Is this soil fertile? Many people ask this question, especially, when they are planning to buy a piece of land and venture into farming.
This question can be accurately answered by a soil test, but every farmer should know a few basics about soil fertility and best practices in soil fertility management.
“In soils, we look at two sources of fertility. First, from the rocks that form the earth,” says M. Weber, the country manager of SoilCares Limited.
According to Weber, the soils provide minerals through weathering, for instance, clay particles and second, the top soil layer that covers our planet, which is formed and replenished by decaying organic matter.
Organic matter is any kind of plant material that is returned into the soil, where it is decomposed by microorganisms to end up with humus.
Humus and clay together form complex aggregates, which can be seen with naked eye. They are black, moist crumbs in a fertile, healthy soil.
The structure of these aggregates provides the soil with positive physical features like aeration, water-retention, easy tillage, avoidance of hardpans and water logging.
But the most important feature of these aggregates is the fact that they always have a negative surface charge, which enables them to attract nutrients like the ones provided by a fertiliser.
These nutrients usually have a positive charge and are attracted
to the negative charge of the aggregates.
They loosely bind themselves to the aggregate, from where they can easily be exchanged again in the soil solution and the crop roots.
Without the negatively charged aggregates, nutrients cannot attach themselves to the soil and are only available to the crop for a short period before they are lost through leaching.
Nutrients uptake by the plant, therefore, depends largely on the availability of such aggregates in the soil, which again depends on the presence of micro-organisms in the soil.
Humus releases nutrients at a steady but slow rate. But some crops are so-called heavy feeders, that is, they need large amounts of nitrogen during the growing season. Often, they need an extra boost at transplanting or when they start fruiting. Others like cabbages even need regular feeding.
The fastest way to give a crop this extra boost is by using home-made liquid fertilisers.
The fertilisers have the added advantage that they are organic, which means they do not upset the microbial soil life and they are also not acidifying as is the case with inorganic fertilisers.
And this is how to make your own liquid fertiliser at home:
One of the most valuable plants to use is stinging nettle (urtica).
It provides a large variety of nutrients and undiluted, it can be used as a powerful pesticide. Stinging nettle is a little low on phosphorus, though.
Susan Akot, the soil expert at National Semi Arid Resources Research Institute (NaSARRI), says to make a liquid fertiliser rich in phosphorus, a farmer should use tithonia, a shrub that grows as a weed or hedge in most parts of the country.
“Another very useful plant is comfrey (symphytum), which is especially rich in potassium and provides Vitamin B12, which stimulates rapid root growth at transplanting,” she says.
To start, you need a bucket, water, machete (panga) and a stirring stick.
Collect the leaves of stinging nettle, comfrey, tithonia or any kind of weeds. Chop them and put the cuttings in the bucket.
Add crushed eggshells to provide calcium. Fill the bucket with water so that the material is completely covered.
Cover the bucket loosely to keep flies and mosquitoes out, but air should be able to get in and out. Stir the mixture several times a day to incorporate oxygen. The mix will start to bubble and stink.
These are good signs that your fertiliser production is well. After two to three weeks, all the green material would have dissolved and only a few harder parts remain as sludge. Remove those with a stick and strain the liquid through a sieve. It should now be clear green and will not bubble.
You can store it in a closed container until you need to use it. For application, dilute a litre of the liquid with 10 litres of water (1:10). Apply directly to the root zone of your crops.
It can be applied weekly. You may also apply it as a foliar feed by straining it through a cloth so it won’t clog your sprayer, and diluting it 1:20 with water before application.
Plants absorb as many nutrients from the soil as necessary for their normal development. After the end of their life cycle plants decompose, and all the elements go back into the soil.
When using the land for agricultural purposes, humans interfere in the cycle of elements in nature. Together with the harvest, they take the nutrients that plants have absorbed from the ground, thus breaking the ecosystem balance.
With each harvest, humans remove 60 to 70 per cent more nutrients from the soil than plant residues give back.
Over time, the concentration of the most important macronutrients in the soil decreases.