|Irrigation and water conservation|
In order to plant all year round, trial plantations have been conducted, mostly with mukau but also with Jatropha in the dry season. In Kiambere, 1ha blocks of mukau were planted in all months from June to December 2008 or 2009. Jatropha was planted in August and September.
Different watering regimes were tried, with the most satisfactory being 4 to 5 litres per week depending on the month (May - July and November - January being colder, hence 4 litres; and February - April and August - October being warmer, hence 5 litres). To avoid run-off, the water was poured manually into small basins constructed around each seedling. At a moistened area of 20cm diameter, this dose of 5 litres corresponds to a rainfall of 159mm (1mm of water per sq metre being equivalent to 1 litre).
The irrigation was done on a top soil of loamy sand and a subsoil going towards sandy loam. In both cases therefore, a relatively high presence of sand, easily penetrable by water and with relatively low moisture retention capacity.The effectiveness of this operation is however greatly enhanced by mulching. This has not been the subject of research so far, but a grass/weed mulch of 5-10cm thick with a diameter of 50-60cm is applied as a standard measure around one-year-old seedlings. However, this mulching is degraded by termites, and has to be renewed every three months. Plans are under way for trials using chipped wood mulch.
Other measures of water conservation include elimination of competing vegetation and construction of small individual water catchments around each seedling. Indications are that chemical weed elimination by a herbicide (e.g. glyphosate) is more beneficial than hoeing, because of less damage to superficial roots around the seedlings. Using a herbicide also diminishes erosion as the dried rests of grasses and weeds are left standing and act as a break to run-off, thus favouring infiltration of surface water.
Half-moon shaped - and other small catchments - are likely to trap more water, but research is needed to study the effectiveness, including the cost, of other kind of catchments, like negarims.