How Little Fertilizer Can You Get Away With For Wheat?

Record fertilizer prices have many farmers asking how little they can get away with, or whether they should be applying fertilizer at all? The answer would be simple if every field responded to fertilizer in the same way. The reality of agronomy is that response to any input is variable, so we are always playing the odds. Fortunately, it’s a gamble that pays back more often than not. However, we should be managing our fertilizer program to pick a winner as often as possible. It is doubly important this year, because grain prices are also very attractive. You don’t want to miss out on opportunities for increasing yields. 

Short Term Considerations - Starter Response

Winter wheat is very responsive to high levels of phosphorus near the seed. Unless your soil tests are way up there, you can expect a kick of 3 to 7 bushels from starter fertilizer. The amount you need to add to get this increase must be high enough to raise the concentration in the seed band, but it only needs to carry the plant until it has a well established root system. Don’t go any lower than 15 lbs/ac (17 kg/ha) P₂O₅ as a starter – 30 lbs/ac (34 kg/ha) of MAP, 5 gal/ac (11.3 litres/ha) of 6-24-6, or 3.5 gal/ac (39.4 litres/ha) of 10-34-0. 

Medium Term Considerations – Meeting This Crop’s Requirements

A winter wheat crop with a well established root system can pull enough P and K out of the soil to carry it through to maturity, IF there is enough in the soil to start with. If your soil test is low for either of these nutrients, then it will pay you to add them as either fertilizer or manure. You can do this by broadcasting, or by increasing the amount applied through the drill. Watch out for the maximum safe rates, which are 13.5 lbs/ac N (15 kg/ha) or 27 lbs/ac N + K (30 kg/ha) of N+K if all of it is going to be banded. 

Long Term Considerations – Crop Requirements Over the Rotation

A 100 bushel wheat crop will remove about 60 lbs/ac (68 kg/ha) of phosphate and 35 lbs/ac (40 kg/ha) of potash. If the straw is removed it will remove 70 lb/ac (79 kg/ha) phosphorus and 120 lbs/ac (135 kg/ha) of potash. If you rely solely on only 15 lbs/ac (17 kg/ha) of P₂O₅ in your starter, your soil fertility levels will eventually decline. You will need to assess for your own farm whether there are other sources of nutrients that will help to make up this shortfall, or where it makes the most sense for you to be operating on the scale from build-up to drawdown of soil fertility.

It still makes sense to use low rates of starter fertilizer on wheat. Even at current phosphorus prices, yield increase will often cover the cost of these applications. Long term, consideration must be given to the soil bank account, and what strategy will keep high yields coming down the road.

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