Agriculture Reference
In-Depth Information
19
Advances in Water
Science, Management,
and Conservation
B. A. Stewart
contents
Abstract .................................................................................................................. 301
Introduction............................................................................................................ 302
Definition of Terms ................................................................................................ 303
Plant Growth-Water Relationships ........................................................................304
Increasing Photosynthetic Efficiency ................................................................ 307
Increasing Amount of Evapotranspiration......................................................... 307
Decreasing the Evaporation Portion of Evapotranspiration .............................. 309
Increasing the Harvestable Portion of Agronomic Crops ................................. 311
Increasing Portion of Field Water Supply Used for Evapotranspiration........... 312
Conclusions/Study Topics...................................................................................... 315
References.............................................................................................................. 315
AbstRAct
Water will become increasingly limited as the world's population increases to a
projected 8 billion by 2025. Agriculture is by far the biggest user of water, but as
population increases and industries grow, the competition among users will inten-
sify. Although about 70% of the world's food is produced from rainfall, irrigation
expansion during the past few decades is the primary reason that food production has
increased at a faster rate than population. Worldwide, about 17% of the cropland is
irrigated and accounts for 40% of the food and fiber production. Irrigation, however,
uses much of the water abstracted from aquifers and surface water supplies, such as
lakes and rivers. Irrigation accounts for nearly 70% of world water abstraction, and
it is more than 90% in some agricultural economies in the arid and semiarid trop-
ics. Agriculture must become more efficient in the use of both rainfall and irrigation
water. There are essentially five ways that improvements can progress. The first, but
perhaps the most challenging, is to increase photosynthetic efficiency. The second
is to increase the amount of evapotranspiration, which is the sum of the water trans-
pired through plant leaves and the water evaporated from the soil surface while the
301
