IJERD – International Journal of Environmental and Rural Development (2023) 14-2

Research article
erd

Review on Causes, Effects, and Management of Soil Salinity
on Irrigated Rice Fields in Tanzania
JIMMY FELIX MACHA
Graduate School of Agro-Environmental Science, Tokyo University of Agriculture, Japan

MACHITO MIHARA*
Faculty of Regional Environment Science, Tokyo University of Agriculture, Japan
Email: m-mihara@nodai.ac.jp
Received 22 May 2023

Accepted 2 August 2023(*Corresponding Author)

Abstract Salinization is a process of increasing concentrations of salts in soil and water. Soilsalinity is the most serious agricultural problem in irrigation agriculture in Tanzania. Severe
salinity can cause significantly lower yields, food insecurity, and environmental degradation.
If not properly addressed, soil salinization can accelerate and potentially expand to currently
unaffected irrigated agricultural land. Despite the efforts made by the government and otherstakeholders, rice production in irrigated rice fields in Tanzania is still experiencing low
yields. Current rice yields are between 2.5 and 4 tons/ha, which is low compared to theaverage rice yields reported in other countries. Salinity problems are caused by the prevailingclimate characterized by high evapotranspiration, geological and geographical characteristicsof the area, quality of irrigation water, and inadequate land use practices. This paper aims toreview available information on the causes and effects of soil salinity on irrigated rice fields
in Tanzania and to provide information on management strategies to adjust soil salinity andimprove soil fertility. References from books, papers, journals, online readings, anddissertation papers from different universities and institutions were used to get information
for this paper review. In this review, the various reasons that cause soil salinity in irrigatedfields in Tanzania have been identified, which are the nature of rocks, poor irrigation
management, and non-compliance with established irrigation regulations. Also, the effects ofsoil salinity in Tanzania have resulted in a decrease in yields, an increase in costs ofproduction, poor quality of products, and water shortages for irrigation. Lastly, somerecommendations identified to solve the challenges of soil salinity include setting up a local
drainage system on affected land, renovating some irrigation facilities, reclaiming theaffected soil with gypsum and manure, and flushing all salt-affected water with non-salt water.
Keywords review, soil salinity, causes and effects, irrigated rice field, Tanzania,

INTRODUCTION
Globally, the challenge of soil salinity in areas that practice irrigation agriculture has been increasing
day after day, resulting in crop production decreasing while also causing land environmental
problems such as degradation, erosion, and siltation. Salinity affects about 800 million ha of arable
lands worldwide and approximately 33 % of irrigated areas (about 74.25 million ha) are currently
considered threatened by soil salinization by various degrees (Shrivastava and Kumar, 2015).
According to Jamil et al. (2011), it’s projected that by the year 2050, there will be more than 50 %of the farmland worldwide, which would become salt affected. Rice is the most sensitive cereal crop
while barley is the most tolerant cereal crop (Munns and Tester, 2008; Karan et al., 2012). Salinity
has serious effects on the percentage of filled spikelet, and grain weight, and can also hinder the
uptake of essential nutrients in rice (Clermont-Dauphin et al., 2010). Most irrigation schemes, which
are especially within arid and semiarid environments, are already experiencing increasing levels ofsalt-affected soil, solely due to the mismanagement of the soils, the use of poor-quality irrigationwater, poor drainage systems, poorly designed and managed irrigation infrastructures, excessive useⒸ ISERD

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IJERD – International Journal of Environmental and Rural Development (2023) 14-2

