Law of Limiting Factor

A law proposed by Frederick F. Blackman in 1905 (‘Optima and Limiting Factors’, Annals of Botany, Vol.19, Issue 2, April 1905, pp281-296) which stated that a plant’s physiological process, in particular photosynthesis, respiration or growth, is dependent on several factors which limit its efficiency and effectiveness, with the factor with the least influencing value determining the rate of the physiological process. Light, temperature, water, nutrients, and air are all significant external factors which influence and limit plant growth. Internal plant factors might be chlorophyll content or cell water content.

Factors will need to be increased in relative amounts to maintain an optimum balance between the factors to achieve optimum physiological functioning. Where an imbalance exists, for example where light intensity is very low then the rate of photosynthesis will be severely limited. If light is not present, then photosynthesis will not take place as it has become a critically limiting factor. A limited supply of oxygen, particularly within a rootzone due to compaction or waterlogging, can result in anaerobic conditions which negatively affects plant growth.

Water is often a noticeable and primary limiting factor during hot dry spells. Where some plant nutrients, especially the macro-nutrients of nitrogen, phosphorus and potassium, are in limited supply then this will negatively impact on plant growth and development. Care needs to be taken in turfculture not to confuse limited growth, which can often be a positive within this context, with growth required in agricultural crops which focuses on maximising vegetative quantitative growth (i.e. productivity), which is clearly not something that is desired within turfculture, where the focus is on qualitative growth.

This law is particularly relevant during the late autumn and winter periods in the UK when grass growth is minimal and in northern areas dormant, with low lights levels and low temperatures. The desire to apply a fertiliser is frequently mistaken in the belief that this can encourage growth, but rather it increases water content within a plant. This is due to the movement of soil solution, which is now at a high concentration of nutrients, into the plant, thereby swelling plant cells. Transpiration and photosynthesis are slow to dormant and the nutrients are not utilised as they would be when plants are growing actively. This increase in plant softness also increases the likelihood of disease attack as well as reducing the durability of the grass plant, which is often seen as an increase in divots on the sward and reduced traction for players. Perceived benefits are often seen as increased leaf size, ground cover, and especially colour, although the latter is frequently achieved due to the small amount of iron that is often included within these fertilisers and this is what produces a greening effect on the grass surface.