Prognosis of salinity and alkalinity. FAO Soils Bulletins

260 Pages·1997·39.61 MB·English

Prognosis
of salinity
31
and alkalinity
F000
AND
ACiAlCUL TU RE
041GANIZATION
OF THE
UNITIM NATiOliS
CONTENT'S
i. INTRODUCTION
SUMMARY OF DISCUSSIONS
REOCKMENDATIONS
IV. WORKING PAPERS
A. Evolution, Extent and Economic Land Classification of
Salt Affected Soil
Paper I Evolution of noil aalinity, alkalinity and waterlogging
Prof. V.A. Kovda
7
Paper 2 Present and potential salt affected soils an introduction
Dr. I. Szabolcs
9
Paper 3 Economic land classification for the prevention and
reclamation of salt affected soils
Mr. W. Peters
15
B. Factors to be considered for Proi7ronin
Paper 4 1. Natural factors
Dr. W. H. van der Molen 31
2. Manmade factors:
Paper 5 Water management and salinity
Dr. Jan van Schilfgaarde
+
Paper 6 Assessing the suitability of water for irrik7ation:
theoretical and empirical approachen
Drs. J. D. Rhoades and S.D. Merrill 69
Paper 7 Soil management and agronomic practicen
Dr. F.I. Massoud 111
a Methods of Proonosis and Monitcrifw
Paper 8 Soil and hydrologic surveys for the prognosis and monitoring
of salinity and alkalinity
Drs. I. Szabolcs, G. Varallyay and K. Da-ab 119
Paper 9 Soils and hydrologic surveys
Dr. K. W. Flach 131
Paper 10 4. Use of aatellite imagery for salinity appraisal
in the Indus Plain
Mr. M. Rafig 141
5. Laboratory and field characterizations
Paper 11 Laboratory analyses of soils related to the
prognosis and monitoring of salinity and alkalinity
Dr. K. Darab 147
Paper 12 Measuring, mapping and monitoring field salinity
and water table depths with soil resistance
measurements
Dr. J.D. Rhoades 159
Page 13 La morphologic des sols affectes par le sel,
reconnaissance ,2t prevision - surveillance continue
Dr. G. Aubert 187
Paper 14 Survey methods lor performance, monitoring and
prognosis of natural vegetation and economic
crops with special reference to salt affected soils
Dr. I.S. Zonneveld 195
Paper 15 6. Modelling of salt movement through the soil profile
Dr. H. Laudelout 213
D. Tentative Guidelines
Paper 16 1. Interpretation of quality of water for irrigation
Dr. R.S. Ayers 221
Paper 17 2. Predicting soil salinization, alkalization and waterlogging
Dr. A. Monem Balba 241
WORLD MAP OF DESERTIZATION
Discussion paper on the preparation of the World Map
of Desertization with particular reference to
salinity/alkalinity problms
Mr. P.J. Mahler 253
Draft Report of an FAO Expert Consultation on the Preparation
of a World Map of Desertization 257
ANNEX 1 Agenda 265
ANNEX 2 List of Participants 267
I. INPRODUCTION
The present need for more food and fibre entails reclamation and development of new
land resources apart from an increaue in the agricultural inputs necessary for greater
production. Irrigated agriculture plays, and will continue to play, a major role in
increasing the food supply - especially in arid and semi-arid regions. it present, heayy
investments are being made in the development of irrigated farming in countries where the
quality of either the soil or the water, or sometimes both, is not good enough to yield an
economic return without the addition of reclamation measures or special management practices.
Moreover, the deterioration of agricultural production on previously productive lands in the
arid and semi-arid zones can be directly attributed to the evolution of salinity and
alkalinity (sodicity).
There is no doubt that the ear/y prediction of these hazards helps the timely setting
up of land protection programmed. Unfortunately this concept had not been given the same
attention as diagnosis and improvement. It is high time to voice clearly that protection
is better than cure and to investigate the methodology of prognosis and monitoring of salt
affected soils.
Thia Expert Consultation was held al; a joint venture between FAO and the ISSS Sub-
Commission on Salt Affected Soils. The meeting took place at FAO in Rome from 3-6 June
197',: and was chaired by Dr. I. Stabolcs, Chairman of the Sub-Commission on Salt Affected
Soils; Prof. Dr. V. 1. Kovda, past President, Dr. R. Dudal, Secretary-General and Dr. J.
van Schilfgaarde, Vice-President of Commission VI on Soil Technology also participated.
The Technical Secretary was Dr. Fathy I. Massoud of the FlO Soil Resources Development and
Conservation Service. Thirteen experta from nine countries, a representative from Unesco
and FAO staff also took part.
The purpose of the Consultation was to obtain expert advice on scientific and applied
research activities in the prognosis of salinity and alkalinity with the objective of pre-
paring a guideline for predicting aalinity and alkalinity and to make recommendations on the
measures needed for the implementation of the prognosis concept.
The followirg subjects were presented for discussion:
extent and evolution of aalt affected soils and economic land classification,
factors to be considered for prognosis,
methods of prognosis and monitoring,
tentative guidelines.
