Our roller coaster winter weather, fueled by an El Nino pattern, has made it difficult for forage and crop producers who should be out applying nitrogen to help improve or maintain a good stand. Right now, many fields are struggling with nitrogen deficiency. There are many reasons, most of which are related to the wet weather we’ve been consistently dealing with since September. If any nitrogen was applied at planting, it has been used up, washed away, or leached out.
Weather projections continue to suggest we’ll see similar wet and cold weather patterns through March and April and there’s also a projected short end of spring in late April. This could drastically shorten the amount of time producers have for positively impacting yield potential from February to May to as soon as March or April. With field conditions continuing to be near saturation, and making trips across the field difficult as well as counterproductive, timing will be short for producers to get needed nitrogen on these fields.
Standard soil test recommendations are to put out 50 lbs. of N/acre on ryegrass and small grains in late winter (late January – February) and another 50 lbs. of N/acre on ryegrass in early spring (mid-March – mid-April). This year, timely action with the winter applications will be absolutely crucial. Even if adequate N was applied at planting, it is likely that little or none of that is still available at this point.
The response of plants to nitrogen fertilization will depend on several factors and has to be considered when determining if and when to apply N. We can look at three different scenarios to illustrate this importance.
Scenario 1) Ryegrass or small grains that have been slow to grow, either because of bad weather or N deficiency (and, sometimes, a late planting). These winter annual forage crops will often respond very aggressively to a winter application (20-30 lbs. of DM per lb. of added N assuming N rates are 40 – 60+ lbs. of N/acre). It follows the basic principle that an organism that has had growth limitations will often grow at extraordinary rates whenever those factors are no longer limiting.
Scenario 2) Ryegrass or small grain plantings that have been growing strong. Winter annual forage crops in this scenario are unlikely to respond as aggressively to N at this time. However, this N is still crucial, as it keeps the plant growing at least at a healthy rate. Therefore, it is important to fertilize them at the same or nearly the same rates because they will need the fertility during the remainder of the season.
Scenario 3) Winter annual forages that have been moderate to severely damaged by disease. These forage crops are unlikely to respond to N application. For example, tillers that are exhibiting physical symptoms of barley yellow dwarf (BYD) infection will die quickly, especially following a hard freeze. Therefore, if more than 30 percent of the tillers in a stand of oats have been damaged by barley yellow dwarf, those plants are unlikely to respond well to N.
Another consideration is the growth cycle of the crop. Oats provide us a good example. Oats generally grow very well in the fall and in the spring, but not very well in the winter. The N recommendations for small grains as winter grazing is to split the nitrogen application, applying 50 (lbs. of N) per acre at planting and 50 (lbs. of N) per acre in late winter before spring growth begins. This applies to oats, as well as to rye, wheat, and triticale. However, the operative part of this recommendation is the final phrase “in late winter before spring growth begins.” The spring growth of rye, wheat, and triticale have already begun or will do so imminently. The spring growth of oats really won’t begin until early March. Therefore, one would be wise to delay the late winter application of N to oats until the end of February.
Last, but certainly not least, one should consider the form of N being applied. If a producer applies ammonium nitrate, the fertilizer quickly dissolves into the soil moisture. Consequently, this source of N is almost immediately available to the plant. However, most of our producers no longer have access to ammonium nitrate. Many of the N products that are most readily available are based on urea. Urea and urea-based N formulations are, chemically speaking, organic forms of N. Urea must be broken down via a biological process to form nitrate, which is the form of N that plants predominantly absorb. Because this process is dependent upon the activity of microorganisms in the soil, weather can affect how rapidly this N becomes available to the plant. Cool and wet weather slows down the conversion of urea to a form of N that is available to the plant. Many producers will put on a significant amount of urea only to find that their crop fails to green up. This is not because they received “bad fertilizer.” It may be the result of the cool, wet weather. This is also the case for winter applications of poultry litter, which has much of its nitrogen tied up in organic material that has to be broken down in warmer temperatures and will not be very helpful with current weather patterns.
Adam Speir is Madison County’s Cooperative Extension Agent for agriculture and natural resources.