Water harvesting and use of technologies that ensure there is plenty of moisture in the soil for crops to grow is part of climate-smart farming, which aims at increasing agricultural productivity and incomes.
There are different methods one can use to harvest water and ensure the soil retains plenty of moisture, especially in arid and semi-arid areas. These are:
Zai (planting) pits:
They are shallow pits used for harvesting water and conservation of moisture in the soil. Once the pits have been dug, one puts in organic matter like manure or compost to increase microbial activities and water infiltration of the soil when it rains.
The pits are good for planting cereals like maize, sorghum, millet and fodder crops in dry areas. Zai pits help improve water and nutrient use, reduce surface run-off and nutrient depletion.
They are 50cm wide and 50cm deep and are dug along a contour for use in growing bananas. If larger pits are dug, they can be used for growing trees. The ditches help in trapping rainwater.
They are 1m by 2m by 0.25m and are dug in sloppy areas so that water can collect in the pits during the rainy season. The pits help in conserving water, reducing run-off and preventing soil erosion.
They are barriers constructed across a river to collect and hold large volumes of water. The stored water can then be used for irrigation during the dry season.
They are barriers constructed across a river to raise the water level and allow it to flow over it. Water from the weir can then be pumped to farms for irrigation purposes.
Water can also be harvested from rooftops and directed into a storage tank or reservoir.
Besides use of technologies like zai, mulching also helps in soil water retention. It has many advantages in crop production. These are:
• It reduces spread of diseases through splashing of pathogens from soil.
• It conserves moisture thus reducing irrigation requirement.
• It reduces evapotranspiration and erosion.
• It increases microbial activity in the soil.
• It increases soil nutrient status
• It improves soil organic matter hence the soil structure.
However, organic mulch is a risk, because it may harbour snails, slugs and rodents and may trap light rain showers, thus prevent them from reaching the crops.
Synthetic or plastic mulches are the alternative and come in different colours such as clear, yellow and black. Black plastic mulch works well in pineapple growing and the results have been good.
Growing of cover crops is another practice that helps conserve soil moisture. The crops include sweet potatoes and pumpkins, which ensure the soil is covered hence reduce moisture loss by evaporation and soil erosion.
Mutua is based at the Department of Crops, Horticulture and Soils, Egerton University