Despite large differences of soil water content between Plant responses to soil water deficit were analysed with leaf water potential c, relative water content RWC, stomatal l. Ž. Ž . calculated with this simple model at each date of soil water. Download scientific diagram | Relationship between soil water potential and soil Influence of salinity stress on photosynthesis and chlorophyll content in date. spatial map for soil texture, providing the potential for ECa mapping as a practical tool to ECa relationships with soil properties and evaluate the usefulness of ECa mapping to infer . as soil water content changed from one mapping date to.
The association between the WIs and grain yield indicates that canopy water content plays a vital role in determining yield of wheat genotypes under optimal as well as adverse growth conditions Babar et al.
Although a large number of indices at diverse wavelengths, based on theoretical perspectives, have been proposed, there is relatively little validation with field data Serrano et al. The objectives of the present study were i to establish which of a number of spectral reflectance indices showed the most reliable associations with the following plant and soil water status related parameters under a range of field conditions: Materials and methods Experimental materials Three types of wheat germplasm were used in this study which were evaluated and selected in previous breeding trials with a larger line number at the International Maize and Wheat Improvement Center CIMMYT.
The first germplasm set was composed of 16 advanced lines ALN previously selected and characterized as drought-resistant lines high yielding among other lines in earlier trials and used in our study during two growing seasons and These sister lines and the two parents SBS-I were evaluated during and For the seasonthe sister lines were reduced from 14 to six lines maintaining the two parents SBS-II based on the grain yield performance.
The third germplasm set consisted of ten lines derived from inter-specific hybridization with wild relatives including the recurrent parents used to breed synthetic derived lines; [as described in Lage and Trethowan et al. The ten synthetic derivative lines SYNDERwhich were previously selected for high grain yield from a bigger yield trial large line numberwas also evaluated under water-stressed conditions during the season.
Weather conditions are mostly sunny and dry during the winter cropping cycle. The soil type is coarse sandy clay, mixed montmorillonitic type caliciorthid, low in organic matter, and slightly alkaline pH 7. Field plots consisted of two raised beds 28 cm apart each 5 m long and 80 cm wide.
Chapter 8 - ETc under soil water stress conditions
An alpha lattice design with two repetitions was used for all experiments. The planting dates were in November and plants reached booting and heading during February—March and were harvested in May. The crop growing seasons for all experiments are referred to as years: Drought stressed conditions were achieved by applying one irrigation before seeding which provided approximately mm of available water and then two irrigations approximately 50—70 mm of available water each were applied prior to the booting stage.
Folicur was applied at the booting, heading, and grain-filling stages at a rate of 0. Spectral reflectance measurements Canopy reflectance was measured in the — nm range and collected at 1. Therefore plant growth is often reduced under saline conditions. The reduced plant growth impacts transpiration by reducing ground cover and is sometimes additionally due to partial stomatal closure.
Other impacts of salts in the soil include direct sodium and chloride toxicities and induced nutrient deficiencies. These deficiencies reduce plant growth by reducing the rate of leaf elongation, the enlargement, and the division of cells in leaves.
The modality depends on the method of irrigation. With sprinkler irrigation, adsorption of sodium and chloride through the leaf can result in toxic conditions for all crop species.
With surface or trickle irrigation, direct toxic conditions generally occur only in vine and tree crops; however, high levels of sodium can induce calcium deficiencies for all crop species.
Since salt concentration changes as the soil water content changes, soil salinity is normally measured and expressed on the basis of the electrical conductivity of the saturation extract of the soil ECe. The ECe is defined as the electrical conductivity of the soil water solution after the addition of a sufficient quantity of distilled water to bring the soil water content to saturation.
ECe is typically expressed in deciSiemens per meter dS m Under optimum management conditions, crop yields remain at potential levels until a specific, threshold electrical conductivity of the saturation soil water extract ECe threshold is reached.
If the average ECe of the root zone increases above this critical threshold value, the yield is presumed to begin to decrease linearly in proportion to the increase in salinity. All plants do not respond to salinity in a similar manner; some crops can produce acceptable yields at much higher soil salinity levels than others. This is because some crops are better able to make the needed osmotic adjustments that enable them to extract more water from a saline soil, or they may be more tolerant of some of the toxic effects of salinity.
The ECe threshold and slope b from these sources are listed in Table As can be observed from the data in Table 23, there is an 8 to fold range in salt tolerance of agricultural crops. It is grown widely in several countries in sub-Saharan Africa and Madagascar.
Cassava was introduced into Africa in the latter half of the sixteenth century from South America and, perhaps, also from Central America, where it is believed to have originated. Globally, there has been widespread production of cassava across continents. Thailand, Vietnam, Indonesia and Costa Rica have been reported as the world leading exporters of cassava [ 8 ].
