Vegetables, fruits and grains are a major source of vital nutrients, but generations of intensive agriculture have depleted our soils to historical lows. As a result, the broccoli you eat today may have less than half the vitamins and minerals it would have had less than a century ago. We can grow our own vegetables using lots of compost and avoiding chemicals, but how do we really know our soil has enough of the appropriate minerals in the right balance to grow truly nutrient dense food?
Nutrient dense food has its full complement of minerals and is the best kind of food to keep you healthy. For food to be nutrient dense, it must be grown in soil that has an abundant and balanced supply of minerals. If key plant nutrients in the soil are lacking or way out of proportion, then the food produced in this soil will not be nutrient dense.
There is also a biological side to it that is equally important to plant health and ultimate food quality. However you first need to bring the minerals into proper balance, then the soil food web (worms, nematodes, algae, amoeba, fungi, bacteria) comes into healthy balance too. When it comes to micro-life, there is rarely a need to import them. When the soil is favourable to the proper organisms, they will predominate, appearing as if from nowhere. Soil biology can greatly assist the plants in assimilating nutrients, but only after the minerals have been brought into balance.
TESTING YOUR SOIL
Remineralisation guided by a soil test is the best method for growing nutrient dense food. Find out what the chemical nature of your soil is by sending a sample away to a soil testing laboratory. Then, add the minerals calculated to bring the soil into a fertility profile that produces nutrient dense food. The lab can recommend what to add to your soil, you can work with a soil consultant or with some research you can make your own conclusions.
YOU WILL TASTE THE RESULT
What are you getting into if you choose to remineralise? Several years of rapidly improving results until you achieve a high level of organic matter and the best mineral balance your soil is capable of. Chemically, soils can be extremely different. Almost all of them are out of balance, at least to some degree. The majority of soils seriously lack essential plant nutrients and it is not unusual for soils to have nutrient excesses, sometimes to the extreme.
A number of years ago I refined my remineralisation program. I scattered fertilisers between the plants and let the spring rains wash them in. The spinach seed crop immediately stopped showing signs of disease, no more plants died, and the survivors began growing rapidly. The garlic crop started growing faster than in previous years. The usual allium leaf diseases didn’t appear. When it came time to dig the garlic, the heads were half again larger than before, and there was no sign of root rot. The remineralised spring vegies tasted better than ever—richer, more complete.
Soil Organic Matter
Soil organic matter (SOM) is an important figure that will show up on your soil test. SOM stops erosion, increases water filtration and builds pore space (soil air). The ideal SOM level varies by climate—the warmer the climate, the more difficult it is to build a high percentage of SOM because decomposition happens faster. If you can build up to around 4–5% in the northern climates of Australia, and around 7% or over in the southern parts, that is plenty.
Unless you are starting a new garden, do not dig in enormous quantities of compost or semi-composted manures. Compost rarely contains the ideal mineral balance to grow nutrient dense food. Excessive additions of compost usually imbalances the soil’s mineral profile and degrades nutritional outcomes. Generally a skimpy scattering of high quality compost (a layer only 6 mm thick) maintains a high organic matter level, and perhaps slowly increases it. To increase SOM fairly rapidly, spread twice that amount. If your soil test indicates you have enough organic matter, ease off on the imports.
BALANCING THE BIG FOUR: Ca, Mg, K, Na
Bringing these four elements into balance is the most important task in remineralising. It may take you a few years to bring your soil into balance with each step you take along the way making big improvements. If all we knew how to do was balance these four major elements and make compost, our agriculture and gardening would be enormously improved.
CALCIUM AND MAGNESIUM (Ca and Mg)
Calcium is an incredibly important plant nutrient that is greatly undervalued by gardeners. However it’s not so much how much calcium is in your soil, but how much compared to magnesium. They must be in balance, with a ratio of 68% calcium to 12% magnesium.
The Ca:Mg balance determines whether the soil is open, airy and loose, or if it’s tight and airless. Many organic gardeners have overused dolomitic lime, producing an excess of magnesium. Then, the soil becomes tight and airless, develops poor drainage, sticks to your boots and crops become diseased or insect attacked. If your soil has excess calcium and a magnesium deficiency, it can become extremely loose and water seems to flow through it without sticking. When calcium and magnesium are in balance, the soil is naturally open, loose and sponge-like, and does not compact easily. This soil requires a lot less compost.
Plants concentrate potassium into their structure—stalks, stems and fibre. Hay, straw, leaves and sawdust are potassium- rich, and these are often used to make compost along with the manure of grass-eaters. When a gardener sets out to build soil fertility by importing massive quantities of decomposable organic matter, they usually import a lot of potassium, and comparatively less of the other nutrients. Soils handled this way are not balanced.
People are often shocked at the suggestion that they should spread sea salt on their garden. It is true that too much sodium wrecks soil, causing it to tighten and shrink to an airless condition in which plants do not grow well. However, sodium will readily leach from soils that are well saturated with calcium, magnesium and potassium, and the sodium levels in the water you are irrigating with will vary considerably. Therefore it’s wise to determine the sodium levels of your soil and then balance deficiencies, keeping in mind whether you irrigate or rely on rainfall.
