Wednesday, January 4, 2012

Growing Sweet Potatoes in Kenya: Mounds Versus Ridges?

I have been always been asked this question many times on the best ways to cultivate sweet potatoes. Which one produces the best yields, planting on mounds or ridges? While in the 90s, most of the sweet potatoes was cultivated in mounds the trends has shifted more and more towards ridges in the recent years due to the commercialization of sweet potato cultivation.

The mounds had several advantages. One was that it produced very huge round tubers with less fibres on the inside. The sweet people grown in mounds was also free from weeds as the soil was carefully prepared by hand and shaped into a fine mound for the planting of vines. Since the soil was so carefully prepared, planting on mounds proved was quite easily and did not cause injuries to the hands. Most of the farmers in rural areas do not have gloves and use bare hands to insert the sweet potato vines into the mounds of soil.

Another advantage of using mounds was that there were less weeds and hence less labour force in weeding.
A disadvantage of the mound was that it was very labour intensive; preparing a mound required careful arrangement of the soil and deep digging to ensure the tubers produced were huge and round. Normally, preparing one mound alone could take even 20-30 minutes hence it was not suitable for large scale farming.

In the 90s most of the sweet potato cultivation was small scale and sweet potatoes was mostly produced on a subsistence basis.  Labour costs in the 90s were also quite low. Another disadvantage was that planting sweet potatoes on mounds led to soil erosion, particularly in hilly areas or when water accumulates in pools on the farm leading to leaching i.e. soil nutrients dissolve in water and permeate deep into the soil beyond the reach of the roots leaving the soil barren.

As a result, most farmers have now adopted ridge cultivation of sweet potatoes. Ridges cultivation is an ancient form of farming, still common in many parts of rural Africa. The ridges are simple "continuous mound" made using an ox-drawn plough which creates a pattern of ridges and ploughs. Ridges were used in Europe from the Middle Ages until the 19th Century, in the America's they were used until the 20th Century and are still used in many parts of North America, Central America and South America. Ridge farming is also common in many farming communities in Africa and Asia.

It involves pairs of oxen or horses pulling a plough across a farm to form little hills of ridges and troughs. For sweet potatoes, the plough should be sharp and should cut deep into the soil to give the sweet potato tubers room for expansion. Normally, the deeper and bigger the ridges, the bigger the sweet potato harvest. Mechanized farming of sweet potatoes is still very elusive since many farms are small holder parcels of land varying in size from quarter of an acre to 20 acres.

With two pairs of oxen, you can make create ridges in an acre of land in two or three days. If the soil is soft, and with a n adequate labour force, you can plant the sweet potato vines on an acre of farm in just one or two days. So normally it takes the small holder farmer just one week to cultivate sweet potatoes in an acre of land. If you were  using mounds and with similar resources and labour force, it would probably take you three weeks.

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