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Title:Sustainability of the Indus Basin: Impact of tertiary salinity/sodicity on wheat productivity, damage assessment and future public policy
Author(s):Siddiq, Akmal
Doctoral Committee Chair(s):Hornbaker, Robert H.
Department / Program:Agriculture, Agronomy
Economics, Agricultural
Chemistry, Agricultural
Discipline:Agriculture, Agronomy
Economics, Agricultural
Chemistry, Agricultural
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Agriculture, Agronomy
Economics, Agricultural
Chemistry, Agricultural
Abstract:The Indus Basin of Pakistan has the largest contiguous canal irrigation system in the world. However, the canal system, as important as it is, has overshadowed the equally important supplementary source of irrigation in the Basin--the groundwater. Today, over 40% of the annual irrigation requirements are met from groundwater and, in many regions, this proportion may be as high as 70% for rabi season when wheat is the dominant crop.
Since the early 1960s, development of groundwater resources has been rapid, indiscriminate, and unregulated. Over three-fourths of about 324,000 private and about 16,000 public tubewells are believed to be pumping brackish groundwaters. The nature and extent of salinization being spread through groundwater irrigation--introduced in this dissertation as tertiary salinization--and its impact on soil health and crop yields is not yet known. No empirical study was found which used the actual farm-level data to explore such issues. This pioneer study was designed to fill some of these gaps.
Two spatially separated research locales, Manawala and Pir Mahal Distributary Command Areas (MDCA and PMDCA), located in Pakistan's Punjab province, were selected for this study in rabi 1991-92 season. Farm-level data on inputs and outputs along with soil and irrigation water samples were collected from randomly selected wheat fields which were spatially spread in the head-, middle-, and tail-reaches of each distributary. Soil and groundwater samples were chemically analyzed to determine the levels of salinities and sodicities. A four-step analytical procedure, including estimation of production functions and policy simulations, was followed to analyze these data separately for both locales.
Five major conclusions can be drawn from this study. First, that a great majority of tubewell (ground-) waters from both locales were not fit for unrestricted irrigation. Second, groundwater quality exhibited a deteriorating head-to-tail-reach trend only in Manawala--it was opposite in Pir Mahal. Third, none of the soil samples showed any evidence of salinity build-up--this finding was unexpected. Soil salinity level, in almost all individual sample fields, was well below the salinity threshold of wheat, i.e., ECe 6 dS/m. Fourth, sodicity, however, was found to have a detrimental impact on wheat yields. The sodicity threshold of wheat was much lower--at SARe 4 (mmol/l)$\sp{1/2}$--than most experimental studies had previously suggested. At this sodicity threshold, wheat yield losses were estimated to be around 411 kg/ha in MDCA and 213 kg/ha in PMDCA. And at the Basin level, even after considering a modest yield loss of 200 kg/ha, wheat production losses might amount to well over 1.3 million mt or Rs 4 billion every crop season. And fifth, soil sodicity increased towards the tail-reach exhibiting significant head-to-tail-reach trends in both locales. Tail-reach farmers, in both locales, were found to be worse off in several different ways.
To effectively mitigate the sodicity hazard, use of a soil amendment is necessary. And for practical and economic reasons, gypsum was found to be the most appropriate amendment. Policy simulations indicated that gypsum application, even at its commercial cost, would result in considerable net profits. So, gypsum subsidies are discouraged.
An overall conclusion is that irrigated agriculture in the Indus Basin, given the modern knowledge and technology, is certainly sustainable both in the short- and in the long-run. However, to maximize the gains from soil amelioration, it is imperative to correctly identify the problem which is region or even reach-specific.
Issue Date:1994
Rights Information:Copyright 1994 Siddiq, Akmal
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9512550
OCLC Identifier:(UMI)AAI9512550

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