Mistakes to avoid when using manure as a fertiliser on farm

Manure can be an effective supplementary organic fertiliser if handled and used correctly. It can, however, be very harmful if applied improperly.
According to Cranmer Kayuki Kaizzi, a Senior Research Officer at the National Agricultural Research Laboratories (NARL) Kawanda, who in 2016 published a Fertiliser Optimiser Training Manual, the nutrient depletion rate of soils in Sub-Saharan Africa is alarming.

He estimates that about 80 per cent of the total arable land has serious fertility and physical soil problems. Generating soil fertility management practices is a key mandate of the National Agricultural Research Organisation (Naro) even though farmers’ adoption rates remain low.
For instance, mineral fertiliser usage averages eight kilogrammes per hectare annually in Sub-Saharan Africa, much lower than the target agreed in the Abuja Fertiliser Declaration of 50 kilogrammes.

But the biggest problem has been inadequate knowledge on proper fertiliser and manure use and other integrated soil fertility management components. Declining soil fertility has affected the land on which the poor depend, thus threatening food security for smallholder farmers.
Smallholder farmers have as result attempted to use manure to improve the productivity. But James Mugerwa the Buvuma District extension worker and Senior Agricultural Officer says that despite manure being a common form of restoring soil fertility among farmers a lot of application and management procedures can make it ineffective.

Soil testing
Mugerwa underscores the role of soil testing as a key factor in farming. “Knowing the missing soil nutrients is key,” Mugerwa says. He explains that the key soil nutrients include nitrogen, phosphorous and potassium (NPK) which must be studied before any application of fertilisers. Others include calcium, magnesium, and sulphur as well as micronutrients that include iron, copper, zinc, molybdenum, manganese, boron and chlorine.
Mugerwa explains that plants exhibit characteristic symptoms when a nutrient is insufficient.
“These symptoms can be used to diagnose the nutrient deficiency and decide remedial actions,” he says.
He prefers to use digital kits which are available at Kawanda and Makerere University College of Agricultural and Environmental Sciences. A comprehensive soil test at these stations can cost between Shs70,000 and Shs150,000.

He cautions on taking the right soil samples for testing by recommending a representative sample which is obtained by creating imaginary diagonals in the garden. The collected samples from about eight spots can be mixed and flattened, preferably, in a basin. The sieving goes on by continuously dividing the sample until one has a few grams to take to the lab. But he cautions that samples depend on the kind of crops one wishes to plant. For guavas and citrus, or any plants that have tap roots, the farmer may dig for samples from the top soil.
Mugerwa stresses that it is essential to obtain a nutrient element analysis of the manure too, before it is used. “Testing soils removes all guesswork. But even manure can be tested to be sure of the proper nutrients being added to the soil,” he recommends.

Management
Organic fertiliser, which is derived from residues of plants, animal and human waste forms the basis of manure production. Mugerwa explains that farmyard manure nutrients normally depend on the nutrient content of the feed given to the animals. This makes it variable in its application although it can be effectively applied in the field before or after sowing the crop. Poultry manure though, has high levels of nitrogen and phosphorous while low on potassium, which is an essential nutrient for plant growth. According to him, such manure needs to be applied in areas that are deficient in nitrogen and phosphorous.
Liquid manure, which is made by soaking animal dung, chopped grass, small tree branches and fermenting human and animal urine for 14 days, is essential for foliar application.

He cautions though that it should be diluted before its application. For leafy crops, he recommends using a ratio of 1:2 meaning for every 20 litres of manure, 40 litres of water should be added. For other crops such as maize and bananas, he suggests a ratio of 1:1. For busy farmers, Mugerwa recommends the use of homemade compost where manure or weeds can be used to replenish the soil. On his demonstration garden basket, he uses banana stalks to create a kind of fence for the manure. It can be deposited until it fills. He says that when the manure is ready, it can feed bananas while at the top, vegetables can be grown to supplement the family diet. Another method he points out is the labour intensive four-pit to compost manure. Trenches or pits of about one metre deep are dug; the breadth and length of the trenches can vary according to the availability of land. The trenches should have a sloping floor to prevent waterlogging. Organic residues are put in alternate layers.
After filling, the pit is covered with a layer of refuse of 15-20 cm. The materials are allowed to remain in the pit without turning and watering for three months. During this period, the material settles owing to reduction in biomass volume. Mugerwa says such a pit should be covered with earth to prevent loss of moisture and breeding of flies. It takes about six to eight months to obtain the finished product when it reaches the fourth pit.

Crop residues is another form organic manure can be available to farmers. Mugerwa explains that the quality of crop residues depends on the crops contributing the residues. For instance, legumes have better quality residues than cereals due to high nitrogen content of more than three per cent in the legumes. He says these can be incorporated as mulch, if not composted just like green manure.

Quality
According to Mugerwa, before crops can be used as manure, it is important to understand the nutrient value they can contribute. Even manure obtained from the same type of livestock can differ drastically in nutrient content.
He says that the quality of animal manure depends so much on the age of the animal, the quality of feed as well as manure management.
He says that farmers need to understand the limits of each crop before considering manure aplications, as different crops react differently to high levels of certain elements.
He illustrates that among crop residues, sweet potato leaves have a high nitrogen content estimated at about 2.3 per cent.