CHAPTER ONE
INTRODUCTION
1.1 Background of the Study
Marginal lands sometimes called wastelands or idle lands can be defined as lands which are of no importance for biodiversity or carbon sequestration. They play no role in food production and in guaranteeing people’s livelihood (Salva, 2008). It has been discovered that they have poor soil containing toxic levels of salt and are deficient in essential plant nutrients. They are generally unsuitable to crops. High concentration of salt particularly in the root zone could cause stress to a plant and eventually damage or kill it. Salt stress often coexist with other abiotic stresses such as drought. Tilman et. al. (2006) estimated that developing countries have vast area of marginal lands (at least 500 million hectares). Genetic analysis has shown that tolerance for abiotic stresses such as salinity could be attributed to germplasm – hormones (Mackill, 2004).
Plant growth has been determined at different levels to involve different metabolic processes in cells and there is a link between the cells and some external factors. Philipson (1987) showed how flowering could be induced in potted grafts of Sitka spruce and hybrid larch species by stem injections of a mixture of gibberellic acid (GA4/7 – a hormone) in combination with drought and high temperature treatments (external factors). Differentiation processes were not controlled just by a single factor, but by a complex, balanced equilibrium of growth regulators and external factors like light, temperature, nutrients, moisture and soil. Researches have indicated that hormones mediate between an external factor and physiological activities (Benjamins and Scheres, 2008; Zhang et al. 2000; Zhu, 2000). The process of tree breeding techniques has advanced and is currently at the phase where certain economic traits such as high wood density, good stem straightness and disease resistance could be induced using a combination of several factors.
Soil salinity has had an adverse effect since ancient civilization by limiting the available land for cultivation and to this day, it continues to affect agricultural productivity in many parts of the world. Soil salinity has been defined as a soil condition characterized by a high concentration of soluble salts. Soils are classified as saline when the electrical conductivity of the saturated paste extract (ECe) is 4 dS/m or more, which is equivalent to approximately 40mM NaCl and generates an osmotic pressure of approximately 0.2MPa (USDA-ARS, 2008). According to FAO report (2008), soil salinity is one of the major factors of soil degradation. More than 800 million hectares of land throughout the world are salt affected. This amount accounts for more than 6% of the world’s total land area. Most of this salt- affected land has arisen from natural causes; the accumulation of salts over long periods of time in arid and semi-arid zones (Rengasamy, 2002). Weathering of parent rocks release soluble salts of various types, mainly chlorides of sodium, calcium, and magnesium, and to a large extent, sulphates and carbonates (Szabolcs, 1989). Other causes of accumulation are the deposition of oceanic salts carried in wind and rain. Apart from natural salinity, a significant proportion of recently cultivated agricultural land has become saline owing to land clearing or irrigation, both of which cause water tables to rise and concentrate the salts in the root zone (Munns and Tester, 2008). Salinity effect is more conspicuous in the arid and semiarid areas where 25% of the irrigated land is affected by salt. Salt-tolerant plants (halophytes) have evolved to grow on these soils. Halophytes and less tolerant plants show a wide range of adaptations. Attempts to improve the salt tolerance of plants have given limited success due to the complexity of their trait both genetically and physiologically. The development of salt-tolerant plants is being pursued from many angles (Zhu, 2000).
1.2 Statement of the Problem
Arable crop farmers try to avoid soils with high salt levels. A growing world population and a decline in arable land area have brought an increasing demand / competition for marginal lands which were previously unsuitable for arable crops, hence abandoned and committed to growing woody perennials (trees).
Agriculturists and most financial institutions are interested in ventures that will bring maximum returns on investment within a reasonably short period. This results in a short fall on the forestry sub-sector because trees are known to have a long gestation period (A major shortfall of the forestry sector in Nigeria). The forester needs to work at utilizing the rejected and unproductive lands for tree growth and at the same time work at developing tree crops that could adapt to harsh soil and climatic conditions. This in the long run will help in revitalizing the land.
1.3 Justification of the tudy
Success with growing trees on rejected/unproductive lands will ultimately result in utilization of such lands, leading to reclamation. It will reduce land hunger and conflict; promote private / individual forestry practices in Nigeria. Making use of such lands will not only make forestry business attractive.
This will increase the production of the marginal lands, improve the conservation of watershed and ameliorate the hostile micro-climate within the area. It will also provide baseline information for further research.
Perennial trees from the forest could be used to remediate soil salinity since their roots can penetrate deep into the soil to reach low water table and draw up moisture for the plant use.
The society will benefit from the result of this research as more land will be available for other users.
Objectives of the Study
The study examines the response of three tree species (Acacia senegal; Parkia biglobosa and Balanites aegyptiaca) to application of hormone (Indole-3acetic acid IAA) and salinity caused by salt (NaCl) stress.
Specific Objectives
(i). To determine the salinity and hormonal levels suitable for the germination of the tree species.
(ii). To determine the salinity levels suitable for the early growth of the chosen tree species.
(iii). To determine the effect of hormones on the early growth of these three forest tree species.
(iv). To study the interaction effects of hormone (IAA) and salt stress on shoot elongation of these forest tree species.
(v). To determine which of the species is more tolerant to salt stress.
1.5 Scope of the study
This research will investigate the growth of these three tree species (Acacia senegal; Parkia biglobosa; Balanites aegyptiaca) in salt concentrated soils found around Dabagi Farm of Usmanu Danfodiyo University Sokoto under a growth hormone (Indole-3-Acetic Acid, IAA).