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How often should soil samples be taken?
by Ron O'Hanlon, President
Member, National Alliance of Independent Crop Consultants, CPCC-I Certified
The quickest answer is “it depends.” The question that has to be answered is “what information do you want from a soil test report?” The old rule of thumb has been that soil samples should be taken every three to four years. This was based on information that both phosphorus and potassium (major nutrients) do not leach readily and, therefore, the changes from year to year would be minimal. However, nitrate nitrogen does leach readily and it has value for the next crop, if there is any residual carryover.
In today’s high-production agriculture, it may pay to take soil samples every year in order to take advantage of any nitrate carryover and to monitor the soil pH and aluminum levels, especially in areas where they may be a concern. Due to the variability in soil testing and sampling, it is good to establish a base level of soil nutrients in order to know when an individual test in a particular year may be a fluke and not representative of the overall soil nutrient level. This is one of the reasons grid sampling on 2.5-acre grids, or even smaller units, has caught on with the farming community. It is important to know what the base nutrient level is for a particular field in order to make valid soil nutrient recommendations.
I would recommend soil testing every year on ground that will be planted back to a crop within a six- to 12-month time period. However, instead of testing for all the nutrients, just select those that are quite variable within this short time period and test the slow-leaching nutrients on a three- to four-year rotation.
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