Improving manure management of small-scale dairy farms in Kenya: Results and experiences of on-farm trials

With a panel of Kenyan and Dutch experts, the NEADAP team selected feasible options with economic potential for piloting on small-scale intensive dairy farms. Cooperation was established with Kiambaa and Limuru dairy cooperative societies in Kiambu County, Kenya. Suitable farms were selected, along with the management and extension staff of the cooperatives.

The following options were trialled or demonstrated and compared with the farmers’ practice on either one or more of the farms:

• Use of covers: i) storage of manure in manure sheds with a (semi)-permanent roof (iron sheets, canvas), ii) manure pile covered with polyethene sheet, iii) manure pile covered with banana leaves; all these treatments were compared with open storage of manure;

• Composting of manure: i) aerobic heap composting, ii) semi-aerobic pit composting; these treatments were compared with the farmers’ practice of drying/piling manure;

• Pit composting of bio-slurry: adopted from the system advocated in Ethiopia;

• Application of manure: incorporation of manure into the soil compared with superficial application. This was demonstrated and only farmers’ opinions were collected.

Some pre-trials were conducted in 2022. Thereafter the trials were implemented by NEADAP staff in cooperation with the farmers and extension staff during the dry and rainy seasons of 2023.

Nutrient losses for the trials with covers and composting were recorded by weighing and sampling the manure, the additional materials and the final products. Samples were analyzed at the Mazingiri Lab at ILRI, Nairobi.

The manure used for the on-farm trials was collected from the dairy cattle kept in the zero-grazing units of the participating farms and stored for a few days. It had on average a dry matter content of 20% and contained 3.8 kg nitrogen (N) and 2.2 kg phosphorus (P) (5 kg P₂O₅) per 1,000 kg ‘fresh’ manure. The manure consisted mainly of dung. Table 1 shows the composition on a dry-weight basis.

Use of covers

Data on nutrient losses on some farms were affected by probably weighing errors and/or an overestimation of the dry matter contents due to sampling errors. This made the data unreliable. But even taking this into account, the more open the storage, the greater the losses. That is, the losses ranked from least to the highest loss were in the following order: polyethene sheet < open roofed shed < banana leaves < open storage. Storage under banana leaves was less effective as the leaves had to be replaced during the trials.

Composting

Nutrient losses in some of the composting trials were also affected by weighing errors and/or a probable overestimation of the dry matter content. On two farms, the farmers’ practice of drying/piling the manure during the dry season led to minimal loss of dry matter (less than 5%) and organic matter (less than 10%) and N losses of up to 22%. This was considerably lower than with aerobic heap composting.

The results from the data on pit composting with manure were too variable to draw conclusions. The results of the composting trials during the wet season were also variable.

Aerobic heap composting of manure with other organic materials led in general to a larger amount of organic fertilizer than when the manure was dried or piled. This was a result of the addition of other (organic) materials to the compost heap. However, the quality on a dry weight basis appears to be lower (lower contents of organic matter, N and C). Heap composting of manure with other organic materials is therefore attractive and beneficial only when these additional organic materials are available. Composting has the advantage that the end product is stable and hygienic, with weed seeds and pathogens being killed by the increase in temperature. Aerobic composting requires also careful management to minimize losses throughout the composting process. Critical factors are the moisture level in the heap, ventilation (oxygen supply) and the C/N ratio of the materials added. If these critical factors are not up to standard, the composting process may be very slow and/or nutrient losses high.

The results of the pit composting with bio-slurry were not conclusive. The end product was easier to handle than the ‘fresh’ bio-slurry.

Opinions of farmers and extension staff

During a focus group discussion with farmers and extension officers, the participating farmers were positive about the results of the trials and mentioned the following:

• A manure shed during the rainy season was more effective in drying the manure than open storage.

• A cover with a polythene sheet gave better quality manure and the manure showed better results when it was applied on land.

• The bio-slurry was better to use with composting and gave a better growth result when used on vegetables.

• Heap composting during the rainy season took less time than drying.

• Incorporating and/or mixing of liquid manure and/or bio-slurry into the soil gave better results on Napier grass.

• Composting needed less space (area) than drying, and this area could be used for growing crops.

The extension staff expressed their concerns about the economics of the use of covers and composting. They also mentioned the following challenges related to composting:

• It needs much attention, extra labour and regular water supply.

• It relies on the availability of green materials (difficult in the dry season) and dry vegetative materials (difficult in the rainy season).

• It takes longer than the drying of manure before the end product is ready for use.

Based on the results of the pilots and other research we present the pros and cons of the options piloted as shown in Table 2.

The pilots showed that it is difficult to measure nutrient losses of manure management practices by means of on-farm trials due to the heterogeneous nature of the manure and/or compost. Experiments to measure nutrient losses should better be done under carefully controlled conditions.

There is no one-size-fits-all solution for improving manure management. Adoption of improved manure management methods will depend on whether they suit farmers’ situations and goals, taking into account the motivation and resources (labour, capital) and potential economic benefit. Creating awareness of the value of manure, a good analysis of the farmers’ situation and advice on feasible improvements will result in better adoption.