Cultivation

6.3 Cultivation

In order to adhere to the recommendations for the conservation of peatlands, the wisest measure would be to avoid cultivation. However, this choice does not correspond with the living conditions and necessities of the local people, nor with their rights. Therefore, recommendations need to be given, which conform to the local realities - i.e. which serve to mitigate degradation of peatlands and yet still allow smallholders to sustain themselves.

Peatlands in Maputaland are favoured grounds for cultivation, because other local soils generally consist of dune sand with low field capacities and low nutrient statuses (Grundling A. et al. 2016).

Peatlands, on the other hand, are fertile grounds and, unless they are located in interdune depression, their water table can be controlled by drainage ditches to achieve a desired depth.

Associated with drainage, however, is the process of peat subsidence (Chapter 4). A farmer who drains a peatland to a depth of 50 cm below the surface level may lose 10-20 cm of peat soil within a few years, and thus she will then need to deepen the drainage ditch again, in order to once again have 50 cm of dry soil. Unless alternative cultivation practices are established, which change the traditional drainage ditch cultivation practice, peatlands will face huge volume losses and degradation within the next decades.

The first recommendation, therefore, is the cultivation of the peatland fringes instead of the peatland centres (Figure 6-2). The nutrient status in the transitional zone between peatland and

dune is considerably higher than in the dune soils (Potential cation exchange capacity: transition zone = 17 cmolc/kg, with 12% organic matter [N=6]; dune = 2 cmolc/kg, with 0.7% organic matter [N=5]; unpublished results from the field campaign 2012). Thus, the transition zone will be able to support a wide range of crops. Pfister (2016) indicates that, of the commonly used crops, the following are capable of growing in the transitional zone: beetroot (Beta vulgaris), cabbage (Brassica oleracea), carrot (Daucus carota), cassava (Manihot esculenta), cowpea (Vigna unguiculata), lettuce (Lactuca sativa), maize (Zea mays), onion (Allium cepa), pepper (Capsicum sp.), pumpkin (Curcubita sp.), sugar cane (Saccharum officinarum) and sweet potato (Ipomoea batatas). As the water levels in the transition zone are usually several decimetres below the surface, this puts them in the same range as drained sites.

Figure 6-2: Alternative cultivation practice in valley-bottom peatlands. Left: Conventional cultivation in peatland centre with drainage ditches and degraded topsoil. Right: Sustainable cultivation at fringe of healthy peatland.

Even if drainage is not eliminated, the blocking of drainage ditches on a seasonal basis will mitigate peat mineralisation. It should become standard practice to block drainage ditches after the cultivation on a drained peatland is complete, to avoid the subsequent continuation of peat mineralisation.

In interdune depressions, drainage ditches do not work, due to the enclosed shape. Cultivation is usually practiced on raised beds, in order to get 30-50 cm distance between the soil surface and the

water level. Organic matter is once again, in this way, exposed to aerobic conditions and subject to mineralisation. Once again a more sustainable way of cultivation is the use of the fringes. As water in interdune depressions cannot drain readily, the risk of inundations is higher here than in other HGMTs. This can badly affect or even destroy the harvest when crops become inundated (see Figure 6-3).

Figure 6-3: Harvest loss due to inundation in the central part of an interdune depression (26°56’47.83’’S, 32°48’57.18’’E). Left: raised bed with sweet potato (Ipomoea batatas) and cassava (Manihot esculenta);

picture taken 16 Jan. 2014. Right: raised bed flooded and plants drowned; picture taken 28 Feb. 2014 (pictures do not show precisely the same spot, but both were taken in the central part of the same interdune depression).

To reduce the risk of harvest losses through inundation, cultivation should be adapted to suit seasonal water table fluctuations (Figure 6-4). Before the wet season, the upper part of the transitional zone should be planted with crops which do not need more than half a year to grow to a mature state. After the wet season, the lower transitional zone can be seeded, following the receding water table.

The use of fire to eradicate weeds should be entirely abandoned. Particularly during the dry months from April to September, the risk of peat loss to out of control fires is high. Drained peatlands, with dry surfaces, are prone to this risk even during the wet season. Instead of being burnt, as part of the preparation of the plot, weeds might be cut and put on the surface as mulch, thereby protecting the soil from insolation and loss of humidity.

Paludiculture - the cultivation and harvesting of plants on water saturated peatland soils - should be considered as an alternative to traditional cultivation. Taro (Colocasia esculenta), locally known as idumbe, can be cultivated under inundated conditions, if the water is running and therefore providing dissolved oxygen (Onwueme 1999). Therefore, on the fringes of streams in channelled valley-bottoms, the cultivation of Taro is possible without the need to alter the peatlands hydrology.

Likewise, without any hydrological alterations being made to the peatland, other non-edible plants have for a long time been harvested for medical uses, weaving products and construction material (Grundling et al. 1998). A good example is the mid-ribs of the leaves of Raphia palms, which are a very light and very robust construction material. Fallen palm leaves are collected without harmful consequences for the ecosystem.

Figure 6-4: Adaptation to seasonal fluctuations at the fringe of an interdune depression: cultivation should move up and down in the transition zone.

Last but not least, melioration of the common arenosols of the dunes can also represent an alternative to subsistence farming on peatlands. Locally little known techniques such as mulching, and the preparation of compost soil from organic household waste are able to enhance soil nutrient statuses, increase water holding capacities, and reduce water losses by evaporation. In addition, they would provide local subsistence farmers with the convenience of establishing plots next to their own houses.