Farmers fertilize pastures for quick, nutrient-dense growth to support their livestock.
Farmers often want to pasture their sheep right after the pasture has been fertilized.
It is far safer to wait to put sheep on fertilized pasture until several weeks later.
The excessive nitrate in fertilizer is harmful to sheep and can poison them. After testing the soil, farmers must decide on a plan to improve the pasture and, if fertilized, keep sheep off the pasture for six weeks or longer.
Want to know more about fertilizer and how it affects sheep?
Problems with Putting Sheep onto a Freshly Fertilized Field
When forage or water contains too much nitrate, it can cause sheep to develop nitrate poisoning.
This is alarming, although chronic nitrate toxicity is rare.
Excess nitrate is more likely found in shallow and surface water sources.
Nitrate levels may increase in cool-season crops and grasses in hot, dry weather or warm-season crops.
When the temperatures are low, or growth has stopped because of frost, plants are at increased risk of high nitrate.
Annual forage crops will gain greater amounts of nitrates than perennial.
The Effects Of Nitrate
Ordinarily, nitrate is converted to nitrite, then to ammonia, and then to bacterial protein in the rumen.
The rumen of a sheep is pretty handy at converting nitrates to nitrite.
But it may accumulate too much nitrite if the sheep consumes an overage of nitrates from either feed or water.
The excess nitrite is then absorbed into the bloodstream and causes hemoglobin to convert to methemoglobin.
Hemoglobin is what transports oxygen in the bloodstream and now isn’t there to do it.
In time, the animal sickens and eventually dies from a lack of oxygen.
The most dramatic nitrate toxicity problems happen when livestock are overly hungry and eat too much of the feed with high ppm nitrate.
Hypomagnesemia occurs as a result of fertilization.
Hypomagnesemia is also known as ryegrass staggers or grass tetany.
This condition is caused by quickly-growing grass with an increased nitrate level.
This prevents magnesium uptake into the plant and, therefore, the sheep.
The sheep then have low magnesium levels.
It leads to clinical signs such as tremors of the face and ears, sudden, involuntary spasms of muscles, laying down, and death.
Lambs suffering from hypomagnesemia have a stiff gait, muscle spasms, or in chronic cases, exhibit more than a 30% slower growth rate.
Acclimating Sheep to Nitrates
Previous exposure, the animal’s age, health status, and diet all play a role in how toxic nitrates are to an individual sheep.
There is no established “safe level” for all feeding conditions.
Sheep can tolerate quite a bit of nitrate if you have conditioned them gradually to eat feed with higher nitrate concentrations.
A healthy sheep can tolerate more nitrate intake than a sickly one.
Diet plays a role in helping sheep tolerate more nitrates.
If they get enough carbohydrates, such as grain, these carbohydrates increase the conversion of nitrate to protein rather than nitrite, which helps prevent nitrate accumulation.
Careful management practices lower the risk of nitrate poisoning.
It’s done by using up and eliminating high nitrate feeds from rations.
Sheep owners should be concerned if plant growth on the pasture is stunted or if they have applied nitrogen more than twice the recommended amount.
What Is the Best Fertilizer for Sheep Pasture?
The very best fertilizer for sheep pasture is probably the sheep themselves.
A 100-pound sheep produces about four pounds of manure daily.
Sheep produce “cold” manure, which is low in nitrogen and immediately usable on plants without burning it, but aged manure is best.
It is recommended raw manure be composted for at least 15 days at 131° degrees Fahrenheit. (55° C) to kill off disease and seeds.
It also neutralizes salt, nitrogen, and ammonium levels.
Composted animal manure, in general, is a natural, slow-release fertilizer, improves soil structure in sandy or clay soil, promotes the growth of beneficial soil organisms, and is gentler on immature plants, making it a valuable soil amendment.
The content of farm manure varies but is generally high in nutrients for plant growth, such as phosphorus and potassium.
Do not use fresh manure on root crops or other edible crops in contact with soil; if you do, it must be applied a minimum of 120 days before harvest.
Fresh manure applications should be at least 90 days before harvest for food crops not in direct contact with soil.
Some other natural fertilizers made from animal products or organic fertilizers all high in nitrogen are:
- Feather meal
- Blood meal
- Hoof and horn meal
- Fish meal
- Crab meal
- Animal tankage
- Bat guano
- Soybean meal
- Fish emulsion
- Cottonseed meal
Using natural fertilizers in soil amendments for sandy soils improves soil texture and is a steady source of nutrients for plant life.
Nitrogen fertilizers ensure energy is available for the plant to use, from roots to leaf, helping regulate water and nutrient uptake.
Types of Fertilizer Delivery
Using quick-release liquid nitrogen means keeping sheep off the pasture for at least a week.
Liquid fertilizer stays on the leaf longer, and sheep ingest it directly.
If using quick-release liquid nitrogen with iron, sheep must stay off the pasture for a month.
Granular quick-release nitrogen releases into the soil but can taste salty and cause the sheep to eat it directly and get nitrate poisoning.
When using granular fertilizer, wait for good rains or watering to dissolve the fertilizer into the soil before allowing sheep to pasture, so they do not inadvertently eat it.
Testing for Nitrates
If you suspect fresh forage or silage has a high nitrate level, get it tested.
There are also many commercial and extension agency testing facilities for accurate nitrate analysis.
Ensure the sample is from the feed or water being analyzed.
Collect water samples in special bottles provided by the testing agency.
Freeze the sample to halt metabolism and keep the nitrate from being lost.
Soil test kits such as this one from Amazon are also available to test your soil before fertilizing.