PhD Soil and Water Management

 PhD Soil and Water Management

This program is by research and course aimed at producing highly qualifies graduates who can critically analyse and synthesize all matters related to soil science and land management for sustainable agricultural insdustry in the greater East, Central and South Africa (ECSA) region.

 The programme's (PhD Soil and Water Management) goals are to develop and strengthen regional human resources and institutional capacity in impact-oriented training and research in soil and water management as an entry point towards sustainable agricultural production in the ECSA region.

Students who graduate from this programme will be able to: 

  1. Interpret advanced concepts of soil and water in harnessing natural resources for sustainable development.
  2. Undertake a critical review of advances in integrated soil fertility management, land use dynamics, land and water resource degradation, harnessing and application in agricultural systems. 
  3. Formulate a wide range of experimental design for use in soil and water research.
  4. Illustrate the role of ICT and modelling tools to guide management of soil and water resources.

Recognize the essence of sound managerial ability and effective communication as platforms for enabling successful holistic approach for research and developmental programmes related to the management of soil and water.

PhD Soil Science

PhD in Soil Science programme is by research only.

 Regulations and Guidelines for PhD degree in the Department of Soil and Geological Science is as per the regulations and guidelines for Doctor of Phylosphy (PhD) degree at Sokoine University of Agriculture as stipulated in the Prospectus and in the “Regulations and Guidelines for higher degrees at Sokoine University of Agriculture”

DSGS Research Agenda



Research areas under DSGS:

  1. Land resources inventory, mapping and evaluation for sustainable land productivity
  2. Microbiology and soil health
  3. Soil mineralogy and pollution
  4. Soil and water conservation
  5. Soil fertility and plant nutrition


  1. Land resources inventory, mapping and evaluation for sustainable land productivity

Background information:

In its most common use, the term land refers to the part of the earth's surface that is not covered by water. FAO (1995) gives land a broader definition which takes into account not only the physical entity, but also the associated physio-biotic and socio-economic as well.

Soil is one of the land resources which, by its importance, has shaped the livelihood and success of many ancient and current communities (Holmes and Hearn, 1942). It is therefore important to map the spatial distribution of the qualities of the soil resource in order to make informed decision about types of land uses we want to allocate and the types of management we will need to implement in specific pieces of land in order to optimize the selected land use types.

The first documentation of spatial soil information in Tanzania was done by Milne in 1936 (Milne, 1936). From that time, several exercises have been done to map the soils of Tanzania. A few exercises have attempted to cover the whole country, but so far, with a coarse scale of over 1:1,000,000; which cannot help farmers and other land users make informed decision at farm scale. Finer scales mapping have been done on request or responding to research question, but they are at varying scales and covering different area which lack continuity. Another feature of these mapping exercises is use of conventional methods which lack flexibility and transferability. The finer scale soil maps are generally owned by different researchers and clients, thus not readily available for public use.

Soil mapping provides basis for land evaluation and crop suitability analyses. It helps to avoid blanket recommendations of soil management such as fertilizer application, irrigation application and crop varieties/types selection.

Currently, researches on soil mapping are leaning towards methods which increase precisions and reliability of the mapped soil properties. The current methods also are geared towards reducing soil survey costs by including modelling and predictive methods.


  1. To classify soils for improved management and communication among the local and international soil information users
  2. To develop and test tools for more reliable, cheaper and finer resolution characterization and mapping of land resources, and make it available for agricultural land use planning decisions and management.
  3. To develop and test novel tools for assessing the suitability of land resources for specified land use types while considering productivity, social, economic and environmental consequences.

Research sub themes:

  1. Soil classification

Research Topics

  1. Research on indigenous soil classification systems and how they can be linked with scientific classification systems to help communication and management of soils for improved land productivity of small scale farmers and other stakeholders
  2. Improved reliability and usability of soil characterization through both qualitative and quantitative methods
  1. Soil/land resources mapping

Research Topics

  1. Developing and testing tools for predictive and digital soil mapping
  2. Spatial data infrastructure (SDI) development and management
  1. Land evaluation

Research Topics

  1. Development and testing of tools and techniques for predicting land productivity
  2. Testing potential of land for precision agriculture
  1. Microbes and soil health

Background information.

Microorganisms play a major role in agricultural productivity of soils. Their positive exploitation could range from enhanced soil fertility through their role in nutrient recycling due to organic matter degradation to provision of plant protection via production of various biologicals and or/ physical pest control. Use of a wide assortment of plant growth promoting microorganisms such as those involved in nitrogen fixation, phosphate solubilization and nutrient scavenging is another area where the microorganisms do contribute directly to enhancement of soil fertility and land productivity.

