the west tend to have a high pH and low organic matter content. The typical pH of our soil varies from 7.2 to 8.2 (alkaline soils). The reason for this is the high amounts of calcium in our soils. In addition, our irrigation water has mainly filtered through the soil, so the pH of our water is also above 7.2. The higher you go in the mountains, the lower your pH will generally be.

The challenge with alkaline soils is that certain nutrients, especially iron, are immobilized in the soil chemistry. Some plants find it difficult to extract iron from alkaline soil. This is why we are seeing a number of plant species with iron deficiency in mid to late summer in eastern Idaho. Symptoms of manganese, copper and zinc deficiency can also appear in alkaline soils (see nutrient availability table below).

Ron Patterson

Because our soils are calcium-based and calcium is a powerful buffer, there isn’t much we can do chemically to lower the soil’s pH. Although sulfur can be added to achieve a temporary drop, it is not economical to apply the amount of sulfur needed to effectively lower the soil pH for a reasonable period of time. Regular application of chelated iron (EDDHA formulation) will help, as chelated iron does not bind as easily to soil chemistry, remaining available for plant use.

There is a silver lining in the fact that the decomposition of soil organic matter will lower soil pH over an extended period of time. However, research indicates that conventional tillage, regardless of organic matter supplementation, will often result in a higher pH than neighboring soil that is not tilled. Tillage introduces more oxygen into the soil, which “burns” organic matter faster and the pH rises. A best practice is to allow the roots of annuals to decompose naturally and introduce organic matter to the soil surface. Microorganisms will slowly break down organic matter and integrate it into the soil structure.

The life in the ground is incredible. Excessive tillage disrupts the ecology of the soil. The soil system has natural checks and balances for pest problems, and fall is a good time to apply some soil construction principles.

So what can we do about it in our yards and gardens?

Find ways to reduce tillage and add 2-4 inches of organic matter each year to help improve your soil. If possible, let the microorganisms do the tillage for you. Have fun getting your garden ready for next year.

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