Great Time To Apply Phosphorus and Potassium

Take advantage of good weather after harvest to broadcast nutrients.

Published on: Oct 4, 2013

The late fall forecast still talks about rain and cooler temperatures. If you get crops harvested and have a dealer ready to spread fertilizer, or else have an employee who dos it with your equipment, now may be the time to apply it.

"P and K tend to stay put where you apply them, so there is typically not a lot of risk about loss from fall applications of these nutrients," says Brian Early, a DuPont Pioneer production agronomist in northeast and east-central Indiana. Before his career with Pioneer, Early operated his own business as a crops consultant, doing plenty of soil testing and making lots of fertilizer recommendations.

Some ask him if it's OK to apply P and K in the fall even on sloping soils. His answer is typically that it is probably OK, as long as gullies aren't likely to form with big rains. A big rain coming soon after application could cause some loss of P and K even on soils with lesser slope, he notes.

Time to apply: Once crops are harvested and if soils are still dry, its a good time to make fall applications of P and K, Brian Early says.
Time to apply: Once crops are harvested and if soils are still dry, it's a good time to make fall applications of P and K, Brian Early says.

Early observes that more and more customers are tending toward using their yield maps to calculate what the crop removed, and then applying P and K to meet crop removal amounts. Some are using variable-rate application to fine-tune how much they apply in various parts of the field.

He believes that applying based on crop removal is a good option, as long as your soils are in good shape on soil fertility anyway, at least as far as P and K goes. Most Indiana soils naturally tend to be relatively higher on P compared to K levels, but in the end, it depends largely on past fertilizer application practices.

He follows that recommendation with a strong push for routine soil testing to monitor nutrient levels. Often if you're on a soil testing program, each field will be sampled once every three or four years.

"That is a report card on how well you're program of applying to replace amounts removed by crops is working," he says.