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Friday, May 6, 2016

Soil test results show need for soil testing

Sunday, April 3, 2011

Mike Milam
A few weeks ago, I received the newsletter from the Plant Protection Program at the University of Missouri. One of the articles was about the Soil Test Summary 2010 for soil samples sent to the university soils labs located at Portageville and Columbia. This article was written by Dr. Manjula Nathan, the director of soil testing services. While this summary emphasizes the need for soil testing, it shows trends for each region and county. The article can be found on-line at http://ppp.missouri.edu/newsletters/ipcm... archives/v21n4/a4.pdf.

The soils test results of the 23,600 agronomic crop samples analyzed by the university labs in 2010 is presented in this report. It is no surprise that the counties in the Bootheel region had the pH or acidity level in the medium to high range; phosphorus in the very high range; and potassium in the medium to very high range. The report concludes that ?a higher percentage of adequately fertilized soils occur in the intensively cropped Bootheel region.? As one might expect, the ozarks had a higher percentage of low fertility soils. While the data show that the majority of our Bootheel soils have adequate fertility, the trend during the past decade shows that the number of soils low in pH, phosphorus, and potassium show the need for farmers to test their soils frequently and to apply fertilizer and lime as recommended. By following the recommendations, producers can avoid the potential yield losses and depletion of the necessary nutrients for plant growth and economically viable crop production.

The data also show that row crops are better fertilized than forage crops. Part of the reason is that the row crops are usually found on the better soils because of the higher commodity prices and a better prospect of economically viability. Also, many of the forage crops are grown in areas that have too much slope and are not suited to row crops. Many of the forage crops are located in the Ozark area which has lower fertility soils.

The University of Missouri Extension recommends that fields be tested for nutrients at least every three years. In my opinion, the best time to soil test is in the fall as soon as the crop is removed from the field. There are several reasons to test in the fall. The first is that the producer has had the growing season to make observations related to plant growth and development. If there are problems in the field, then soil fertility needs to be ruled out. The second reason is that if agricultural lime needs to be applied to neutralize excess soil acidity, then there is more time for the reaction to occur prior to planting.

In wet years, it is often hard to soil test in the fall so producers will delay testing until the spring. I can?t stress enough the importance of soil testing. However, soil testing can be done any time of the year. The nutrient management plan is one of the building blocks of a successful farming operation. In dry years such as last year, the results might underestimate some of the nutrients that were not utilized by the plants.

In addition to the nutrient recommendations of the soil test, the recommendations will also address soil acidity and lime recommendations. It is best to keep the pH of the soil in the 6.0-6.5 range. pH is the measure of acidity or alkalinity in the soil.

Applying agricultural limestone must be done prior to planting or in the fall after harvest. So we are getting close to the limit for lime application this spring. However, for the soybean-wheat double crop system, if lime is needed, it can be applied after the wheat has been harvested.

Since it is getting late for lime application, producers need to be aware that even the slightest amount of acidity neutralization can be beneficial. The full benefit from late applications may show up the following year. In the event, that late liming is needed, it is best to use a lime material with the highest ENM possible. The ENM or effective neutralizing material is available from the dealer and this is a combination of several factors including particle size and the purity of the product. The smaller the particle size, the faster that the neutralization will occur. Since agricultural lime generally has a mixture of particle sizes, some neutralization will take place and it might be enough make conditions for favorable in the root zone.

The soil test will also recommend the type of lime needed. If calcium is low, then the white or calcitic lime should be applied. If magnesium is low, then the red or dolomitic limestone is needed. Some growers try to get pelletized lime to apply for quick reaction, but this is very costly.

The take home message is that fields need to be sampled so that the nutrient management plan will be a success. If lime is needed, the longer the opportunity to react with soil acidity will result in better conditions in the root zone.

It has been observed that during times of economic uncertainty, producers will cut back on their nutrient levels and soil testing. One difference now is that many producers have signed up for federal government farm programs that include nutrient management.

University of Missouri Extension programs are open to all

Dr. Michael R. Milam is an agronomy specialist and county program director with University of Missouri Extension in Dunklin County.

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