Fertility for Perennial Stands

Knowledge Nuggets.

• Fertilizing any type of crop in not an exact science. The soil-plant environment is a dynamic eco-system that is always changing and is a very complex mixture of organic matter, minerals, insects, nematodes, bacteria, fungi, water, gasses and weather interactions. Any disruption of these components can change the availability of nutrients.

• Water and nutrient supply are the two most important factors controlling the growth of a forage crop. There are 20 nutrient elements that are needed for plant growth. A deficiency in any nutrient can limit productivity. There are eight commonly deficient nutrients. The major nutrients include: nitrogen (N), phosphorous (P, in the form of phosphate P₂O₅) and potassium (K, in the form of potash K₂O). The secondary nutrients include: sulphur (S), magnesium (Mg) and calcium (Ca). The minor nutrients include: zinc (Zn) and boron (B).

• One ton of alfalfa (dry matter basis) removes 58 lb N, 14 lb P₂O₅, 60 lb K₂O, 6 lb S. On ton of grass forage (dry matter basis) removes 35 lb N, 10 P₂O₅, 50 lb K₂O, 5 lb S.

• Periodically soil test to determine availability of plant nutrients and to identify the soil nutrients that are not in adequate supply.

• Fertilizer recommendations for essential nutrients based on averages from soil tests coupled with field experience of normal growing conditions provide a good base for fertility programs.

• Yield goals should be considered and be based on historical rainfall information. Adjusting fertilizer rates based on realistic yield goals is essential to maintain environmental quality and to obtain maximum economic returns.

• Maximum return per unit of N fertilizer will be reached if:
  a. adequate soil moisture is present,
  b. tame forage stands are fertilized,
  c. weeds are controlled,
  d. no soil limiting factors such as extreme pH, salinity, or poor drainage are present.
  
• In general, nearly all grass-based stands will benefit from nitrogen fertilization. If the stand includes a high proportion of legumes, nitrogen fertilization is less important since legumes fix atmospheric nitrogen.

• General annual fertilizer recommendations: 30-110 lb N/acre for grass stands and no N fertilizer if stand is more than 35% legumes; 0-45 lb P₂O₅/acre for grass stands and 0-60 lb P₂O₅/acre for legume stands; 0-35 lb/acre K2O for grass and legume stands; and 0-35 lb/acre S on well-drained and grey wooded soils. Potash and sulphur levels in soils are very variable, soil testing is highly recommended.

• The best time to apply fertilizer is early in the spring when the plants begin to grow.

• Prior to establishing forages, consider front loading or pre-placement of soil stable nutrients like P and K to improve the long-term nutrient status of the crop. Pre- placement of these nutrients makes them more available to establishing plants rather than waiting for broadcast fertilizers to migrate into the root zone.