Thesis colloquium Laura Nienhuis

Looking at effective precipitation and effective soil moisture depletion depth of on farm CA practices. Two main soil management treatments: conventional tillage and no-tillage, and four sub-treatments: 1) 1.5 t/ha maize stover mulch; 2) 3.0 t/ha maize stover mulch; 3) dolichos cover crop; and 4) pigeon peas cover crop with bush pruning mulch.

Organisator Hydrology and Quantitative Water Management

do 23 januari 2014 14:00 tot 15:30

Locatie Lumen, building number 100
Droevendaalsesteeg 3a
6708 PB Wageningen
+31 317 481 700
Zaal/kamer Lumen 1

Establishing possible effects of various Conservation Agriculture practices on the seasonal water balance in the Laikipia District (Kenia)

 Supervisors: R. Dijksma, G.E. van Halsema and B. Okoba

Smallholder farmers in sub-Saharan Africa, who practice rainfed agriculture, are often  in a vulnerable position concerning food production. Highly variable rainfall and not sufficient rainfall are two major constrains in the Laikipia District, Kenya. In order to improve the situation for local farmers it is important that the productivity of rainfed agriculture is upgraded. A way to realize this is by implementing the concept of Conservation Agriculture (CA), which relies on three basic principles: 1) minimum soil disturbance; 2) permanent organic soil cover; and 3) diversified crop rotations. Proponents of CA claim amongst others that it increases yield, improves soil moisture holding capacity and fertility of the soil, and also reduces labour requirements, if the concept is fully adopted. This leaves no room for local circumstances like limited access to herbicides and cover crop seeds or labour constraints, which are often limitations. So, smallholder farmers are  often unable to adopt CA fully. Therefore a need is generated to adapt the concept and getting a better insight in the contribution of the three individual principles to the benefits of CA, i.e. which principle contributes to what extent and to what extent should the principle be applied.

Consequently the study is focused on mulching and no-tillage as components of CA., Effects of various CA practices on the seasonal water balance are investigated. Two main soil management treatments, namely convention tillage (CT) and no-tillage (NT), and four sub-treatments; 1) 1.5 t/ha maize stover mulch; 2) 3.0 t/ha maize stover mulch; 3) dolichos cover crop; and 4) pigeon peas cover crop and bush pruning mulch, results in seven different treatments. These treatments are allocated randomly. The study consist of three on-farm replications. Field measurements such as monitoring soil moisture changes by using a profiling neutron moisture meter, recording precipitation and observing crop performances of each individual treatment through the season contributes to the conducting of a field water balance and the specification of various CA effects.

Despite the experimental set-up no substantial conclusions can be drawn concerning differences between the various treatments, i.e. concerning effective precipitation and effective soil moisture depletion depth, as the period was unexpectedly wet. Therefore no soil moisture stress occurred and no significant differences were perceived. Besides, the analysis made it clear that majority of the access tubes were liable to cavities in the vicinity, which affects the quality of depletion trees. The seasonal water balances per individual plot were consequently based on a relative small amount of soil moisture changes. The depth and quality of the depletion trees were not satisfactory and water balances are inaccurately. So no distinct difference between the seven treatments were visible. Hence data of 2011 is used to investigate potential consequences on a larger area if the concept is adopted by most farmers in the area. Although most CA treatments show a reduction of outflow in terms of runoff and deep percolation on plot scale, the consequences on a larger area are site specific and the up-scaling should be carefully executed.