Soil testing for nutrients

The fall of the year is an excellent time to take soil samples to prepare for next year. Nutrient levels are best tested in the fall because if the soil test indicates that the acidity level needs to be neutralized, lime can be applied and incorporated. This will allow the neutralization process to begin and it gives it more time to react prior to planting.

Due to the economic conditions of low prices and low yields, many producers have been cutting back on their fertilizer and lime use. University Outreach and Extension recommends that fields be tested at least every three years. If a problem is noted prior to harvest, it might be good to take a soil test to determine if current nutrient or acidity levels negatively influenced the yield potential.

I have noticed that many fields do not get the proper attention until after problems are observed during the cropping season. At this point, yield has been lost. Having highly acidic soils will decrease yields. It is one of the most common yield-limiting factors in many of our sandy fields. The problem is two-fold. First, the acidic conditions make plant growth difficult. Roots growing in the hostile soil environment can't take up soil nutrients. The acid conditions favor the uptake of manganese, a trace element that will cause stunting and other symptoms. The second part of the problem is that agricultural lime provides nutrients such as calcium and magnesium. When these elements are not in the soil, deficiencies can occur.

We recommend that our Southeast Missouri soils should be in the 6.0-6.5 range for most of our crops. When the pH is 5.3 or below, the soil acidity effects can cause severe yield reductions in the affected areas. To keep this in perspective, a survey of soil test results from this area showed that about 25 percent of our soil samples had a pH of 5.5 or less, much less than the desired range. A pH of 4.0 is 100 times more acid than a pH of 6.0. It disturbs me that each year I see far too many samples in the low 4 pH range. Many producers do not recognize the symptoms of excess soil acidity. As I mentioned, thrips injury is often confused with soil acidity problems. Herbicide injury, seedling disease, and poor stands are often confused with the physiological disorders of soil acidity.

My experience has taught me that anytime I see unusual patterns in the field, then I consider soil pH. I have a pocket pH meter that I can use in the field. During the summer months, I keep the pH meter and the testing supplies in my vehicle. Often the symptoms are sporadic across the field. Some parts of the field have normal looking plants. Other parts of the field have stunted plants. The leaves are often crinkled and the new leaves are pale green with gray-green veins. In some cases, if the manganese levels are low, the leaves will not be crinkled nor have as many of the other symptoms. However, the yield potential is still lowered in these fields. In addition, it has been shown that when the pH is below 5.0, about 70 percent of the fertilizer is not available to the plants. In addition to neutralizing excess acid, agricultural lime provides for better soil structure and the conditions are more favorable for the microorganisms living in the soil. The most commonly applied lime in this area is the red or dolomitic limestone (calcium magnesium carbonate). If the pH is low and large amounts of calcium are not needed, then this lime will work well. If calcium is needed, then the white or calcitic limestone is needed. If the pH is very low and you need a faster acting lime, then pelletized lime, which is much more expensive, would be a better choice. Pelletized lime is very finely ground and will react quickly because of the smaller particles. In order to spread the lime, the particles are glued together to form a pellet. It is important to follow the directions for use and wet the pellets prior to incorporation. Keeping the soil test levels in the normal pH range is important to everyone. The producer will not get the top yield and his cost of production will be higher. The landlord will get more much due to the improved yields. Land value is also based on yield average. If the production drops, then the value of that land will drop as well. The lending agencies also have a stake. If I were a banker, I would like to see evidence that the fields have good production potential.

For more information about soil testing or to get the free boxes to put the samples, call the Dunklin County University Extension Center at (573) 888-4722. University Outreach and Extension programs are open to all Dr. Michael R. Milam is an agronomy specialist and county program director for University Outreach and Extension in Dunklin County.