What's your excuse for not doing soil sampling?

Monday, October 3, 2011

If it's just somewhere on your 'to-do' list, or you have no intention of sampling at all, think again

by KEITH REID

Late summer through early fall is an ideal time to collect soil samples. The fields after harvest are easy to travel across, a few showers have softened the ground to make sampling easier, and there's lots of time to get the results back for planning next year's fertilizer program.

Despite this, I am sure that some of you still have soil sampling on your "to do" list, or have no intention of sampling at all. Let's look at some of the more common excuses I hear for not sampling, and see if they hold up to scrutiny.

"I always put on what the crop removes." This approach may work on many fields, but it does not account for the slow release of nutrients into the soil as minerals break down, so it probably means you are spending more than you need on fertilizer. It will also break down at either extreme of soil fertility levels, underfeeding the crop if soil fertility is very low, and risking environmental harm if nutrients are applied that the crop doesn't need. 

Without a soil test, you have no way of knowing if you are at either extreme.

"I'm going to apply manure anyway." While manure is an excellent source of nutrients for crops, and should be utilized as effectively as possible, the nutrient balance in manure seldom matches crop needs. There will always be too much or too little of one or more nutrients, depending on application rates. Nutrient deficiencies or excesses can develop in the soil unless you are monitoring the situation with regular soil tests.

The other challenge with manure is that the amount available may not match crop requirements. Extensive livestock farms, where livestock numbers are low, are generally exporting nutrients off the farm and should be supplementing with fertilizer. Intensive operations, on the other hand, are usually importing a lot of nutrients in the form of feed, which are then spread on the field, resulting in nutrient accumulation.

"The reports intimidate me." Modern soil test reports include a lot of data, but that can sometimes get in the way of finding the information most important for your operation. 

Concentrate on the big three – soil pH, phosphorus and potassium – and you will have eliminated most of the nutrient limitations to crop yield.  Don't be afraid to ask a Certified Crop Adviser, or call the Agricultural Information Contact Centre (1-877-424-1300) if you still need help interpreting the numbers on your soil test report.

"The tests are too expensive." If you are having a lot of samples analyzed at once, and particularly if you haven't been soil testing for a while, it can look like a pretty big check to the lab if you don't have confidence that the numbers will mean something.

It can help, however, to put the costs for soil analysis into perspective. If a regular soil analysis costs $20 per sample (most are less), and each sample represents 20 acres (it could be up to 25 acres), then the analytical cost is $1 per acre. When you consider that the recommended sampling interval is once every three to five years, the cost per acre per year drops to $0.20-$0.33.

Put another way, this represents the cost of somewhere between half a pound and a pound per acre of either phosphate or potash, or the value of one-twentieth of a bushel of corn.

"I don't have time to collect the samples." Farmers always have lots of tasks competing for their time, so it becomes a matter of making soil sampling a high enough priority.

Many farmers I know help to justify the investment of time by adding value to the sampling process. Walking over the fields after harvest with a probe and a bucket gives them the opportunity to look for patches of perennial weeds that are developing, or to assess annual weed control in the previous crop, or to scout for problems with drainage that need to be addressed. 

Alternatively, if there is no time without more pressing demands, you can hire a crop consultant to collect the samples and prepare them for analysis. BF

Keith Reid Keith Reid is manager (Eastern Canada), Soil Nutrient and GHG
Management, Agriculture and Agri-Food Canada, Guelph.