ILSOYADVISOR POST

Soil Testing Frequency

The first article in my soil testing series, “How often should I test my soil?”, gave a brief history of soil testing and how it has been adapted over time. At the end of that article, I suggested that appropriate soil testing frequency depends on how precisely you wish to manage fertility inputs and eliminate guessing. When deciding how tightly to manage your soil, consider the following.

How much are you guessing?
A farmer who begins a career in their early 20s could be farming for 40 years. Adhering to the minimum standard of testing soil once every four years, that farmer will test the soil 10 times, leaving 30 years without collected data or valuable information. From this perspective, the minimum doesn’t make a lot of sense.

Generally, home gardeners don’t require an intense system of data collection. Testing once every 4 or 5 years is more than adequate to gauge the nutrient levels in the soil of most home gardens. Typically, home gardening’s impact isn’t intense enough to cause great soil changes. 

Commercial growers, on the other hand, can benefit greatly from annual complete soil data collection. This not only allows a commercial grower to better control cost while enhancing soil health, but it also shows consumers that the grower is making an effort to provide environmentally friendly food by applying only what is needed just before it is needed.

Soil health is important, and we need to monitor and measure it frequently, just like chemical tests. Soil health can ebb and flow with management and if we start down a course to improve it we should measure change along the way, see how we are doing and what the outcome of those changes means to productivity.

What is growing in your soil?
For those with pastures, what constitutes an adequate soil health management system depends on how intensely the pasture is grazed and what supplemental food sources are available to the pasture. If used for grazing and livestock waste is the only major food source, a more intense soil health data collection system is appropriate. Livestock alone many not be able to maintain the highest soil health levels. 

Commodities such as corn, soybeans and wheat tend to be grown on larger acreages. Often in these cases, growers overlook the value of intense soil data collection. When growing commodities, ownership or control of the land as well as land costs can be important factors in selecting a soil management strategy. More intense sampling and management practices allow growers to control costs more easily. The slim margins involved in growing commodities make it important to scrutinize each expense in the operation and work to optimize efficiency.
 
Cation Exchange Capacity
The characteristics of the soil itself can guide your soil management decisions. Heavy soils that usually have a greater exchange capacity are a little more forgiving than low-exchange, light (timber) soils. The condition of heavy soils may not change as quickly as that of lower-exchange soils, which should at least be considered for a biannual testing program. The lower the exchange capacity, the more quickly soil changes because of fertility applications and the more frequent soil testing becomes necessary.

At the end of the day, it is ultimately up to you as the producer to decide how intense you feel a soil testing program should be.  More soil testing is better because it allows you to make better fertility and soil management decisions in real time rather than relying on a set of soil test numbers generated only once every four years.

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