Plant nutrients and soil

Adequate cultural practice needs to be adhered to in order to provide the correct environment for these mechanisms of growth to take place. Once the correct physical and biological environment has been achieved, the final step is to plan a tailor-made nutrition programme.

This is essential not only for rapid establishment, vigour and appearance of the sward, but also to ensure that it performs as a hard-wearing and dependable surface upon which to practice sport.

Cation exchange capacity (CEC)

The CEC of a soil or rootzone is a measure of its propensity to hold and release various elements and compounds such as plant nutrients. In explanation, many of the major plant nutrients such as potassium, magnesium and some forms of nitrogen are positively charged. Positively charged ions are known as ‘cations’ and are attracted to, and loosely retained by, negatively charged soil particles which are known as the ‘clay-humus-complex’ and consist of clay minerals bound to particles of organic matter.

The ability of a soil or substrate to retain nutrients largely depends upon the content of clay and organic matter. As a general rule of thumb, a sandy soil or rootzone with little organic matter will have a low CEC, while a clay soil with a high content of organic matter will have high a CEC. Clearly, a high CEC soil is desirable to hold a bank of nutrients which can be accessed by grass roots but this has to be considered alongside drainage and aeration which are also highly important. In practice, the treatment of low and high CEC soils calls for two different approaches.

For a more in-depth discussion on managing your turf in relation to CEC, speak to your local professionally qualified Germinal Seeds Representative.

Soil pH and nutrients

It is important to recognise that the pH value of a soil greatly affects the availability of nutrients to plants. Very low pH levels (less than 5.0) should be avoided as some elements found naturally in soils can become toxic and/or can ‘outcompete’ desirable cationic nutrients. Low pH can be monitored by regular (4-5 times per year) testing and liming if necessary.

At higher pH levels (above 8) some nutrients such as manganese, iron and zinc get converted into insoluble compounds and become less plant available. In these situations, it is important to recognise that these nutrients may need to be supplemented in readily available forms as part of a fertiliser programme.

Effects of soil pH on nutrient availability

Macronutrients

Nitrogen (N)

Nitrogen is the key element to fuel growth in the grass plant.  The supply of nitrogen can determine green colouration of leaves, damage recovery, disease resistance, drought tolerance and density of root and shoot growth.

Key points:

• N is essential for rapid plant growth.
• N is a major component of amino acids – the building blocks of proteins.  Some proteins act as structural units of cells, while others act as enzymes which are required in important metabolic processes.
• N is the single most important nutrient that can be applied to achieve a positive effect on the growth of grass.
• N is often highly mobile within a rootzone and prone to leaching in many forms.  A combination of slow release base feeds and quick release granular or liquid feeds should be considered as part of a fertiliser plan.

Phosphorus (P)

Phosphorus (P) is present in the plant cells.  It provides the mechanism for using and transforming energy.  It is necessary for seedling development and should be one of the main constituents of a pre-seeding fertiliser.  Adequate supplies promote rooting and tillering.  Phosphorus is highly immobile in the soil.

Key points:

• P is an essential component for the process of photosynthesis.
• P helps with the transformation of solar energy into chemical energy, proper plant maturation and stress tolerance.
• P effects rapid growth.
• P encourages root growth.  It is particularly effective in spring and autumn.

Potassium (K)

Potassium is essential in the plant growth and development process.  It is the principle salt found in cellular fluid in plants and as such, lowers the freezing point.  It also also helps to maintain an osmotic gradient which is important for grass turgor and for grass to access soil moisture reserves.  As a result it is useful for resistance to heat, cold and frost damage.

Potassium encourages the rooting of grasses and gives turf increased wear tolerance.  High potassium levels tend to reduce the risk of disease such as fusarium. Potassium acts as a catalyst in many processes including transpiration, respiration and photosynthesis.

Key Points:

• K is absorbed by plants in larger amounts than any other mineral element except nitrogen.
• K indirectly regulates many enzymatic processes that contribute to plant growth.
• K readily leaches from rootzones with a high sand content (low CEC).
• K should ideally be applied in the gentler sulphate form which reduces the salt stress effect

Secondary nutrients

Calcium (Ca)

Calcium is found in fairly large quantities within the grass plant.  Calcium ions have a strong influence on the absorption of other ions by the grass plant, especially the uptake of potassium and magnesium.  Supplementary applications are seldom required as sufficient levels are found in water supplies.

• Ca is an essential part of plant cell wall structure.  It provides for normal transport and retention of other elements as well as strength in the plant.

Magnesium (Mg)

Magnesium serves several physiological functions within the grass plant.  It is a constituent of chlorophyll and involved in the translocation of phosphorous within the plant.  It is essential for the green colour in the plant.

• Mg is part of the chlorophyll in all green plants and essential for photosynthesis.  It also helps activate many of the plant enzymes needed for growth.

Sulphur (S)

The role of sulphur is primarily as a constituent of certain amino acids.  High free levels can indicate anaerobic soils.

• S is essential along with N for the production of protein.
• S promotes activity and development of enzymes and vitamins.
• S helps chlorophyll formation.
• S improves root growth.
• S helps with resistance to cold.

Micronutrients

Boron (B)

• Helps in the use of nutrients and regulates other nutrients.
• Aids production of sugar and carbohydrates.
• Essential for seed and fruit development.

Copper (Cu)

• Important for reproductive growth.
• Aids in root metabolism and helps in the utilisation of proteins.

Iron (Fe)

• Essential for formation of chlorophyll.

Manganese (Mn)

• Functions with enzyme systems involved in the breakdown of carbohydrates and nitrogen metabolism.

Molybdenum (Mo)

• Helps in the use of nitrogen (a component of the enzyme for that purpose).

Zinc (Zn)

• Essential for the transformation of carbohydrates.
• Regulates the consumption of sugars.
• Part of the enzyme systems that regulate plant growth.
• Plays a role in the formation of chloroplasts and starch.

For advice on fertiliser requirements, talk to our amenity grass experts.