Many factors impact the decision to fertilize pastures. They include:
- the variation of rainfall across the state;
- varying types of grazing systems;
- irrigation or the lack of irrigation;
- type of livestock being produced;
- different management objectives.
In general, the addition of fertilizer will improve forage quantity and quality. Table 1 shows that the fertilized plots consistently produced more forage during both dry and wet seasons than non-fertilized plots.
The way in which a producer utilizes forage determines if it is profitable to fertilize. Table 2 demonstrates the amount of nutrients removed from soil by different forage management alternatives.
One ton of grass hay will remove about 50 pounds of nitrogen, 15 pounds of phosphorus, 40 pounds of potassium, 5 pounds of sulfur and 3 pounds of magnesium from the soil. These nutrients, mined from soils, must be replaced by nutrients from commercial fertilizers or manures. Forage production will be reduced if nutrients are not replaced. In low fertility soils, desirable forages may slowly die and be replaced by weeds or brush.
Nitrogen, when added to soils, causes an acidic reaction and, in sandy areas of Texas, will contribute to low pH. Liming will be necessary to raise the pH to prevent growth problems and also increase nutrient absorption.
When plants have adequate available nutrients, growth is not slowed.
Under any moisture situation, grasses must have sufficient plant nutrients available to produce maximum forage levels. Adequate fertilization also causes grasses to be more water efficient. Numerous research and county forage demonstrations have shown that, without fertilization, 16 to 20 inches of water are necessary to produce 1 ton of low quality forage. With adequate fertilization, plant growth is not restricted by a nutrient deficiency and the grass can produce 1 ton of good quality forage with only 4 to 6 inches of water.
Table 1. Forage management in Brazos County Pasture.*
|Treatment||Dry matter (lbs.) Per acre 1990-dry season||Dry matter (lbs.) Per acre 1991-wet season|
|Fertilizer only-no weed control||645||2587|
|Unfertilized and no weed control||377||1385|
*Evaluations conducted by David Bade, Extension Forage Specialist, the Texas A&M University System.
Table 2. Nutrients removed by different forage management alternative.
|Nutrient||Nutrients (lbs./acre) removed to produce 500 lbs. beef/acre||Nutrients (lbs./acre) removed to produce 6 tons of hay/acre|