Dry soils and soybean tolerance for starter fertilizer

Most farmers and agronomists should be very aware of the extensive Manitoba research that applied phosphorus fertilizer does not increase soybean yield.  However, phosphorus replenishment of soil with P is important.

Some farmers may still will wish to add some starter fertilizer with soybeans, since in this study (Phosphorus Fertilization Beneficial Management Practices for Soybeans in Manitoba), the seed placement of phosphorus only reduced stands significantly in 7 of 28 sites (1 in 4 cases).  Before growers jump to the conclusion that soybeans tolerate high rates of fertilizer with the seed, let’s review these cases:

  • In almost all cases, soybeans were seeded in moist to wetter soils – as soon as soils were fit to allow traffic.  Row spacing ranged from 7-12” with knife or disk openers.
  • The 7 cases of stand damage highlighted the risk factors:
    • 3/7 = disk openers with row spacings of 12” (so low seedbed utilization)
    • 3/7 = sandy soils (less water holding capacity and buffering)
    • 1/7 = dry seedbed (higher risk)

Our traditional safe seedplaced fertilizer guideline for soybeans is no fertilizer for rows wider than 15”, and up to 10 lb P2O5/ac when seeded in narrower rows.  These limits may even be too high when soils are drying as at present.  We do not expect any advantage to this seedplaced P, so the safest option is to avoid any with the seed.

Again – a review of risk factors for seedplaced P:

  • Soil moisture:  dry = riskier
  • Sol texture: sandy = riskier
  • Seed opener:  narrow or disk = riskier
  • Row spacing: wider = riskier
  • Fertilizer rate: more = riskier

These factors are all considered in the  Seed Placed Fertilizer Decision Aid posted at https://www.ipni.net/toolbox

Submitted by:  John Heard, Crop Nutrition Specialist, Manitoba Agriculture

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Preplant Banding Ammonia & Urea in Corn

A very efficient placement method for rates of nitrogen that can’t be placed at seeding is the preplant band. Despite the popularity of direct or one-pass seeding this is still used in crops where some pre-plant tillage is done – like for corn.

The past few years, more often in dry springs, I have seen stand thinning using this practice. When the corn row falls directly over the N band (be it ammonia or urea), seedlings are injured, stunted and sometimes killed. This leaves a repeating pattern in an angle across the field.

There are some standard guidelines if using this practice:

  • Stand thinning may occur where the seed row intersects the N band. Band N on an angle so that it intersects just a short length of row.  OR if the injection placement can be controlled with accurate GPS guidance positioning technology, split with the future corn row.  Six inch separation should be sufficient.
  • Place the nitrogen deep. Banding at 3” depth may be sufficient for slot closure and N retention in the soil – but this will only be an inch or so below the seed. The original guideline calls for 4” vertical separation of injection point and seed.
  • The toxicity will be worse under dry conditions and on sandier soils.
  • Waiting a certain period of time offers only a slight increase in safety.  Injury can still occur even if planting is delayed for a considerable period of time.
  • Increasing plant populations to account for such thinning will not eliminate the appearance of gaps in the row.

Figure 1 is of corn thinning over a preplant urea band.


Figure 1: Corn thinning over a preplant urea band (Photo by John Heard, Manitoba Agriculture)

Figure 2 is of corn seedling based on their proximity in intersecting the shallow placed preplant ammonia band.


Figure 2: Impact of shallow placed preplant ammonia band on corn seedlings (Photo by John Heard, Manitoba Agriculture)

Submitted by: John Heard, Crop Nutrition Specialist, Manitoba Agriculture

Follow Manitoba Agriculture on:
Twitter: @MBGovAg
YouTube: www.youtube.com/ManitobaAgriculture


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Safe Liquid Fertilizer Rates for Corn

Much of Manitoba’s corn receives liquid phosphorus as a starter in the seedrow.  But we cannot apply sufficient amounts with the seed to meet full crop removal (about 44 lb P2O5/ac for a 100 bu/ac crop).  The safe amount of seed placed fertilizer depends upon soil type, moisture, row spacing and seed furrow opening.  Ontario guidelines base the safe rates of fertilizer on N and K content of the starter fertilizer.  For 30 inch rows no more than 10 lb N/ac should be seedplaced – enough to provide 34 lb P2O5/ac of 10-34-0 liquid fertilizer or 8.5 US gal per acre.  But based on South Dakota  studies such rates could cause stand thinning of 4-9% depending on soil moisture and texture. Most farmers will not be pushing starter rates this high as they should have the bulk of their P needs met through a safer placement strategy.

More on these safe rates of fertilizer is posted on Manitoba Agriculture’s website at: http://www.gov.mb.ca/agriculture/crops/soil-fertility/print,safe-rates-of-seed-placed-phosphorus-for-manitoba–narrow-row-and-row-crops.html

Submitted by: John Heard, Crop Nutrition Specialist, Manitoba Agriculture


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Watch Seed Placed Fertilizer Rates!

Submitted by: John Heard, MAFRI Crop Nutrition Specialist

Soil moisture conditions vary widely across the province.  Those seeding into dry soils should be aware of the increased risk of damage to germination and establishment.  Placing fertilizer with the seed is a choice of compromises – crop response to added nutrients and ease of application versus stand injury.  Phosphorus is the nutrient of top priority to reserve for seed placement.  Others such as nitrogen and sulphur have flexibility in soil movement and can be placed elsewhere.  For more specifics on safe placed fertilizer rates see:



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