ROLE OF PHOSPHORUS (P) IN APPLES
Phosphorus is a primary apple nutrient like nitrogen and potassium which is essential for overall development and growth of apple tree. Nitrogen, phosphorus and potassium are three major apple nutrients as these nutrients are utilized by the apple tree in large amounts. It is important as it plays a vital role in root development, insufficient phosphorus levels can result to poor root development and hence stunned growth of the plant. Phosphorus is a component of key molecules such as amino acids, proteins and nucleic acids. It plays a main role in both photosynthesis and respiration. The percentage of phosphorus in a fertilizer, as a phosphorus pent oxide is represented by the middle number on the bag expressed (e.g. 12-32-16).
KEY ROLE OF PHOSPHORUS (P)
- It helps in root formation and growth.
- It promotes flowering and seed production.
- It helps in fruit set and development.
- It helps in maximizing bud development.
- It helps in energy transfer and protein synthesis.
- Adequate phosphorus levels results in earlier crop maturity.
- It improves fruit quality.
- It helps in building resistance to plant diseases.
- It is important in cell division and development of new tissue.
PHOSPHORUS AVAILABILITY AND UPTAKE
Majority of phosphorus in soil is in insoluble form which is unavailable to plant. Soils may contain variable amount of phosphorus, however much of the phosphorus is unavailable to the plants. In soil it may consist in three different forms:
- Solution phosphorus.
- Active phosphorus.
- Fixed phosphorus.
In this form very small amount of phosphorus is available in soil. Phosphorus exists in orthophosphate form and small amounts of organic form. Plant uptakes only orthophosphates form and is relatively mobile.
This form is the main source of available phosphorus to the plants. Phosphorus is in solid phase which is easily released to the soil solution. It contains inorganic phosphates which are attached to small particles in soil.
It contains organic compounds and insoluble inorganic phosphorus compounds. Phosphorus in this form remains unavailable to the plant and have very little impact on the fertility of the soil.
Phosphorus uptake takes by entering through the root hairs, root tips and outer cells of the roots. It is taken up mostly in primary orthophosphate ion but some is taken as secondary orthophosphate ion. It may be stored in the roots or may be transported to the other parts of the plant.
DEFICIENCY OF PHOSPHORUS IN APPLE
Phosphorus deficiency is most difficult to diagnose than a deficiency of nitrogen and potassium. However some common symptoms are as under:
- Poor root growth resulting in stunned growth of the tree.
- Purple coloration of leaves.
- Reduced flowering and seed formation.
- Poor fruit set.
- Reduced leaf size and shoot growth.
- Reduced fruit size and lesser fruit color.
- Delayed fruit maturity.
WHEN AND HOW MUCH TO APPLY?
- Silver Tip Stage – It helps in root development and flower formation.
- Pea Stage – It helps in fruit development.
- Post harvest— It helps in bud development and tissue making.
An average standard apple tree requires 350gms to 450gms of phosphorus (P) annually. So the dosage should be adjusted according to the frequency of the application.
- SINGLE SUPER PHOSPHATE 16% P2O5
- DI-AMMONIUM PHOSPHATE 46%P2O5
- TRIPLE SUPER PHOSPHATE 46%P205