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Soil Micronutrients and How To Optimise Them In Your Compost

Written by Angus Stewart

In an earlier blog we looked at the various soil-derived macronutrients such as nitrogen, phosphorus and potassium, that are required in relatively large quantities. In this blog let’s have a look at the soil-derived micronutrients which are essential for plant growth, but are only needed in very tiny amounts, such that they are usually measured in parts per million. These are boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), and zinc (Zn).

The soil-derived micronutrients are alternatively known as trace elements, and the tiny quantities of them are used in the plant to synthesize various substances such as enzymes and plant growth regulators, without which the plant will not grow properly. When they are deficient in the soil, we often see discolouration of the foliage. One of the most common examples of micronutrient deficiency we often see in the garden is a shortage of iron that shows up as yellowing of the new foliage growth between the leaf veins which usually remain green, as shown in the image below. This becomes even more pronounced during winter when it is even harder for the plant’s roots to take up iron from the cold soil.

Another key factor in your soil’s ability to supply micronutrients is pH, that is, whether your soil is alkaline, neutral or acidic. If the pH of your soil or compost becomes either too acidic or too alkaline, the micronutrients can become locked away in chemical forms that are unavailable to plants. Simply by bringing things to a pH close to neutral, you can transform nutrients from being unavailable, to one that plants can take up readily. Tumbleweed Worm Farm and Compost Conditioner is designed specifically to take care of this problem, and a sprinkle across your worm farm or compost bin will go a long way in ensuring that you not only recycle all the nutrients from your household organics, but that you also end up ensuring those nutrients are readily available to the plants in your garden.

Our goal in creating and maintaining a healthy garden soil is to replace any nutrients we remove from them when we prune our plants or harvest our vegetables. We also need to ensure that we replace micronutrients in the correct balance for what is being removed. For many gardeners, the vegetable garden is the place where most nutrients are being harvested where they then go to the kitchen. The bottom line is that any food wasted in your kitchen usually contains, on average, the sort of balance of nutrients you are looking to replace. When we compost these, we are able to recycle a significant percentage of these micronutrients instead of sending them to landfill. Whatever method of composting you use; you will be making a significant individual contribution to sustainability when it comes to soil-derived macronutrients.

To optimise the supply of the micronutrients from your compost here are some key tips;

  • Always use a percentage (30-40 is a good rule of thumb) of nutrient-rich ingredients as part of your compost raw materials such as kitchen scraps or animal manure
  • Use the compost as soon as possible after it is ready. A good test is to raise some fast-growing seedlings such as radish or lettuce, and if they grow normally the compost is ready.
  • If you can’t use your compost straight away, put a cover over it to stop the nutrients leaching out
  • Test the pH and if it is below 6 add lime, or if above 7 add powdered sulphur. Both materials can be purchased from your local nursery or hardware retailer.



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