Soil test. Soil test. Soil test.
Those are words repeated often by Saskatchewan Agriculture soil specialist Ken Panchuk when talking about balancing the four main nutrients for crops – nitrogen, phosphorus, potassium and sulfur.
Soil testing is becoming even more crucial for crop production because the levels of nitrogen have become increasingly variable from one field to the next.
“We need to get more farmers soil testing,” said Panchuk. “That’s the message.”
He said there are three main things adding to the nutrient variability.
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This year’s drought is the most obvious reason. Without adequate moisture, the uptake of nitrogen was quite variable.
Some fields of wheat, for example, used the available nitrogen to produce high protein levels, drawing down the nitrogen levels in the soil.
Other wheat fields produced average protein levels, leaving more nitrogen in the soil.
Without soil testing, it can be a guessing game as to how much of the nutrients, mainly nitrogen, will remain in the soil for next year’s crop.
As well, said Panchuk, the mineralization process that makes nitrogen available to crops is reduced in dry soils. Producers with summerfallowed fields need to remember that.
Panchuk is encouraging farmers to test their summerfallow fields. There is still time to do the soil test this fall, but Panchuk said all producers should be soil testing on a regular basis to assist with crop planning.
A diversity of crops is also adding to the nutrient variability.
Some crops are more likely to deplete soil nutrients than others. A wheat crop takes up a lot of nitrogen, and much of that has to be replaced with fertilizer. Pulse and alfalfa crop residues release some nitrogen as they decompose. Soil test labs take this into account when fertilizer recommendations are made.
Panchuk said he visited a Saskatchewan farmer this fall where 20 fields were soil tested. The residual nitrogen levels were as low as 10 pounds per acre in one to as high as 70 lb. in others.
The third thing adding to the variability in nutrient levels is the shift toward minimum or zero tillage for crop production.
Producers need to be aware that during the first few years of reduced tillage, the crop residue on the surface will be slower to break down, delaying the return of nutrients to the soil.
But as the organic matter accumulates, a better environment is created for the microbes that decompose the crop residue. Moisture conserved by the straw is also beneficial to the soil microorganisms.
A healthy microbial population means the straw will decompose faster, and the nutrients will be returned to the soil sooner until reaching a new equilibrium, Panchuk said.
