By Harry Brook
Last week I talked about nitrogen, primarily applied to annual crops, preferably banded, next to the seed row. But what about nitrogen fertilizer on perennial crops? This is another kettle of fish. It must be applied to the soil surface and risks of losses are greater, unless you have irrigation. Remember, every pound of hay or grass removed from a field takes nutrients out of that field. If you have a hay field or pasture that is no longer productive, take a soil sample to see where the nutrient levels sit. Chances are that it could use some fertilizer.
If the hay land is primarily grass, I can almost guarantee the soil is short of nitrogen. The more legumes are in the hay mix, the more nitrogen will come from the alfalfa. However, even a good alfalfa/grass hay stand is exporting large amounts of phosphorus, sulfur and potassium off the field. Those nutrients will have to be replaced sooner or later if you wish to keep up productivity.
If the hay field is primarily grasses, then using a nitrogen fertilizer should give a big boost to hay production. There are a few conditions that need to be met. One of these is the type of nitrogen you are using.
Urea, at 46% nitrogen, is the highest concentration of nitrogen in a fertilizer, other than anhydrous ammonia. However, left alone on the soil surface, it will start to denitrify and lose nitrogen to the atmosphere as temperatures warm. There are products that can be used to prevent the denitrification of urea but they only extend the safe period for 10 to 14 days. There are other products that can slow the loss of nitrogen but you still need at least half an inch of moisture to dissolve the fertilizer prill and take the nitrogen into the root zone.
Some people use a liquid formulation of nitrogen, 28-0-0. It is a mixture of urea and ammonium nitrate and the urea portion is still susceptible to denitrification and losses to the air. Ammonium sulfate, 21-0-0-24, Is a safer product to use to fertilize perennial crops but you have to use significant volumes to get much nitrogen into the soil. There is also a benefit from sulfur addition when using ammonium sulfate.
If you have livestock, manure is an excellent fertilizer source to apply to perennial hay crops. It can provide the whole range of nutrients. You need to test your manure to make sure you know what the analysis is. And you have to spread it thinly enough so that you don’t kill off the plants through shading. Depending on the tonnes applied per acre, manure can provide nutrients for several years after application.
Don’t bother using any ESN treated urea for hay. As with cereal and oilseed crops, the grass and legumes take up most of their nitrogen early on for plant growth. The problem with ESN is that is does not provide enough nitrogen early on, when it is needed. It will, however, keep down losses due to volatilization, leaching and denitrification.
When conditions are right, with timely and adequate rains, you can expect nitrogen fertilizer to increase the production of grass hay and pasture by 50% or even more. In some years, it can certainly be worth it. For a short video interview about fertilizing hay and pasture, see the link below. Remember, on the prairies, moisture is our number one limiting nutrient.