Volume 40, Number 12 | JUNE 10, 2014
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PRACTICAL PRODUCTION TIPS FOR THE PRAIRIE FARMER
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Fertilizer toxicity can kill a seed Too much fertilizer too close to the seed can create a toxic environment. Here’s how to recognize the problem if you have it BY ANDREA HILDERMAN
T
he last thing any farmer wants to do is create a toxic environment at seeding time by applying too much fertilizer so close to the seed that it prevents normal germination and establishment. Fertilizer is not the only culprit when it comes to poor emergence. Seeding too deep, poor seed quality, disease, insects, dry soil or flooding can cause problems for seed emergence. However, with modern seeding equipment and one-pass seeding regimes, it pays to be aware of the havoc toxicity from fertilizer can wreak. Most nitrogen used in Western Canada is applied in the form of either granular urea, compressed anhydrous ammonia (AA) gas or liquid urea ammonium nitrate (UAN). When anydrous ammonia is injected into the soil, the pressure is lost and the AA reverts to its gaseous form, releasing the ammonia (NH3) into the soil. Ammonia reacts with water in the soil to form ammonium ions (NH4+) that adhere to soil organic matter and soil particles. Both ammonia and ammonium ions at high concentrations are
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very toxic to seed and seedlings. And so, AA must be banded into moist soil and the furrow must be closed to prevent ammonia loss. If side-banding, ensure that there is good separation between the AA and the seed row which should prevent ammonia from moving into the seed row and injuring seed or seedlings. When urea is applied to the soil, it is transformed by enzymatic reactions to form ammonia gas, which reacts with water to form ammonium ions — as in the case of AA. However, urea is also a salt, which poses another danger to seed and seedlings: salt toxicity. If a high rate of urea is applied in the seed row, seed mortality can be increased due to high salt concentrations. The seed and seedplaced fertilizer are competing for moisture around the seed, with the seed likely to lose the battle and become dehydrated or even killed. Seed-placed urea poses risks of salt, ammonia and ammonium toxicities to seed and seedlings. Liquid UAN is 50 per cent urea and 50 per cent ammonium nitrate. The urea half behaves as already described with regards to formation of ammonium and the salt toxicity. The ammonium
nitrate portion separates into the ammonium ion (NH4+) and the nitrate ion (NO3-). Studies show that nitrates at the typical concentrations of applied fertilizers are not as toxic to seeds and seedlings. Consequently, if UAN is placed close to the seed it may also pose salt as well as ammonium toxicity to seeds and seedlings.
Soil moisture needs to be assessed every year SIGNS AND SYMPTOMS Typical signs of fertilizer toxicity are poor germination, large gaps in the rows and poor-looking seedlings. If you dig into the soil, you will find swollen dead seeds or seeds with very short or no radicles at all if these problems are due to fertilizer toxicity. If the seed did imbibe enough moisture to start germination and a radicle and a plumule formed, you will find brownish roots with stubby or blunt tips. In
healthy plants, the roots should be whitish, narrow and long. Due to poor root formation or lack of root formation, the shoot that forms runs out of nutrients and energy and may fail to push through the soil. The extent of the damage depends on the concentration of the salts in the soil. The seed may germinate and shoots might be able to emerge but they’ll look as if they were trampled on and there can be gaps in the field or areas with weak, sickly plants. If it rains enough before the seeds die, the salt concentration is reduced and the damage minimized. If the damage is severe, there are no effective remedies, except possibly reseeding if there is sufficient time left to do so. There may be a significant volunteer problem. However, there are strategies that can help growers prevent this sort of damage in the first place.
TOXICITY PREVENTION “Farmers should be aware of the guidelines for seed placed f e r t i l i z e r, ” e x p l a i n s P a t r i c k Mooleki, provincial soil and nutrient management special-
In This Issue
ist for Saskatchewan Agriculture. “We have fact sheets that provide guidelines for safe rates of seed-placed fertilizers, which are dependent on soil moisture and soil texture.” Farmers are advised to seedplace only safe rate of fertilizer based on the crop, soil texture, soil moisture, width of seed row openers and row spacing as stipulated by the guidelines. The rest of the fertilizer must be applied away from the seed either before or after seeding. During seeding, fertilizer should be applied in the side-band or in the mid row, depending on the equipment at hand. Farmers who want to apply more fertilizer with the seed should consider replacing part of the urea with a polymer-coated fertilizer such as ESN. Consult suppliers for guidelines. Generally, if the season starts off very dry, it would be beneficial to reduce the amount of seed-applied fertilizer. “What a farmer might have applied in a previous season with the seed is not necessarily going to be the right amount to apply in the next season,” explains Mooleki. “Soil
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Wheat & Chaff ..................
2
Features ............................
5
Crop Advisor’s Casebook
8
Columns ........................... 14 Machinery & Shop ............ 19 Cattleman’s Corner .......... 44
Lemken showcases new implements
SCOTT GARVEY PAGE 24
Adding minerals to your nutrition plan
DEBBIE CHIKOUSKY PAGE 47
FarmLife ............................ 51