By Harry Brook
Fertilizer prices seem to be in a race with crop prices to the top. Fertilizer is an essential input but there are a lot of questions around how much to apply with the crop and what will give you the biggest bang for your input dollar. To make a wise decision related to fertilizer, you need a little information.
For starters, how much of last year’s fertilizer is left in the soil for this year’s crop? Drought conditions usually result in some carryover. Where is it in the soil – the top foot of soil or two feet down? Soil testing is a must this year to get the most out of the fertilizer already present. Fertilizer is too costly to apply excess amounts.
Of the nutrients, nitrogen and sulfur can move in the soil water. Nitrogen can be lost to denitrification, when soils are saturated and the urea or ammonium are broken down by anaerobic bacteria into nitrogen gas and lost to the atmosphere. It can also be lost to leaching where excess rain or water can move it down in the soil profile and eventually out of the rooting depth. Sulfur, in sulfate form (the only form that plants can absorb) also moves in water and can be lost to leaching.
Putting your nitrogen fertilizer in a concentrated band near the seed row is the best way to prevent nitrogen losses to the air or below ground. Fall application of fertilizer can save time but it does expose fertilizer to more conditions where losses can occur. Most modern seeders now have a double shoot system. However, you still need to include some fertilizer in the seed row for starter purposes. In cool seeding conditions, a bit of phosphorus in the seed row may prevent temporary deficiency symptoms from showing up and give the germinating crop a boost. It is important not to put too much fertilizer with the seed due to the risk of seed burning.
All fertilizers are salts. Seed burning is when the fertilizer, as it breaks down too close to the germinating seed, goes into the soil water and creates a zone of high salt content. If it gets too high, the germinating seed cannot get enough water by osmosis and dies. The safe amount of fertilizer, with the seed, depends on seed size, soil texture and moisture conditions. The safe rate of seed-placed fertilizer also depends on the amount of seedbed the fertilizer is spread over, known as seed bed utilization. The greater the seedbed utilization, the more fertilizer can be safely applied.
Click HERE for information on the safe amount of fertilizer to place with seed.
Most people band fertilizer in the soil, which reduces the potential for losses but there are strategies that further reduce the potential for loss. There are three main additive types that decrease nitrogen losses. They are nitrification inhibitors that slow the fertilizer nitrogen conversion from ammonia to nitrate. It is the nitrate form that plants take up. Nitrate is also broken down into N2 gas or washed out of the root zone. Urease inhibitors slow or prevent the dissolving of urea where, under dry conditions, it will volatilize and gas off. This gives time for rainfall to come and dissolve the granules into the soil water. A third treatment to nitrogen is a polymer coating on each prill, which limits the moisture getting to the nitrogen. This allow the product to provide a stream of nitrogen over time, rather than a lot at once.
Whatever fertilizer products or additives you use for nitrogen application, make sure you minimize the potential for losses. Sky-high fertilizer prices encourage you to make the most of your fertilizer dollar.