Nutrient use efficiency is always a hot topic as fertilisers of all formulations remain a significant on-farm cost. Therefore, accurate soil testing, analysis, and interpretation are paramount in a bid to get the best out of nutrients applied to the land, either in the form of fertiliser or organic manures.
It pays to get the basics right 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 is possible to see and calculate the base saturation of calcium and magnesium within the soil.
In table one the amount of calcium carbonate required to neutralise each kilogram of nitrogen supplied by these fertilisers.
This is because 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, and readily leach in the soil solution.
Soil structure is enhanced by the application of calcium as it plays an important role in aggregation due to its ionic charge, size, and hydration effects on the soil colloids. Soil aggregation or flocculation is the process by which soil colloids and organic matter clump together to form aggregates. This aggregation of soil is commonly referred to as tilth.
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It produces pore space, allowing 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 greater stabilisation of soil organic matter.
Ensuring enough exchangeable calcium (Ca2+) is present in the soil provides this essential element for plant growth and reproduction, where it plays 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 soil structural problems and antagonism with other nutrients. In a growing number of areas, a lack of magnesium is becoming an issue.
Before trying to strip this element out of a soil, it is essential to consider its balance with calcium, as both are vital for crop and animal health.
Magnesium plays a key role in the formation of chlorophyll and acts as an anchor for nitrogen in every cell of the chloroplast, creating the dark green of a healthy plant. Its major role is enabling the phloem to transfer products of photosynthesis, such as sugars, down into the roots. Additionally, as a main component of chlorophyll, magnesium has a key role in the production of ATP, the plant’s energy storehouse, 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 table two and shows how nutrient utilisation improves at an optimised pH, achieved by correction with the appropriate liming materials, such as Calcitic or Dolomitic Lime. The table, produced from the work of Dr Snyder, is further supported by the findings of Catherine Henault.
The latter’s research found 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. Research across France’s acidic soils estimated that potential N2O emission reductions averaged 15.7%.
If nutrient 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 neither sustainable nor profitable, especially when a simple, low-cost solution such as liming with a quality product is available. The payback is generally between 4:1 and 7:1. Calcium’s and magnesium’s roles in soil health, plant growth, and animal health have been underplayed for too long. Quality agricultural production requires a balance of all nutrients, but this has not been helped by a focus on macro elements in farm nutrition budgeting.
While macros may be important for the final step of crop production, they do not improve soil health.
Ensuring the correct balance of cations, with calcium as the dominant one, will improve soil health. The cascading benefits are that soils operate aerobically with improved biology, reduced GHG emissions, and an increased ability to sequester carbon.
Healthier soils grow crops of better quantity and quality, utilising fertilisers more efficiently and 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 should not be considered only for pH remediation on a five-year liming cycle.
They should be part of a farming business’ and nutrient advisor’s annual nutrient toolkit. Apply little and often to keep the soil in a healthy balance and improve NUE.
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