During the Expert Consultation there was a short special seeeion following the
decision by the Administrative Committee on Coordination of the United Nations to entrust
FAO with "the preparation of a world map of areas affeoted and areas likely to be affeoted
by the procese of desertification." The meeting considered the purpose of the map, having
taken into oonsideration the constraints, and then outlined the acope of the mil) which, it
is intended, shall be published by the end of 1976; to this end the master oopy of the map
ahauld be ready by mid 1976.
Aukno.,:ledgements
The Conmiltation acknowledged its satisfaction with the work undertaken during its
deliberations and with the recommendations formulated. It recognized the importance of
this meeting as an international forum for exchanging information and promoting better
understandin,'; of the factor..; to be considered in and methodology of prognosis and
of salinity and alkalinity. It expressed its appreciation to FAO, in cooperatimoonnit owriintgh
the ISSS Sub-Commission on Salt Affected Solis, for convening and servicing the meeting.
The Consultation also extended its thanks to national and international institutions and
org...ni2ations for releasing their experts to participate in this venture.
SUMMARY OFDISCUSSIONS
The Consultation considering the high investment involved in land reclamation
and irrigation projecte and the seriouenees of possible failure of ouch projects and,
recognizing that protection is better than cure, felt that proper planning ehould be
baeed on:
saund economic and social justifications, not only on a ehort term basis but
aloo on a long term one;
investigations on soile, hvdrology, hydrogeology, topography, vegetation,
climate, groundwater dept.h and quality, artesian water, irrigatian water quality
and quantity and crops;
murveys that are carried aut regarding the land properties related tc salt and
water movement;
suitability of the land for development, not only within the project boundaries
but as part of the surrounding land characteriatics or the watershed area;
efficient management that is formulated in tes of specific environmental
conditions.
The Consultation recognized the importance of prognosis of aalinity and
alkalinity which should be baeed on knowledge of processee involved, and realising
the neceasity of achieving and maintaining favourable salt balance and the value
of early predection of potential'nazardo, considered that meaaures should be taken
to monitor regularly salinity and alkalinity changes by testing:
salt concentration and comeoeition of the soil, 7.rigation and
groundwater quality, depth to goundwater, water transmitting
propertiee of the aoil, environmental factors affecting evapo-
transpiration, crop performance and yield.
Also coneideration ahould be given to uaing proper water management practices
to puah salte below the active rcot sone, to adequate drainage gyetems being provided
and to desalination of the groundwater being maintained, eepecially where conditions
become favourable for upward water movement and evaporation. Care muet be taken in
land levelline:
and other cultivation techniqueo, including muichir4 and fallewing.
It was stressed that crop rotations should be considered not only in terme of their
economic return, but also in terms of the suitability of crops in connection with
noil and water qualities and their effect on the nalt balance.
The Coneultation took noto of the new developments in the field of methodo-
logy, such as remote eensing, modelling and 6011 reuistanoe measuremente that
facilitate the procese of prognoeis and monitoring. They also felt that related
eeuipment and procedure for verificetien needed to be developed further. The use
of the soil conductivity measurement technique was considered to be of particular
intereet.
It appeared to the Coneultation-that a considerable gap still exiete between
the basic principles available in the fielda of soil and water sciences and their
application to solve probleme of salt affected eoils. Thie gap was recognized to
be due to inefficient application of existing saand practicer; or to the delay in
diesemination of available knowledge. It waa felt, therefore, that exteneion
services in soil and water management ahauld be strengthened and that training, at
various levels from planners to farmers, be stressed in the theoretical and practical
aspects of causes, diagnosis, monitoring and remedies of salinity and alkalinity.
The discussion during the Conoultation reflected the general acreement on
the main factors and processes affecting salinity and alkalinity but tnere was a
difference in views on the relative weight of some of those factors and in the
methodology of prognonis. These differences in approach were due to different types
of management systems. In order to make specific recommendations, avoiding risks of
over generalization, it was guggeeted that research stations and institutes continue
or initiate investigations on quantification of the various parameters of the Emit
balance appropriate to a regional condition. It was also felt that new methodology,
such as remote sensing, should be evaluated for prognoeis and monitoring of ealinity
and alkalinity and that modelling could eery° as a tool in oecuring better manage-
ment'of irrigated lands and, therefore, ite practical application shaufd be verified
under field condition°. The discussion on the methods of aosessment of water quality
for irrigation stressed that water quality criteria should be adapted to specific
conditions.
RECCMMENDATION3
The following recommendations were formulated by the Consultation on the
presentation
basis of the and discuceion of the papers, with special reference to
those dealing with methodology.
The Consultation, aware of the sericrusnesa of the potential hazards of
salinization and alkalization of existing and newly irrigated landn and on their
environment, realizing the necessity of the early prediotion of the unfavourable
changos in the aalt balance, recognizes the importance and need of guidelines for
prognosis and monitoring of salinity and alkalinity and recommends that FAO, in
cooperation with the ISSS Sub-Commiesion on Salt Affected Soils, oontinue the work
in this field.
The Consultation recognizing that prognosis and monitoring of salinity and
alkalinity neede to be based on an analysis of the processes involved and on care-
fully selected and quantified parameters, recommends that FAO make full use of
research data available in institutions dealing with problems of salt affected soils.
