Tips on Tree Nursery Practices V: Plant Nutrition
The nutrient demands for crop vary by development stage. Plugs and rooted cuttings require low fertility levels; nutritional needs increase as they become established. Actively growing plants have the highest nutrient demands.
Knowing the optimal pH range for each crop will help determine if an acidic or basic fertilizer should be used. If not sure, a pH range of 5.6-6.2 would be safe with 5.8 as the generally accepted optimum pH. Low uptake of micronutrients (boron, copper, iron, manganese, zinc) can occur if medium’s pH is above 6.5. Certain macronutrients (calcium and magnesium) can become less available below 5.4.
1. Phosphorus – Most crop require only 5-10 ppm P for adequate growth especially during early root development.
2. Potassium-Calcium-Magnesium ratio – Potassium (K) fertilization rate above 200 ppm can have an antagonistic effect on Calcium (Ca) or Magnesium (Mg) uptake by the plant. Supplying the plant with a K-Ca-Mg ratio (ppm) of 4:2:1 will limit any antagonisms.
Another example of mineral antagonism is the nitrogen-potassium (N-P) interaction; a 1:1 ratio is recommended.
3. Water Stress (too much water) – Constant saturation of the medium can lead to macro- and micro-nutrient deficiencies. When overwatering reduces oxygen levels, root growth can be limited and water uptake slowed. Elements such as calcium are transported via water flow and deficiency symptoms can develop rapidly. Also the inactivity of the root systems due to saturated conditions can lead to insufficient uptake of all nutrients, particularly iron (Fe) and phosphorus (P).
4. Soluble salts level – Soluble salts refer to the total dissolved salts (fertilizers are salt-based) in the medium at any given time and is measured by electric conductivity or EC (salt is a conductor of electricity). When the EC of the medium is too low, growth is stunted and mineral deficiencies are observed. Deficiency symptoms such as lower leaf yellowing (nitrogen), lower leaf purpling (phosphorus), and lower leaf interveinal chlorosis (magnesium) are common when the EC values are below 0.25 mS/cm.
When the EC of the medium is too high, planr growth is stunted. Problems can occur when EC values are above 1.25 mS.cm
UPV Centennial Forest 