Seed Placed Fertilizer – Safe Rates

A reminder that if seedbeds turn dry, the safety margin shrinks when applying seed placed fertilizer.  Seedburn can result from ammonia toxicity and/or salt content of fertilizers.

For nitrogen, our Soil Fertility Guide provided safe guidelines for seed placed urea on cereals and canola across a range of soil types and seed-fertilizer configurations.  With the increased popularity of narrow seed and fertilizer spreads with disk drills, the safe rates are reduced.  For example, safe urea rates for cereals vary from 10 to 25 lb N/ac going from sand to clay soil using disk openers on 6” row spacing.  These guidelines are for moist soil and should be reduced by 50% if seedbed moisture is lower when weather is hot and windy.

The safe rates of seed placed phosphorus depends on the crop, with cereals being quite tolerant compared to soybeans, dry beans and canola.  With a disk drill as described above, cereals can tolerate 50 to 60 lb P2O5/ac as mono ammonium phosphate while rates would be 20 lbs/ac for canola and less for beans.   If there greater seedbed utilization (i.e. narrower rows or a wider seedrow with less fertilizer concentration) rates could be more liberal.

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

 

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Spring Options for Applying Nitrogen Fertilizer in 2017

With the wet conditions and delayed harvest experienced in parts of Manitoba in fall 2016, very few farmers were able to complete their fall fertilization program.  Since early seeding is important for optimizing crop yield, producers will be looking for ways to apply their N requirements efficiently without delaying the seeding operation.  In addition, soil reserves of N are variable and margins between crop revenue and input costs are modest; therefore, optimizing nitrogen fertilizer use efficiency is important.  To achieve these objectives for a spring fertilization program will require use of a 4R nutrient stewardship strategy:  applying the right rate of the right fertilizer source, with the right placement and at the right time to minimize losses of fertilizer N to the environment and optimize the crop’s access to the fertilizer.

For more detailed information, see the on-line factsheet at http://www.gov.mb.ca/agriculture/crops/seasonal-reports/pubs/spring-n-options-17.pdf

Submitted by John Heard, Crop Nutrition Specialist, MB Ag

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Surface N Applications & Dry Soils

Planting is proceeding at full tilt and some questions are arising about surface N applications.  When urea forms of N are surface applied, they are vulnerable to hydrolysis (the cleaving of the urea molecule with water) and subsequent losses of ammonia gas (NH3) called “volatilization.  This is a well established risk  and risk factors are well known, and more information can be in the article Volatilization Losses From Surface Applied Nitrogen on the MAFRD website.

Conditions favouring high volatilization potential are:

  • high soil temperatures
  • moist conditions, followed by rapid drying
  • windy conditions
  • high soil pH (>pH 7.5)
  • high lime content in surface soil
  • coarse soil texture (sandy)
  • low organic matter content
  • high amounts of surface residue (e.g. Zero tillage)
  • nitrogen source: urea>UAN solution
  • UAN application: broadcast UAN> dribble or strip UAN

Our observations in Manitoba have been that urea or UAN solution (28-0-0) applied to bone dry soil actually suffers little volatilization loss  since there is little moisture to drive hydrolysis. At this point with dry conditions forecasted, the riskiest situation may be by exposing your applied N to enough soil moisture to start the volatilization process – such as applying immediately after some soil disturbance like seeding or secondary tillage.  Likewise, very shallow incorporation through seeding or harrowing may start this process.  Light rains of 1/10″ may also be enough to start this volatilization process, yet inadequate to incorporate the urea molecule.  Generally rainfall of ¼ to 0.4” is considered sufficient to incorporate surface urea or UAN.

If you must apply urea or UAN to moist soils or in other high risk situations, a NBPT urease inhibitor like Agrotain is recommended.  Although volatilization losses on already dry soil surfaces are usually low neither is this surface N doing any good until rainfall is received.  A strategy of waiting until imminent rainfall may still be a preferred option.

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.

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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.

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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

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Fall Fertilizer Decisions Based on Soil Temperatures

 

 

Growers should be monitoring soil temperatures to guide fall nitrogen management.  Provincial weather station soil temperatures are posted at: http://www.gov.mb.ca/agriculture/weather/soil-temperature.html

The principle of fall fertilization is generally to delay applications until soils have cooled so microbial activity is curtailed.  That way less of the stable ammonium form-N (NH4+,) that is held on clay and OM, is converted to nitrate (NO3-) which can leach or denitrify.

The rate of nitrification of banded N to nitrate is illustrated in the following table from http://www.gov.mb.ca/agriculture/crops/soil-fertility/a-fall-fertilization-refresher.html

 

Table 1. Nitrification rates of ammonia to nitrate form-N from banded urea (calculated from Tiessen et al, 20031).

