Forage Focus: Grazing Livestock Affects Pasture Fertility

By Rory Lewandowski, Extension Educator, Athens County and published in BEEF Cattle newsletter by Ohio State University Extension . At the February Ohio Forage and Grasslands Council annual conference, Dr. Dave Barker, an Ohio State University forage specialist, presented some of the research he is doing regarding the effects of livestock grazing upon pasture fertility.
calendar icon 18 May 2007
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Probably the main message that came across in his presentation was that animals move nutrients. Grazing animals move nutrients within a pasture paddock, between pasture paddocks and move nutrients off the farm as animal product. One of the main effects of grazing from a pasture fertility standpoint is to concentrate nutrients into patches through urine and manure deposition.

The main nutrient contained in urine is nitrogen. Urine accounts for about 70% of the nitrogen returned to a pasture by grazing livestock. According to Dr. Barker, one urine patch can have a nitrogen application rate equivalent to about 1000 pounds/acre. This is too much nitrogen to be effectively used by grass growing in the area, so there are high nitrogen losses. Leaching losses, where nitrogen moves down through the soil and out of the rooting zone, account for nearly 50% of the nitrogen in a urine patch according to a German study cited by Dr. Barker. Another 22% of the nitrogen is lost to the air by volatilization as ammonia.

The manure or dung patch also concentrates nutrients where it is deposited by the animal. Research indicates that the phosphorus in a manure patch can be equivalent to 220 pounds/acre. In areas where livestock "camp" or hang out, the soil potassium levels can be 4 to 10 times higher than the pasture average. While nitrogen application rates can be similar to that applied to an area through urination, losses are much lower because the nitrogen is bound up in an organic form that is more stable. Nitrogen leaching losses under a dung patch were found to be only about 4% of the total nitrogen applied. Losses of nitrogen through volatilization measured about 5%.

Nutrients are moved within a pasture paddock and between pasture paddocks by livestock and their patterns of urine and manure deposition. Water tanks, shelter/shade areas, salt/mineral feeders and areas where hay is fed are all places where manure and urine are deposited more heavily. There are strategies that can be used to increase the uniformity of urine and manure deposition throughout a pasture field.

One of the most effective strategies is to increase the stocking rate so that livestock cover more surface area within a paddock. Another way to achieve this effect is to provide the same number of animals with a smaller paddock size. Salt and mineral feeders should be located away from the water source and from any trees/shade so that manure distribution is increased across the paddock. If there are high and low nutrient areas, use a grazing rotation and paddock structure that will move nutrients from the high nutrient areas to low nutrient areas.

Finally, recognize that nutrients are moved off the farm as animal products are sold. Those nutrients can be replaced as purchased feeds are brought on to the farm, fed to livestock and recycled through the manure and urine. Nutrients may also be replaced through fertilizer application. With the cost of nitrogen fertilizer continuing to move upward, livestock owners should also be increasing the legume content of their pastures to take advantage of the nitrogen fixing ability of leguminous plants.

Pasture fertility and nutrient concentrations within a pasture are not uniform, but are dynamic and changing, reflecting the movement of livestock using the pasture. Good grazing management can help to increase the uniformity of nutrient deposition leading to an increase in pasture productivity.

May 2007

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