Pollution of Water Resources from Agricultural Fields and Its Control - Practices of Irrigation and On-farm Water Management - page 243

transient and highly variable hydrological phenomena related to the use or misuse
of land, they may also result from atmospheric decomposition of local or distinct
origin. Agricultural practices are the major nonpoint source of groundwater and/or
surface water pollution.
7.2 Types of Pollutants/Solutes
Solutes are chemicals that are dissolved in water. Solutes are of two types:
7.2.1 Reactive Solute
Reactive solute is a solute that reacts with soil during transportation. As a result, it
does move with the same velocity of water. Examples are K and Ca.
7.2.2 Nonreactive Solute
Nonreactive solute is a solute that does not react with soil or other chemicals during
transportation. This type of solute moves with the same velocity of water. Examples
are Cl and Br.
7.3 Extent of Agricultural Pollution
7.3.1 Major Pollutant Ions
The growing needs for agricultural commodities due to the ever-increasing pop-
ulation dictate intensification of agricultural activities through the application of
irrigation, chemical fertilizers, and pesticides. Application of fertilizer as an agricul-
tural practice is a major contributor to the total load of pollutants in the soil. Despite
increased agricultural productivity, the deleterious effects of these chemical fertil-
izers on the surface and groundwater quality are of alarming concern throughout
the world. Many commercial chemicals are used extensively to provide plants with
the primary nutrients like nitrogen (N), phosphorous (P), potassium (K), and sul-
phur (S). Leaching of these nutrients as deep percolation loss from the root zone of
agricultural crops continue to endanger the long-term groundwater quality in many
rural areas of the world. The fate of nitrogen in the soil is of major concern because
of the potential hazard for N, applied in excess of the natural decomposing capacity
of the soil, to contaminate shallow and deep aquifers.
Contamination of groundwater by nitrate has been a problem in many areas of
the world for many years and continues to occur. During the last two decades, many
cases of groundwater contamination from extensive fertilizer applications in water-
sheds utilized for agricultural purposes have been reported worldwide. The major
ion concentrations in such cases of groundwater pollution are nitrate (NO 3 - ), sulfate
(SO 4 -2 ), potassium (K + ), and phosphate (PO 4 -3 ).