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Fertilizing Pastures: Toxic Versus Nontoxic Fescue
GREENFIELD, MO.
According to Jill Scheidt, an agronomy specialist with University of Missouri Extension, when fertilizing pastures, it is important to only make replacement applications.
“Annual hay crops can take a large amount of nutrients out of the soil that should be replenished over time to keep productivity high and weed pressure lower,” said Scheidt.
Cool season grass hay like fescue can remove 9 pounds of phosphate and 34 pounds of potash per ton of hay removed. Hay from clover and cool-season grasses such as fescue can remove 8 pounds of phosphate and 38 pounds of potash per ton of hay removed.
“Adding more fertilizer than the pasture needs can negatively affect plant growth,” said Scheidt.
Adding moderate to high amounts nitrogen to a toxic fescue field causes the endophyte in the fescue to produce more toxins.
According to Craig Roberts, MU state forage specialist, applying 50 pounds of nitrogen to a pasture will cause ergot alkaloids to increase slightly.
“However, if you continue to apply much more nitrogen, for example, 100 pounds of nitrogen, ergot alkaloids increase exponentially. It is safer to use a low rate of 40 pounds per acre of nitrogen on a toxic fescue field in the fall,” said Roberts.
If a spring nitrogen application is made, Scheidt says it must be assumed that dry matter will be removed. When nitrogen is spring applied in excess, a toxic fescue pasture will experience quick growth. This growth is not always a positive thing.
“If grass becomes too tall, it will smother itself as well as legumes that are under the canopy. Excess nitrogen also prevents legumes from doing their job; a reduction in nitrogen fixation and legume yield will occur with too much nitrogen. Plants waste nitrogen that they do not need. Fall is the best time to fertilize pastures,” said Scheidt.
Legume populations are especially important in toxic fescue fields. Legumes add higher quality to the pasture, dilute toxins and even out the yield distribution with late spring and early summer growth.
A higher rate of nitrogen can be applied in the fall to nontoxic fescue. Scheidt says a little nitrogen is needed to stimulate growth because animals prefer nontoxic fescue over toxic fescue. Sixty-five pounds per acre in the fall is a good amount; a low level of nitrogen can be applied in the spring to non-toxic fescue as well.
“Nontoxic fescue pastures require better management than toxic fields. Nutrients that have been removed by haying or grazing must be replaced in order to maintain a stand,” said Scheidt.
As always, a soil test is the most accurate way to obtain a fertilizer recommendation.
“Remember to sample hills, watering areas, old fence lines and shade areas separately from the rest of the field in order to obtain a representative soil sample,” said Scheidt.∆
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