Published on International Journal of Agriculture & Agribusiness
Publication Date: March 31, 2019
Kokerai Letticia Kudzai & Kugedera Andrew Tapiwa
Zimbabwe Open University, Faculty of Agriculture, Department of Agriculture Management
Ministry of Agriculture, Lands, Resettlement, Water and Climate, Department of Crop and Livestock
Low crop productivity has been due to poor soil moisture and inherent soil fertility. Most soils in smallholder farming areas are inherently infertile leading to reduced grain yields. The use of insitu rainwater harvesting and integrated soil fertility management has the potential to increase food security in smallholder farmers. The objective of the study was to review the effects of different resources used in ISFM and types of insitu rainwater harvesting. Most farmers are resource poor who are not able to able to raise funds to buy inputs such as inorganic fertilisers hence the adoption of insitu rainwater harvesting and integrated soil fertility management (ISFM) has the potential to increase grain yields. The results reviewed results show that sorghum production was very low at 514 kg ha-1 which is below the expected to increase food productivity. ISFM and rainwater harvesting also improves soil fertility, soil moisture availability and microbial activities which promotes crumb structure. This improves soil fertility over a short period of time. Insitu rainwater harvesting has the potential to increase moisture availability to crops during dry periods and increase crop growth.
Keywords: Insitu, rainwater harvesting, integrated, soil fertility & small grain.
Rainwater harvesting and ISFM has the potential to increase food productivity in semi-arid and arid areas in most sub-Saharan countries. Most smallholder farmers in these areas are not able to raise funds to buy mineral fertilisers hence the use of ISFM has the potential to boost soil fertility. Rainwater harvesting has the potential to improve soil moisture and improve crop growth.
2. Effects of soil moisture scarcity in crop productivity in arid and semi-arid areas
In semi-arid and arid regions, water scarcity due to poor rainfall patterns and low rainfall received has been a major impediment to rainfed agriculture. Low crop productivity in arid and semi-arid areas is due to marginal and erratic rainfall, exacerbated by high runoff and evaporation losses as a result of high temperatures (Mzezewa et al., 2011) among other factors. Bahri et al. (2011) pointed out that Africa has a particularly high spatial and temporal variability in rainfall when compared with other continents. Marginal and highly variable rainfall combined with unpredictable droughts largely influence economics of agricultural production among the smallholder farmers in the rural areas (Mutekwa, 2009) especially in marginal areas of Zimbabwe, Kenya and other southern African countries. Dry spells which is a common phenomenon in the semi-arid areas increases water evaporation losses, decreases soil moisture, disturb the root uptake capacity of the crop and consequentially lead to low yields (Fox and Rockström, 2003). Increasing the productivity of rain-fed systems in the arid and semi- arid areas of Africa will be crucial as they cover the majority of agricultural lands. There is need to integrate rainwater management such as the use of tied ridges and zai pits to complement soil moisture deficit in the semi-arid areas. There is need for farmers to use water management options to increase soil moisture. In order to deal with the challenge of water scarcity which is a threat to food security, water harvesting techniques are being used in water management for rainfed agriculture (Mati, 2005). Many studies done in arid and semi-arid regions of improved land and water management practices have shown to reduce yield gaps (Pala et al., 2011). Furthermore, improved water management can be a catalyst for economic growth among the rural farmers in the semi-arid areas. Researchers have provided a vast array of options to address the challenge of water scarcity and enhance agricultural productivity in the semi-arid areas. Among the water harvesting techniques are tied ridges, zai pits, negarims, semi-circular bunds and half-moons (Nyamadzawo et al., 2013). This study uses tied ridges as a soil water harvesting technique promoted in the semi-arid areas of Zimbabwe to improve sorghum productivity.
3. In-situ rainwater harvesting (RWH)
In situ RWH, otherwise known as soil-water conservation, comprises a group of techniques of preventing runoff and promoting infiltration. The aim is to retain moisture that would otherwise be wasted as runoff from the cropped area (Ngigi, 2003). Rainwater is conserved where it falls, but no additional runoff is introduced from elsewhere. In-situ RWH works where the soil water holding capacity is large enough and the rainfall is equal or more than the crop water requirement, but moisture amount in the soil is restricted by the amount of infiltration and or deep percolation (Gichangi et al., 2007; Belenchew and Abera, 2010; Kathuli and Itabari, 2013). In-situ rainwater harvesting techniques are simpler, more affordable and adoptable by resource poor smallholder farmers in arid and semi-arid areas (Mudatenguha et al., 2014). The technique increases the amount of water stored in the soil profile (Ngigi, 2003) and reduces surface runoff by increasing infiltration rates of rainwater leading to more water available in the plant root zone (Motsi et al., 2004). There are many in-situ rainwater harvesting techniques which include tied ridging, pot-holing, zai pits/ planting pits, mulch ripping and ridging.
