The drought monitor report as of April 2 is showing conditions moving from no dryness to abnormally dry for much of Southwest Kansas and we are still mostly abnormally dry. The six to ten-day outlook (April 9 to 13) indicates near normal temperatures and a 33 to 50% chance of leaning to above normal precipitation. The eight to 14-day outlook (April 11 to 17) indicates a 50 to 60% chance of likely above normal for temperatures and near normal to slightly below normal for precipitation.
Depending where your farm in Kansas, you may or may not think much about soil pH. However, it plays a critical role in crop production and soil health. The pH of a soil is a measure of the acidity or alkalinity of a solution, in this case the soil solution. It measures the concentration of hydrogen ions. A pH of 7 is neutral with a number less than 7 being acid and above 7 basic or alkaline. A pH of 6 is ten times more acid than 7 and 5 is 100 times more acid. For our crop plants, the optimal pH range is 6.2 to 7.2. Why does soil pH matter?
• pH influences nutrient availability. The range just mentioned allows nutrient availability in the proper amounts. As soils become more acid, certain nutrients can be tied up, some can become too available and toxic, while some elements like aluminum become available and damage plants. If soils are too basic it can also tie up certain nutrients. Low pH can also decrease the cation exchange capacity of the soil.
• As soils become more acid, the microbial and fungal communities change. As the pH decreases, beneficial bacteria are eliminated and harmful fungi predominate. This happens as the pH approaches 4.
• Acid soils with free aluminum damage plant roots, especially wheat. Grasses in general are negatively affected as they have a shallow fibrous root system compared to dicot taproots. A major problem with acid soils exists with legume crops such as soybean and alfalfa. As the soil pH falls below 5, the bacteria that infect the roots and provide nitrogen (rhizobium species) won’t infect the roots so no nitrogen is provided and it would all have to come from fertilizer which is cost prohibitive. This is why it’s so necessary to raise the pH before planting alfalfa.
• Herbicide efficacy is affected. At lower pH levels, herbicides like atrazine are ineffective while at high pH, herbicides like sulfonyl ureas can stay hot for extended periods of time in the soil. And for the crop, damage can occur if the rate isn’t adjusted for high pH.
Most of the western half of Kansas, with the exception of the sandhill areas, have pH levels above 7 and for several reasons, including parent material and rainfall tend to stay that way. The sandy areas south of the river here, depending on cropping systems and nitrogen fertilizer additions do need regular liming. The exception is often under irrigation where the hardness of the water helps maintain higher pH levels. True South-Central Kansas, Reno County and south not only tend to become acid but also have enough aluminum to damage crops, especially wheat. North-Central and Northeast Kansas soil also need liming, depending on cropping patterns.
Next week: adjusting soil pH.
Dr. Victor L. Martin is the agriculture instructor/coordinator for Barton Community College. He can be reached at 620-792-9207, ext. 207, or martinv@bartonccc.edu.
