Abstract
The increasing demand for water worldwide has resulted in the emergence of wastewater use
for irrigation. Field experiments by (i) irrigation with wastewater of different blends in
combination with recommended standard fertilizer dose and no fertilizer, (ii) irrigation with
wastewater and different fertilizer doses, and (iii) irrigation with wastewater and varying
specific nutrients evaluated the efficacy of wastewater irrigation. The study was done at the
experimental farm of the Bangladesh Agricultural University at Mymensingh in Bangladesh
during 2007/2008–2009/2010 crop seasons to investigate the effects of irrigation by municipal
wastewater of Mymensingh on the growth, yield and quality of wheat and potato and on the
properties of irrigated soils. Both crops were irrigated by five different blends of wastewater
and freshwater, and two fertilizer doses. The composition of the irrigation treatments
(wastewater: freshwater) was I1 (0 : 1), I2 (1: 3), I3 (1 : 1), I4 (3 : 1) and I (1: 0), and the
fertilizer levels were Fo (no fertilizer) and F₁ (recommended standard dose). The growth and
yield variables and yield of the crops were significantly higher in 13, I4 and Is compared to
those in the control treatment, I₁. Wastewater caused an increase in plant height, spike length,
spikelet per spike, grain per spike, 1000-grain weight, leaf area index, above-ground dry matter
and grain yield of wheat; and plant height, vigority, area coverage, leaf area index, stem per
plant, number and weight of tuber per plant, above-ground dry matter and tuber yield of potato
in I3 - I5 compared to I1. On the average over three years' study, I4 produced the highest yield
followed by I5 under fertilized condition in both crops. The significantly higher growth and
yield variables of the crops in the fertilized treatments than in the unfertilized ones with the
most improved values in the raw wastewater-irrigated treatments implied that the nutrient
contents of the wastewater was inadequate to meet up the fertilizer requirement of the crops.
Thus, I4 and, with a reduced fertilizer dose, I5 provided the best condition for wheat and potato
production under fertilized condition. Wastewater reduced bulk density and increased hydraulic
conductivity of the surface soil. It significantly elevated soil organic C; total N; available P and
S; and exchangeable K, Na, Ca and Mg; the increase was the highest in the surface soil.
Wastewater elevated the N, P and K in the plants and grains/tuber. It insignificantly raised pH
and electrical conductivity of soil extract. Of the wastewater-fertilizer dose combination, 75%
of standard fertilizer dose produced the maximum grain yield, while 100% of standard fertilizer
dose provided the most improved growth variables and straw yield. Wastewater with varying
levels of N and P exerted significant influence on the growth and yield variables as well as the
yield of wheat, but the varying K levels showed insignificant effects on them. The effects of
omission of N in degrading the growth and yield variables, and yield were more prominent than
that of P; the K omission virtually showed no effect. Irrigation by wastewater could save
20-25% of the recommended fertilizer for wheat and 10-15% for potato cultivation. The
wastewater irrigation helped realizing a high net return (US$ 1294 ha for wheat and US$
2856 ha for potato) and a high benefit-cost ratio (2.43 for wheat and 2.54 for potato) from the
crops and thus demonstrated its efficacy in irrigation.