3.1 Tied ridging
Tied ridging is a semi-permanent ridge with annual ties which are usually 0.5 to 0.65 times the height of the ridge (Munodawafa and Zhou, 2008; Nyakudya and Stroosnijder, 2013) and ties are constructed across furrows annually at a height of about 1m. The ridges maybe constructed by hand or mechanical ridger. These ties are constructed to reduce surface runoff (Motsi et al., 2004) and also reduce soil erosion. The ridges are laid across the min slope at a grade of 0.4-1%. The ridges once constructed they are not destroyed for six seasons depending on crop rotation by the farmer (Mati, 2005). Spacing between the ridges depends on row spacing of the crop. Once constructed the ridge ties are spaced at 2m intervals to prevent runoff flow. The effectiveness of tied ridges depends on soil, slope, rainfall and design characteristics. On Vertisol tied ridging was seen to produce goods grain yields compared to tied ridges on others soils (Mudatenguha et al., 2014). Tied ridges are used as a soil moisture conservation technique which reduces surface runoff and increases infiltration of rain water. Tied ridges have been seen as effective rainwater harvesting technology (Motsi et al., 2003) and can be used with other rainwater harvesting combination such as infiltration pits (Nyamadzawo et al., 2013). The use of tied ridging rain water harvesting has been seen to increase yields of sorghum, millet and other crops.
Ridges need to be reshaped during the growing period of the crop as animals during off seasons destroy the shape. Tied ridging have an effect of reducing surface bulk density, maintains soil fertility by reducing losses of soil nutrients in surface runoff and improves soil water retention and available water holding capacity (Hulugalle, 1990). In Mali, tied ridge increased grain yields of sorghum in rotation with legumes by 10 % compared to simple ridging under low average rainfall in the sahelian zone (Kouyaté et al., 2012). Sorghum grain yield increased by 30 to 50 % in farmers’ fields practising tied ridging with animal drawn equipment in the areas of Koutiala and Tominian in Mali (DRSPR, 1990). Tied ridging in combination with integrated nutrient management had the potential to improve crop production in semi-arid zone of Kenya (Miriti et al., 2007) and other arid areas such as Zimbabwe. Chepkemoi (2014) reported that intercrop and crop rotation of sorghum under tied ridges with application of Minjingu Rock Phosphate (MRP) and Farm Yard manure (FYM) is a viable technology for increased soil moisture, nutrients, and crop yield.
3.2 Pitting system (Planting pits)
These are shallow holes dug to a depth of 15-25cm with a diameter of about 30 cm (Rockström, 2000). These are dug to break the crusted soil surface, store water and build up soil fertility. These planting pits has variations which include Zai, Katumani pitting, Planting pits, Tassa, Half-moon, Chilolo pits and Five by nine pits (Ibraimo and Munguambe, 2007). These are usually done in arid and semi-arid areas where rainfall ranges between 350-600 mm per annum. Farmers can place 4-8 seeds in a Zai pit to increase plant population. Organic manure preferable from cattle and other forms of manure are added and mixed with soil to improve soil fertility, structure and conserve moisture in the pit (Itabari and Wamuongo, 2003; Mati, 2005). In areas like Tanzania where rainfall is high, farmers dig up to 0.6 m and adds 20 litre bucket of manure, place 15-20 seeds of crops per pit and yield are more than double those from conventional tillage system (Mati, 2005). Chilolo pits are techniques which comprises a series of pits which are about 22 cm wide and 30 cm deep (Ibraimo and Munguambe, 2007). They are spaced 60 cm within rows and 90 cm between rows, while rows are running along the contours. Cattle manure, compost and compound fertilisers together with ashes (to expel termites) are added and mixed with soil to improve soil fertility. Two to three seeds of either maize or sorghum are added per hole and covered with soil. The technique has been seen to triple yields and crops survive even during dry spells periods as the techniques conserves moisture (Mati, 2005).
Ridging is a technique that results in a ridge/furrow system. When constructed the ridges have an inverted “V” shape and the furrows are “V” shaped. Both the ridges and furrows become less pointed as the cropping season progresses due to the effect of rainfall which erodes some of the soil and practices such as weeding using hoes. Construction spacing of ridges ranges from ≤ 1 .0 m t o 2.0 m and ridge height ranges from 0 .1 m t o 0.4 m with ridges with narrower spacing being shorter. Wider-spaced and higher ridges therefore use up more top soil during construction and lead to deeper furrows than narrower-spaced and shorter ridges. The 1.0 m-spaced ridges can be constructed using high wing ridger or a mouldboard plough but wider-spaced ridges require tractor drawn ploughs which can produce required ridges by farmers. In other researches ridges are identified by their spacing that is 1.0 m ridges refers to ridges with a ridge spacing of 1.0 m. Ridges are established on a slope of 1% (Munodawafa and Zhou, 2008; Vogel, 1993) or at zero gradient. The 1% slope provides a gradient for less erosive flow of water along the furrow. Planting is done on top of the ridge once the ridge is moist throughout (Motsi et al., 2004).