It was concluded that cassava production in the tropical Nigeria needs to increase with the rising population and this has been significantly influenced by the changing climate and the poor soil quality conditions arising due to soil degradation [ 8 ]. This invariably laid credence to the pertinence of galvanising strategies for boosting cassava production and export in the tropical Africa. This review will however consider soil quality, water characteristics and their synergy for suitable and optimum production of cassava in tropical soils.
World cassava production in source: Soil quality and cassava production The demand on soil resources in increasing, especially for new and conflicting soil functions like enhancing food security, improving water quality, disposing urban and industrial wastes and mitigating climate change.
Thus, soil quality and its management are more important now than ever before, especially in developing countries that are characterised by high risks of soil degradation, predominantly resource—poor and small landholders [ 4 ]. Soil quality is the capacity of soil to perform specific functions of interest to human. Soil quality has historically been equated with agricultural productivity.
Soil conservation practices to maintain soil productivity are as old as agriculture itself. Soil quality is implied in many decisions farmers make about land purchases and management and in the economic value rural assessors place on agricultural land for purposes of taxation. Furthermore, soil quality is defined as the ability of a soil to perform functions that are essential to people and the environment [ 9 ].
Soil quality is not limited to agricultural soils. The first step in science of agriculture is the recognition of soils and of how to distinguish that which is of good quality and that which is of inferior quality.
However, in spite of numerous definitions of soil quality, reviewed reports suggest that the widely accepted definition of the concept of soil quality was laid down by the Soil Science Society of America SSSA in which states that soil quality is the capacity of a specific kind of soil to function within natural or managed ecosystem boundaries, sustain plant and animal productivity, maintain or enhance water and air quality and support human health and habitation.
Soil-Water-Crop Relationship: A Case Study of Cassava in the Tropics
Soil functions keep changing with time and are different with developing compared with developed countries [ 4 ]. Larson and Pierce [ 10 ] defined soil quality as the capacity of a soil to function within the ecosystem boundaries and interact positively with the environment external to that ecosystem. Three soil functions are considered essential: However, no soil is likely to successfully provide all these functions, some of which occur in natural ecosystems and some of which are the result of human modification.
Hence, soil quality depends on the extent to which soil functions to benefit humans. The qualities of tropical soils are imperative indices towards the sustainable production of cassava.
Cassava is known to be a heavy feeder, and literatures have opined that more than average output is obtainable from cassava grown on marginal lands. However, in view of the ever-increasing population of the tropical Africa most notably in Nigeriaand with the production rates seldom meeting the increasing market demands of the produce, production of cassava on quality soils is therefore an imperative factor which when juxtaposed with good management and adequate climatic conditions, the production of cassava can be improved.
Samson Odedina, while demonstrating the profitability of cassava production enterprise to young people and emerging farmers noted that farmers obtain an average yield of 8—10 tonnes of cassava per hectare, adding that the yield is far below the potentials of the crop. He further stressed that if the soil conditions are well managed, farmers can get up to 50—60 tonnes per hectare if they follow the recommended soil management practices.
This increasingly justifies the pertinence of the quality of soils used for cassava production in tropical Nigeria. In addition, the FAO in reported that cassava has the reputation of causing serious erosion when grown on sloppy soils [ 11 ].
Researchers have also argued that this reputation is undeserved, since cassava is often grown on already-eroded soils where few other crops can survive and be productive.
Nevertheless, concise reviews of related literatures generally maintained that cassava production on slopes causes increased erosion on an annual basis than other crops grown under the same circumstances.
Soil water content and water potential relationships [Chapter 4] - NERC Open Research Archive
Cassava, in conjunction with common bean Phaseolus vulgarisupland rice and cotton, tends to cause considerably more erosion than cereals like maizepeanut, sugarcane, pineapple or sweet potato. This was predominantly attributed to the fact that cassava needs to be cultivated at a relatively wide spacing. Contrarily, once the crop canopy is closed, erosion is usually minimal during the remainder of the crop cycle Figure 2. The soil condition used for the production of cassava in Nigeria is of utmost importance if the demands for the produce are to be met before the year Figure 3.
For good growth of cassava, the soil used for production must have adequate room for water and air movement and for root growth. Also, the rising pressure on agricultural lands has made it difficult to obtain high-quality lands for sustainable production of deep-rooted crops like cassava. The insurgence of climate change and its effects on tropical soils has also increased this malady.
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- 1. Introduction
These, therefore, lay emphasis on the true need of establishing soil management techniques aimed at boosting soil physical, chemical and biological conditions—which are main indices for soil quality towards the optimum production of cassava in this high-demand region of West Africa. Hence, based on reviewed statistics, cassava production in Nigeria will increase greatly with optimum soil, environmental and management conditions.
Cassava demand and supply projections in Nigeria . Soil quality assessment for cassava production Soil is likely to show great variability in their physical, chemical and biological properties because the soil is a heterogeneous unit. Knowledge of variability of soil properties is highly indispensable as this can affect crop yield.
