Project addresses soil fertility and yield challenges of sweet potato production in the high altitudes

Preparation of compost mounds

Preparation of compost mounds

Project activities at the Alkena and Kiripia sites are well into developing a protocol for technologies, with the intention to improve soil fertility and productivity of sweet potato mound and tuber yield as part of farmer interventions.

Sweet potato is the staple food crop for the high altitude highlands areas however its yields have declined over the years due to a number of factors including continuous cultivation of the same varieties over generations; pests and diseases (weevils, scab and virus); high rainfalls with high and prolonged cloud cover; increased population, and limited options for improved fallow.

Deficiencies of potassium (K) and phosphorous (P) in volcanic soils give poor crop yield in older sweet potato gardens. These deficiencies are attributed to repeated cycles of sweet potato cultivation and nutrient removal by tubers and vines that contain high amounts of K and S or through the burning of weed and crop residues that release S (SO2) into the atmosphere.

Sweet potato needs moderate nitrogen (N) and low phosphorous (P) and is a high user of potassium (K). P is required for good root development, and sweet potato extracts P from the soil. This characteristic is good in the volcanic soils in the highlands.

Farmers under these environmental challenges have developed the compost mounding system to plant sweet potato where large quantities of dry biomass are used and soils are added to make these mounds. Materials added to the compost vary from place to place but the commonly used are weeds and Mischanthus Spp dry leaves, even Imperata cylindrica.

Studies are conducted under this project to assess the effects of fallow periods and compost material type on productivity of sweet potato mound and tuber yield of sweet potato variety at the Alkena and Kiripia sites. This study will look at the;

  1. effects of different fallow periods on tuber yield of common sweet potato varieties,
  2. effects of different plant species and compost types on yield of common sweet potato varieties, and
  3. interaction of different fallow periods, plant species and compost type on yield of common sweet potato varieties.
Dried Mexican Sunflower compost material

Dried Mexican Sunflower compost material

The different fallow periods under study are zero fallow, six months fallow and more than a year’s fallow. The compost materials used are Miscanthus Spp (pitpit), local vegetation (whatever plants found growing near the site), and Tithonia diversifolia (Mexican Sunflower).

To assess the common cultural practice of trash burning before constructing mounds; sweet potato mound craters were placed with the compost materials and burnt while similar treatments was left unburnt (control).

Soil samples taken before the studies in these sites showed very low levels of P, and K under acid soils, which are the characteristics of a typical high altitude volcanic soil. Field days will be conducted during harvests and farmers will be trained on the importance of fallow periods, compost materials, sweet potato variety and burning of trash before constructing sweet potato mounds.


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