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Integrated Pest & Crop Management



AUTHOR

Peter C. Scharf
University of Missouri
Division of Plant Sciences
(573) 882-0777
scharfp@missouri.edu

Missing Out on Fall Applications of P & K

Peter C. Scharf
University of Missouri
(573) 882-0777
scharfp@missouri.edu

Published: November 3, 2009

Traditionally most P and K fertilizer applications have been made in the fall. Timing is not crucial and usually more field days are available in the fall.

That is not the case this year. The weather has delayed harvest way past normal dates for most of Missouri and much of the midwest and mid-south. For producers, getting their crops in is their main concern. Fortunately, missing normal P & K applications this fall will not affect next year's production in most fields.

No matter what past fertility management has been, applications of P and K next spring should produce the same yield as P and K applied this fall. It will add to the spring workload for both producers and service providers, and it's doubtful whether there is enough equipment to apply P and K to every field in the spring. As many producers found out last fall and this spring, there may not be any time in the spring for P and K applications after missing them in the fall.

For fields that missed P & K applications last fall and this spring, potential for some yield loss is increased if applications are missed again this fall and next spring. However, where fertility has been maintained at soil test levels recommended by the University of Missouri or private labs, most fields can probably make full yield even with two years of missed applications. Fields that have lower test levels are at more risk of yield loss and should be prioritized for P and K applications whenever that becomes possible.

Wheat is a special case in that spring applications won't help. Fall is the time when P nutrition makes the biggest difference. P is crucial to get adequate fall growth and tillering, which in turn is crucial to yield. For wheat that has already been planted, adequate soil test P can substitute for fall P applications if they were missed. If wheat was planted, P was not applied, and soil tests are marginal or low, it's already too late unless we get a long mild spell after application becomes possible. If anyone is still considering wheat planting, ensuring adequate P and some N before or near planting gives the greatest chance of success. In most years, soil can supply adequate fall N for wheat, but with all the rain we've had it's probably not wise to count on that this year. If wheat is far behind and an opportunity comes, a small N application during a warm spell any time during the winter may pay off.

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