How to make your soil give you higher yields

It is common knowledge that the challenges of climate change and variability are affecting many sectors of Kenya’s economy. Previously, drought and famine used to occur in a predictable cyclic pattern of 10 year intervals, allowing for disaster preparedness.

This is no longer the same as drought, crop failure and famine have become more frequent and irregular.

In addition to the complications brought about by scarcity of water, simple commercial irrigation systems that can be used for mitigating the impact of drought on crops that are often too expensive for smallholder farmers.

Even under rain-fed systems, farmers can manage the impacts of droughts on crop performance through best management practices for water and nutrients. Whilst most agricultural areas receive more than 1200mm of rainfall, a crop of maize, beans or tomatoes will perform optimally to maturity with between 300 and 600mm of rainfall. In most instances, managing losses of such water can provide sufficient water to support crop growth to maturity.

At the core of adapting smallholder farming systems to changing climate is understanding the interaction between soil, water and nutrients. Healthy soils with high organic matter hold water and nutrients, allowing plants to utilise them for various growth stages. For example, good soil could hold and supply crops with water from one good rain day for more than three weeks. In contrast, poor soils will lose water more easily, leading to early water stress.

Just as best fertiliser recommendations are site specific, climate adaptation techniques may also be regional specific. For example, in Meru, Embu, Nyeri, Maragua and other regions where farmlands are steep, the steep sections of the farm could lose in excess of 100 tonnes of soil per hectare per year from erosion. Sudden, high intense rainfall, which is a common characteristic of climate variability, could double the amount of soil that is lost annually from such farms.

Such loss of top soil is also associated with huge nutrient losses and exposure of subsoil that restrains crop root growth and which is poorer in water retention capabilities. Crops grown in such soils are more prone to moisture stress even when the duration of rain delay is short. For such soils, the strategy should be to manage soil organic matter and nutrient through soil conservation so that healthier soils can hold water and nutrients for a longer time for crops to use.

Other technologies for this and other arable regions include intercropping and rotation of legume with cereals. In addition to improving soil fertility and reducing soil erosion, intercropping and rotation ensures better soil cover, reducing soil moisture losses by evaporation.

Acidic soil is a common concern in over 30 percent of agricultural land in Kenya, often reducing crop yields by more than 20 percent in spite of fertiliser application. Soils tend to acidify when they are low in organic matter and soil organic matter can be enhanced through application of manure and crop remains.

By appropriate and regular application of organic resources, it is therefore possible to simultaneously reduce soil acidity and improve soil water holding capacity. Farmers should target getting a very good crop during the best season and preserve for drier season.

This can be enhanced through the use of climate forecast data to inform decisions to apply sufficient nutrients during the season with better chances of good crop.

Data consolidated by the Alliance for Agricultural Revolution in Agriculture-funded Kenya soil health consortium and the International Plant Nutrition Institute (IPNI) show that for regions like Makueni, Tharaka and Gachoka, farmers can harvest over 40 percent more maize if climate information is made available to them in good time.

When the forecast shows lower expected rainfall, such farmers can grow crops like pigeon peas, cow peas, green grams and watermelons which are more tolerant to moisture stress.

Farmers can also dig holes known as Zai pits to help conserve water.

Two to four feet in length, breadth and height, Zai pits are simple but effective technologies for harvesting rain water for use by plants beyond the rain duration.

Once a pit is dug, it is filled with a compost of leaves and stems and then topped with manure. It holds water and the food is grown on top.

Through a combination of Zai pits and appropriate nutrient management farmers in semi-arid regions of Kenya are producing maize, mangoes and other crops profitably even during the drought periods.

Climate adaptation strategies that are based on water and nutrient management will function even better when access to appropriate inputs like fertilizer is assured at the most appropriate time, so as to match the timing of rainfall with appropriate seeds and fertilizers during the crop planting phase.

Dr. Mutegi is a soil scientist and farming systems analyst at IPNI Sub-Saharan Africa Program, and a Project Manager, Soil Health Consortia for Eastern and Southern Africa.  [email protected]