Pollution control and ensuring general environmental safety is an important undertaking which has been mentioned in different national documents including the Environmental Management Act 2004 and the National Environmental Policy (NEP) of 1997. The pollution control and general environmental safety can be achieved through the use of microorganisms ranging from those involved in general biodegradation of sewage regimes to those involved in complex tasks such as plastic degrading microorganisms and those involved in bioremediation of heavy metal and/or persistent organic pollutants (POPs)-contaminated soils and water systems. As a nation, we need to improve the contribution of microbiological aspects of soils to overall soil health, increased land productivity and general environmental safety. We also need to explore various beneficial soil microorganisms that enhance soil fertility and thus increase sustainable agricultural productivity of the soils



  1. To collect and test N2 fixing consortia with superior qualities and produce a registered commercial grade bio-fertilizer
  2. Assess phosphate solubilizing microorganisms (PSM) consortia for the preparation of inoculant-based bio-fertilizer
  3. Development of superior strains (natural or trained) of microorganisms with capabilities to degrade plastics
  4. To isolate and identify suitable micro-organisms capable of solving the problem of heavy metal and organic pollutants
  5. Enhance plant growth and suppress soil-borne diseases using rhizobacteria and fungi


Research sub themes

  1. Nitrogen (N2) fixation

Research Topics

  1. Preparation and testing superior biological nitrogen fixing bacterium inoculum for use under diversified climatic conditions
  2. Improvement of NITROSUA to attain commercial biological fertilizer status


  1. Phosphate solubilizing microorganisms (PSMs)

Research Topics

  1. Isolation, identification and characterization of PSMs
  2. Development and testing of phosphate solubilizing microbial inoculum using the existing phosphate rocks in Tanzania


  1. Plastic degrading microorganisms

Research Topic

Development and testing of microorganisms to be used as tools for environmental cleaning of plastics


  1. Heavy metal and persistent organic pollutants (POPs) contaminated site bioremediation

Research Topic

  1. Isolation, characterization and use of microorganisms with the capability to bioaccumulate, biodegrade or biostabilize both harmful heavy metals and persistent organic pollutants (POPs).
  1. Plant-growth promoting rhizobacteria and fungi

Research topics:

  1. Isolate and characterize rhizobacteria and fungi with plant-growth promoting hormones and test their ability to enhance plant growth.
  2. Isolate, characterize and test antibiotic producing fungi and rhizobacteria for crop protection and for suppressing soil-borne diseases


  1. Soil mineralogy and pollution


Soils occur with a lot of minerals and elements/metals; some could be beneficial or toxic to plants and the environment depending on their concentrations. In soils, metals above the background level can be toxic to plants and may decrease microbial biomass by killing or disabling soil organisms. Some metals, such as cadmium (Cd), lead (Pb), Cr, Ni, mercury (Hg), thallium (Tl), uranium (U), thorium (Th), and arsenic (As), are carcinogenic and highly toxic.

These metals are often considered as contaminants and are nonessential to most living organisms and thus, when occur in soils at high concentrations, could be of concern to agricultural produce and food chains. Source of high concentrations could be due to weathering of parent rocks and contaminations associated with human activities such mining and improper applications of fertilizers or pesticides. Hence, identification and quantification of minerals and metals in soils are essential for proper utilization of these resources and protection of the environment.


  1. To identify and quantify heavy metals pollutants in agricultural soils and their pathways to plants, animals and human beings.
  2. To device innovative solutions to mitigate heavy metal pollution on agricultural soils
  3. To create awareness to the community on the safety of agricultural produces and water used for domestic consumption and irrigation.


Research topics

  1. To profile levels of heavy metals pollutants in agricultural soils
  2. To assess effect of different agronomical practices on heavy metal pollution
  • To develop strategies for mitigating heavy metal pollution on agricultural soils


  1. Soil and water conservation


Tanzanian agriculture and food systems have the potential not only to meet the local food demand but also produce a surplus for export. Achieving the above requires addressing critical limiting production factors specifically soil and water. Need for improving soil and water management have been stipulated in ASDP II and the National Five Year Development Plan 2015/16 – 2020/21. Soil and water are inefficiently managed resulting in an inefficient utilization of the two natural production resources. The situation is worsened by the changing climate resulting in declining productivity due to reduced soil moisture. This necessitates development of innovative agronomical practices for conserving available soil moisture. The soil and water conservation research should aim at mainstreaming appropriate soil and water management technologies into farming systems which will result into their sustainable use and meeting the needs of current and future generations.


