Soil fertility - Farm Radio Scripts

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Backgrounder

Key Information

Soil health is a particularly pressing issue for Africa. Tropical soils have a tendency to rapidly degrade due to human activities. In many places, there is a limited amount of good farmland and there is a high rate of nutrient depletion in soils in many areas. A recent study has shown that soil fertility can have a greater impact on maize harvest than variations in temperature, rain, or CO₂. (1)

African soils are often low in nutrients to begin with. If you add to that the combined effects of short fallow times, continuous cropping, slash-and-burn agriculture, too much tilling, and other factors, soils can become seriously degraded or depleted. Also, overusing inputs such as synthetic fertilizers and herbicides can leave residues which accumulate and hinder the work of micro-organisms. A buildup of salt in the soil, often associated with irrigation, can deplete fertility and limit crop yields.

Fertile soil has the following properties:

It is rich in the nutrients which are necessary for plant nutrition, including nitrogen, phosphorus and potassium (N-P-K).
It contains trace elements which are also critical for plant nutrition, but are needed in much smaller quantities than N-P-K. These include boron, cobalt, copper, iron and several others.
It contains good levels of organic matter, which improves soil structure and its ability to hold water.
The soil pH is balanced.
It has good soil structure, so it holds water well, and drains well.
It contains a range of macro-organisms (earthworms, termites, etc.) and micro-organisms (fungi, bacteria, etc.), that support plant growth and health.

Learn more about soil health.

There are several strategies to improve soil fertility and reduce soil degradation. These techniques are promoted by conservation agriculture and circular and regenerative agriculture practices. These include:

Fertilizers and composted manure
Intercropping and crop rotation
Cover crops and mulching
Minimal tillage

Fertilizers and compost

Fertilizers are organic or mineral substances that increase the supply of nutrients in the soil, directly increasing plant growth, and are applied to crop fields to increase productivity. Fertilizers contain one, two, or several of the essential mineral nutrients required by plants, including the major nutrients nitrogen, potassium, and phosphorus. To ensure increased crop production and to minimize the negative environmental effects of fertilizer use, fertilizers need to be applied in the right way. One way to ensure increased crop production and minimize environmental harm is to use fertilizers effectively and efficiently. The 4R approach to applying fertilizers (4R Nutrient Stewardship) specifies four essential principles: right source, right rate, right time, and right place. Learn more.

Organic fertilizers are derived from naturally-occurring waste, including crop residues and animal manure. They release elements such as nitrogen, phosphorus, and potassium into the soil gradually through the action of soil microorganisms. This ensures that plants do not suffer from excessively rapid effects that would prevent them from developing normally. Organic fertilizers are less harmful to soil and plants than chemical fertilizers.

There are several techniques for making compost, discussed in this backgrounder. A common one is pit composting. Steps for pit composting:

Dig a pit about three metres wide and one metre deep. The pit should preferably be located in a shaded area away from direct sunlight and water infiltration.
Stabilize the walls by coating them with cement and stones. Provide a ledge of about 20 centimetres.
To the pit, add chopped or ground crop residues, about 20 centimeters thick. Water until moist.
Cover this layer with ashes and then a layer of manure about 10 centimeters thick. Water generously and cover with ashes.
Alternate layers of straw or crop residues, ash, manure, and ash again until you reach the edge of the pit. Water evenly to keep the compost moist.
Turn the contents of the pit weekly to accelerate mineralization and decomposition. The compost will be ready after 40 to 50 days.

Alternatively, you could build a compost pile above ground and use tree poles or wire mesh to shape the pile and cover it with a black polythene sheet.

This technique can be labour intensive when it comes to turning, in particular the first few turns.

It can be particularly beneficial to include nitrogen-rich organic residues in compost. Farmers can select darker green leaves that are likely higher in nitrogen than yellow leaves. Dark green leaves, which tear easily, are low in lignin. Dark green leaves low in lignin and which do not have an astringent (bitter) taste (from polyphenols) make the best fertilizer and can be incorporated directly with annual crops. Learn more here.

Intercropping and crop rotation

Some crops can grow together in the same field without interfering with each other (called companion planting), and others support each other’s growth. Maize and beans support each other’s growth (called mutualism), as beans produce nitrogen which the maize plant consumes. The tall maize plants protect the beans, and deep-rooted legumes like pigeon pea can break through hardpans, helping the maize roots penetrate deeper soil. Learn more.

Alternatively, farmers can alternate which crops are planted on a section of land, a practice called crop rotation. Growing one crop on one piece of land season after season is called mono-cropping, and it can increase the incidence of pests and diseases, and deplete the soil.

One major reason for rotating crops is that “taking crops” such as maize, sorghum, and millet require more nutrients from the soil than others. Similarly, cassava does not add much value to the soil, apart from helping to break it up, which is good for aerating the soil. Planting these crops on the same piece of land year after year can seriously deplete soil nutrients and diminish yields. Other crops take very little from the soil, but add nutrients. These are called “giving crops.” Legumes like groundnuts, cowpeas, pigeon peas, lablab, and soya beans are in this category. When rotating crops, it is advisable to alternate between “giving crops” and “taking crops.” Learn more in our backgrounder on conservation agriculture.

