Sodium (Na) is an essential mineral required by all animals in a wide range of physiological functions. Certain root crops – e.g. sugar beet, carrots and parsnips – are responsive to sodium fertilisers, some of which can be used to replace potassium inputs. In grass, sodium improves forage palatability and reduces the risk of metabolic disorders such as hypomagnesemia (grassland staggers) in livestock.
Beneficial mineral for root, grass and forage crops
Increases the sugar content of plants and improves grassland palatability
Grass or forage which is not being grazed may be less palatable due to a lack of sodium
Due the size of the sodium cation, it is easily lost from the soil making it difficult to build soil sodium reserves
Best applied little and often to improve grassland palatability or in the seedbed for arable crops
Sodium containing products include SweetGrass, Agricultural salt (50%) and Kainit (26%)
Sodium is not considered an essential plant nutrient, however certain crops benefit from applications of sodium - predominantly high sugar crops including sugar beet and fodder beet, grassland and other root crops.
In grassland systems, it is important to maintain an adequate amount of sodium within forage - around 0.15% on a dry matter basis. Sodium application will not have any effect on crop growth but helps improve forage palatability. This is due to its role in synthesising sugars - specifically fructose, sucrose and fructans. Improved grassland palatability can boost forage intake, leading to greater levels of milk or meat production from grass.
Independent research from Bangor University suggests forage intake is increased by around 18.6% on average when sodium is applied alongside nitrogen applications. In dairy cows, this resulted in a 9.3% increase in milk yield.
Sodium is able to mimic the role of potassium in many situations and so can be useful when potassium concentrations in the plant are low.
Sodium is essential for all animals. It is required for maintaining osmotic pressure, water regulation and helps transport nutrients to where they are needed. It is also involved in nerve impulse transmission and muscle function.
For ruminant animals, sodium has an added importance in saliva, which is produced in vast amounts to help to buffer the acid produced from fermentation in the rumen.
If there is a lack of sodium, animals substitute sodium for potassium which leads to resorption of magnesium in the blood, leaving animals vulnerable to hypomagnesemia (grassland staggers). To help prevent this, the potassium:sodium ratio of the forage should be kept at 20:1 or below.
Sodium exists in the soil as a positively charged nutrient (Na2+) and so, in theory, is able to bind to negatively charged clay particles within the soil.
However, of all the positively charged nutrients sodium is the smallest and regularly has to compete with other much larger nutrients (E.g. Ammonium, calcium and potassium) for space on the exchange sites on the clay particles.
Because of this, it is difficult to build soil sodium reserves easily.
Since sodium is not plant essential, plants are unlikely to show visual signs of sodium deficiency. In grassland, deficient plants are likely to have a lower sugar content, be less digestible and less palatable.
Where is the risk of deficiency highest?
Sandy soils with a low clay content
Low organic matter soils
Soils with a high potassium index
A Broad Spectrum (BS) soil analysis can help determine the quantity of sodium which is likely to be available for crop uptake and can be used to tailor fertiliser plans and to help prevent deficiencies within the season.
Tissue testing is also useful to determine the sodium concentration of the plant mid-season in order to compare against optimum levels. Although laboratory results may be available too late to correct the deficiency in the current crop, they can be useful for decisions on sodium use for future crops.
Blood tests on livestock can help indicate whether there is a sodium deficiency within the animals diet.
Because sodium is much smaller than other positively charged nutrients, such as calcium, potassium and ammonium, it is less likely to bind to clay particles and so is vulnerable to being leached, particularly in sandy soils with a low clay content.
Refined sources of sodium with low hygroscopicity are more suitable for storing than standard agricultural salt.
There are benefits to applying sodium to grass throughout the growing season. Potassium uptake is highest during rapid spring growth and applications of sodium can help maintain optimum potassium:sodium ratios for animal health. During the summer, as grass becomes more fibrous and less digestible, sodium can increase forage palatability, digestibility and intake.
Avoid applying large rates of sodium to light, sandy soils or in areas of high rainfall to avoid potential nutrient loss.
Best applied little and often to minimise losses. To improve grassland palatability, RB209 suggests regular dressings of 10 kg/ha of sodium throughout the season.
Standard = 23-0-0 + 5SO3 + 5Na2O
Improves grassland palatability and subsequent forage intake, leading to higher milk or meat production
0-0-0 + 50Na2O
Salt mined from natural deposits, commonly used to fertiliser sugar beet
0-0-11 + 5MgO + 10SO3 + 26Na2O
Multi-nutrient mined from natural rock deposits. High in sodium