BALANCING THE NEXT FOUR: P, S, B, N PHOSPHORUS (P)
Phosphorus fertiliser seems expensive, especially when building levels that create nutrient-density. However pushing soil phosphorus levels well beyond sufficiency is highly desirable despite the cost. Phosphorus determines the speed at which plants grow and buffers plants against the effects of cold weather. If plants are short of phosphorus, growth will slow, leading to small yield, lower nutritional quality and poorer flavour. It is worth bringing your garden to the highest useful level.
Sulfur, in partnership with nitrogen, forms key pieces in several essential amino acids and crucial enzymes. When sulfur is abundant, these are plentiful and the plant is able to form a broader range of proteins. Flavour is more abundant and so is nutrient-density. When sulfur is short, plant proteins are less complete and have lower feeding value. Sulfur has long been used as a fungicide; ground to a fine powder, it is dusted on plants to prevent or fend off diseases. Possibly why this works is because the diseased plants were seriously short of sulfur in the first place. Small doses are recommended so it doesn’t disrupt the soil biology.
Boron has a unique and vitally important job to do. The miniscule tubes that plants use to conduct moisture must be lined with boron. If these tubes don’t get enough boron, they don’t function effectively, which means the plant can’t drink effectively and nourish itself.
Clockwise from top left: Bagging up the mix of soil to be tested; Taking a sample of soil to be tested; Measuring out supplements.
Nitrogen is the most noticeable plant growth accelerator, rapidly turning light-green leaves to a darker colour, indicating more chlorophyll is present. Dark-green leaves grown on fully remineralised soils can contain over 20% protein, which is ideal for human and animal health.
Nitrogen levels are unstable and move up and down rapidly with the season and with the crop cycle, therefore it’s not generally reported on a soil test. Different garden vegetables have different nitrogen needs. For instance, broccoli and cauliflower are heavy feeders and beetroot and kale are low feeders (tomatoes fall in the middle). So it depends on what you are growing as to how much nitrogen you need.
Gardeners can aspire to gradually eliminate all imported nitrates (including organic sources such as chicken manure pellets) as the soil comes into mineral balance and begins to produce its own nitrates in abundance. But this conversion will take several years, so it’s best to initially import potent organic concentrates such as seedmeal, feathermeal or fishmeal (try sourcing from your local stockfeeds or nursery). Then reduce these concentrates as your SOM increases on your soil test.
There are several biological nitrate sources we can encourage long-term, the main one being growing green manure crops such as broad beans or lupins, then digging them in and sowing your crops a few weeks later. It may not be a gardener’s desire to have beds continually allocated to green manure crops, in which case you may need to continue to use small amounts of organic concentrated nitrates, using the smallest effective amount on the highest demand crops.
MINOR NUTRIENTS: Fe, Zn, Mn, Cu
Your soil test will give you an indication of the soil’s status regarding minor nutrients (iron, zinc, manganese and copper) and you can add more according to your deficiencies. The targets you’re aiming for will depend on the opinion of your soil consultant or soil test laboratory. All these nutrients are essential, but each react in different ways to each other and the balance is important to get right. They are available as sulfates and you can source them from your local stockfeed store or nursery.
Of the essential micronutrients such as cobalt, selenium, molybdenum and the like, a few grams in an entire acre is plenty, but their complete absence means catastrophe for both the plants and the animals eating them. Add too much more than necessary of some of them and the entire ecosystem is poisoned. The great majority of soils are adequately supplied with micronutrients, and routine use of kelp meal or a trace mineral fertiliser like Azomite will insure against micronutrient deficiencies.
GETTING YOUR SOIL TESTED
- STEP 1. Take a soil sample—check out soil laboratory websites for how to do this.
- STEP 2. Post it to a soil testing laboratory, such as the ones listed below. If you would like the laboratory to provide you with recommendations, you will need to ask for these.
- STEP 3. Once you’ve received your results, it’s time to interpret them. If you want to interpret them yourself, you can use a book such as the one this article is based on. Some labs will give you recommendations, if asked. Or, if you would like more specific local recommendations, contact a local soil consultant/agronomist.
- STEP 4. Source your recommended minerals and nutrients.
- STEP 5. Mix them in a bucket then dig them in or mix into soil surface with a rake or hoe. If you can, delay sowing for a few weeks to allow the nutrients to blend in with the soil.
IS IT ORGANIC TO REMINERALISE?
Organic certification agencies allow the addition of sulfate trace elements if and when a soil analyst says to remineralise them—this includes copper, zinc, manganese and iron sulfate. Added in small quantities, they do not harm soil life. Mined minerals such as limestone and dolomite have not been synthetically treated and are allowable under organic certification. They are available from your local stockfeed store or nursery. Borax is also a naturally occurring mined rock, and available in the supermarket. Certifiers also allow the use of potassium sulfate if you need potassium, but not potassium chloride.
Building a healthy, balanced mineral soil profile does not have to be in conflict with your organic gardening practises. Testing and remineralising your soils using natural materials is the intelligent way to create the healthiest soil, the most nutrient dense food, and therefore the healthiest you.
This is an edited excerpt from Steve Solomon’s book The Intelligent Gardener: Growing Nutrient Dense Food (New Society Publishers 2012).
To see our easy to read nutrient sources table and to read more about Pip HQ soil sample case study go to www.pipmagazine.com.au/news/soil-sample-case-study/