When working with perennial forages, soil fertility is vital because it affects the quality of the forage that the animal eats. Animal health and production is related to the nutrients the animal receives from the forage. The best way to determine the fertility level and corrective fertilizer requirements of a current or future pasture is from a soil test. Soil tests tell us the soil pH; nitrogen (N) recommendations; phosphorus (P) and potassium (K) levels and recommendations; as well as secondary and micronutrient status. For a new pasture, soil tests samples should be collected and analyzed well in advance so the types and quantities of recommended fertilizers can be incorporated into the soil at the time of field preparation. At this same time, lime should be applied to achieve a soil pH of at least 6.3. (Note: on a new full cultivation seeding of a field with a pH range of 5.8-6.5, applying 4 tons/ac of lime followed by working it into the soil along with the fertilizer suggested by the soil analysis would not be excessive, followed by an annual top dress of 2 tons/ac.). In addition to correcting pH, lime is a source of valuable Calcium, which all living things require. To see what effect pH has on utilization of N,P,K and how much is potentially wasted see the chart below.
Fertilizer Utilization Chart. Without the proper pH, fertilizer cannot do its job. It is imperative that the pH be adequate to limit the amount of wasted fertilizer. (Source: Chris McCracken, Barenbrug, USA.)
% FERTILIZER UTILIZED |
% WASTED | |||
SOIL pH |
Nitrogen (N) |
Phosphate (P) |
Potash (K) |
|
Extremely Acid |
30% |
23% |
33% |
71.34% |
Very strong Acid |
53% |
34% |
52% |
53.67% |
Strongly Acid |
77% |
48% |
77% |
32.69% |
| Medium Acid 6.0 pH |
89% |
52% |
100% |
19.67% |
| Neutral 7.0 pH | 100% |
100% |
100% |
0 % |
NOW YOU SEE WHY SOIL pH IS SO IMPORTANT --$$$$$$$$
(Note: Nutrients in fertilizers are stated on the labels. The percentage of actual N, P, and K is expressed as a ratio by weight and in the order of N-P-K. E.g., a 10-10-20 fertilizer contains 10% N, 10% P and 20% K. Thus 100 lbs of this fertilizer contains the actual element (in unit lbs) of 10 lbs/N, 10lbs/P and 20lbs/K with the remaining 60 lbs being filler. Urea a common form of N is rated 46-0-0 which yields 46 unit/lbs of N per 100 lbs of fertilizer. )
The pH of the soil is important, but why the pH is what it is, should be considered more important. The base saturation levels of Calcium, Magnesium, Potassium, Sodium and Hydrogen levels determine the pH. You can have a high pH and still have a shortage of Calcium in the soil. Calcium however, is the one element that drives the production of quality forage. A good source of Calcium is Gypsum, which is Calcium Sulfate. Sulfur is also very important for creating high quality proteins in forages. Most soils are low in this element.
All grasses need nitrogen (N) on a periodic basis during the growth cycle to attain and maintain optimum production. Nitrogen is a consumable fuel just like gasoline is to an engine. It is consumed daily as the plant grows. This is true even when grasses are planted with clover or other nitrogen fixing legumes. Legumes are a money saving source of N especially during the summer and should be used where possible. Alice white clover can provide up to 150 unit/lbs of N per acre/year. Even with clover, optimum production still requires about 150-200 unit/lbs. of supplemental N per acre/year. This assumes that the proper levels of Phosphorus and Calcium are present. Without these, the performance of N alone is greatly reduced. Apply 50 unit/lbs of N in the spring as soon as the soil is 50 degrees or warmer, with the remainder applied in 3-4 equal doses throughout the growing season, but not later than mid-September. N should be applied with moisture, either from irrigation or rain for the best results. On established pastures, take a soil test every 2-3 years, then top dress on the recommended levels of P and K in the fall, allowing winter action to incorporate.
Persistency of forages is related to balanced fertility. A healthy plant is more likely to tolerate the stress of winter and summer. All plants and animals need balanced fertility (nutrition.) This includes micronutrients as well. Constant removal of nutrients resulting from harvest of crop and pasture has left some soils very low in micronutrients (copper, zinc, manganese, boron, etc.) Do not let the word “micro” deceive you. You do not need much, but you do need enough.
Call your local Extension Agent for details on where to get a soil analysis run. If, for some reason, a soil test is not possible, a reasonable pre-plant fertilizer recommendation is: N = 30 - 40 lbs.; P2O5 = 70 lbs.; and K2O = 50 lbs. of unit/lbs of N, P, K (nitrogen, phosphorus, and potassium, respectively) per acre.
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