The what of
•Water and soil conservation
•Increased soil fertility and
The how of trench beds
•Bottom porous layer; tins, branches
•Layers or mixtures of: dry organic material, green
wastes, manure, ash, lime, bones and soil to ground
•Build up 30cm mixture of topsoil and manure –
shape for water conservation and planting seed.
Sequence cont; Clockwise –soil, water, next layers.
Finalise seedbed plant multipurpose plants, water.
The why of
•In the ‘normal beds’, where manure is incorporated into the topsoil (S1n, D1n,
•the pH was almost neutral on the soil surface (e.g. pH=6.41 for Sizakele's normal
bed),but pH was quite low (acidic) deeper down in the soil (e.g. pH=4.09 at 20
cm depth;and pH=4.29 at 50 cm depth for Sizakele's normal bed).
•In the trench beds, pH was close to neutral throughout the profile (i.e. at all
•after one production season.
Acidity in Sizakele (S), Dladla (D) and Ketiwe's (K) normal and trench
beds (JD Sturdy, 2008)
increases phosphorus in the soil
•Phosphorus quantities were very low in deeper soil layers in all non-trenched
•The lowest phosphorus values are shown in red = the least favourable
conditions. The dark-yellow columns showthe resultsfor trenchbeds. In
Sizakele’ trench bed the
•phosphorous was high at the soil surface as well as at 30 cm depth (72 mg/l),
•Ketiwe’s trench bed it was also very favourable (98 mg/l). The highest
phosphorus isshownin blue = favourable.
gives good potassium levels in soil
•Deep trenching has improved the levels of potassium (K), probably mainly
through the incorporation of wood ash during trench packing/construction.
Potassium dissolves readily and can therefore move through the soil profile, but
is not as volatile as nitrogen, and can therefore accumulate in the soil for use
over longer periods.