Sodium in the soil
- Sodium occurs only in a compound form in soils, predominantly as salts.
- Sodium does adsorb onto clay minerals but the bond is weaker than that of potassium ions and therefore sodium has a higher propensity to be leached Therefore in areas of high rainfall such as trpicall or sub-troical climates, soils are generally depleted in sodium which is washed down into deeper soil layers
- In contrast, in arid or semi-arid areas an accumulation of Na in the top soil frequently occurs because the rate of evaporation exceeds the replacement of water from the soil. This often results in a deterioration of the soil structure which has a negative effect on the water and air balance of the soil. In addition, the pH becomes more alkaline with an increasing Na content.
Sodium in the plant
Sodium does not fulfill the criteria for a plant nutrient because plants can also complete their life cycle without sodium and it can be replaced by plant nutrients for the function it performs (e.g. by potassium in osmosis). Moreover, it is a valuable constituent of plants used for feed. Thus, sodium is one of the useful elements.
- One exception is natrophilic crops (e.g. Chenopodioideae) – Positive effects on yield and quality from the application of fertiliser with sodium can be demonstrated. Sugarbeet as the most important crop species in this group is well known example which has a relatively high sodium requirement. Sodium supports the synthesis of glucose and its conversion to fructose which is stored in the beet.
- Sodium controls osmotic pressure in plant cells and results in a more efficient use of water.
- Na ions can often substitute K ions in some metabolic and osmoregulatory functions and therefore the two nutrients are interchangeable to varying degrees according to plant group
- Sodium is important for some C4 plants (e.g.. amaranth) for CO2 uptake
Sodium in animals
- In animal nutrition, a sufficient supply of sodium is an important factor in maintaining the productivity of the animals. Sodium deficiency results in loss of appetite, decreased milk production, weight loss and has implications for health and fertility of the animals.
- Approximately 2g Na kg-1 DM in the basic ration is necessary to satisfy the daily requirement for Na in dairy cattle. Field studies have demonstrated that in many regions the average sodium content of grassland is just 0.1-1g Na kg-1 DM and therefore clearly below the required amount.
- Sodium containing fertilisers such as Magnesia-Kainit have been successfully used for over a century for greatly increasing the sodium content of grassland and can guarantee meeting the Na demands of the animals.
- Studies and trials have demonstrated that besides an improved Na supply from the nutritional point of view, the increased sodium also has a major effect on palatability of forage which can increase dry matter intakes by around 10%.