Proper soil nutrients are required for forage plants to maximize growth. Data indicates our forage plants use 20+ elements to live and grow. All are equally important for growth, but vary greatly in amounts needed.
Of these, nitrogen, phosphorus, and potassium are usually required in the largest amounts followed by calcium, magnesium, and sulfur. These are generally known as macro-nutrients.
All others, while still essential and vital for plant growth, are called micro-nutrients only because they are needed in lesser quantity.
Plants take these elements and solar energy from the sun, organize them in correct combinations and amounts to allow them to grow and produce forage.
Improving productivity
If you’re trying to improve forage productivity in your hay fields and paddocks, evaluate soil fertility. Trying to implement any type of grazing management system is rather useless if plants lack sufficient nutrients, because they can’t grow properly.
Soil testing or plant tissue tests are the two main ways to evaluate fertility levels. Soil testing in pastures may not be perfect because test procedures were developed using tilled cropland to estimate nutrient status. However, using data derived from a soil test is still one of the best tools we have to assure fertility and pH levels are satisfactory for plants to thrive and grow.
Vegetative growth. Soil pH should be in the 6.0 – 6.5 range to allow proper uptake of minerals by forage plants from the soil. Nitrogen is associated with lush vegetative growth, phosphorus is required in adequate amounts for flowering, and potassium is necessary for durability and disease resistance.
Nitrogen is often the most limiting nutrient in grass f orage production because of the amount of nitrogen grass plants can use. If legumes are present in sufficient quantity (30-35 percent of the total), no additional nitrogen may be needed since the legume plant can fix nitrogen from the atmosphere and store it on its root system.
Bacteria
Rhizobium is a group of bacteria in the roots of legumes which form nodules or knots where the nitrogen is stored.
The bacteria can take nitrogen from the atmosphere and put it into a form that the plant can use. This nitrogen is then available to the legume plant and surrounding grass plants for growth.
Amounts of nitrogen fixed in a plant’s roots can differ according to the legume used. Clover varieties may fix 50 pounds or more of nitrogen per acre each year while some alfalfas may produce 150 pounds per acre each year.
Nutrients can also be supplied to soil in other ways to meet plant needs. Manure can be hauled in and spread, along with commercial fertilizers or other products, to increase soil nutrient levels.
Feeding hay to livestock in pastures provides additional nutrients, too.
In pasture situations, nutrients are not removed as quickly as hayfields due to the way the crops are harvested. While livestock in pastures may move nutrients, they don’t take several pounds of nutrients off the fields like we do with hay harvests. A very high percentage of all nutrients in the forage consumed by livestock are recycled via manure and urine. Controlling where these nutrients are deposited is most easily accomplished when using rotational grazing methods.
Effects
Smaller paddocks can reduce “mining” effects keeping nutrients closer to where they originate. Large paddocks typically allow livestock to move many forage nutrients to a few shady areas where they hangout for long periods during hot summer days. If nutrients are continually moved away from portions of a field deficiencies may occur. Something will usually grow, but it just may not be the plants you want. Listed in the adjacent box are a few nutrients, their functions in plants, and indicators that may be noticed if soils are deficient in nutrients.
Soil tests should be done every 3-5 years, but I know that won’t always happen. So, if you have seen any of the symptoms listed in the box in your forages, a soil test should be taken and nutrients added where needed.
For most consistent laboratory soil test results, it’s best to sample fields the same time of year each time samples are taken. This allows better tracking of trends in soil nutrient values over time, which can be as important as an individual test result.
Benefits
A couple of points you should remember. Volatilization of the urea form of nitrogen will likely occur and not fully benefit your forage plants if: 1) lime has been broadcast on the field within the last 9-12 months, 2) in warm weather, if a rain event of at least half an inch of rain does not occur within 48-72 hours of application to “wash” the nitrogen into the soil.
Good grazing management practices may help producers avoid nutrient deficiencies in forages. Strong, healthy and vigorously growing plants develop large root systems that capture nutrients at times when weak shallow rooted plants cannot.
If you have not tested your soils in a while, take a good look at your forages. Don’t let soil nutrient deficiencies reduce your forage’s ability to grow and produce the maximum quantity and quality forage possible for your livestock.
Soil mineral deficiency
symptoms seen in plants
Nitrogen
Regulates vital chemical reactions in stem growth; necessary for chlorophyll and genetic material formation; stimulates leafy growth Pale green or general chlorosis and yellowing of leaves; usually appear in the tips of older leaves (bottom of plant) first; forage just does not have that dark green color; less tillering in grasses and reduced yields.
Phosphorus
Associated with root formation, flowering, & fruiting Leaf tips look burnt sometimes; purple or reddish color on older leaves; overall stunting of the plant; reduced yields.
Potassium
Associated with movement of water, nutrients & carbohydrates; stimulates early growth Symptoms appear on older leaves first; yellowing and/or scorching along leaf margins moving toward center; white spotted leaf edges; poorly developed root systems; reduced yields; reduced disease resistance; white clover dominance around urine patches.
Calcium
Part of cell walls & structural strength; enhances uptake of negatively charged ions Young leaves small & distorted; large numbers of dandelion and buttercup plants appear; reduced germination of clover seed; decreased forage palatability.
Magnesium
Central element in the chlorophyll molecule; energy transfer tool for the plant Loss of green color (yellowing) between veins; see grass tetany in ruminants.
Sulfur
A part of all proteins; acts as an enzyme activator Young leaves turn pale yellow-green; shoots are stunted Note: Field and climate conditions affect expression of symptoms; tissue tests assure diagnosis.
