Agriculture Reference
In-Depth Information
8.3.6.1
WATER STRESS
Water availability is expected to be highly sensitive to climate change and
severe water stress conditions will affect crop productivity, particularly
that of vegetables. In combination with elevated temperatures, decreased
precipitation could cause reduction of irrigation water availability and in-
crease in evapotranspiration, leading to severe crop water-stress condi-
tions (IPCC, 2001). Vegetables, being succulent products by definition,
generally consist of greater than 90% water (AVRDC, 1990). Thus, wa-
ter greatly influences the yield and quality of vegetables; drought condi-
tions drastically reduce vegetable productivity. Drought stress causes an
increase of solute concentration in the environment (soil), leading to an
osmotic flow of water out of plant cells. This leads to an increase of the
solute concentration in plant cells, thereby lowering the water potential
and disrupting membranes and cell processes such as photosynthesis. Wa-
ter stress, particularly at the tuber forming stage, can also lead to a higher
susceptibility of potatoes to postharvest development of black spot disor-
der (Hamouz et al., 2011).
Vegetable crop water requirements range from about 6 inches of water
per season for radishes to 24 inches for tomatoes and watermelons. Precise
irrigation requirements can be predicted based on crop water use and ef-
fective precipitation values. Lack of water influences crop growth in many
ways. The effect depends on the severity, duration, and time of stress in
relation to the stage of growth. Nearly all vegetable crops are sensitive
to drought during two periods: during flowering and two to three weeks
before harvest.
8.3.6.2
LEAFY VEGETABLES
Cabbage, lettuce, and spinach are generally planted at or near field ca-
pacity. Being shallow rooted, these crops benefit from frequent irrigation
throughout the season. As leaf expansion relates closely to water avail-
ability, these crops, especially cabbage and lettuce, are particularly sensi-
tive to drought stress during the period of head formation through harvest.
Overwatering or irregular watering can result in burst heads. Broccoli and
cauliflower, although not grown specifically for their leaves, respond to
irrigation much as the leafy vegetables do. Broccoli and cauliflower are
