Each year, we take more than 50% of what the soil gives to us in form of “food” (the parts of the plants we eat) and we “give back” less than 25% through composting.
This means we are losing anywhere from 25% to 50% each year that IS NOT COMING BACK through our regular compost.
Compost, as well, will only have the minerals present in the plants or materials we added. Some amount of these minerals will leach out through processes such as heavy rain, wind, etc.
This means that if we started with some imbalance, this will not be magically replenished by using locally made compost: we need to add more, and this “more” will have to come from someone else unless we have a big farm where we can use manure, etc.
In ideal conditions, we would have this “extra” coming from animal and even highly composted human manure or urine (human urine, for example, contains nitrogen, phosphorus and potassium, for those interested in these topics, read: http://www.goveganic.net/article217.html )
In ideal conditions we would also have all our kitchen scraps plus all plant materials, leaves, grass, hay and other sources for both carbon and nitrogen.
But plants need much more than the usual NPK (nitrogen, Phosphorus and Potassium), they need things like potassium, magnesium, sulphur, boron, iron, copper, etc…, so where do we get these from?
If you want truly nutrient-dense crops, you may use either full spectrum or nutrient specific fertilizers.
Here is a list of what you can and cannot use according to SOUL (the Society for Organic Urban Land Care)
Good to use and highly recommended:
- Compost: I run workshops and plan to write a post on this!: Good compost is an excellent source of microbes to remediate an abused landscape, bad compost just makes it worse and it may add diseases and pests to your garden…you can always have a small composting box in your apartment or townhouse (as I do) with either worms or Bokashi (I have both plus a rotating composting bin)
- Effective Microorganisms: The micronutrients are not contained in the product but are made available to plants through the metabolic activity of the microbes. Use as foliar treatment for quick results, or apply to soil containing sufficient organic matter.
- Aerated compost tea: This type of tea is “brewed” at room temperature in specialized vessels (compost tea brewers), from carefully chosen compost, and with additional food for the bacteria, fungi, protozoa and nematodes whose populations explode under the created conditions. Food sources generally include molasses, kelp, rock dust, and humic/fulvic substances. Brewing time ranges from 12 to 48 hours, depending on temperature and type of apparatus.
- Plant extracts: Herbal teas and liquid manures are plant extracts. Herbal teas usually consist of one fermented plant extract, while liquid manures are made by fermenting a mixture of herb plants in combination with fish or seaweed extracts. Some plants commonly used are stinging nettle, horsetail, comfrey, chamomile and clover, or a mixture of locally harvested “weeds”.
- Biochar blends: check under resources for details on where to get this and how to use it.
Safe to use (but we may still have some concerns such as those coming from animals or being mined):
- Fish meal
- Fish emulsion
- Rock dusts (Commercially available dusts are: Glacial rock dust, also referred to as glacial moraine dust. From natural deposits; Basalt dust. Usually finely ground basalt; Granite dust. Usually finely ground granite; Volcanic rock dust. From natural deposits.
Some you may use with care (as the source may be contaminated):
- Blood meal (good source of nitrogen for things like lettuce, tomatoes, etc)
- Bone meal (excellent source of phosphorus and calcium)
- Fishbone meal (same as above)
- Colloidal (soft) rock phosphate
Also be careful with:
- Mushroom manure: this is horse manure used in the commercial production of mushrooms. After the horse has absorbed what it needed, the mushrooms have extracted yet more nutrients from the manure. Unless it is from an organic production facility mushroom manure contains significant pesticide residue. The mushroom growers also add calcium to the manure, which can make it very alkaline.
- Chicken manure: from non-organic broiler production contains high levels of arsenic (roxarsone and arsenilic acid are added to non-organic chicken feed to control parasites and enhance weight gain) and should never be used in food gardens. It is illegal (in the U.S.A.) to feed arsenic treated feed to laying hens, but who actually knows what the chickens were fed. Chicken manure can easily contain 50 milligrams of arsenic per kilogram of manure. Composting does not remove this arsenic, but instead concentrates it. In the soil the organic arsenic is converted to inorganic forms which are easily absorbed by plants, or leach with the flow of water.
- Dolomite lime: It is a perfectly good fertilizer if you need the magnesium, but can cause severe problems to the soil and plants when its use unbalances the calcium : magnesium ratio.
- Limestone/calcium carbonate
- Gypsum: Because it reduces salt levels in soil, it is effective in coastal and arid regions. However, it doesn’t work in sandy soils and it can deposit an excess of calcium in regions where the mineral is already abundant. Additionally, in areas with poor salinity, it pulls out too much sodium, leaving the location deficient in salt.
Full spectrum fertilizers NOT to use:
- Corn and corn gluten meal
- Canola seed meal
- Cotton seed meal
- Flax seed meal
- Soybean meal
Good sources if you don’t have the time to make some yourself or go around and buy in bulk are:
- The organic gardener’s pantry: http://www.gardenerspantry.ca/
- West Coast Seeds: https://www.westcoastseeds.com/shop/garden-supplies/fertilizers/
- Raven Wood Biochar
The soil is depleted by many factors: you take some of the matter when you take the vegetables you grow in it, but soil is also affected by compaction and erosion. This may happen through rain, wind and the fact that we take part of it in form of plants (therefore, there is less and less soil each time)
The best way to replenish those layers is to add good organic matter in form of well-cooked compost, compost tea, EM, cover crops and…more soil (check “home-made soil” for instructions how to “make” or recycle your own soil). The reason we need more soil is because OM (organic matter) decomposes slowly and doesn’t provide a lot of nutrients by itself: the nutrients are in the minerals!
If you can find a safe and good source of soil to add to the final layer of your plot/container, you will help the compost and the rest of the OM with volume and some of the missing minerals (i.e. nutrients) we lose each year with the harvest.