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Plant Science
Metabolic Regulation: Crop Nutrition

Peter Barraclough

Research Leader: Dr Peter Barraclough
Assistants: Caroline Shepherd; Janina Jones
Visiting scientists: Rafael Lopez-Bellido; Zlatko Svecnjak

Crop nutrition and physiology
Fertilisers are essential for maximum yield, but excessive amounts can depress yield and pollute the environment. We would like to be able to advise farmers how to fertilise crops optimally, that is to tailor applications so that they just meet crop needs at all times, but this is not easy in a maritime climate. Basically, the problem is one of predicting how much nutrient will come from the soil and how much nutrient the crop is likely to need during the growing season - both of which depend on the weather. We are studying how nutrient supply affects the growth of sources (leaves and stems) and sinks (grains and tubers), and in particular how this interacts with environmental variables such as light, temperature and water. The aims are to better understand the physiological requirements for nutrients under different growing conditions from which reliable diagnostic tests can be developed. This will provide the basis for more effective fertiliser management in the move towards precision farming and sustainable agriculture. Currently, the Group's activities are focussed on NPK nutrition of wheat, rape and sugar beet with funds being provided by BBSRC, HGCA, and BBRO.


NPK in wheat
Nitrogen drives the growth and yield of wheat. Yields have doubled in the UK since the 1960's due in no small part to the ability of short-strawed varieties to respond to large dressings of N. Despite much progress in understanding the behaviour of N in plants and soils, accurate fertiliser recommendations continue to elude the industry. We are trying to develop quick and easy indicators of crop N status at key stages of growth so that in-season fertiliser adjustments can be made for grain yield and quality. But optimal response to N requires that other nutrients are non-limiting, so work is also being done on P and K using Rothamsted's unique long-term P and K sites.

Nitrogen diagnostics in wheat
Plant N status is traditionally assessed through total-N in dry matter, but this is neither quick nor easy to measure and interpretation of the results is far from straightforward. We are investigating alternatives to total-N such as the chlorophyll and nitrate pools. Chlorophyll is closely linked to nitrogen and could well be a good surrogate indicator of plant N status. It is easily estimated in single leaves with a Minolta 'SPAD' meter for example, and also in crop canopies with multi-spectral scanning radiometers.

Wheat variety trial and instruments useful for on-farm monitoring of crop N status

  Variety x N interaction trial
Variety x N interaction trial 		 
  Minolta SPAD meter
Minolta SPAD meter 		Canopy radiometer
Canopy radiometer 		 

Phosphorus diagnostics in wheat and rape
It has long been known that plants over-supplied with P store the excess as simple inorganic phosphate ions (Pi) in cell vacuoles. This stored Pi could be a universal indicator of plant P status, its presence indicating that plant P needs have been met. For winter wheat and oilseed rape, we found that P requirements for yield were satisfied with a phosphate concentration of 4-5 mM in plant sap. Phosphate in sap is easily measured on-farm using test-strips and a hand-held reflectometer. At Rothamsted, phosphate concentrations of 4-5 mM were achieved with a soil Olsen-P of 9 ppm.
Stored phosphate in winter wheat
Stored phosphate in winter wheat


Potassium requirements of sugar beet
Correct potassium nutrition is very important for sugar beet as too little or too much can reduce sugar yields, the latter as a result of poor sugar extraction during processing. Work at Rothamsted has shown that maximum sugar yield from modern varieties was obtained when root K reached 50 mM at a soil Kex of 160 ppm. Root K concentrations increased with soil Kex and with increased N supply. Beet was found to be unresponsive to fresh K fertiliser even on ostensibly K-deficient soil.

K deficient sugar beet
K deficient sugar beet


HGCA Topic Sheets