THE EFFECTS OF SOIL MOISTURE CONTENT ON THE GROWTH AND DISTRIBUTION OF SORGHUM ROOT SYSTEMS

 

ABSTRACT

Crop production is influenced by on-site soil moisture availability and application of water conservation methods for dry areas. This research explored the interactive effects of spate irrigation as an application method and the soil moisture conservation techniques. The objective of this research was to analyze the effectiveness of soil moisture conservation techniques and its correlation to water productivity for sorghum production under spate irrigation. The soil water holding capacity was investigated based on four moisture conservation techniques; mulching, ridging, ridge-furrow mulch and control. Soil moisture was monitored for 125 days under which Seredo sorghum variety was planted. A field experiment was set up using a Randomized Complete Block design (RCB), with three blocks each covering an area measuring 10 m by 10 m with replications. The effect of the treatments on moisture retention was monitored using digital YL-69 moisture sensors installed at 20 cm and 40 cm depths respectively. In addition, the crop coefficient and crop water requirement (CWR) were assessed during the crop’s growth period under the different treatments. Normalized Difference Vegetation Index (NDVI) was estimated from growth images obtained from sentinel 2 and then the NDVI used to establish the crop coefficient (Kc). The reference evapotranspiration was determined using the Hargreaves method and the values were then combined with the crop coefficients to obtain the crop water requirement. Results show that K_c values ranged from 0.44 in the initial crop development stage to 0.91 in the mid-season stage and varied with the type of moisture conservation technique. The K_c linearly increased with the increase in NDVI under the different moisture conservation techniques, with a regression coefficient ranging from 0.75 in the combined ridges and mulch to 0.86 in the mulch treatments. The maximum crop water requirement values under each moisture conservation technique were 41.8 mm, 95.1 mm, 177.6 mm and 82.6 mm in the initial development, mid-season and late stages respectively.  In addition, the seasonal water requirement of sorghum variety ranged from 386 mm to 395.7 mm. The combined ridges and mulch had the highest water productivity of 2.08 kg/m³ as compared to the ridges, mulch and finally the control which had values of 1.83 kg/m³, 1.66 kg/m³ and 1.45 kg/m³ respectively. The findings from this study are important as they can be used by agriculturalists, farmers and relevant stakeholders in prioritized soil moisture conservation for increased sorghum crop production especially in ASAL areas.

 

 

CHAPTER ONE

INTRODUCTION

1.1 Background information

Water that infiltrates into an agricultural field can be conserved for increased crop production. Several field water application methods into the field exist. These include basin, furrow, border, sprinkler, drip and spate irrigation methods. In this research, spate irrigation was explored as a way of utilizing flood water for crop production in arid and semi-arid lands. It involves the diversion of flood water to agricultural fields through a dry riverbed (Kyagulanyi et al., 2016). Spate irrigation is usually practiced when the rate of evapotranspiration is greater than the precipitation rate to cater for crop water deficit. Spate irrigation is being practiced in some parts of Africa, Asia and America (Steenbergen et al., 2010). Kenya has a land mass of 582,000 km² out of which approximately 80% is Arid and Semi – Arid Land (ASAL) that receive a mean annual rainfall less than 750 mm. The ASAL supports about 20 % of population in Kenya. This clearly shows that Kenya is poorly endowed with a potential for practicing rain-fed agriculture. However, the recurrent flash floods can be used for spate irrigation which targets 50,000 ha as outlined in Kenya’s Vision 2030 development blue print (GOK, 2007) and other sectorial plans.

This will also help in achieving Sustainable Development Goals (SDG’s) number 1 and 2 which focus on no poverty and zero hunger. With increased food production, there will be reduced food security issues and in turn improved livelihoods. Therefore, this study focused on the use of soil moisture conservation techniques in spate irrigation in Ol Donyo Nyoike area, Ewaso Nyiro South Drainage Basin. Ol Donyo Nyoike area is one of the areas in Kajiado County that face frequent flooding and has a large potential for spate irrigation. These conservation measures are meant to increase the amount of moisture content in the soil and in turn improve the agricultural productivity in the study area.

