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The Right Nitrogen System For You

 
Each farm will base its nitrogen application practices on time, labour, equipment and cost. Often losses in efficiency in one area can be compensated for by improvements in another. The “best” nitrogen (N) system is not universal, but will depend on the major limiting factors on each individual farm. Here are key points to consider for the six most common systems.
 
1) Pre-plant banding
 
–Banding N in concentrated rows below the soil surface tends to be the most efficient form of application under Western Canadian conditions. Placing fertilizer below the soil surface protects the ammonia portion from volatilization losses. Placing the fertilizer in a band reduces the contact between the fertilizer and the soil microorganisms, reducing immobilization of both ammonium and nitrate. Banding also slows the conversion of urea to ammonium and ammonium to nitrate, which can reduce losses by denitrification and leaching. Ideally, bands should not be disturbed by pre-seeding tillage or seeding operations.
 
–All forms of N fertilizer perform well when applied as a spring pre-plant band, provided that the fertilizer is separated from the seed. Anhydrous ammonia (NH3) should be placed at least 4 inches below the soil surface and, if possible, seeding should be done perpendicular to ammonia bands. There is no need to delay seeding after application if anhydrous ammonia is placed at recommended depths, especially on moist clay soils.
 
–Pre-plant banding may delay seeding and dry and disrupt the seedbed, especially in clay soils.
 
2) Surface applications immediately before or after seeding
 
–Broadcast applications cover a lot of acres in day.
 
–Because of the high potential for volatilization and immobilization losses, surface applications of N tend to be less efficient than in-soil banded applications. Efficiency of surface applications tends to improve in higher rainfall areas. Efficiency is lower on high pH soil, since high pH encourages the production of ammonia gas.
 
–Urea or UAN sources of N can be lost by volatilization until they are incorporated or move into the soil with precipitation. Tillage during conventional seeding operations is generally sufficient to incorporate urea or UAN solution and reduce volatilization.
 
–Ammonium or nitrate sources in close contact with crop residues may be subject to immobilization as the residues decompose.
 
–Stranding of broadcast fertilizer in dry soil above the active portion of the crop’s root system may be a problem in some weather conditions.
 
–High rates of broadcast urea-N applied without incorporation on fields seeded with disc-openers may concentrate pellets in the seed-furrow and cause seedling damage to sensitive crops like canola.
 
–For post-emergent N delivery, dribble-banded UAN, which reduces contact with crop residues and soil, will generally be a better choice than broadcast urea for surface applications. Urease inhibitor can improve results for urea (see next paragraph). Volatilization losses with dribble banded UAN will be lower than with urea, both because the UAN provides a portion of the N as nitrate and because UAN does not increase initial pH at the application site to the same extent as urea. Use of a dribble-band rather than a spray application reduces contact between the fertilizer and crop residue, reducing immobilization.
 
–Urease inhibitors such as Agrotain applied with urea or UAN slow the conversion of urea to ammonia and ammonium. This allows more time for the urea to move into the soil before it is converted into ammonia and ammonium. The slower conversion also reduces the concentration of ammonia at the soil surface, reducing the rate of volatilization. As volatile losses from UAN are generally lower than from urea, the benefit of using the urease inhibitor may be lower with UAN than with urea.
 
–While a higher rate of fertilizer may be required to compensate for the reduced fertilizer use efficiency for surface applications, this may be a practical compromise for some growers.
 
3) Placement in the seed row
 
–Excess N with the seed can lead to seedling damage due to combination of salt and ammonia toxicity. This damage can reduce crop yields, reduces response to nitrogen fertilizer and reduces nitrogen use efficiency. Seedling toxicity may also delay crop emergence and reduce crop vigour.
 
–Safe rates of seed-placed N depend on a number of factors including environmental conditions, soil type, width of the seed/fertilizer band, row spacing and fertilizer source. Lower the rate in light-textured soils, low soil organic matter, cool growing conditions, low soil moisture, in the presence of salts or free lime, or with the use of wide row spacing. For more detail about determining safe rates of N fertilizer that can be applied with cereals and canola, please refer to the Manitoba Soil Fertility Guide.
 
–Placement of fertilizer in the seed-row eliminates an extra pass for fertilizer application. It also eliminates the extra expense, draft requirements and soil disturbance required to side-band the fertilizer requirements.
 
–Seed-row placement is a form of shallow banding, and will reduce N losses compared to broadcast.
 
–A reasonable compromise may be to apply a portion of the fertilizer with the seed and broadcast or dribble-band the remainder.
 
–A controlled-release product like ESN, may increase the rate of N that can safely be applied with the seed. At 100%, ESN can be used at 3 times the safe urea rate. A blend of half ESN and half urea can be used at 1.5 times the safe urea rate, assuming a low level of damage to the ESN protective coating.
 
Source : Albertacanola

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