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Coldwater, Michigan | Urea is a good product, better if handled properly. When urea goes into the soil it causes an extreme change in the soil pH in the immediate area of contact. This is because of water and urea combining, and the resulting chemical reaction. After a short period of time this rise in pH settles down and is not a further potential problem.
Here is where the rub comes in: In light, sandy, moist, soils there is good potential for problems if planting is pushed too soon. Why in light soils? Light soils because of the CEC can not buffer that change in pH like a medium, or heavy soil can. How you apply the urea can affect your result: If you band the urea, and plant beside the band it may not be a problem. If broadcasting urea, the whole soil surface will be going through this change in pH. It creates a "HOT" zone and you are placing the seed directly into it when you plant, if broadcast.
Many of you are aware that Nh3 can kill the seedling if planted directly over the application trench if you follow the Nh3 application too soon. The change the Nh3 is going through is the same issue with the urea. Too soon, potential damage.
With the urea, if you wait a week to 10 days it usually isn't an issue because the conversion has passed and the soil pH has settled down. Then it usually is safe to plant into. The weather following application has some effect on how fast this conversion takes place. There has been extensive result done at some universities on this effect. There is also some work done using the urease inhibitors. These tend to slow the release of the urea and thus limit the amount of damage potential.
If you are a seed placer ( we sell seed placed fertilizer products at LFB Solutions) while the fertilizer product used in the seed trench may be relatively safe even on light soils, combining that fertilizer product with broadcast urea tends to make the affect worse. That is why when you are out to buy your seed placed fertilizer product you should be asking about the urea content. Urea is not safe in contact with the seed. If you broadcast urea, a certain amount will be in contact with the seed, so you can see where I'm coming from.
Most liquid seed placed fertilizers that have some potash content, and a nitrogen content of 7-9% are potentially a problem on lighter soils. Some of these analysis would look like 9-18-9, 8-19-3, 9-19-3, anything with potash in the blend, and a nitrogen rate similar to the above. 10-34-0 while salty, doesn't use urea to get the nitrogen content. On lighter soils it can actually be safer than the above listed analysis. Not saying I recommend 10-34-0 for seed placement, merely saying in some situations it may be safer than some of the "LOW SALT" products on the market.
Nuff said!
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Fertilizer effect on soil