of irrigation water and climate change (Kashenge-Killenga, 2010). Most irrigation water qualities
have adverse effects on the physical properties of soil because it is mostly connected with the buildup
of sodium ions on the soil exchange complex. The quality of water can impact the volatility of thesoil aggregates which eventually leads to the dispersion of the clay particles and the clogging of soil
pores. When underground water is made to move to the soil surface by evapotranspiration, the soluble
salts condense on the soil particles on the surface and form a white crust.
Irrigation practices affect land by increasing the rates of leakage and groundwater recharge
which results in the rise in the water table. The water tables when it rises bring salts into the plantroot zone which affects both plant growth and soil structure; then the salt remains behind in the soil
surface after the water has been taken up by plants or lost due to evaporation (Popay et al., 2009).
Soil salinity is generally measured by electrical conductivity (EC) (Allison and Richards, 1954;
Sonmez et al., 2008; Scudiero et al., 2017). A soil is considered saline if the EC of a saturation extract
exceeds 4 dS m-1 at 25°C (Sonmez et al., 2008). Soil salinity or EC may be measured on the bulk soil(ECa), in the saturation paste extract (ECe), in soil: water ratio suspensions of 1:1 to 1:5 such as 1:1,
1:2, 1:2.5 and 1:5 or directly on soil water extracted from the soil in the field (ECw) (Allison andRichards, 1954; Sonmez et al., 2008; Kargas et al., 2018). Like other countries in Africa, soil salinity
in Tanzania contributes to one of the most serious ecological and environmental problems in most of
the irrigation schemes, so understanding the causes and effects of soil salinity in various irrigation
schemes in Tanzania, will provide an opportunity for the government to come up with enabling
policies to solve this challenge help farmers to practice irrigation agriculture that will specificallyeliminate and reduce the problem of soil salinity in their respective areas. This is because among thefactors that contribute to the increase in soil salinity are methods that are used by farmers in
irrigation agriculture, like the use of fertilizers application and improper uses of irrigation facilities.
The objective of this paper is to review the information on the causes and effects of soil salinity
on irrigated fields and to come up with information on management strategies to control the
problem.
OBJECTIVE
This review study tries to sum up and review available information on the causes and effects of soil
salinity on irrigated rice fields in Tanzania. And it provides information on management strategies
to adjust to deal with this challenge of soil salinity on rice irrigated fields in Tanzania to strengthen
Irrigation Agriculture so that it can bring productivity and income to farmers in Tanzania.
METHODOLOGY
The methodology used to get information for this paper are references from papers, journals, online,
and dissertation papers from different Universities and Institutions.
Causes of Soil Salinity on Rice Irrigated Fields in Tanzania
The main source of salt in arid and semi-arid areas includes rainfall (Rengasamy and Olsson,1991), mineral weathering (Gunn and Richardson, 1979), irrigation and various surface water(Mehanni and Chalmers, 1986; Rengasamy and Olsson, 1993), groundwater which redistributes
accumulated salts during evaporation, chemical applications (Rengasamy and Olsson, 1993) and man
activities (Dregne, 1976). These sources, coupled with environmental modifications, lead to threedifferent classes of salinization and sodicification that are grouped so for management purposes.
These classes include Saline soils that have ECe > 4 dS m−1 at 25° C and ESP < 15 (high soluble salts
and low exchangeable Na+). Sodic soils have ECe < 4 dS m−1 and ESP > 15 (low soluble salts andhigh exchangeable Na+). Saline-sodic soils are characterized by ECe > 4 dS m−1 and ESP > 15 (bothsalts and exchangeable sodium are high), pH15%, and pH>8.5) (Allison and Richards, 1954). In
Tanzania, some studies have been done to determine the sources of soil salinity in irrigation schemes,Ⓒ ISERD

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IJERD – International Journal of Environmental and Rural Development (2023) 14-2

those studies identify various reasons from different areas that do irrigation farming, and some ofthose reasons are as follows.
Table 1 Case papers used for gathering information used in this study
Researcher
and year of
publication

Research title

Journal name andpublished dateCauses of soil
salinity

Effects of soil
salinity

Management ofsoil salinity

Meliyo etal. (2017)

Evaluation of Salt
Affected Soils for Rice(Oryza Sativa)
Production in Ndungu
Irrigation Scheme Same
District, Tanzania

Sustainable
Agriculture
Research, 6 (5262017-2656)

Naturelocation of the
Irrigation area

Decrease inyields.

Manure andlimestone
application

Reclamation of sodic
soils in northern
Tanzania, using locallyavailable organic andinorganic resources

African Journal of
Biotechnology 6,
no. 16.

Soil characterization forsalt problems inselected rice irrigation
schemes

Journal ofAdvances in
Developmental
Research, 3(1).

Poor
Irrigation
Management

Exploring farmers’
perception, knowledge,
and management
techniques of saltaffected soils to enhancerice production on small
land holdings.in
Tanzania
Extent of Salt-Affected
Soils and Their Effects
in Irrigated and
Lowland Rain-Fed Rice
Growing Areas. ofSouthwestern Tanzania

Cogent Food &Agriculture, 8(1),2140470

Fertilizer
application

Makoi et al.
(2007)

Kashenge etal. (2012)

Omar et al.
(2022)

KashengeKillenga etal. (2016)

Poor Irrigation
Management
Noncompliance

Decrease incultivationarea.
Increase incosts ofproductions

The local
drainage system
infarms
The local
drainage systemin farms

Water
Shortages

Extension tofarmers on
irrigation
management
Application ofdrainagesystem

High costsof
production
Decrease inyields.

Renovation
facilities
Flashing salt
water

Poor
Irrigation
Management

Climate Change
and Sustainability
in Agriculture,
97-126

Poor drainage
systemDecrease incultivation
Area.

Poor
Irrigation
management

Increase incostsof production.

Extension
services tofarmers
Proper Irrigation
management

Firstly, the cause of soil salinity in irrigated fields in Tanzania is the natural location of an area,
most schemes which are experienced soil salinity due to the nature of rocks in their respective areas,
and this normally happens to the water source which is the source of water is from Spring or aquifer.
Irrigation salinity occurs due to increased rates of leakage and groundwater recharge causing thewater table to rise. Rising water tables can bring salts into the plant root zone which affects bothplant growth and soil structure. This is common in an area surrounded by a mountain like in the
Kilimanjaro region irrigation scheme as the Ndungu source of its irrigation water has salinity due tothe nature of the rock (sedimentary rock) which causes the soil salinity.
According to Makoi, J. H. (2007), the strong reason for the soil salinity in areas where they are
doing Irrigation Agriculture in Tanzania is poor irrigation management, which is often contributed
to the farmers themselves not knowing the methods and principles of Irrigation Agriculture. This ismuchly related to knowing when and how to irrigate (irrigation schedule), application of fertilizer,
and poor drainage system which causes accumulation of water which in the end results in soil salinity
irrigating with saline water adds salt to the soil and increases the need for applying more irrigationwater to leach salts past the plant root zone.
Another source of soil salinity is non-compliance with various laws and guidelines set under theirrigation laws in the country, which states that before starting an irrigation scheme, the source ofⒸ ISERD

