The role of calcium and magnesium in soil health
NUTRIENT use efficiency is always a hot topic as fertiliser of all formulations is still a significant on farm cost. Therefore, accurate soil testing, analysis and interpretation is paramount in a bid to get the best out of nutrient applied to the land, either in the form of fertiliser or organic manures.
It therefore pays to get the basics right first before applying any nutrients. Planning to correct the soil’s pH must be the first task rather than an afterthought. With good soil analysis results it will be possible to see and calculate what is the base saturation of calcium and magnesium within the soil.
Table one lists the amount of calcium carbonate required to neutralise each Kg of nitrogen supplied by these fertilisers. The reason for this is that most inorganic fertilisers are based around negatively charged anions, sulphates, nitrates or chlorides which when dissociated from the soil, combine with the dominant cation calcium in the soil and leach readily in the soil solution.
Soil structure is enhanced by the application of calcium as it plays an important role in its aggregation due to the way its ionic charge, size, and hydration acts upon the soil colloids. Soil aggregation or flocculation is the process by which soil colloids and organic matter clump together to from aggregates. It is this aggregation of soil which is commonly referred to as tilth. The aggregation produces pore space which allows the soil to function aerobically, roots to develop without the impedance of compaction and water to drain.
Calcium also affects numerous biological processes in the soil, including nitrogen transformation processes such as nitrification. This biology is enhanced by the aerobic conditions described above and flourishes when calcium is readily available.
This optimised soil state then has a greater ability to sequester carbon and is less prone to denitrification due to the greater stabilisation of soil organic matter.
Ensuring that there is enough exchangeable calcium (Ca2+) present in the soil provides this essential element for plant growth and reproduction, where it has unique roles in maintaining the expansion and structural integrity of cell walls, lipid membranes, and signalling responses to developmental and environmental stimuli.
The often-overlooked nutrient in soil analysis is magnesium. In certain areas the over-application of local cheap maglime has caused both soils structural problems and antagonisms to other nutrients. In a growing number of areas, a lack of magnesium is becoming an issue. What must be considered before trying to strip this element out of a soil is what is its balance with calcium as it is essential for crop and animal health.
Magnesium has a key role to play in the formation of chlorophyll and acts as an anchor for nitrogen in every cell of chloroplast, creating the dark green of a healthy plant. Its major role is in enabling the phloem to transfer products of photosynthesis, sugars down into the roots. Also, as a main component of chlorophyll, it has a key role in the production of ATP, the energy storehouse of the plant, and activates more enzymes in the plant than any other nutrient.
Therefore, balancing the soil with a good lime enhances nutrient use efficiency (NUE) which is key to the profitability of all farming operations. This efficiency is detailed in the chart and shows how nutrient utilisation is improved at and an optimised pH, achieved by correction with the appropriate liming materials which would initially be either calcitic or dolomitic lime.
Table two is produced from the work of Dr C Synder and is further backed up by the findings of Catherine Henault et al (2019) – the latter’s work finding a correlation between optimised soil pH and a reduction in the denitrification pathway where N2O is released from soils. Maintaining a minimum soil pH of 6.4 is considered essential. The results from the research across France’s acidic soils estimated the potential N20 emissions reduction averaged 15.7%.
Ensuring enough exchangeable calcium (Ca2+) is present in the soil provides this essential element for plant growth and reproduction, where it has unique roles in maintaining the expansion and structural integrity of cell walls, lipid membranes, and signalling responses to developmental and environmental stimuli.
If lack of utilisation efficiency figures are used for a soil at a pH of 6, 11% of nitrogen and 48% of phosphorus are potentially wasted by not optimising pH. This level of financial loss is not sustainable or profitable, particularly when a simple low-cost solution such as liming with a quality product is available. The payback is generally between 4 & 7: 1.
Calcium’s and magnesium’s role in soil health, plant growth and animal health has been underplayed for too long. Quality agricultural production has a requirement for a balance of all nutrients, this has not been helped by a focus on the macro elements in farm nutrition budgeting. While the macros may be important for the last step of
crop production, they do not improve soil health.
Ensuring that the correct balance of cations, calcium being the dominant one, are provided as required, will improve soil health. The cascading benefits of this are that soils operate aerobically with an improved biology, which has reduced GHG
emissions and an increased ability to sequester carbon.
Healthier soils grow crops of better quantity and quality utilising fertilisers more efficiently, helping further reduce the carbon footprint of the industry. The food produced from these soils is also more nutrient dense and less prone to wastage.
Calcium and magnesium are nutrients that should not be considered only for pH remediation on a five-yearly liming cycle. They should be part of farming business and nutrient advisers’ annual nutrient toolkit. Apply little and often to keep the soil in a healthy balance and improve NUE.