Fertilizing for a Profitable Wheat Crop

Growing a profitable wheat crop depends on many factors, including choosing the proper variety, planting at the right time and into the right soil conditions, controlling weeds, and minimizing harvest losses. Fertilizer management is an important part of this package, and can help to ensure the rest of your investment has a chance to pay off.

Nitrogen

A wheat crop needs most of its nitrogen in the spring, during the period of rapid growth through to grain fill. Fall nitrogen requirements are much more modest since the amount of crop growth will be small, but the crop cannot grow without any nitrogen at all. The amount that is needed could come from the soil supply of nitrogen, or from a starter fertilizer. Research has demonstrated that adding one part nitrogen for every four parts of phosphate in a starter fertilizer will increase the uptake of phosphorus. I suspect that cool soil conditions will have a far greater influence on crop growth than any nutrient deficiency, so the added nitrogen will not make much difference.

Some consultants have suggested that adding extra nitrogen at planting can help to compensate for late planting by encouraging a more vigorous stand. We know that nitrogen does encourage vegetative growth, but I haven't seen any data to support whether this practice really works. I would welcome any plot results you can provide.

Phosphorus

One thing that field trials have shown is that, if you are going to apply any fertilizer to wheat at planting it should be high in phosphorus, and it should be banded with the seed. In 7 field trials co-ordinated by the Thames Valley Regional Soil and Crop Improvement Association, banded mono-ammonium phosphate at 50 pounds per acre provided an average yield response of 9.4 bushels per acre. A broadcast application of the same fertilizer at 200 pounds per acre gave only a 2.6 bushel response, so the importance of banding is evident. It does not appear to matter whether the fertilizer is liquid or dry, as long as it is placed with the seed and at a high enough rate. Thanks to Peter Johnson for providing the data.

Potassium

Conventional wisdom was that potash acts as an "anti-freeze" in the plant, so most potash was applied to wheat in the fall. Recent trials, however, have shown an advantage to spring application where potash is required. This appears to be related to the chloride in muriate of potash, which may have a role in reducing disease pressure on the crop. While the yield response is not large enough on its own to justify a potash application, it does make sense to apply the K in spring if you are going to apply it anyway.

Micronutrients

The one micronutrient that is deficient in a number of fields is manganese. This element is easily tied up in alkaline soils, or in muck soils, so a deficiency can occur even though there is lots of manganese in the soil. Symptoms of a deficiency are stunted, pale coloured plants, sometimes with faint inter-veinal striping. The pattern in the field is often more diagnostic than the symptoms on individual plants, with deficiencies evident on eroded knolls or in muck hollows. A foliar application of manganese sulphate in the spring, after growth has commenced, is generally adequate to overcome the deficiency, although there are a few highly deficient fields where a fall foliar application is necessary. Otherwise, winter survival of the crop is compromised.

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