Potato Review Group

Contents

Background:

Availability

Influence on potatoes

Phosphorus application:

Application to soil

Application to foliage

Application of phosphorus as phosphite

Checking phosphorus status:

Phosphorus concentration in foliage

Further information:

Phosphorus notes

Phosphorus model

Top of page

 

Background

Availability

  1. Only a small proportion of phosphorus in soil is available to plants; tests for soil phosphorus are designed to measure that proportion. More …
  2. Phosphorus has very little mobility in soil and uptake depends upon root growth, while phosphorus deficiency can restrict root growth. More …
  3. Uptake of phosphorus from soil is restricted if soil is dry, see Phosphorus chemistry
  4. Diffuse pollution of phosphorus is a concern where loss of soil particles occurs. Do not apply more than required by the PRG Phosphorus Guidance Model.

Influence on potatoes

  1. Phosphorus influences the number of progeny tubers: phosphorus deficiency in the period before the onset of tuber bulking may restrict the number of progeny tubers. This appears to be an influence on the number of tubers formed, rather than on the proportion retained. Seed tubers which have been excessively pre-sprouted (sprouts >10 mm; or >500 degree days >4oC) show a reduced response to application of phosphorus. More …
  2. Phosphorus influences tuber yield as well as number of progeny tubers. More …
  3. Phosphorus applied to foliage is readily taken up and transported around the plant in both xylem and phloem.
  4. Foliar application of phosphorus can alleviate transient deficiencies and application when stolon tips are swelling has not been shown to be harmful. More …

Top of page

 

Phosphorus application

Application to soil

  1. Calculate requirement according to the PRG Phosphorus Guidance Model.
  2. To be available within the root zone phosphate fertiliser should be incorporated into soil, as phosphorus is immobile in soil unless applied to soil which is already saturated with phosphorus.
  3. Banding of phosphorus fertiliser can provide a high concentration available to developing roots and may be of advantage where root growth is restricted (e.g. by nematodes or lack of water) or competition with other minerals in soil restricts availability of phosphorus.

For more information on application of phosphorus to soil see Phosphorus chemistry

Application to foliage

  1. The concentration of phosphorus in the petiole of the 4th leaf provides a good indicator of availability of phosphorus for growth. Guidance on sampling and identification of the 4th petiole is available here.
  2. Early season measurements can be used to check the success of fertiliser applications.
  3. If phosphorus is deficient early in the season or a transient deficiency is expected due to lack of water, foliar application of phosphate can be beneficial. More …
  4. Apply 7 – 10 kg P­2O5 per ha.
  5. Ammonium polyphosphate or mono ammonium phosphate should be suitable for foliar applications.
  6. Uptake of foliar applied nutrients can be improved by admixture of a suitable product.

Top of page

 

Application of phosphorus as phosphite

  1. For specific uses phosphorus may be applied in the form of phosphite (H3PO3) instead of phosphate (P­2O5).
  2. Phosphite can aid plant health but does not supply nutritional phosphorus; if plants are deficient in phosphorus, application of phosphite can reduce phosphorus uptake.
  3. Application of phosphite can rapidly stimulate plant resistance responses.
  4. Application of phosphite may improve root health and thus uptake of nutrients.
  5. Application of phosphite can improve resistance to tuber blight and application to crops for storage can be particularly beneficial, such applications should be made during tuber bulking.
  6. Not all phosphite products are well formulated; be sure that any phosphite product used contains stabilised phosphite, as unstabilised phosphite will be rapidly converted to phosphate.

Use these links for more information on phosphite and disease resistance and use of phosphite.

Top of page

 

Checking phosphorus status

Phosphorus concentration in foliage

  1. The concentration of phosphorus in the petiole of the 4th leaf provides a good indicator of availability of phosphorus for growth. Guidance on sampling and identification of the 4th petiole is available here.
  2. Early season measurements can be used to check the success of fertiliser applications.
  3. If phosphorus is deficient according to the data below, there may be a potential to phosphorus to foliage, depending on the stage of crop development.

Petiole P data

Top of page

 

Further information

Phosphorus notes

Nutrition 2020 (Includes introduction to / review of phosphorus)

Application of phosphite for disease resistance 2020 (Regulation of plant defence genes; transport of phosphite in plants; resistance to tuber blight infection)

Applications to seed and soil 2020 (Includes experiments with a novel phosphorus fertiliser)

Phosphorus application theory 2019 (Guidance on phosphorus application)

Phosphorus update 2018 (Phosphorus availability in soil and interaction with other nutrients)

Foliar micronutrition 2017 (Experiments showed some response to Steric P, but not to addition of “Avail” to phosphorus fertiliser)

“Nutrisphere” and “Avail” 2016” (Background to products suggested to aid availability of N and of P)

Nutrient experiments in 2014&15 2016 (Includes steric P)

Measuring soil nutrients 2016 (Summary of soil sampling for phosphorus)

Phosphites 2015 (Phosphite interacts with plant disease resistance to suppress some diseases)

Nutrition experiments in 2014 – presented 2015 (Includes steric P)

Phosphate and phosphite for potatoes 2014 (Availability of phosphorus in soil; disease suppression by phosphite as a result of increased plant resistance)

Calcium phosphite application 2012 (Foliar application of phosphite + calcium can improve calcium uptake and retention)

Phosphite and disease resistance 2012 (Phosphite can suppress some diseases, particularly oomycetes such as late blight, by stimulating plant resistance)

Foliar nutrient applications 2011 (Experiments showed benefits of phosphite applied to foliage in combination with calcium or cytokinin)

Nutrition experiments 2010 (Experiments on foliar phosphite application showed potentially detrimental effects from inappropriate timing)

Phosphorus nutrition 2009 (Phosphite can improve plant health and nutrient uptake but phosphite suppresses phosphate starvation sensing)

Nutrient combinations 2008 (Deficiency of one nutrient may reduce response to others)

Phosphite for potatoes 2008 (Introducing use of phosphite)

Phosphorus 2004 (Phosphorus is important for tuber production but physiologically aged seed tubers may show poor response)

Phosphate 1997 (At sites where root growth is poor there may be greatest response to soil applied phosphate; petiole samples can be used to measure uptake)

Foliar nutrient uptake 1997 (PRG research showed that a suitable surfactant can increase uptake and efficacy of foliar applied phosphate)

Foliar application of nutrients 1994 (PRG research showed that a suitable surfactant may be required with foliar application of phosphate)

Seminar 1 Notes 1992 (Chapter 11: some methods of measuring available P in soil. Chapter 12: Response to foliar application of phosphate in PRG experiment.)

 

Phosphorus guidance

For background information on the model see Phosphorus chemistry

Download the PRG Phosphorus Guidance Model (Excel spreadsheet) here:
PRG Phosphorus Guidance Model

 

Top of page