Mulching and Tied Ridges as A Moisture Conservation Strategy to Improve the Yield of Sorghum (Sorghum Bicolor) in Semi-Arid Parts of Swaziland
Abstract
An experiment was conducted to determine the effectiveness of soil moisture conservation techniques on improving sorghum yield in a semi -arid rural area of Swaziland. The four treatments were; plan ting sorghum on flat soil (F), planting on tied ridges (T), planting on mulched soil (M) and planting on a combination of tied ridges and mulch (TM). Sorghum planted on flat soil was used as control in the experiment. The sorghum variety 8625 was planted. The experiment was complete randomized design and each treatment was replicated three times. The parameters measured were; grain yield, total biomass yield, soil moisture suction and grain moisture content at harvest. The grain yields from all the other treatments (mulching, tied ridges, tied ridges with mulching) were higher than those of the control (flat planting). The grain yield from TM was the highest at an average of 10.002 tons/ha. It was significantly different from that of T and F (p<0.05). The gr ain yields for M, T and F were 8.790 tons/ha, 8.202 tons/ha and 6.785 tons/ha respectively. Total dry matter yield was the highest for TM, at 36.980 tons/ha. Soil moisture suction for TM was the lowest at 11.6 centibars, indicating that moistur e was readil y available to the crop for a longer period than all the other treatments. Grain moisture content for all the treatments was below 20%, and the mean grain moisture content for all the treatments were not significantly different (p>0.05). The results showed that a combination of tied ridges and mulching provided superior results in terms of grain yield, dry matter yield and soil moisture suction. Mulching and tied ridges also yielded results that were better than the control (F).
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Introduction
Sorghum (Sorghum bicolor) is one of the widely grown cereal crops in Africa, and it is grown in marginal areas of the southern Africa where other crops such as maize would normally fail. It is known for thriving under soils generally classified as poor (Chisi, 2004). It is the fourth most important food crop globally in terms of sources of energy and protein in human nutrition and fifth on global production (Basavaraja et al., 2005). It is the second major food after maize that has C4 photosynthesis (Taylor, 2004). Industrially, the grain is used to manufacture wax, starch, syrup, alcohol, dextrose agar, edible oils and gluten feed (Gwari et al., 2006). As food, the grain is used in making fermented and non-fermented porridge and traditional dishes where it can be mixed with legumes (Muui et al., 2013). Sorghum is one of the drought tolerant crops that may be adopted for areas with adverse climate conditions (Ottman and Oslen, 2009). The optimum temperature for the growth of sorghum is 27-32 °C. Sorghum production can be sustained under fluctuating rainfall conditions of approximately 400 mm to about 800 mm but can survive even in drought conditions of less than 300 mm annual rainfall (Du Plessis, 2008).
Mulch is any material placed on the soil surface to conserve moisture, lower soil temperatures around plant roots, prevent erosion and reduce weed growth. It can be derived from either organic or inorganic materials (Sinkeviciene et al, 2009). It is through the water that is retained under the mulches that this technique is able to achieve improved yields. However improper mulching materials and practices may have little, or negative impact on the crops planted (ISA, 2011). The practice of mulching has been proven to significantly improve the growing conditions of horticultural crops (Testahunegn et al., 2012). A good layer of mulch will help to preserve moisture and suppress weed germination (Cregg and Schutzki, 2009). A layer of about 7 to 10 cm is appropriate for most organic mulches (Kwambe et al., 2005; Jauron, 2013).
Tie-ridges are a soil and moisture conservation structures that involve the construction of small rectangular basins formed within the furrow of cultivated fields mainly to increase storage and to allow more time for rainfall to infiltrate the soil (Wiyo et al., 1999). The stored water can be usable to the plants for a longer period of time better than it can be used in a situation of runoff (Gichangi et al., 2012; Belenchew and Abera, 2010). Adoption of soil moisture conservation techniques such as tieridges and mulching has shown improved soil moisture retention in a wide range of environments (Balenchew and Abera, 2010).
The effectiveness of the moisture conservation techniques has not been widely investigated in Swaziland. This experiment intends to establish the most effective soil moisture conservation technique that may be suitable for sorghum production at a semi-arid region of Swaziland.
Conclusion
Based on the results of this study, it can be concluded that the combination of tied ridges and mulch (TM) was effective in retaining s oil moisture. The tied ridges and mulch treatment (TM) recorded the highest (11.6 centibars) average moisture content when compared to the other treatments. The effect of the moisture retention was significant on the sorghum yield as well. The tied ridges + mulch treatment (TM) also recorded the highest grain (10.022 tons/ha), and dry matter yield (36.768 tons/ha). The conservation of moisture using tied ridges and mulch in the semi -arid region of the country which receives comparatively less rainfall could have a positive effect on sorghum yield.