The Future Okavango
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Ongoing Research

SP03 - Report on research activities

1. Introduction

Fig. 1: Overview of the spatial distribution of the TFO Research sites along the Okavango catchment
This report gives an overview of research activities conducted in 2011 at the TFO research sites (Fig.1). The first field trip for soil surveys took place in March/April at Mashare (Namibia) and Seronga (Botswana). On the second field trip in September/October 2011 the soil survey of the Angolan site in Chitembo was done and first field measurements and device installations regarding carbon dioxide and soil water dynamics were realised on each research site. Beside the field work numerous soil parameters are already analysed in the laboratories in Germany as far as soil samples were available and in Botswana. To implement sustainable land use techniques a conservation agricultue training program with an additional trial of soil amendments was initiated on small scale agricultural sites in the Mashare region.

2. Soil Survey

On the basis of prestratified point grids, according to land use and landscape units, for every core site sampling points were identified for a later field survey. The points chosen are located on nearly perpendicular transects to cover the spatial heterogeneity of soil types within the different landscape units (Fig. 3 a - c). On each sampling point a pit was dug to a depth of at least 85 cm and the resulting profile wall was subdivided into horizons. These horizons were described according to their colour, texture, bulk density, humus and carbonate content as well as their root density and distribution.

Fig. 2: Soil scientist at work
Fig. 3 a-c: spatial setting of the soil survey transects with sampling points (effective 27.10.2011)
Outlined area show spatial extend of the core site (5 x 20 km2)
a) Chitembo, Angola - Two transects going E-W through the valley of the river Cusseque (1st order) and one in N-S direction through the valley of a tributary river (2nd order)
b) Mashare, Namibia - One transect is going E-W along the Okavango riverside and on with N-S extension into the dry forest area of the Kalahari Duneveld
c) Seronga, Botswana - The extension of riverside parallel transect is here in NW-SE direction with two perpendicular transects going into the hinterland

In addition to soil related parameters topographic features like slope inclination and curvature as well as vegetation composition were recorded. When lab analysis is done it is possible to describe preliminarily results regarding soil physical and chemical properties (an example is shown in fig. 4).

Fig. 4: Example of a soil profile description at a field of the Mashare Agricultural Development Institute. Mashare/Namibia

3. Field Measurements

On the basis of the soil survey six different locations for detailed analysis regarding soil water balances and dynamics were already chosen. At these spots volumetric soil water content and soil water pressure heads are logged twice a day at depths of 10, 20, 40, 80 and where possible 160 cm. Combined with weather data and laboratory analysis these measurements will be used to calibrate soil water balance models like SWAP and Hydrus 2D/3D.
Fig. 5: Soil water measurement devices installed in a profile in Chitembo / Angola

Grey Probes: TDR Probes to measure volumetric water content (ML2x Theta Probes by Delta T Devices)

Green Probes: Gypsum block like probes to measure soil water pressure heads (Watermark)

Pink Probes: Temperature probes (Watermark)
To quantify soil carbon stocks and the dynamics between soil related pools and the atmosphere carbon content, CO2-efflux measurements were conducted. Efflux measurements with a mobile closed chamber device (LiCor 8100A) allow flux quantification of CO2 per surface unit. This technique was already applied at the core sites Chitembo, Mashare and Seronga, whereas soil gas profile analysis to gain information about microbiological activities throughout the year was conducted at the Namibian core site.

Fig. 6: CO2-Efflux measurements with LiCor 8100A device and closed chamber on a fallow acre in Mashare / Namibia

4. Laboratory Analysis

Fig. 7: Changes of pH and total carbon amounts along the N-S transect at the core site Mashare / Namibia
Several soil physical, chemical and biological parameters were determined in the laboratory including pH as well as total carbon storage, as shown in figure 7. Preliminary results indicate that the soils dominated by sand in the Kalahari Sandveld show low pH-levels in combination with very low total carbon content in contrast to the more loamy soils near the riverside with higher pH due to the existence of calcretes in depressions between levees. Soils with higher total carbon content in the Kalahari Sandveld can be found in dry river beds where insufficient aeration leads to a reduced decomposition of organic matter.

5. Farmer Training

After the selection of willing farmers in the Mashare area, the training on conservation agriculture techniques began during the dry season 2011. The aim of these techniques is to improve rain-use-efficiency and nutrient supply by using the same spots for seeding every year. Two different techniques were applied, depending on the availability of draft animals. Where oxen had been available rip lines were drawn (Fig. 8), if not, basins were dug by hoes (Fig. 9). After preparing the fields, test amendments were applied to the sub-plots. These amendments consist of various fertilizers, effective microorganisms, molasses and husks (Fig. 10). At the end of the cropping season 2011/2012 the comparison between yields and crop quality of treated plots and conventionally cultivated plots will give first information about the suitability of these techniques and amendments to this area of Namibia.

Fig. 8: Drawing rip lines by oxen for conservation agriculture

Fig. 9: Amending trial plots with lime

Fig. 10: Adding fermented millet husks to basins