Why a healthy canopy is essential for potatoes

There is a general consensus amongst plant physiologists that the potato crop yield is limited by the source of photosynthate as opposed to the size of the ‘sink’ i.e. the number of developing tubers following ‘tuber initiation'. It helps us consider what is important in ensuring we maximise the plant’s ability to fill the ‘tuber sink’ thus producing as many marketable potatoes as possible, and improving profitability.

In practical terms, we should ensure that:

1. Plants produce a full canopy of leaves as quickly as possible (rapid early emergence)
2. This full canopy is healthy, maintaining its ‘greenness’, for the duration of the tuber bulking phase
3. The plant is able to translocate the sugars (sucrose) produced in the leaf down to the developing tubers as they ‘bulk’

Point 1 is achieved partly through the use of fertiliser applied prior to, or ‘placed’ at planting. Once the canopy, or Leaf Area Index (LAI), is at approx. 4, 90% of incoming solar radiation will be intercepted by the green leaves. This is converted by photosynthesis into ‘chemical energy’ known as ATP. This chemical energy is used during photosynthesis to produce sugars that are utilised to maintain the leaf canopy, and most importantly are transported to the developing tubers as they expand or ‘bulk’.

Biostimulants can be used to relieve abiotic stress

The ideal crop uses very limited amounts of the sugars to maintain its canopy, thus partitioning the majority into the tubers. This is referred to as a high Radiation Use Efficiency (RUE). During this tuber ‘bulking’ phase the yield will be increasing at up to 5 t/ha/week. When considering how to minimise the energy that is required to maintain a canopy, we need to focus on how we reduce the plant’s respiration to a minimum. A plant’s respiration rate will increase when it comes under stress, either biotic (insects and pathogens) or abiotic (drought, heat etc). Such a response reduces the amount of sugar produced during photosynthesis that is available for yield formation (tuber bulking). It is essential to manage these stresses out of the production system. For biotic stress then good pest, disease and nutrient management is the answer. Abiotic stress relief can be aided by the use of biostimulants.

Foliar nutrients are effective in managing nutrient deficiencies

Nutrient deficiencies can be monitored through plant leaf analysis. Data from Yara Analytical laboratories reveals some of the key nutrient deficiencies found in potatoes to be phosphate, potassium and magnesium. Phosphate is of particular importance due to its role in the transport of the sugars from the leaf down to the ‘bulking’ tubers. The transport mechanism is an energy-demanding process and the chemical energy is stored by the plant in the phosphate-based molecule ‘ATP’. Magnesium, the central component of chlorophyll (leaf greenness), clearly has an important role in keeping the leaf canopy greener for longer. Potassium helps the plant regulate water and nutrient movement from roots, through the plant, to the leaves. Water movement itself is also a necessity in the transport of sucrose down to the ‘bulking’ tubers.

In conclusion, by removing both biotic and abiotic stress you will ensure a healthy, well-functioning potato canopy. This will give the best chance of maximising the important ‘tuber bulking’ period, and result in high, marketable potato yields.

Recommended action

• During full canopy cover, 2 applications with 14 days in between
  YaraVita Magphos K @ 5 l/ha 
  YaraVita Biotrac @3 l/ha