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IJERD – International Journal of Environmental and Rural Development (2023) 14-2

water must be measured and tested to see if its water complies with the required quality for irrigation,
including measuring the level of salt and consider the installation of salt control infrastructure as adrainage system in the scheme. Some people do not follow the guidelines set by the Irrigation
Commission responsible for Irrigation Agriculture in the country.

Source: NIRC

Fig. 1 Soil affected by salt (A); yields of paddy affected by salt ( B ) at irrigation schemesin Tanzania due to poor irrigation management
Effects of Soil Salinity on Rice Irrigated Fields in Tanzania
Soil salinity is an environmental stress affecting agriculture globally, substantially reducing
cultivated land area, crop productivity, and quality. Farmers can keep salinity problems in check byusing fertilizer. It is widely recognized by soil scientists that soil salinity reduces crop yield.
Salinity not only decreases the agricultural production of most crops, but also, affects soil
physicochemical properties, and the ecological balance of the area. The impacts of salinity include—
low agricultural productivity, low economic returns, and soil erosion (Hu and Schmidhalter, 2005).
In Tanzania, soil salinity has caused various challenges, but the biggest one is the decrease in yields
production, as statistics show that almost five percent (5%) of the area suitable for agriculture inmany irrigation schemes in Tanzania is not cultivated due to soil salinity problem also there are somecases in some Irrigation scheme where they usually produce 3-4 t/ha now they are producing 1-1.5
t/ha due to problem of soil salinity (Luzi-Kihupi et al., 2015). Being not cultivated and abandoned
automatically leads to a decrease in Production yields in a particular area and affects farmers' income
incomes. Also, soil salinity, causes production costs to increase for farmers in Tanzania. as many ofthem use various methods to reduce salt, including using a lot of fertilizer so that their plants arehealthy remaining, others also use gypsum to improve the soil structure damaged by salts. By doing
all of this it leads to an increase in the cost of production (Kashenge, 2016). Another effect of soil
salinity in Tanzania is irrigation water shortages, this is because in Tanzania most of the farmers
reduce the salinity in their fields by applying much water to fields to flush out the water affected bysalts and also to balance salt-affected soil, so a lot of water is used to flush out and by doing that it
leads to shortages of water for irrigation on downstream. Water shortages downstream lead toconflicts among the farmers in most of the irrigation schemes in Tanzania (NIRC).
DISCUSSIONManagement to Control Soil Salinity
There have been various efforts taken by farmers to control soil salinity in their irrigated fields toeliminate or reduce the problem, also governments, stakeholders, and research institutions arecontinuing to come up with a different approach to controlling soil salinity.
Provision of drainage system to the area affected, this method is mostly used by most farmers,
they create local drainage systems on farms to remove water with salinity from the soil, and therefore
the amount of soil salinity automatically is reduced and the drained water is removed through theⒸ ISERD

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outlet. The other suggested ways of removing soil salinity recommended by researchers are such torenovate and close supervision of water inlet and outlet canals to prevent leakage of water between
blocks, affected fields require reclamation by the use of gypsum, farm-yard manure, good drainage
and flushing using good quality water, It is essential that drainage water, with its salt load from theaffected soil, be removed from the scheme, the use of farmyard manure at a rate of 3 to 8 tons/ha isrecommended to boost soil organic matter and improved soil infiltration to facilitate washing of salts
to minimize the effect of salts (Meliyo, 2016). The farmyard manure will also supply some nutrients(N, P, and K) that were limiting in some soils and therefore need to be added to improve riceproductivity andSoil reclamation will probably need to be a continuing practice in the most affectedareas. The most economical solution to maintain productivity will probably be a combination of salttolerant variety selection and soil amelioration practices (Mdemu, M.L., 2020).
CONCLUSION
Controlling soil salinity, sustainable soil, and irrigation water management practices have a vitalrole in the production of rice at irrigation schemes in Tanzania country. Many approaches areavailable to rehabilitate salt-affected soils. These include physical methods (irrigation anddrainage management); chemical amendments (gypsum, H2SO4, combined application gypsum
with other organic amendments); and biological approaches (screening salt-tolerant genotype,growing ameliorating crop species, crop species in rotation, etc.). The agro-ecological conditionsin Tanzania are comparable to many other countries where these approaches have successfully
been tested. Therefore, there is a good potential for adopting these practices that will increase
economic benefits to farmers.
ACKNOWLEDGEMENTSFirst, I thank God for his blessing to me, special thanks to research fellows in the laboratory ofTokyo University of Agriculture for his supervision, mentorship, guidance, and advice. Lastly
many thanks to JICA for the financial support of my research.
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