Furthermore, it is recomendad that FLO promotes scientific and applied research,
exchange of ideas, training and demonstration especially in developing countries in
order to ensure experience on effective soil, crop and water management at the
planning, engineering and operational levels and also on diagnosis and monitoring
of salinity and alkalinity.
The Consultation was infovmed of the FAO/UREP Project on "A World Assessment
of Soil Degradation." This assessment would include salinity and alkalinity hazards
besides other forms of soil degradation. The Consultation recomendo that the work
salinity alkalinity
to be carried out on prognosis of and be closely linked and
coordinated with the FAO/UNEP project on soil degradation and ser-ves as a basis for
promoting the development of monitoring activitiee in irrigated areao.
The Consultation being informed that the ISSS Sub-Commission on Salt Affected
Soils would hold an inr-between Congrees meeting: International Congress on Managing
Saline Water for Irrigation: Planning for the Future, in Texas USA in August 1976,
recommends that a drdft of the guideline, to be prepared by the FAO Seoretariat, on
prognosis and monitoring of aalinity and alkalinity be ready prior to that date and
be presented for comments to the meeting of the Sub-Commission.
IV. WORKING PAYhRS
A. Evolution. Extent and Economic Land Classification
of Salt Affected Soils
Paner 1 EVOLUTrION OF SALINITf, ALKALI= AND WATERLOGGING -11
by
V. A. Kovda
Director, Inz;ttutu of Agrochemistry Soil Science
,!?c,
of the Academy of Sciences of the USSR
Why are the baste principles of land reclamation and development, which have
been known for a long time, not put into practice in the sane way as the new know-
ledge we have gained? Some factors effecting this lack of application of the
principles are:
the need for simplified presentation of the scientific material to farmers,
surveyors, engineers and planners;
dissemination of what in already known is lagging far behind;
there is a "domination" of ignorance - almost a determination to resist
change in
some sectors;
the lack of training and extension services;
the lack of infrastructures and organizational set-up;
vi, social problems.
It is the ta:;k of international organizations (FAO, Unesco, etc.) to promote
ways and means to overcome these problems. They know how and have the basic infor.-
mation. For instance, in arid countries they should help create internal auxiliary
servicee in topography, hydrology, soil interpretation, management and irrigation.
It is
true that there are natural difficulties beyond the influence of man to
delay and retard the reclamation of saline, alkali and saline-alkali soils. Exare-
pies are found in USSR AH well as in Texas and other places. In the past ages great
differences have been created by nature in the humid, sub-humid, arid and extra-
arid areas and all theee can be affected by aalinization. Today we have marshalled
much information on factors affecting the soils: on their fertility, their physical
destruction
(eome of the bent chernosems in USSR have suffered), salinity, oeconAary
ealinization, micro-structure, pH, soluble aalt content, crusting - particularly
1/
Notes taken during Prof. Kovda's speech.
after watering, and what could be called "vertiaolization" below the arable horizon
which is not due to heavy machinery.
During this work of desalinization and reclamation, the great benefit of
leaching, what we call in some cases "capital leaching", waa recognized. Leaching
under good management conditions not only decreases salinity, but stabilizes it for
future control, reduces the groundwater 1)vel and also the ealinity of the ground,-
water.
Even when salinity has been stabilized, extensive drainage is necessary to
maintain the condition of the soil. In mar' casos vertical drainage alone is not
sufficient but must be accompanied by deep horizontal drainage (e.g. the central
lowlands of Armenia). Tubewell drainage can also be of use.
Care must always be taken to desalinize goundwater and not only in the soil
root zone. It has taken too long to realize the important role played by groundwater
in nalinization and it is about time to agree on the importance of desalinization of
the groundwater. Nowadayn, we know the critical concentration in groundwater and
that the salt content must be kept below certain levels. It depends on the chemistry
of the soil, the climate, capillary action, etc. And we also know that in reclama-
tion work and to prevent secondary salinization the water table level must be
reduced.
For many years work ha u been done in Tajikistan and in the heavy soils near
the Caspian Sea to reclaim soils and to prevent salinization and alkalization. In
theae areas the reduction of the groundwater level, even to a depth of 4 m, played
a major part in reclaiming them. In USSR a minimum depth of 5 m to groundwater is
favoured.
We recently discovered the importance of artesian effect and aa a result, in
some extreme cases, it may be necessary to investigate the ponaibilitiea of reducing
groundwater depthe to 100 m, but this of couroe will be a very expensive procedure.
In the diRcussion it became clear that working on dissemination of available
data does not mean that continuing collection of basic information for technology
ahould atop. Rather that one must follow the other; there is much information
already available, now organizations like FAO and Unesco can help to ensure that
it in passed through the national infrastructures right down to the farmer and
peaaant who must apply it.
In this regard a suggention was made to recommend the establishment of re-
gional centren for land reclamation with subregional or national applied research
institutes. Field demonstrations and experimental farms are eseential in speeding
up the delivery of resulto to farmers, planners and other usera. The aim is to have
a network according to the economic possibilitiee of the country and the variability
of local conditiona.