 

Agricultural productivity in semi-arid areas depends on water availability. Despite being endowed with recurrent flash floods, Ewaso Nyiro South Drainage Basin is an arid and semi-arid area with an average of 600 mm of rainfall per year (Gichuki et al., 1998). This amount of rainfall is highly variable in terms of spatial and temporal distribution. This in turn leads to very low amounts of rainfall in some areas and others who depend on the flood water only. This prompts the need for application of conservation measures to help in maintaining optimum soil moisture content at any given time. Globally, different techniques to conserve soil moisture content have been developed (Thomas et al., 1997; AHI, 2000). The conservation measures are mainly used to retain soil moisture and nutrients with the end goal of increasing crop yields. Utilization of rainfall, good irrigation practices and control of runoff depends on the water retention characteristics of the soil. Different methods and equipment have been developed to ensure reliable measurement of moisture content in the soils. These methods include: gravimetric method, neutron scattering method and more recently the use of real time soil moisture sensors (RTSMS). The Time Domain Reflectometry (TDR) and capacitance probe methods are mainly used because they can measure both temporal and spatial changes in soil moisture content (Jones, Wraith, & Or, 2002).

 

The main parameter evaluated in the assessment of spate irrigation efficiency is water productivity (WP). According to Mdemu et al. (2009), improving water productivity is one important strategy for addressing future water scarcity. Molden (1997), stated that water productivity (WP) takes different forms with different units. According to Heydari (2014), WP is an indicator of agricultural productivity in relation to the crop’s consumptive use of water. Productivity enhancements are accompanied by optimum resource utilization and maximization of the marginal production. Improving water productivity in agriculture reduces competition for scarce water resources, and subsequently lead to enhanced food security. Since water is a scarce resource, water productivity, is a critical indicator on performance of the system with respect to production (Rao, 1993)

1.2 Statement of the problem

According to Rono (2013), degradation of natural resources in Ol Donyo Nyoike area has led to the occurrence of frequent flash floods. Despite the cyclic occurrence of flash floods in the subcatchment, the amount of flood water available for spate irrigation in the area has not been determined. To ensure the success of agriculture in the arid areas, the amount of flood water in the area should be estimated for optimum water utilization. Different soil moisture conservation techniques can be applied on agricultural land to preserve moisture and in turn improve the irrigation efficiency and water productivity (Thomas et al., 1997; AHI, 2000). However, the effectiveness of moisture conservation techniques for improving the moisture retention and water productivity has not been widely investigated in Ol Donyo Nyoike. According to Heydari (2014), insufficient amount of water within a region leads to insufficient hydrological information about the water requirement for various crops. Since little agriculture is practiced in Ol Donyo Nyoike due to limited water sources, there is insufficient information about crop water requirement (CWR) for various crops. The information on effectiveness of soil moisture conservation techniques and its correlation to water productivity for sorghum production under spate irrigation is scanty hence the need for investigation in this research.

 

1.3 Objectives

1.3.1 Broad objective

The broad objective of this study was to analyze the effectiveness of moisture conservation techniques in water productivity of spate-irrigated sorghum in Ewaso Nyiro South Drainage Basin.

1.3.2 Specific objectives

The specific objectives were to:

1. Evaluate the effectiveness of moisture conservation techniques (mulch, contour ridges, a ridge-furrow mulch and no conservation measure) on soil moisture retention for sorghum field under spate irrigation.
2. Determine the Crop Water Requirement (CWR) for sorghum crop growth under different moisture conservation techniques using remotely sensed and NDVI data.

• Determine the water productivity (WP) of sorghum in assessment of the effectiveness of spate irrigation under different moisture conservation techniques.

1.4 Research questions

1. How effective are the soil moisture conservation techniques in retaining soil moisture for spate-irrigated sorghum field?
2. How does the CWR of spate irrigated sorghum determined using remote sensing vary with different soil moisture conservation techniques?

• How does the WP of spate irrigated sorghum vary with different soil moisture conservation techniques?

 

1.5 Justification

Ewaso Nyiro south sub-catchment, specifically Ol Donyo Nyoike group ranch, experiences flash floods which affect the neighboring Kamukuru town and even cause damage to property. However, if well managed, these flash floods can be of beneficial use in spate irrigation for food production to address recurrent food insecurity. A study on the effect of different conservation techniques on the crop yield under spate irrigation is important in determining which methods are recommended and applicable for moisture retention. These findings are important as they can be used by agriculturalists, farmers and relevant stakeholders in prioritized soil moisture conservation for increased crop production.

 

Specific crop study for the region is important in the development of sustainable agriculture since most of the people from the region suffer cyclic drought and famine occasioned by erratic rains. Sorghum was chosen for the study because it is the most preferred crop in the area and can either be used as food crop and/or as fodder. Also, sorghum can tolerate temporal waterlogging which is a common experience in the sub-catchment. Therefore, the study of sorghum’s evapotranspiration was important in that it helped in determining the crop water requirement in relation to the quantity of water available.

 

THE EFFECTS OF SOIL MOISTURE CONTENT ON THE GROWTH AND DISTRIBUTION OF SORGHUM ROOT SYSTEMS

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