By Keotshepile Kashe, Oarabile Mogobe, Thebeetsile Moroke & Mike Murray - Hudson.
Flood recession agriculture involves reliance of moisture left in the soil as flood water recede (Barrow, 1999). It is based on residual moisture and natural fertilization of the floodplain. Many rivers around the world are quite large with seasonal flooding to support flood recession farming (Adams, 1993). In Southeast Asia, dry-season flood-recession rice is an ancient land-use system that, taking advantage of the fertile silt deposited by the annual floods, is both extremely productive and sustainable (Fox and Ledgerwood, 1999). In the Sahel, there is river Niger in Mali and Lake Chad, and in semi-arid Africa, there is Sudd in Sudan and the Okavango Delta in Botswana (Adams, 1993).
The Okavango Delta of northern Botswana is possibly the most pristine of Africa’s large wetlands (Gumbricht et al., 2004; Kgori et al., 2006), and support a major tourism industry and communities’ livelihood (Gumbricht et al., 2004; Wolski and Murray-Hudson, 2008; Magole and Magole, 2009; Kgathi et al., 2012). It was declared a Ramsar site-a wetland of international importance in 1997 and was recently inscribed as a Natural World Heritage site in 2014. This wetland is supplied by the Okavango River, which flows from the tropical highlands of Angola into Kalahari basin (Bauer et al., 2004). The river discharges about 10 km3 of water onto the delta each year, supplemented by about 6 km3 of rainfall, which supports about 2500 km2 of permanent wetland and up to 8000 km2 of seasonal wetland (McCarthy, 2006).
Flood recession farming is an important livelihood activity for the poor riparian communities in Africa and some parts of Asia. This farming system provides moisture conditions similar to irrigated farming and utilises residual moisture retained within the root zones of crops. The unlimited moisture in flood recession farming makes it more sustainable and profitable as it produces more yield than dry-lands farming. It has no costs associated with inputs other than land and labour, and consequently, has a very high net return to energy expenditures (Saarnak, 2003). In the Ngamiland district of Botswana flood recession farming locally known as molapo farming is practiced along the edges of the river channels or seasonally flooded depressions on fringes of the Okavango Delta (Bendsen, 2002).
Planting of crops start in September when floods start to recede. Maize is the main crop grown in molapo farms, with secondary crops such as sweet sorghum, sorghum, beans, pumpkin and watermelons (Bendson, 2002; Vanderpost, 2009). Maize is the main staple food for countries in Southern Africa as they depend on it for more than half of their calorie intake (Setimela et al., 2010). In Botswana, it is the most cereal consumed and supplies a larger percentage of the daily calories in most of the diets of Batswana (Lekgari and Setimela, 2002). DAR (2011) report indicated that the total hectarage for Ngamiland was 9,899 hectares of which 10% (987) was under molapo farming. Yields from molapo farms, although lower than the expected yield, are much more than those obtained from dry-land farms (Molefe et al., 2014). In sorghum for instance, grain yield ranges from 1,800 to 2,900 kg ha-1 (Bendsen, 2002; Arntzen, 2005); whereas, under rain fed it can be as low as 121 kg ha-1. Literature on maize grain yield in molapo farms is currently not available, probably due to the fact that most molapo farmers prefer to grow maize as a cash crop where it is sold as green mealies early in the season to get better price before produce from the dry-land farms enter the market.
The climate of the Okavango Delta makes molapo farming much more suitable and sustainable than dry-land farming in semi-arid savannah due to low (~490 mm) and erratic rainfall in the area (Molefe et al., 2014) with high evaporation of 2172 mm a-1 (McCarthy, 2006; Wolski and Savenije, 2006). In addition, most of the Delta is covered by infertile sandy soils with low moisture retention capacity (Mubyana et al., 2003; Motsholapheko et al., 2011). These harsh climatic conditions are the major causes of crop failure in semi-arid dry-land farming. Soils in molapo farms are fertile because of the annual deposits of silt laid down by the retreating floods, and that partly explains why molapo farming is more productive than dry-land farming.
Molapo farming in the Okavango Delta is an important land use and the basis for subsistence livelihoods of the local poor and vulnerable communities (Motsumi et al., 2012) (Figures 1 and 2A, B and C). Despite its significant contribution to rural livelihoods, the productivity of molapo farming has not been extensively investigated. The objective of this study was to evaluate yield potential of maize in molapo farming.
The study was conducted in the Okavango Delta (Figure 3) situated in the northern part of Botswana. The Okavango Delta is the world’s largest inland formed by the Okavango River. The size of the delta varies dramatically from year to year depending primarily on the rainfall in Angola (Kgomotso and Swatuk, 2006; Wolski and Murray-Hudson, 2006). The area covered by water enlarges from its annual low of 2500 to 4000 km2 in February–March to its annual high of 6000 to 12000 km2 in August–September (McCarthy et al., 2004). The variation is closely linked to rain fall in the catchment area of Cuito and Cubango rivers in central Angola, which respectively receives annual rainfall of 876 and 983 mm (McCarthy et al., 2000; Wolski and Murray-Hudson 2008). Local rainfall also contributes significantly to the delta with an annual average of 490 mm (Anderson et al., 2003; Gumbricht et al., 2004), and is one distinct rainy season from November to March (Wolski and Savenije, 2006).