Dig for Victory: Soil III


Dig for Victory is a primer for the kitchen gardener. Every few weeks or so we’ll publish a new post to build on our technical knowledge of gardening. You’re under the capable hand of Steve here. Let me know what you think and if you’d like anything in particular to be covered. Enjoy!

Imagine a row of your favourite vegetable swaying gently in the afternoon breeze—for me, it’d be purple and white striped eggplants—now walk along and harvest a few kilos. In your hands is about 75 percent water, with the reminder being nutrients mined from the soil. In order to have a sustainable food production system, we need to understand nutrients and how to replace them.

Nutrients in theory
Whilst Chemistry was dry for many of us during school, it’s important for gardeners to understand the building blocks of matter. Phosphorus, Nitrogen and Potassium are what we call macronutrients, while micronutrients—so called because they are needed in small amounts—are elements like Molybdenum, Magnesium, Zinc, Calcium, Copper, Iron and Boron. These nutrients are vital for plant health; if they’re deficient, severe problems can occur.

Macronutrients and micronutrients are readily available organically. At this point I should point out that “organic” means from an organic source—composted once living stuff, manure or ground up rocks. “Inorganic” tends to mean highly concentrated minerals manufactured through industrial processes. This is where the term “organic” to describe the system of agriculture, originates.

Feeding the soil as opposed to the plant is the key differentiator of organic agriculture. The system is founded on the feeding of micro and macro organisms, building up organic matter in and on soils to retain water and nutrients, and the encouragement of a diversity of flora and fauna above the ground to create a harmonious ecosystem—one that has a number of different colours, flowers, habitats and visiting species.

The idea is that healthy soils grow healthy plants that are better equipped to fight off pests and disease. And indeed, healthy ecosystems—above and below ground—have a diversity of organisms eating other organisms to keep pests at manageable levels.

Nitrogen, Potassium and Phosphorus, often referred to as NPK, contribute towards making proteins, regulating energy transfers, assist with growth through cell division, strengthen plant tissues and build cell walls—among many other functions. Micronutrients contribute towards building cell walls, forming chlorophyll, respiration, regulating electron transfer and metabolising other nutrients. These are needed in smaller amounts; they’re sometimes antagonistic towards macronutrients and potentially harmful to humans.

Nutrients in practice
The two things gardeners want to know are, “Where do I get these nutrients?” and “How do I measure out the amount required?”

All the nutrients you need are available in animal manures—blood and bone, seaweed, grass clippings and vegetable scraps—in differing levels. In my garden beds that sees a rotation of vegetables over the growing year, I put in a bag of well-composted chicken manure annually. I apply compost to the soil surface, which I then fork through, and also mulch beneath my veggies with either aged grass clippings or straw. I make compost from a mixture of animal manures, wood ash, straw, grass clippings, large volumes of veggies scraps (if I have them) and old vegetation (e.g. pumpkin vines from cleaning old beds). Over the last 12 months I‘ve also added finely ground up basalt rock powder; this adds a range of macro and micronutrients and has a honeycomb structure, good for encouraging bacteria and water holding capacity.

Different vegetables have different needs, and also for the part you want to harvest. Leafy vegetables, like lettuces and Asian greens, have high Nitrogen needs and appreciate the levels available in poultry manures. Whereas root vegetables—like carrots—will develop too much top growth at the expense of root development if the soil is high in Nitrogen. I grew a wonderful carrot crop after garlic this year without any extra additives. On the other hand, beans appreciate Potassium, blood and bone or a load of well dug in compost. Likewise, garlic likes fertile soils but doesn’t like too much Nitrogen as it tends to grow too leafy.

Actually it all depends on time, what’s available and what I can afford at the time. During summer, a friend drops around trailer loads of grass clippings weekly that I use to make compost. Yet last autumn’s load was mostly fallen oak leaves. Most of it went into compost bins to break down for the next 12 months; I mixed the remainder with grass clippings. After leaving it for a couple of months, I spread it around several beds as weed-suppressing mulch. It works brilliantly and will eventually break down into beautiful water holding organic matter—especially as those particular beds will receive a good top dressing next spring with the compost I’m currently making. It doesn’t bother me that the leaves are still recognisable and haven’t fully broken down yet, as I know all those millions of bacteria, slaters, beetles, worms, slugs, lizards and other soil life don’t rest over winter, like I tend to.

cc photo by fred_v

In refusal of cheap fast food at university, Steve Fleischmann began growing vegetables. He is pragmatically organic with 20 years’ experience in Australia and overseas. Once a bush regenerator and project manager for youth environmental projects, he now works at Mamre Farm in Western Sydney with refugees, people with a disability and youths. Building soils, encouraging biodiversity and growing heritage varieties allows Steve the opportunity to feed his family, develop small scale enterprises and pass on knowledge and skills. Follow Mamre Farm on Facebook.

Dig for Victory
1. Soil I: soil type, improving soil and soil health test
2. Soil II: soil compaction and ph test
3. Soil III: Nutrients
4. Plants and naming
5. Adapting to a new climate
6. Dig for Victory: Planning for the win

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