We had a visit from Peter Norwood the other week. Peter is a farm consultant from Maffra and a specialist in animal nutrition. Peter had been visiting central Victoria speaking to Landcare members and farmers about soil health and links with plant and animal/human health.
Peter advocates the Albrecht approach to soil health, which is to “feed the soil and let the soil feed the plants” – a famous William Albrecht quote. When the soil contains the correct chemistry, the plant will be able to acquire all its necessary nutrients in the proper amounts. This means that instead of focussing on the simplistic notion of NPK (Nitrogen, Phosphorus, Potassium) as the key minerals for soil fertility, as conventional agriculture tends to, that farmers focus instead on balancing the soil and ensuring a diverse array of minerals and micronutrients are available for plant uptake.
The chemistry of the soil has a direct impact on animal productivity and health – soil imbalances will show up in animal health issues and ultimately farm profitability. We have worked hard over the years to build up our soil health using composts, rock phosphate, oversowing pastures, and rotationally grazing our paddocks, working towards achieving what Albrecht would define as the ideal soil.
The Albrecht view – and carried on by Neal Kinsey – is that an ideal soil is composed of 45% minerals, 5% humus* and 50% pore space. The pore space is crucial to hold moisture, air and provide a beneficial environment for soil organisms.
Soil chemistry (particle size and charge – linked to Cation Exchange Capacity*) affects soil physics (the structure, strength and water holding capacity) which in turn affects soil biology (microbes, bacteria, fungi and other organisms).
It helps to have an understanding of the Periodic Table and the size and charge of atoms, but when soil chemistry and physics are right, the environment for the biology will also be right. That is why so much emphasis is placed on achieving the exact level, or ratio, for each nutrient based on the specific requirements of each different soil.
The ideal soil mineral makeup is 60% Calcium, 12% Magnesium, 500 ppm Phosphorus, 4.5% Potassium, 1.5-3% Sodium and 10-20ppm Zinc. Rather than measuring excess or deficiency as an specific amount, Albrecht considers the ratios between cations. The ratios between Ca:Mg, N/K and Zn/P are as important as their individual levels – if not in balance, growth will be affected.
Calcium and Magnesium are actually two of the most critical minerals, not Nitrogen. As well, trace minerals, such as Manganese, Copper, Boron, Zinc, Iodine, and Chlorine, etc. are vitally important because the metabolic cycles in plant and animal production rely on them for healthy function. This is another reason that organic farmers tend to focus heavily on soil health, since supplementation and intervention are restricted in biological agriculture.
We are becoming more interested in exploring the metabolic cycles in plants and animals as we pursue health and productivity on the farm – more on this in future blogs. But it all starts with the soil.
* Humus: a dark, organic material that forms in soil when plant and animal matter decay. Whilst organic matter refers to the organic fraction of the soil that is composed of both living organisms and once-living residues in various stages of decomposition. Humus is only a small portion of the organic matter. It is the end product of organic matter decomposition and is relatively stable.
** Cation Exchange Capacity is defined as the degree to which a soil can adsorb and exchange cations.
Cation – a positively charged ion (NH4+, K+, Ca2+, Fe2+, etc…)
Anion – a negatively charged ion (NO3-, PO42-, SO42-, etc…)
Soil particles and humus have negative charges on their surfaces. Mineral cations can bind to the negative surface charges, or the inorganic and organic soil particles. Once adsorbed these minerals are not easily lost when the soil is leached by water and they also provide a nutrient reserve available to plant roots. These minerals can then be replaced or exchanged by other cations (i.e. cation exchange)