Cover crops and mulch

Covering the soil can reduce the growth of weeds and reduce erosion of the top layer of fertile soil. It also conserves soil moisture, especially in dry regions. Cover crops and mulch can maintain soil cover. To control erosion, farmers should maintain 30% soil cover after harvest.

Farmers can plant food or cash crops as cover crops. Using leguminous cover crops like mucuna, sun hemp, and lablab beans can reduce the use of chemical fertilizers by 60-80% without lowering yields. Farmers should take care to select a cover crop that does not interfere with the growth of the main crop. These can be intercropped to grow at the same time as the main crop. Or the cover crop can be planted when the main crop is being weeded or after it is harvested (relay cropping, sequential cropping).

Mulching covers the soil with crop residues from main crops and cover crops. In arid areas during dry seasons, the mulch covers bare soil and create a humid environment that allows farmers to plant cover crops. It is best to get mulch from leguminous shrubs or trees, like Calliandra, Leucaena, Tephrosia, Crotalaria, Sesbania, and Gliricidia, tithonia which add nitrogen to the soil as they cover it. Though they add nutrients to the soil, legume crop residues decompose quickly when used as mulch. To make legume mulch last longer, mix it with grass species. Living fences, which act as windbreaks, can also be pruned for mulch and livestock fodder. Learn more in our backgrounder on using permanent soil cover.

Minimal tillage

Traditionally, small-scale farmers dig up every part of the field to maintain a clean field, and sometimes make planting ridges. Minimum tillage, in contrast, involves disturbing the soil only where seeds will be planted. The rest of the field is left intact. This protects the soil from the elements, especially heavy rain.

Farmers can implement minimum tillage by using a hoe or ox-drawn tools such as rippers. Farmers who use hoes dig planting basins in well-spaced rows, ensuring that they break through the hardpan. Farmers who use oxen often use the Magoye Ripper, a strong tine that can be fitted on any ordinary plough frame to rip lines in the field deep beneath the hardpan.

Breaking the hardpan with a hoe or ripper enables rainwater to sink into the ground instead of running off. Crops can then extend their roots beyond the hardpan, follow moisture deeper in the soil, and survive through normal dry spells.

Minimum tillage can improve soil structure and soil fertility over a number of years. It can also increase the level of moisture in the ground. Learn more about these and other conservation agriculture practices.

Gender equality and inclusion considerations

When talking about farming in general, it’s important to consider the gender division of labour; control over resources and assets, including income; decision-making power; time use and unpaid care work; and gender positioning in the value chain. When discussing soil fertility, it’s important to consider access to and control of land. Women often farm on poorer quality lands as it is all they can access, meaning they have worse soil fertility.

Women and men may prefer different crops for intercropping or cover crops. For example, in Tanzania, women small-scale farmers prefer cover crops that reduce weed growth, while men prefer cover crops that can earn extra income from selling in markets. In general, women are typically responsible for weeding, so cover crops can reduce the workload of women. Women may want to pursue intercropping to increase the types of food available for their households. But women may lack access to the inputs, like seeds, to pursue intercropping.

Some farm implements may not be suitable for women. For example, the Chaka hoe weighs 4-5 kilograms, and ripping requires using oxen.

Producing some types of organic fertilizer requires a lot of labour, time, and strength. This may be difficult for women, especially mothers of young children who are very busy. Composting can be made easier by dividing the work into groups. During the composting process, only the first steps (turning the pile) are difficult. After several weeks, the organic matter becomes soft and easy to turn.

Radio spots

1) Soil fertility practices

NARRATOR: Farmers! If your crops are struggling because the soil has lost its fertility, don’t worry. You can restore your soil and boost your harvests with simple regenerative farming practices.

Before the planting season starts, manually clear the weeds with a machete to eliminate them. Then use a hoe or a machete to dig holes for sowing seeds or seedlings, to reduce soil disturbance.

As crops grow, spray on natural bio-pesticides to eliminate pests and diseases. Only apply chemical pesticides to eliminate the stubborn pests and diseases.

Mulch, compost, and manure can boost soil fertility and help retain moisture. After harvesting, practice crop rotation by planting different, unrelated crops. For example, if you grow maize one season, plant legumes like beans the next. This improves soil health and helps prevent pests and diseases.

Plant fodder trees like calliandra, faidherbia albida, leucaena, and gliricidia, ficus species in rows 10 meters apart. These can be fed to your livestock, and also make soil fertile, shade the growing crops, and minimize soil erosion.

2) Strip cropping

NARRATOR: Farmers! Strip cropping is planting different plant families on land divided into strips near each other. For example, groundnuts can be planted together with hibiscus. The crop strips are changed every season to practice crop rotation.

