Agriculture Reference
In-Depth Information
Q of about 600 mm, which is considerably less than the 1150 mm necessary to pro-
duce maximum grain yield (this value can be graphically determined by the tangent
on the curve to a line constructed through the origin); and (3) assuming a constant
water cost, the maximum net profit will normally occur at a value of field water sup-
ply exceeding ET
m
but less than Q
m
(unless water is free) and will decrease as the
water price increases for fixed land but increase with higher fixed production costs.
conclusIons/study toPIcs
Agriculture is the biggest user of water in the world. Approximately 70% of all water
abstracted from surface and groundwater supplies is used for irrigation, and this
accounts for about 40% of the food and fiber produced. Increased irrigation during
the past 50 years has been the primary reason that food and fiber production has
increased faster than the increase of population. Irrigation expansion in the future,
however, will be constrained because of limited water resources and increased devel-
opment costs. Only 15 to 30% of rainfall is actually used by crops for transpiration.
Runoff accounts for 10 to 25%, and the remainder is lost by evaporation from the soil
surface. There are well-established relationships that can be used to develop manage-
ment practices to increase the efficiency of water utilization from both irrigation and
precipitation.
•
Evapotranspiration is the sum of the water evaporated from the soil surface
and transpired through the leaves of a growing crop between time of plant-
ing and harvesting.
The agronomic yield of a crop increases linearly with an increase in amount
•
of water used by evapotranspiration.
The use of mulch can decrease the evaporation portion of evapotranspira-
•
tion so that more water is available for transpiration because there is a direct
relationship between plant growth and transpiration.
RefeRences
Bandaru, V., B.A. Stewart, R.L. Baumhardt, S. Ambati, C.A. Robinson, and A. Schlegel. 2006.
Growing dryland grain sorghum in clumps to reduce vegetative growth and increase
yield.
Agronomy Journal
98:1109-1120.
Briggs, L.J. and H.L. Shantz. 1913. The water requirement of plants: II. A review of the litera-
ture.
USDA Bureau Plant Industry Bulletin
284.
Briggs, L.J. and H.L. Shantz. 1917. The water requirement of plants as influenced by environ-
ment.
Proceedings of the Second Pan-American Science Congress
3:95-107.
Caryl, C. 2007. Cool, clear water.
Newsweek
October 1, p. 71.
Evans, L.T. 1980. The natural history of crop yields.
American Science
68:388-397.
Food and Agriculture Organization (FAO). 1996.
Food Production: The Critical Role of
Water
. Background paper for the World Food Summit. Rome: Food and Agriculture
Organization of the United Nations.
Food and Agriculture Organization (FAO). 2003.
World Agriculture: Towards 2015/2030. An
FAO Perspective
, J. Bruinsma, Ed. Rome: Food and Agriculture Organization of the
United Nations.
