THOUGHTS ON FALL-APPLIED P AND K

The value of a bushel of corn has dropped  and continues to go down.  Fertilizer prices have not changed.  This situation has farmers thinking about fertilizer plans this fall.  Money spent for this input is substantial and producers are asking if this time for a change in their traditional use plans.  It’s probably appropriate to summarize thoughts on the application of potash and phosphate fertilizers this fall.

Nothing has changed for those who now use or plan to use a CONSERVATION TILLAGE planting system.  This can be ridge-till, strip-till, no-till or any combination of these three.  Placement of phosphate and /or potash in a band below the future row is one of the keys to success for any of these planting systems.  For most of Minnesota, it is most practical to apply this band in the fall.  Banding in the spring is a viable option if soil texture is a loam, sandy loam or a silt loam.  In an ideal world, this band should be at a depth of 4 to 5m inches.  The band should be placed, if at all possible, within 3 inches of the future row.  This is a challenge that can be achieved when the conservation tillage planting systems are used.  The use of a deep band can and should be complimented with a band of approximately 3 gallons of 10-34-0 as a pop-up at planting.  This pop-up placement is now used by a majority of farmers in Minnesota.

Options are more varied for those who do not use conservation tillage systems.  SOIL TEST VALUES should be the first consideration.  Using current University of Minnesota guidelines, BROADCAST applications of phosphate and potash are not needed in a fertilizer program for corn if the soil test value for phosphorus (P) is higher than 20 ppm as measured by the Bray procedure or 16 ppm if measured by the Olsen test.  For soil test potassium, the cutoff value is 160 ppm.  Even at these high values, use of a pop-up would still be a good management practice–especially if corn is to follow corn.  Many fields have been sampled this summer and this fall would be an excellent time to take a hard look at use of a broadcast application.  This application may not be needed for next year’s corn crop.

At lower soil test values for P and/or K, a BANDED placement can be substituted for a broadcast application.  In the past, University of Minnesota guidelines suggested that rates of phosphate and potash could be halved if banded placement was substituted for a broadcast application.  Nothing has changed.  This change in placement can produce a substantial savings in fertilizer costs.

There are several options for the use of the band.  The band can be applied at planting or in the fall prior to planting.  If applied in the fall, some form of precision guidance will be required so that this band will be close to the future corn row.  This might be a major challenge.  In addition, any band applied before planting looses effectiveness if disturbed by either fall or spring tillage.  If disturbed, the efficiency compared to a broadcast application probably disappears.  So shallow tillage is essential if a preplant band is used as a separate operation in a planting system.

Several years ago, there was considerable interest in applying phosphate and/or potash on the soil surface followed by some type of tillage.  Although this practice may have improved uptake of P and/or K , there was no associated increase in yield and this did not become a popular practice.

It’s possible from a logistics standpoint, banding at planting may be a problem if potassium is low and rates of suggested potash could be high.  Supplying a substantial amount of potash in a band is not practical if the grower is equipped to apply fertilizer near the seed in fluid form.  We’re restricted by low percentages of potash in mixed fluid fertilizers.  For these situations, it might be best to broadcast the potash and apply phosphate in a band.  Most phosphate requirements can be satisfied if applied in a band near the seed at planting.  If a dry starter fertilizer is used at planting, most requirements for phosphate and potash can be applied in a band.

It might seem early to be planning for fertilizer application for next year.  The first step is serious consideration of the results of a soil test.  Analysis of soil will be needed before there can be in plans for the application of P and/or K this fall.  There are several attachments for planters that can be used to apply fertilizers in a band.  It’s not too early to start planning and looking.