A study of the variability trends of soils is essential in order to highlight the soil potentials and enhance their management and productivity [ 14 ].
They emphasised that it is important to be aware of the effect of spatial variability of soil properties when choosing indicator variables of soil quality for crop production. Although when, how and where to collect soil samples for soil quality determination may differ according to the objective of the assessment being made, management history and current inputs should also be considered to ensure valid interpretation of the information.
Soil quality assessment for agricultural production is an important operation towards sustainable crop and livestock production in tropical Africa. Owing to the high degree of variability that is characteristic of tropical soils, there is a need for the assessment of soil condition and capability to offer suitable crop outputs.
Fundamentally, soil productivity for cassava production is a function of soil quality and management. Soil quality assessment is the process of measuring the management-induced changes in soil as we attempt to get soil to do what we want it to do. The ultimate purpose of assessing soil quality is to provide the information necessary to protect and improve long-term agricultural productivity, water quality and habitats of all organisms including people [ 16 ].
Basically, Soil Science Society of America [ 3 ] reported that soil quality is an inherent attribute of a soil that is inferred from soil characteristics or indirect observations. The MDS may include biological, physical or chemical soil characteristics otherwise known as soil quality indicators Figure 4. Showing key indicators of soil quality . Furthermore, the US Department of Agriculture [ 19 ] defined soil quality indicators as physical, chemical or biological properties, processes and characteristics that can be measured to monitor changes in the soil.
The types of indicators that are the most useful depend on the function of soil for which soil quality is being evaluated. Sojka and Upchurch [ 20 ] highlighted that while recognising some controversies about the basic concept of soil quality, considerable progress had been made in the s in identifying the indicators of soil quality.
However, indicators of soil quality can be generally categorised into four groups: Visual indicators This may be obtained from observation or photographic interpretation. Exposure of subsoil, change in colour, ephemeral gullies, ponding, run off, plant response, weed species, blowing soil and deposition are only a few examples of potential locally determined indicators.
Visual evidence can be a clear indication that soil quality is threatened or changing [ 21 ].
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Adeoye and Agboola [ 22 ] maintained that for sustainable cassava or any other crop production, the presence of spear grass on the field to be cultivated is a good indication of a soil with good fertility conditions. Physical indicators These are related to the arrangement of solid particles and pores. The soil physical characteristics are necessary part of soil quality assessment for cassava production because they often cannot be easily improved [ 23 ] during the course of the cropping season.
Lal [ 18 ] reported that important soil physical parameters to be assessed include soil aggregation, available water capacity, texture, saturated hydraulic conductivity, bulk density, infiltration rate and rooting depth.
Researchers have further stressed the need for establishing a quantitative assessment of these soil physical parameters in order to predict biomass productivity, soil organic carbon dynamics, transport processes of water and solutes, etc.
Chemical indicators Assessment of soil quality based on soil chemistry, whether the property is a contaminant or part of a healthy system requires a sampling protocol, a method of chemical analysis and an understanding of how its chemistry affects biological systems and interacts with mineral forms and standards for soil characterisation and suitability classification for cassava production in tropical soils.
In light of these, Larson and Pierce [ 10 ] laid emphasis on those chemical properties that either inhibit the root growth or affect nutrient supply due to the quantity present or the availability.
Nevertheless, Abua [ 26 ] highlighted the importance of maintaining high levels of nitrogen and phosphorus in the soils as chemical indices for quality soils to be used for cassava production in southern Nigeria.
Biological indicators Basically, microorganisms and microbial communities are dynamic and diverse, making them sensitive to changes in soil conditions [ 27 ]. Their populations include fungi, bacteria including actinomycetes, protozoa and algae. However, some soil organisms such as nematodes and bacterial and fungal pathogens reduce plant productivity. Visser and Parkinson [ 28 ] reported that diverse soil microbiological criteria may be used to indicate deteriorating or improving soil quality, and measurement of one or more components of the nitrogen cycle including ammonification, nitrification and nitrogen fixation may be used to assess soil fertility and soil quality.
Nevertheless, USDA [ 19 ] devised biological indicators of soil quality to include measurement of micro- and macro-organisms, their activity, or by-products; and also suggested measurement of decomposition rates of plant residue in bags or measurement of weed seed numbers, or pathogen population can also serve as biological indicators of soil quality.
Water is regarded as the most important of the four soil physical factors that affect plant growth mechanical impedance, water, aeration and temperature [ 29 ]. The optimal moisture conditions for any crop vary depending on many factors such as soil type, climate conditions, growth rate and habit, etc. The water movement in soils for any given crop production a case study of cassava is defined by the soil water characteristic curve.
The soil-water characteristics also known as the soil-water retention or desorption curve can be described as a measure of the water holding capacity i.