When strip cropping, farmers should not plant the same family of crops since that can increase pests and diseases infestations.

Now let us discuss some benefits of strip cropping.

Strip cropping improves soil fertility, and suppresses the growth of weeds.

Strip cropping disrupts pests’ movement and lifecycle on a farm.

In strip cropping systems, pests and diseases spread slower because different crop varieties separate their host plants.

Growing different crops in strips prevents the build up of soil diseases.

3) Making composted manure

NARRATOR: Farmers! To grow healthy foods while protecting the environment, apply compost manure or any other kind of manure. Livestock produce the best manure when their feed includes crop residues of legumes like beans, and also peas like cowpeas or pigeon peas. Here are seven steps for making compost manure.

First, gather both dry and green leaves, crop stalks, ashes, soil, water, and a long stick.

Second, cut the dry leaves in small pieces.

Third, dig a hole 1.5 metres long, 1.5 metres wide, and 25- 50 centimeters deep. Alternatively, you could build a compost pile above ground and use tree poles or wire mesh to shape the pile and cover it with a black polythene sheet.

Fourth, place crop stalks that are 15-25 centimeters thick at the bottom of the hole and sprinkle water on them.

Fifth, add a layer of dry leaves and another layer of green leaves.

Sixth, spread ashes on top of the leaves.

Seven, add a layer of soil, about five or ten kilograms in weight. Make sure you spray a little water on top of each layer.

Repeat adding layers in the same way until the heap is one and a half metres high, then leave the heap to decompose.

After two days, check the temperature of the heap by inserting the long stick into the middle of the heap. If the stick is warm, the composting is going well. If it isn’t warm, sprinkle more water.

Your compost will be ready in three to seven weeks, depending on what types of materials you use and how long it takes them to break down.

Making compost manure is easy. And it boosts your yields.

4) Intercropping

NARRATOR: Farmers, do you know that intercropping with the right combination of crops can boost your yields? What is intercropping? Intercropping is growing two or more crops together in one field.

Sometimes intercrops are grown close together, and sometimes in different rows.

Sometimes fast- and slow-growing crops are planted together. The fast-growing crop is harvested first and the slow-growing crop continues maturing.

And sometimes you can plant a second crop after the first crop produces fruit.

Intercropping improves soil health and environmental biodiversity. It also attracts beneficial insects that control pests and increase yields.

To start with, why not plant a deep-rooted crop with a shallow-rooted crop? Or a tall crop with a shorter crop that needs shade?

Farmers! Intercrop to increase your yields and eat healthy.

5) Cover crops

NARRATOR: Farmers! Do you know how cover crops can help your farming business? Cover crops ensure that your soil is covered. And that has five main benefits.

First, it controls soil erosion, maintains and conserves soil moisture, and slows evaporation.

Second, leguminous cover crops add nitrogen to the soil, improving soil fertility and yields.

Third, many cover crops grow quickly and can mature during the short rains.

Fourth, cover crops reduce weed growth, decreasing the need for constant weeding and reducing labour costs.

Finally, some cover crops are food for both humans and livestock.

Cover crops can work for you!

Farmer stories

Royd Michelo, in Lusaka Province, Zambia, intercropped maize, beans, and pumpkins, and in the midst of drought, his compound was one of the few green spots amongst dry, barren land. In 2024, Nkhondola village had been hit hard by drought. But on Mr. Michelo’s compound, trees and crops thrive and despite the drought, he expected a good harvest. A farmer for 40 years, he and his family have embraced agroecology, using mulch and animal manure to restore their land.

In 2023, Sadiq Ayo’s farm in northern Uganda was plagued with drought, caused by climate change. To cope, he plants soybeans as a cover crop, to protect the soil from the sun and to add nutrients when the leaves decompose. Soybeans are drought-resilient. He also plants in fields that were abandoned for 50 years because they were too wet.

Markos Chneshu from Ethiopia practices conservation agriculture to improve his soil fertility, including mulching, rotating crops, and intercropping. When we spoke to him in 2019, he was busy cutting dried maize and pigeon pea residues, and placing them on his field as mulch. Mulch covers the soil, thereby reducing the evaporation of soil moisture. By covering the soil, crop residues also suppress weeds. In addition, when they decompose, the residues add nutrients and organic matter to the soil, improving soil structure. And when the mulch is a leguminous crop such as pigeon peas, it boosts soil fertility.

Souleymane Diao farms in the Casamance region of Senegal. To boost his harvest, he makes organic fertilizer with a mixture of straw, cow dung, and water. He adds a layer of straw and cow dung, then water and tramples it until it is well-mixed and compact. He adds more straw, dung, and water and mixes again, repeating until the compost pile is one-metre-high, then covers it with a tarp. One month later, the natural fertilizer is ready to use. Mr. Diao also uses “zero grazing.” He encloses a one-hectare space and allows eight to 10 cows in every night. The animals mix their dung and urine with grass as they move. After several months, the space is fertilized and Mr. Diao sows his crops.