Every field season, I view several crops that are experiencing plant nutrient deficiencies. Many of these fields are rarely, if ever, soil sampled, tested and managed according to soil test recommendations. I also walk a few fields that have been soil sampled and managed according to soil test recommendations, but because of environmental or management conditions still have nutrient deficient plants. Based upon the apparent dichotomy of the previous statements, what role should soil testing play in your farming operation?

First, let me state that soil sampling is not a perfect science. However, you can make it a valuable component of your agronomy program by following a few basic principles.

The standard soil sample collection depth is 62Ú3 inches. This depth was chosen because it represents the old "furrow slice." It also represents approximately 2 million pounds of soil per acre, a convenient conversion number. Many people advocate different sampling depths, especially in perennial forages or no-till row crops, where much of the applied nutrients or nutrient-rich plant residues may be accumulated near the soil surface. I generally do not recommend changing sampling depths because the soil test calibration recommendation equations were developed for the standard soil depth.

The number of soil cores (or slices) taken per sample collected should be between 12 and 25. Generally, the more, the better. Fewer than 12 cores per sample could lead to poor representation if one of the cores is extremely high or low in a given nutrient. If nutrients have been banded in the past, at least 20 cores per sample are needed to increase the potential to even out placement induced nutrient micro variability.

Resampling should be done every 2 to 4 years, depending upon crop grown, fertilizer applied and other agronomic components. For consistency, resample fields the same time of year and preferably after the same cropping sequence that was present during previous samplings.

Tradition has set the maximum acreage represented by one "composite" soil sample to be 20 acres. Therefore, an 80-acre field needs at least 4 separate soil samples. Try to divide sampling areas from fields greater than 20 acres into "sub fields" or management zones. These can be based upon soil type, history, yield potential, field geography, field use or any other "intelligent" choice.

Precision agriculture programs may sample in a tighter acreage pattern. Some programs use standardized grid samples. Other precision programs use some kind of management zone. MFA's precision program often offers a combination of composite, grid and management zone sampling. This offers producers the most applicable agronomic and economic options.

Regardless of the geographical collection pattern, basic soil sampling procedures must be followed. Consistency is the key to an effective soil sampling program.

Even with consistent sampling, there are always anomalies associated with soil testing. Don't be too alarmed if some of your soil tests come back different than expected, or are inconsistent across space or time. Soil is a complex combination of physical, mineral, biological and organic residue systems working together. Given this medium, some unexpected measurements must be tolerated.

Several soil nutrients do not respond predictably across cropping system environments. Soil pH fluctuations are based upon a combination of weather, fertilizers applied, crops grown, crop yield and several other variables. Similarly, soil potassium and phosphorus fertilization, immobilization, crop uptake, luxury consumption and erosion losses are not uniform over time. Mobile nutrients such as nitrogen, sulfur and boron do not move predictably through agricultural systems. A soil test every four years is a poor overall indicator of crop needs for these mobile nutrients. Non-mobile micronutrient (zinc, copper, iron, manganese) solubility and availability vary for several reasons.

Because of the complex nature of soils, regular resampling and long-term monitoring of your soils are very critical components of any soil testing program. Keep resampling components such as soil depth, previous crop, calendar date, sampling interval, acreage and location as identical to previous samplings as possible. Failure to do so will reduce the accuracy of your agronomic nutrient-tracking program. If you have a few samples where soil tests come back unexpected, sample those areas again to make sure sampling error did not occur.

As producers, you can soil sample yourself or hire it done. I believe that when hiring any service, you get what you pay for. Use the most qualified agronomy services available.

Soil sampling is just one component of crop nutrient management. Next month, I will discuss the basics of soil testing and nutrient recommendation programs. Additionally, Lyndon Brush, who works in agronomy services with me, will summarize the results of soil test analysis trend data monitored across our region.