ABSTRACT

Flood recession farming locally known as molapo farming in the Okavango Delta is practiced along the edges of the river channels or seasonally flooded depressions on its fringes. It relies on residual moisture and natural fertilization of the floodplains, and is promoted as being more productive than dry-land farming. However, the productivity of this low-input farming system has not been extensively investigated. The objective of this study was to evaluate the yield potential of maize (Zea mays L.) in molapo farming. Two molapo field experiments and one dry-land experiment were conducted at Matsaudi and Lake Ngami, and Shorobe, respectively, in a randomized complete block design with four replications. Maize grain yield and plant height were measured from six consecutive plants from the centre row. The results showed that maize grain yield and plant height were significantly (P < 0.05) higher at Lake Ngami than at either Matsaudi or Shorobe. Late planting at Lake Ngami coincided with rainfall in November providing even and abundant soil moisture which contributed to better productivity of maize. Similarly, soil fertility was also better at Lake Ngami. Maize grain yield although lower (2.41 t ha^-1) at Matsaudi and Shorobe (2.58 t ha^-1) than at Lake Ngami (3.4 t ha^-1), it is much higher than yields normally obtained by small-holder farmers in semi-arid zones in sub-Saharan Africa, where yields are often less than half of the potential yields. Similarly, plant height was significantly (P < 0.05) higher at Lake Ngami (235 cm) than either Matsaudi (194 cm) or Shorobe (192 cm). It could be concluded that timely planting of maize in molapo fields supplemented by rainfall is capable of producing better yields in semi-arid regions where water is the most limited resource to crop production

Key words: Flood recession farming, dry-land farming, Okavango Delta, maize, yield.

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.

 

Study area

 

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).

 

 

As stated earlier, the inundated area varies in size from year to year. This seasonality of inundation gives rise to three major hydro-ecological zones, namely: permanent swamp, seasonal (regularly flooded) floodplains and occasional floodplains (Wolski and Savenije, 2006). The seasonal floodplains are areas where molapo farming (Figure 2) is practiced (Oosterbaan et al., 1986).

 

 

 

The actual study sites were Matsaudi (19°49'31.2''S, 023°36'19.5''E) and Shorobe (19°44'34.8''S, 023°41'27.7''E) along the Thamalakane river and Lake Ngami (20°30'28.1''S, 022°47'06.7''E) (Figure 3). The sites were selected because of their contrasting hydrology.  Lake Ngami   is   the   terminal   end   of   the Okavango Delta and floods recede slowly from molapo fields resulting in late planting mostly in November. In Matsaudi, molapo fields are along the Thamalakane River and flood recession starts early giving  farmers  an opportunity to plant early in September.

 

Shorobe village is located in the lower part of the Okavango Delta. CSO, (2011) indicated that the population of Shorobe was 1,031. The local communities of this village sustained their living through basket-making, dry-land and flood recession (molapo) farming (Kgathi et al., 2007). Matsaudi is located on the eastern end of the Okavango Delta near Shorobe village. In 2011, its population was 345 (CSO, 2011). Molapo fields in Matsaudi are fed by the Santantadibe and Gomoti Rivers and backflow from the Thamalakane River. The main livelihood activities are molapo and dry-land farming, livestock rearing and fishing.

 

Lake Ngami occupies the south-west part of the Okavango Delta. It was originally fed by the Thaoge River, the western distributaries of the Delta. It last received inflow in 1989 and has since 2004, been receiving considerably inflow from Xudum distributary and is now considered its terminal portion (Wolski and Murray-Hudson, 2006). Lake Ngami is surrounded by three villages of Toteng, Bothathogo, Bodibeng and Sehithwa, with a population of 902, 555, 778 and 2 748, respectively (CSO, 2011). Livelihood activities for people in these villages include livestock rearing, molapo farming, dryland farming and fishing.

 

Climate

 

Maun and Sehithwa agro-meteorological weather stations were used as reference points for Matsaudi and Shorobe, and Lake Ngami respectively. Sehithwa station does not record maximum and minimum air temperature and uses Maun as its reference point. The hottest month during the crop growing season was October (35.4°C) and coolest was May (26.2°C) (Figure 4). The long-term (2004/2005 to 2013/2014) average seasonal rainfall was 341.39 and 471.63 mm, and the mean seasonal rainfall was 578.50 and 556.9 mm for Sehithwa and Maun, respectively. There was a dry spell in Matsaudi prior to sowing in September with no rainfall and only 7 mm for the month of October (Figure 4). However, in Sehithwa, 15.4 mm was recorded prior to sowing in November and 137.2 mm in December (Figure 5).

 

Hydrology of the Thamalakane River

 

Flooding of molapo fields along the Thamalakane River in 2013/2014 season began in mid-June when floods reach Maun and the water level in the river rose from 1.605 to a peak of 2.515 in September and dropped to 1.658 m in December (Figure 6) as the floods started to recede. The maximum inundation was reached by the end August and floods started to recede by the beginning of September allowing farmers to start ploughing and planting crops.

 

 

Field operations

 

Land preparation at molapo fields (Lake Ngami and Matsaudi) was done by donkey drawn mouldboard plough, whereas, in dryland (Shorobe) it was by tractor drawn mouldboard plough followed by discing to level the soil before planting. Soil samples were collected before ploughing and the main chemical properties of the soil from the study sites were presented in Table 1. Maize hybrid (Zea mays cv. ‘SC 403’) was sown in 0.7 m rows at 60,000 plants ha^-1 in a randomized complete block design with four replications on the 4^th September, 15^th November and 24^th November 2013 at Matsaudi, Lake Ngami and Shorobe, respectively. No starter or post emergence fertilizer was applied. Weeding was done when necessary to maintain weed-free conditions until crops were harvested.

 

 

Data collection

 

Maize was harvested on the 5^th January, 27^th March and 4^th April 2014 at Matsaudi, Lake Ngami and Shorobe, respectively. Measurements were taken at harvest. For plant height and grain yield, six consecutive plants from the centre row were randomly selected. Plant height was recorded in the field and was considered to be that of the highest leaf.

 

Statistical analysis

 

Data were analyzed using the statistical software R i386 3.0.1. Diagnostic plots were used to check  the homogeneity  of  variance and normality of data for each response variable. Data for plant height and maize grain yield were compared using means and standard errors and represented as standard error bar plots.

 

 

 

 

 

Maize plant height and grain yield were significantly higher (p < 0.05) in molapo field at Lake Ngami compared to the other molapo field at Matsaudi and dryland field at Shorobe. Maize plants at Lake Ngami were taller (235 cm) than at Matsaudi (194 cm) and Shorobe (192 cm), which exhibited no significant difference (Figure 7). Similarly, grain yield was greater (3.40 t ha^-1) at Lake Ngami than at Matsaudi (2.4 t ha^-1) and Shorobe (2.58 t ha^-1) (Figure 8).

 

 

 

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