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By George Katongole
Mulching, as we know it, is an important practice in small-scale farming aimed at conserving water during the dry season by preventing water from evaporating and preventing run-off during the rainy season by cushioning the impact of raindrops and slowing runoff.It is done by covering the soil between the plants with a layer of cover materials. This proven method also protects the soil all year-round and suppresses weed by blocking out the sunlight. Mulching also increases organic soil matter. But the practice is labour intensive while there are suggestions that it can introduce new pests and diseases into a field.With the harvest period upon us, the materials are in plenty. Ordinary grass makes a good soil cover as do maize, rice and sorghum straws as well as manure.“It goes down to planning. It is always advisable to plan mulching during the dry season such that much moisture can be preserved as the crops are growing,” Timothy Njakasi, an agricultural consultant in Mukono District, says.Organic vs inorganicThere are two types of mulching, that is to say, organic and inorganic. Most farmers are used to organic mulch, which has traditionally been used. Organic mulch is made from decomposable materials such as grass clippings, wood chips, dried leaves, and straws. On the other hand, inorganic mulch is composed of river rock, stone, or crushed gravel. Lately, plastic mulch, which utilises polyethylene film to shield plants, is becoming popular with commercial vegetable farmers who use drip irrigation. Farmers that practice hydroponic farming also use this method of mulching. Many highly recommend it as a helpful practice in producing clean crops since it acts as a barrier between the fruits and the soil. As a bonus, many organic mulches are free or low cost. According to Njakasi of Kasenge Riverford Organic Farm in Mukono District, the choice of mulching materials depends on cost.
“Most of our local farmers cannot afford plastic mulch. We advise farmers to use locally available materials. It is about managing expenses. Farmers should look into the profitability of their operations,” Njakasi explains.Best practicesMulching is an exact science and it is therefore paramount that a farmer understands the different types of materials and how they can be applied considering the right timing.Seasonal crops, especially vegetables such as tomatoes, okra and cabbages, among others, require mulching whereas other water management practices are applied in perennial crops such as coffee, instead of mulching. The effectiveness of mulching normally depends on the ability of the farmer to achieve the desired outcomes or else it will become uneconomical.According to James Mugerwa, a retired extension worker in Mukono, who is working as a consultant, the mulch material is spread manually by maintaining a layer of between 3-6 inches (7-15cm) deep around the growing plants. He advises that for vegetables, the mulch should not bury the plants or shade them out. An important observation he makes is to use only dry plant materials that do not rot quickly.“Dry mulch is what we encourage farmers to use in order to avoid burning the crops when the mulch is composting. Green mulch has a tendency to release heat during that process which can be harmful to the root system of the crops,” he says.Mugerwa advises farmers to apply organic mulch after the first heavy rains saturate the soil.Njakasi, an organic farmer, explains farmers with organic produce need to pay extra attention to the source of their mulch. “Mulch contaminated with crops sprayed with pesticides compromise the quality and spirit of organic farming,” Njakasi explains. Likewise, he adds, mulch from sick crops must be avoided as this would transfer pests from one garden to another.As a general rule, Njakasi explains, farmers must ensure that mulch is free of weed seeds. He says this is done by ensuring that for instance, hay and compost, reaches a sufficiently high temperature to kill weed seeds.He adds that the ultimate objective is to preserve moisture in the soil in order to grow healthy plants.
An agronomist demonstrates how mulching is done. Photo/FARM BIZNjakasi explains that the material to be used largely depends on the crops one wants to mulch. Cabbage and tomatoes, for instance, it is recommended to mulch as early as possible to avoid fungal infections. “Infections normally reside in the soils and can damage the crops when not attended to early enough,” he notes. Yet for bananas, Njakasi adds, it is advisable to begin with live mulch like jack beans and use dry mulch when the plantation is already established,” he notes.Additionally, all experts agree that mulching must be applied hand in hand with other agricultural practices especially digging trenches, cover cropping, crop rotation or fertiliser application. “Mulching alone is not enough without proper garden sanitation practices,” Mugerwa explains.How much mulch?Mulch has traditionally been used in Uganda for quite a long time. According to extension workers, mulch should first of all be applied at least two feet away from the banana stem in order to encourage bananas to have more vertical roots. When mulch is applied too close to banana stems, it is said to encourage development of more superficial lateral roots which do not hold firmly against winds and exposes the plant to water shortage during the dry spell.Mugerwa explains that there are two cardinal rules for using organic. First, the farmer must lay the mulch on soil that is already weeded with a thick layer enough to discourage new weeds from coming up through it.RisksBut mulching has associated risks. According to a study published on the InfonetBiovision website, mulching can lead to a process termed as nitrogen immobilisation. When carbon-rich organic material such as stalk or straw is applied to the soil, the website explains, the decomposing microbes multiply quickly. For their growth, they need nutrients, especially nitrogen.Therefore, if applied plant material does not contain sufficient nitrogen, the microorganisms will take it from the soil. During this period, the crops may suffer from malnutrition.The experts therefore advise on using old or rough plant materials at least two months prior to the planting season to minimise the risk.Mulching is also associated with multiplication of slugs, snails and termites under the mulch layer which may cause damage to the crops. Additionally, pests such as stem borers may survive in the stalks of mulch materials which could pose a risk of disease to the crops. This calls for crop rotation to overcome these challenges.
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