Phil Needham takes a long-term view in his fertilizer management. It all begins, as you’ve heard before, with soil tests and with plant tissue tests. The Kentucky-based wheat agronomist and author of “Taking Your Wheat Yields to the Next Level” uses these tests to determine the immediate mineral deficiencies in a field. But more importantly, he collects these results to determine the production capacity of a piece of land.
Needham will divide each field into two to four management zones, based on soil type, topography and productivity. By now you know which parts of a field yield best and which yield worst. A yield monitor on the combine will add an extra level of precision to these zone boundaries, but you don’t need a yield monitor to identify major productivity differences within fields. Needham then submits a soil sample for each zone. Each zone will have a minimum of 12 sub-samples and each sample location is recorded with a handheld GPS. This enables the farmer or agronomist to return to the same sites, giving him a consistent benchmark over time.
In a direct seeding situation, he will sample the top four inches, and then take another sample from four to 24 inches. He suggests the four-inch sampling depth for major and minor elements in fields that have been direct seeded for five years or more. “This is because phosphorus and other nutrients including potassium, zinc, manganese, iron and copper don’t move a significant distance within the soil, so when such nutrients are either surface applied or banded alongside the seed, the nutrients tend to accumulate in the top four inches,” he says.
So if you divide a field into two zones and have two composite samples (top soil and subsoil) per zone, you’re paying for four tests per field.
Needham also recommends pulling a few soil samples in the four to eight inch range to check phosphorus levels in the deeper root zone. “We’re seeing some very low readings when we get down from the surface,” he says. “And since a top-yielding wheat field will draw 60 to 70 per cent of its phosphorus from deeper than the upper four to six inches, this could be a limiting factor.” You can’t do much about this apart from using deep banding technology. Some farmers have successfully implemented deep-placement of phosphorus, Needham says, but this practice is not aimed at farmers who are direct seeding.
Needham goes back into the growing crop, using the same GPS coordinates he uses for soil tests, and takes tissue samples. These are best taken at the three-to four-leaf stage and whole plants should be submitted to a lab for analysis, he says. Tissue testing at this stage will identify specific nutritional weaknesses so you can take corrective measures.
Soil tests may tell you which nutrients are available, but plants may not be able to pick them up, he says. Tissue tests give you a more accurate determination of plant-available nutrient, especially for copper, zinc, manganese, sulphur and chloride. Even if you don’t plan on top dressing fertilizer, this is an excellent tool for planning your fertility mix for the following crop.
HOW TO USE THE INFORMATION
Farmers will use soil tests and tissue tests to determine the immediate fertilizer needs of a field. But the next step — the step that will advance your wheat production practices — is to use this information to determine your management zones in the field. “Based on soil type and topography, there are some parts of a field or a farm that will produce 50-bushel wheat and other parts that will produce 80-bushel wheat, to use round figures,” Needham says. “So you want to feed the high-yield zones more than you feed the lower-yield zones. Historically, farmers are not good at making that decision.”
Consistent seeding depth into a firm, unbroken seedbed is a critically important part of Needham’s wheat management system. (Read the article in the November Grainews, page 6) That is why Needham prefers the combination of seed-placed fertilizer and mid-row banding. Most of the fertilizer requirements go through the mid-
row bander, but you need to put some starter fertilizer down with the seed to maintain early plant health until the roots reach the mid-row bands of fertilizer.
On 7.5-inch spacing, for example, he recommends no more than 20 pounds in total of nitrogen, potassium and sulphur with the seed. Not 20 pounds each. That’s the total. Use ammonium phosphate fertilizer with the seed to provide phosphorus as well as nitrogen.
With wider row spacing, you’ll have to reduce the amount of nitrogen, potassium and sulphur proportionately. For example, 15-inch narrow seed rows should not have more than 10 pounds per acre of nitrogen, potassium and sulphur.