  1. To develop technology for assessing and predicting changes in soil water.
  2. To develop site specific mitigation strategies for conserving soil moisture
  • To assess the impact of climate change on major farming systems in Tanzania
  1. To develop and test climate change adaptation and mitigation measures

Research Themes

  1. Climate smart agriculture (CSA):

Research Topics:

  1. Identification and testing of the suitability of climate-smart agricultural practices in soil and water conservation
  2. Establishment of crop sensitivity to key attributes of climate change.
  • iii. Development and testing/validation tools for predicting vulnerability and resilience of priority crops to climate change
  1. Rainwater harvesting technologies:

Research Topic

  1. Enhancing rain water use efficiency through multiple approaches.
  2. Integrate indigenous knowledge into soil and water resource management
  1. Soil fertility and plant nutrition

Despite the fact that most farming in Tanzania is undertaken by poorly resourced and poorly educated small holder farmers, most of it is undertaken in old nutrient depleted landscapes. This results to poor crop productivity, since plants performances largely rely on soil fertility and its management. Therefore, there is a need to revise strategies for improving fertility status of these landscapes. Tanzania is now striving to improve crop productivity so as to make the nation food self-sufficient. In its current move for industrialization as described in the Second National Five years Development plan 2016/17 – 2020/21, the country also wants to promote productivity, such that the industries get sufficient agricultural based raw materials within the country.


  1. To develop effective site specific soil fertility management for improved crop production
  2. To assess potential use of different types of soil organic matter in improving crop production and soil quality
  3. To device strategies to restore degraded agricultural lands.
  1. Soil fertility management

 Research topic

  1. To develop relevant integrated soil fertility management packages
  1. Maintaining soil organic matter resources

Research Topics:

  1. Assessment of alternative means of enhancing the soil organic matter status  under specific  cropping systems
  2. Manipulation of soil organic matter quality and decomposition for prolonged nutrient release
  • Crop residue management and its impact on soil quality and land productivity


  1. Management and rehabilitation of degraded land resources

Research Topics:

  1. Unlocking the potential of bioremediation of salt affected soils in flood plains and irrigated soils in semi-arid areas.
  2. Formulating new approaches in root-zone salinity management in flood plains and semi-arid environment
  3. Identification and testing of chemical and biochemical approaches in soil acidity and Aluminium toxicity management
  4. Assessment of the performance of different approaches in the management of polluted soils.

Commercial Lab

 The commercial laboratory is section within the department services offered which aimed at serving customers from defferent area in a commercial basis


  • Soil testing for agricutural purposes.
  • Water analysis for Irrigation purposes.
  • Plant tissue analysis.
  • Fertlizer testing for Quality (These are done mostly for elemental basicaly impurities).
  • Manure nutrients analysis.
  • Sampling ( under request)




Soil testing is an important diagnostic tool for determining the nutrient needs of plants and for environmental assessments. Some soils are inherently deficient in plant nutrients. Other soils had sufficient levels of nutrients in the past, but removal with crop harvest has depleted the reserves. Thus, soil testing is widely accepted and used in most advanced crop-production areas of the world to determine fertilization needs for crops. Soil testing can also be used to identify application rates of waste materials containing nutrients or other elements that could harm the environment. Waste materials such as animal manures and industry by-products may provide various plant nutrients. However, high application rates to soils designed to dispose of the material at a low cost may result in nutrient loads that are harmful to plant, animal, or human health. Nutrient management regulations are being developed to address land application of waste materials. Soil testing is required in many regulations and management guidelines to assess environmentally harmful levels of certain elements and to determine limits to application rates.

Soils are tested routinely for the primary nutrients phosphorus (P), potassium (K), and nitrogen (N). In some regions, soils are also routinely tested for other primary nutrients such as calcium (Ca), magnesium (Mg), and sulfur (S), and for other nutrients required in very small amounts by crops such as boron (B), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), and zinc (Zn). Soils receiving waste materials are also tested for elements such as arsenic (As), cadmium (Cd), nickel (Ni), lead (Pb), mercury (Hg), and selenium (Se) among others.

Two of the primary plant nutrients, N and P, may have harmful effects on the environment when applied to soils in excessive amounts. Excessive N and P applications to agricultural fields and ineffective nutrient, soil, and water conservation practices are increasing nutrient pollution in many regions of the world. However, the basic concepts of soil testing also apply to other elements. Phosphorus is included with the group of elements with relatively low mobility in soils (Ca, Cd, Cu, Fe, Mg, Mn, Mo, Ni, Pb, and Zn among others). N, especially in the nitrate form, is included with the group of elements with greater mobility (which include B, Cl, S, and others). Important concepts include the meaning of a soil-test value, soil-testing quality, use of soil testing to determine economically optimum nutrient application rates, and use of soil testing for environmental assessments.

