Harvest is approaching and it is time to plan for soil testing this fall.

Many farmers cut back or skipped P (phosphorus) and potash (K) this crop year. This makes soil testing for the 2010 crop important.

First, it will help plan for fall P and K fertilization programs. Second, it will allow for needed P and K to be placed where it is needed. Fall applications of P and K have many advantages. Check them out.

High P and K prices in 2009 caused many farmers to alter their fertilization programs. What did this do to their soil fertility? What effect will this have on 2010 crops? Are P and K soil values falling, staying the same or increasing?

Soil testing this fall is the best program to determine what is needed to keep crop yields profitable.

1. Know if P and K are needed.

2. Put the P and K where it is needed.

3. Use the right rate of P and K.

Grid sampling followed by Smart sampling, coupled with variable rate applications, are the answer to many problems. Soil type is not the best way to identify variability in the fertility status of a field.

P and K needs are best determined using a 2.5- to 5-acre grid.

Here are some questions farmers are now asking.

1. When should soil sampling be done? Fall or spring are excellent times to soil sample. Fall sampling is popular in the South because many soil testing labs are not as busy in the fall as they are in the spring. Whenever sampling is done, do it at approximately the same time each sampling period.

2. How often should soil samples be taken?A soil test recommendation is normally good for three years. Therefore, soil sampling can be done on a three-year rotation. Many farmers are using a two-year rotation. This is best due to high yields and nutrient removal and high N rates being used on corn. Depending on what crops are grown, sample after that crop with the greatest removal rates of P and K. To monitor pH, sample after high N-requiring crops like corn.

3. How deep should a sample be taken?Sample depth should be 6 inches. This is important because the soil lab recommendations are calibrated for a 6-inch analysis.

Make sure that the sample depth remains constant for all samples and years.

High yields and soil fertility levels

Nutrient uptake and removal with today’s crop yields in the Mid-South are great and have an impact on soil fertility programs.

A plus for soil sampling is the determination of pH. A soil test is the best, if not only, method for determining soil pH. The soil test measures the pH and lime requirement and this produces a lime recommendation. pH and lime are extremely important in a soil fertility program.

To keep crop yields high and profitable, know pH and lime needs, and apply the lime. While lime can be applied at any time, fall is an excellent time to apply lime.

Another plus for a soil test is the measurement of the cation exchange capacity (CEC) of the soil. CEC provides a great amount of information about a field. Mainly it classifies the soil as a clay, sand or silt. This determines if fall K applications can be used, the lime rates to correct low pH, the potential compaction problems and much more.

Fertility note for rice

Phosphorus deficiency in rice is being found in rice fields in the Mid-South region. Look for this problem in fields with a pH greater than 6.5. When potash deficiencies are found, the pH is usually low, below 6.0.

Zinc is an important micronutrient for rice. Soil test reports show that many rice fields in the Mid-South have a pH above 7.0 and some approach 8.0. High pH and high phosphorus soil levels reduce availability of zinc and can cause zinc deficiency. The zinc ion is a cation and levels in the soil can be built by soil applications of a zinc fertilizer.

Zinc can be applied in a preplant dry source or as a foliar after emergence.

Zinc deficiency is exhibited by yellow discoloration of the top leaves.