Ancient Soil Amendments

This is the first in a series of blogs, about ancient soil amendments used in the garden. Each blog will discuss a common and specific type of soil amendment used in the garden, along with documentation for its use, as well as occasionally discussing why a particular soil amendment was chosen, or its relation to modern gardening practices. The original blogs, along with other gardening related blogs, can be found here.

After several years of gardening in a space, you will notice a steady decrease in how well the garden produces. For the modern gardener this is annoying, but very few of us in the western world live or die based on the production of our garden. During the Middle Ages, without grocery stores and mega-farms, this was a serious issue.

it is generally accepted that you have to add something to the soil to improve soil productivity. Typically this is done either by straight up adding something to the soil (a soil amendment) or by completing a process (a soil improving practice). Both have an important role. If a soil doesn’t have a characteristic or a mineral, it may be faster and more efficient to simply add what is missing. If the soil is merely low or constantly being drained of a mineral it might make more more sense to regularly perform a task, or build in a system, to replenish the soil.

The modern gardener, even the modern farmer, deals with soil decline quite simply – we order soil amendments from our farm supply or hardware store. If our soil lacks nitrogen, we buy a fluid or pellet mix to spread out and and water in. Obviously, our agrarian ancestors could not do this. Before I discuss the ways pre – industrial societies dealt with decreases in soil productivity, it will help to understand how it happens.

One aspect of soil health (which determines productivity) is fertility. According to the Queensland Government, soil fertility decline occurs when nutrients being removed from the soil in harvested products exceed nutrients being added to the soil. These nutrients can be removed in three ways – by growing crops, soil erosion, and leaching. These first two methods – growing crops and soil erosion cause most of the problems.

Growing crops both draws out and adds in nutrients to soil. Some plants (like peas) add soil nutrients like nitrogen to the soil if most of the plant is allowed to grow, die and compost in the space. Others, (like corn), need large amounts of soil nutrients in order to create healthy foods which is difficult to get back. The nutrients are generally pulled out of the soil into plants through their root structures. For example – lead in soil can be removed through growing (and than disposing) sunflowers through a process called phytoremdiation. If you plant too much of one type of plant – or don’t use proper balance, you hurt the soil health.

Erosion is when wind or water is able to remove nutrients, organic matter, clay or the soil itself from a piece of land. It “decreases nutrient bio-availability, root growth, plant fertility, biological productivity, moisture retention, and water filtration of soil, and erosion perpetuates further erosion” (Palmer, 2009). Although we commonly associate this problem with the “Dust Bowl” of American history, erosion happens every day. Stan Buman says soil can – in best case scenarios – only rebuild at a rate of .24 tons per acre. The same report found that the average soil loss in modern farming practices is 5.8 tons per acre. In a best case scenario, with no-tilling, you will still loose about .22 tons per acre, or just slightly less than you can rebuild. These numbers are designed for big farms but the point is clear – with any tilling or turning over at all, you wil loose soil – and also lose nutrients.

Over the following months, I will share some discussions about each of the different soil amendments and soil improvement practices I have found reference to in medieval or pre-medieval texts. Some of these may seem familiar to you as techniques we use in permaculture or modern organic farming, others may be new. Enjoy the reflection on the past – and I hope you generate some ideas on what you can try in your own gardens!