Let us think for a few minutes about how farmers should manage their soil to get better crop yields.
Modern farmers know how to look after the soil. They know exactly what the soil is for. It’s the place where dead organic matter decomposes and where plant food and water are stored for the crops. If farmers look after the soil, the soil will have water and plant nutrients in it, so it will be healthy and grow good crops.
Farmers must manage soil in different ways. They must manage it
- To keep plant food in the soil.
- To keep enough water and air in the soil.
- To drain the soil when it has too much water (waterlogging).
- To stop the soil from being washed away (erosion).
You can help to keep your soil fertile if you know the story of the soil.
Before you make a garden, the land is usually covered with a forest. Where is the plant food in such a place? The roots of the tall trees have taken the plant food from the soil and carried it up to the branches and leaves.
When you grow crops such as sweet potatoes or yams in the garden, some of the plant food will go into the roots of the crops, then into the stems and leaves. So then the soil has less plant food. If you grow many food crops in this garden and do not put any plant food back into the soil, all the plant food will be taken out of the soil by the crop.
After you have harvested a crop, leave the dead top parts, and the grasses and weeds on the soil. These all contain some plant foods. If you dig these plant foods into the soil and bury them, they will add humus to the soil.
But, if you burn all the dead plants, the plant food comes out quickly from the ash into the soil. Then it may be washed away by the rain before a crop can use them. Burning trees, shrubs, or crop residues makes the soil poor because the plant foods are left loose in the soil and are easily washed away by rain. If you burn the land all the time, it will turn into poor grassland.
Wise farmers know that plant foods can be lost from the soil. So it is important to manage the soil so that it always contains a supply of plant food.
Just as some animals always eat one kind of food, so a plant always takes out of the soil more of some plant foods than others. So if you grow the same crop in the soil every year, the crop may use up most of certain kinds of plant food in the soil. For example, maize crops take a lot of potassium from the soil, and sugarcane takes a lot of nitrogen from the soil.
Wise farmers should not grow the same crop on the same land every year. Instead, they should try to grow different crops in the soil each year.
For example, if you grow sweet potatoes in the garden one year, you may grow beans or some other crops the next year to keep the soil fertile. The best kind of rotation is when a legume crop is grown every third year. Legumes are plants such as beans and peas, which have small lumps called nodules on their roots. These plants can add nitrogen to the soil and they make the soil richer.
A mulch can be any light loose material that is laid over the soil around the plant. It will improve soil structure and texture. For example, you can put a layer of dead leaves or grasses on top of the soil around the growing plant.
Well, there are two reasons for using mulch on the soil. When the dead leaves and stalks of a mulch get wet from the rain, they become soft and begin to break down. Soon they are added to the soil as small pieces of organic matter. This organic matter is useful because it holds water and food for the plants.
The mulch also stops weeds from growing with the crops and stealing water and plant food from them.
There are two things you should think about with regard to soil water. You must do what you can to give your crops enough water, but you must also make sure that there is not too much water in the soil.
If you bring water onto your land, this is called irrigation. To irrigate the soil you must find a supply of water near your fields or garden. You will have to dig a long ditch or channel in the soil to carry the water to your land. This channel must not be too steep or the water will rush too quickly along it. It is good if the water flows slowly along the irrigation canal.
If your land is on a hillside, the channel must take water across the upper part of the land. Then you can make water flow out of this channel into many small channels that flow down the hillside and take the water to the crops.
When there is enough water in the soil for the crops, you must be able to stop more water from coming into the fields or garden. Most plants will not grow if there is too much water lying on the soil. When the water lies on the ground it makes the soil cold and keeps air out of the soil. Plants such as coffee and cocoa need well drained warm soils and all plant roots need air.
If there is too much water in your soil you should make drains in your land. These will let the water run out of the soil. This is how to make a drain.
a) First, dig a main drain down the middle of the garden plot so the water can run downhill to a creek. Main drains must be deep and wide and made to flow down to the lowest part of the garden land to a creek, a dam, or a flowing river.
b) Then, dig side drains to run into the main drain. They should not be at right angles to the main drain but should point in a direction that flows down the main drain.
If the soil is sandy it is difficult to make channels or drains because the soil particles won’t hold together and will easily be washed away by the running water. Clay soil is ideal for making drains.
– END –
By McRei Kei, Rural Broadcast Officer, National Broadcasting Commission, Papua New Guinea
- “Good soil and water management increases harvests” in World Neighbors in action, Volume 21, Number 3E, published in English, French and Spanish by World Neighbors, 5116 North Portland Avenue, Oklahoma City, OK 73112, U.S.A. This newsletter is available at no cost for people in developing countries
- Knowing your land (1988, 41 pages), booklet #101, published by INADES-Formation, P.O. Box 14022, Nairobi, Kenya.
- How to prepare your land (1988, 48 pages), booklet #102, published by INADES-Formation, P.O. Box 14022, Nairobi, Kenya.
- Vanishing land and water: soil and water conservation in dry lands, (1988, 117 pages), by Jean-Louis Chleq and Hugues Dupriez, published in French and English by Terres et Vie, 13 rue Laurent Delvaux, 1400 Nivelles, Belgique. Also available from CTA (Technical Centre for Agricultural and Rural Co-operation), P.O.B. 380, 6700 AJ Wageningen, Netherlands.