Average soil temperature at band depth Days for 50% conversion to nitrate Days for 100% conversion to nitrate
1 oC

5 oC

10 oC

15 oC

20 oC

190

40

20

13

10

380

80

40

25

20

 

So as soils cool and eventually freeze, the microbial activity is reduced such that ammonium-N is retained in its stable form.  If one chooses to apply nitrogen before Mother Nature provides cool soil – they may consider using one of several enhanced efficiency fertilizers – N-Serve, eNtrench, ESN or SuperU. 

Submitted by: John Heard, Soil Fertility Specialist

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Farm Management Resources Updated

MAFRD’s Farm Business Management staff have updated several online farm financial management resources on the MAFRD Business & Economics webpages at:

Updates include:

For further information, support and resources, contact the MAFRD Farm Business Management Team at http://www.gov.mb.ca/agriculture/business-and-economics/farm-business-management-contacts.html

Submitted by:  Pam de Rocquigny, MAFRD Cereal Crops Specialist

 

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Fall Nitrogen Applications

Fall nitrogen applications will be commencing shortly.  There is an important rule and several guidelines for legal and efficient use of nitrogen.

RULE: November 10.  Nitrogen and phosphorus applications must be made before this date to comply with regulations under The Nutrient Management Regulation of the Water Protection Act (C.C.S.M. c. W65).

GUIDELINES:

A)     Cool soil temperatures – when nitrogen is applied to cool soils, the biological conversion to the nitrate form is reduced.   The following table (adapted from Manitoba research by Tiessen et al) illustrates the dramatic impact of cool soils on slowing nitrification rates.  Conversely  on warm soils this conversion is rapid, and we wish this to happen during the growing season.  But once nitrogen is in the nitrate form it is vulnerable to leaching losses and denitrification under wet soil conditions.

Table 1.  The estimated rate of conversion of ammonia-N  from banded urea to nitrate-N. (Heard from Tiessen et al, 2003)

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Growers and agronomists can measure soil temperatures at the depth of injection.  Soil temperature at 2” depth under sod is posted for a number of Manitoba sites at MAFRD’s Ag-Weather Program website: http://tgs.gov.mb.ca/climate/SoilTemp.aspx

B)     Banding N in the ammonia form also slows conversion to nitrate.

C)      Nitrification inhibitors can slow this conversion. These include the DCD component in SuperU, nitrapyrin in eNtrench for urea or N-Serve for anhydrous ammonia.

D)      Controlled release products, like ESN,  slow the physical release of urea, which in turn slows this conversion to nitrate.

Following the 4R Approach – especially source, time and placement – will maximize performance of fall applied nitrogen fertilizer.

Submitted by:  John Heard, Crop Nutrition Specialist, MAFRD

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Still Lots of N Fertilizer Options when Seeding is Delayed

In a spring when seeding is delayed, field operations should be minimized to permit seeding as soon as possible. Preplant applications of N, in particular may be compromised to advance seeding dates.

There are a wide variety of options for applying nitrogen fertilizer efficiently, which are discussed in the article by John Heard, Crop Nutrition Specialist with MAFRD, available at the following link:  http://www.gov.mb.ca/agriculture/crops/soil-fertility/n-fertilizer-options-when-seeding-delayed.html

 

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Do I Need to Apply Zinc to my Soybeans?

Question: When we grew edible beans in the 90’s, we were advised to use zinc. My notes show it was not so much a yield factor, it was for maturity.

We have generally high organic matter (8% and up), most pH is over 7.8 , clay soils, and our phosphorus levels are reasonbe to high at 28ppm -all factors that my notes say tie up Zinc. Some fields are ok for zinc at 4 to 6 ppm but some are lower at or less then 1 ppm. So should I be putting on a zinc product as a safe guard or are soybeans totally different from edible beans?

Answer (supplied by John Heard, MAFRI Crop Nutrition Specialist):

Zinc deficiency is rare in soybeans as compared to edible beans.  Manitoba studies have documented edible beans respond well to applied zinc fertilizer when soil test levels are below 0.5 ppm DTPA extractable zinc.  Soybeans are much less sensitive to low soil zinc levels deficiencies and have  not responded to zinc fertilizer applications in North Dakota and Minnesota studies.  At 11 Minnesota sites in 2011-2012, there was no soybean response to applications of either zinc, sulphur, manganese, molybdenum or boron (see attached reference http://www.smallgrains.org/2013SGU/KaiserSoybean.pdf ).

The main nutrients to watch in soybeans are nitrogen (through proper rhizobium inoculation) and phosphorus and potassium.  Based on your high phosphorus soil tests (26 ppm P) and the high K potential associated with high clay content, your soybeans may do quite well on residual fertility.

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