Soil Electrical Conductivity (SEC)

 The preferred index to assess soil salinity is electrical conductivity. Electrical conductivity measurements are reliable, inexpensive to do, and quick. Thus, EC is routinely measured in many soil testing laboratories. The EC is based on the concept that the electrical current carried by a salt solution under standard conditions increases as the salt concentration of the solution increases. A sample solution is placed between two electrodes of known geometry; an electrical potential is applied across the electrodes, and the resistance (R) of the solution between the electrodes is measured in ohms. Electrical conductivity is expressed in micromhos per centimeter µmho cm−1) or in millimhos per centimeter (mmho cm−1). In SI units the reciprocal of the ohm is the siemen (S) and EC is given as S m−1 or as decisiemens per meter (dS m−1). One dS m−1 is one mmho cm−1.

The electrical conductivity of the extract of a saturated paste of a soil sample (ECe) is a very common way to measure soil salinity. In this method, a saturated soil paste is prepared by adding distilled water to a 10- to 50-g sample of air-dry soil and stirring. The mixture should then stand for several hours so that the water and soil react and the readily soluble salts dissolve. This is necessary so that a uniformly saturated and equilibrated soil paste results.



General considerations to take into account when making lab test of irrigation water are listed below:

- Usually 1L of sample is sufficient

- All samples should be labelled to indicate date, location, time and other pertinent data.

- Take seasonal samples for representative data due to variation of water quality by climate conditions

- Take samples before and after the treatment plant for recycled water and other representative samples when appropriate such as after the storage tank, etc.


There are four basic criteria for evaluating water quality for irrigation purposes:

  • Total content of soluble salts (salinity hazard)

  • Relative proportion of sodium (Na+) to calcium (Ca2+) and magnesium (Mg2+) ions  sodium adsorption ratio (sodium hazard)

  • Residual sodium carbonates (RSC)  bicarbonate (HCO3-) and carbonate (CO32−) anions concentration, as it relates to Ca 2+ plus Mg2+ ions.

  • Excessive concentrations of elements that cause an ionic imbalance in plants or plant toxicity.


Soil fertility evaluation does not rely on soil testing alone. Visual diagnosis of plant nutrient deficiencies, in-field measurements of plant nutrient status, laboratory analysis of tissue nutrient concentrations, and remote sensing of plants can all be valuable tools in identifying plant nutrient deficiencies, so that they can be corrected or prevented. Soil testing can be used before planting or in season to guide nutrient applications. Plant tissue analysis can be used in season to identify or confirm visually observed nutrient deficiencies. When combined with a soil testing program, plant tissue sampling and testing or analysis can be very useful in determining the cause of visual deficiency symptoms. There are many tools available for in-field plant analysis, including the leaf chlorophyll meter that measures light absorption at specific wavelengths and handheld or equipment-mounted photometers that measure light reflectance. These tools are often used to calculate various vegetative indexes based on the ratio of light reflectance at different wavelengths to estimate sufficiency or predict nutrient need through more advanced algorithms. However, these types of diagnostic tools are beyond the scope of this article, which is limited to traditional visual diagnosis and plant tissue analysis.

It is important to take a holistic approach to soil fertility management and interpret tissue test results in the context of soil test results, field conditions, plant health, and other potential plant stresses. Many factors can influence relative nutrient availability or the ability of a plant to take up available nutrients, causing a nutrient deficiency to be expressed visually or in tissue nutrient concentrations. For example, a grower may visually identify P deficiency in a corn field due to the presence of stunted, purple-colored plants. If only a tissue sample was collected and it showed P deficiency, the grower may then conclude that additional P is required. However, a soil sample may reveal that there was adequate P in the soil, but that the pH was low, limiting P availability, evaluation of the whole plant could reveal that a root disease, such as Pythium root rot, induced the above-ground P deficiency symptoms. In either case P fertilizer was not truly required, even though a tissue test alone would have indicated that it was. There are many examples where soil nutrient concentration is not the culprit of a deficiency identified visually or through tissue analysis, so caution should be applied when interpreting plant tissue concentrations. A valuable application of tissue testing is to confirm nutrient deficiencies within problem areas observed in a field. For example, many nutrient deficiencies result in plants exhibiting interveinal chlorosis. If the symptom is exhibited sporadically across the field, tissue samples can be collected from within the affected regions and compared with results from samples collected from unaffected regions. This comparison along with soil test results from both areas can be used to narrow which specific nutrient might be causing the symptoms. However, it is important to remember that it is not enough to identify a nutrient deficiency, the cause must also be determined before corrective action can be taken. It does no good to apply a nutrient that is deficient if soil compaction, pH, root disease, or other problems are limiting uptake of that nutrient by the crop.

The results of tissue analysis are highly dependent on how and when the sample was collected. Some of the essential elements are considered mobile nutrients within plants because they can be translocated from mature plant parts to the areas of the plant that are actively growing (meristem), so that deficiencies will occur initially in the older parts of the plant. Conversely, immobile nutrients cannot translocate and therefore deficiency symptoms are typically exhibited initially in the youngest part of the plant.


DSGS laboratory offer a broad range of analytical services to the fertilizer industry