Sunken beds reduce frost losses

Sunken and raised seedbed phot by Pushpandra Singh.jpg

Crops growing on a sunken and raised seedbed. Sunken seedbeds can help farmers reduce frost losses. Photo by Pushpandra Singh.

Farmers living in frost prone areas can reduce losses due to dehydration by growing susceptible crops in sunken seed beds, whose soil is warmer than the surface.

Apart from reducing the amount of water required for irrigation, the sunken seed beds also help in protecting crops such as peas, beans, dolichos, French beans among, others against harsh weather.

Tea, coffee and other perennial cash crops are susceptible too.

“Places like Limuru experience frost, which at times leads to scorching of peas, beans and other short season crops. Loses of up to 100 per cent can be recorded on severe occasions. But sunken beds are warm and they least expose the stem s to the adverse cold drops,” Agronomist Patrick Nyauma said.

The cold season has set in Nairobi and most Central and Rift Valley regions will experience low temperatures until about August. The weather will remain gloomy for most days.

After cold seasons, clear, calm and dry nights cause the freezing of the atmospheric suspended water droplets to below 20C.

The cold droplets, which form ice, fall on the ground to cause loss of heat from the soil. When the ice falls on the crops, it cause the leaves to lose water. The water lost from the cells is bound into ice, leaving the crops ‘thirsty’ in two to three days. The leaves and herbaceous stems turn brown.

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The sunken beds are about one or more feet deep. The rate of heat loss in the trenches is slower than the surface. That means even if freezing water droplets are deposited in the banks, the fairly warm condition would turn them into liquid water.

The sunken seed beds are prepared by digging out the top soil, which is mixed with manure and other organic matter before being taken back into the trench.

The manure not only helps in binding the soil particles, but also improves the soil texture as well as the water retaining ability, Nyauma said.

Given that the base is ‘hidden’ away from long hours of the direct sunlight, loss of water is minimised. In controlling leaching of minerals, other farmers prefer laying a polythene lining before replacing the soil into the trench.