4.3 Quantitative and Qualitative Response of Crops
to Irrigation with Wastewater
The quality of water used for crop irrigation can impose a major constraint to
agricultural productivity because of its influence on soil fertility and crop yields.
Therefore, the knowledge of the effects of the water quality used for irrigation on
crop yield response is critical to the understanding of necessary management criteria
for long-term productivity as well as to develop the most suitable irrigation schedule
to get the optimum plant yield and the desired profit from irrigation. These aspects
are of particular importance if considering that the continuous decrease in water
resources in the world in general, and in arid and semi-arid regions in particular, is
continuously forcing farmers to use wastewaters and modify the conventional
irrigation practices.
The plant responses in terms of yield and quality of agricultural products to
wastewater are often contrasting; generally, either positive or negative and sometimes even neutral effects have been reported for crops. Positive effects of treated
wastewaters reuse on the growth and production of cultivated crop, as well as on the
chemical and microbiological characteristics of crop products, were observed within
the experimental trials of the already mentioned In.Te.R.R.A project.
Field experiments were carried out in different pedoclimatic conditions of the
Apulia region (Southern Italy) with the aim to evaluate the quali-quantitative
response of several horticultural and vegetable crops to the irrigation with municipal
and agro-industrial-treated wastewaters [3, 17, 18, 60]. At the same time, the
hygienic traits of crop products, such as the presence of Coliforms, Escherichia
coli and Salmonella, and the risks for human and environmental health related to the
reuse of this irrigation source, were verified. Horticultural crops, such as processing
tomato (Lycopersicon esculentum Mill.), artichoke (Cynara cardunculus L. subsp.
scólymus Hayek), broccoli (Brassica oleracea L. var. italica), and vegetable crops
for fresh consumption, such as lettuce (Lactuca sativa L.), fennel (Foeniculum
vulgare Mill.), melon (Cucumis melo L.) and cucumber (Cucumis sativus L.),
were examined. The results obtained indicated that the qualitative traits of crop
products (e.g. dry matter content, diameter, soluble solid content, titratable acidity,
pH) were similar to those obtained when the crops were irrigated with conventional
water.
In some cases, when the amounts of nutrient elements (N, P, K) supplied to the
crops by wastewater were higher than those supplied by conventional water, also the
productive response of the crops, in terms of both total and marketable yield, was
positive. During the considered crop cycles, a sporadic presence of pathogenic
microorganisms was observed in the soil and, only in rare cases, on the aerial part
of the plants. However, in no case the presence of pathogenic microorganism was
possible related to the wastewaters microbiological quality, because other potential
contamination factors, such as vector insects, aerosols, wild animals, birds,
processing and harvesting personnel, endogenous environmental factors, can likely
have played a role in microbial contamination of soil and plants [83]. As
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G. Gatta et al.
to Irrigation with Wastewater
The quality of water used for crop irrigation can impose a major constraint to
agricultural productivity because of its influence on soil fertility and crop yields.
Therefore, the knowledge of the effects of the water quality used for irrigation on
crop yield response is critical to the understanding of necessary management criteria
for long-term productivity as well as to develop the most suitable irrigation schedule
to get the optimum plant yield and the desired profit from irrigation. These aspects
are of particular importance if considering that the continuous decrease in water
resources in the world in general, and in arid and semi-arid regions in particular, is
continuously forcing farmers to use wastewaters and modify the conventional
irrigation practices.
The plant responses in terms of yield and quality of agricultural products to
wastewater are often contrasting; generally, either positive or negative and sometimes even neutral effects have been reported for crops. Positive effects of treated
wastewaters reuse on the growth and production of cultivated crop, as well as on the
chemical and microbiological characteristics of crop products, were observed within
the experimental trials of the already mentioned In.Te.R.R.A project.
Field experiments were carried out in different pedoclimatic conditions of the
Apulia region (Southern Italy) with the aim to evaluate the quali-quantitative
response of several horticultural and vegetable crops to the irrigation with municipal
and agro-industrial-treated wastewaters [3, 17, 18, 60]. At the same time, the
hygienic traits of crop products, such as the presence of Coliforms, Escherichia
coli and Salmonella, and the risks for human and environmental health related to the
reuse of this irrigation source, were verified. Horticultural crops, such as processing
tomato (Lycopersicon esculentum Mill.), artichoke (Cynara cardunculus L. subsp.
scólymus Hayek), broccoli (Brassica oleracea L. var. italica), and vegetable crops
for fresh consumption, such as lettuce (Lactuca sativa L.), fennel (Foeniculum
vulgare Mill.), melon (Cucumis melo L.) and cucumber (Cucumis sativus L.),
were examined. The results obtained indicated that the qualitative traits of crop
products (e.g. dry matter content, diameter, soluble solid content, titratable acidity,
pH) were similar to those obtained when the crops were irrigated with conventional
water.
In some cases, when the amounts of nutrient elements (N, P, K) supplied to the
crops by wastewater were higher than those supplied by conventional water, also the
productive response of the crops, in terms of both total and marketable yield, was
positive. During the considered crop cycles, a sporadic presence of pathogenic
microorganisms was observed in the soil and, only in rare cases, on the aerial part
of the plants. However, in no case the presence of pathogenic microorganism was
possible related to the wastewaters microbiological quality, because other potential
contamination factors, such as vector insects, aerosols, wild animals, birds,
processing and harvesting personnel, endogenous environmental factors, can likely
have played a role in microbial contamination of soil and plants [83]. As
94
G. Gatta et al.