Agriculture Reference
In-Depth Information
HOPI AGRICULTURE
In the southwestern U.S., the Hopi have been practicing agriculture for more than 500 years in an arid landscape
vegetated mostly by desert-adapted plants. Their success is based on a multi-faceted strategy: they take advantage
of natural water concentration and storage, build structures to harvest water, and plant crop varieties adapted to the
local conditions.
Total annual precipitation in the areas where the Hopi grow crops, averages only 24 to 34 cm. Nearly all this
precipitation is concentrated into two short periods of the year. In the winter, it falls mostly as snow in the mountains;
in the late summer, it comes in short downpours during convective thunderstorms. This precipitation regime poses
several challenges to agriculture. Crops can't be grown during the cold winter when precipitation is most plentiful,
and the summer rainfall is usually too intense and short-lived to percolate down into the soil; most of it is lost as
runoff.
The Hopi have learned that the local topography and soil allow them to turn these challenges to their advantage.
They plant their main crop, corn, in arroyos. The soil in the arroyos is a sandy loam deposited by many years of
flash floods, and it is covered by pure sand, blown up over the soil surface by summer winds. It sits on top of a
layer of shale, which forms an impermeable barrier. When the winter snows melt, the runoff flows down the arroyos.
It easily penetrates the sandy soil and is trapped there by the layer of shale. When the dry spring begins, the top
layer of sand is quickly dried by sun and wind into a crust, which serves to protect the lower layers of soil from
desiccation.
The Hopi plant their corn crop in late spring, placing each seed in a six- to ten-inch deep hole to give it access
to the belowground moisture. This moisture is sufficient to allow germination and development of the corn until
the summer rains come in July or August.
To get the most from the later summer rains, the Hopi build a system of dams and ditches each year. These
structures serve a dual purpose: they protect the corn crop from potential flash floods and they spread the flow of
water into a sheet, slowing it down and allowing it to percolate into the soil. Managed in this way, the summer
rains provide enough additional moisture to allow the corn to mature, and deposit alluvial soil that renews the
fertility of the fields. As an added benefit, the alluvial deposit dries out to produce a cracked and hardened surface
that protects the water stored in the soil below, much like the sand crust had done previously.
The final component of the Hopi management strategy is to plant a local strain of corn. The plants stay relatively
short, allowing them to withstand the gusty winds that frequently occur during the season, and they produce a long
taproot that can access moisture deep in the soil.
GRAZING SYSTEMS
In regions where rainfall is both limited and highly unpre-
dictable, natural vegetation is made up of a mixture of
water-seeking, drought-resistant shrubs and perennial
grasses and annual species that can germinate and com-
plete their life cycles in the short period that water is
available. The drought tolerance of the perennials is com-
bined with the drought avoidance of the annuals to form
a system that can produce biomass during most of the
year. In many parts of the world, this type of ecosystem
is associated with extensive populations of native grazing
animals. When we consider the ability of grazing animals
to move in search of adequate forage, such ecosystems
reflect considerable adaptability and diversity.
Interestingly, some of the earliest domesticates of
grazing animals are thought to have come about in areas
of more extreme, semiarid environments. Animals that
were preadapted in the wild state to subsisting on sparse
vegetative cover, such as wild relatives of sheep and goats,
provided an important means for humans to survive in an
otherwise hostile environment. Nomadic herding is
thought to be an important form of early agriculture.
Today, many managed grazing systems take advantage
of the ability of pasture or range ecosystems to maintain
production of biomass in the face of low and highly vari-
able rainfall. In most cases, natural range is managed with
specific stocking rates and timing to adjust to the natural
dynamics of plant growth in response to rainfall. Animals
are moved from one part of a range to another during the
year as forage availability shifts. In other cases, such range
is improved with the introduction of drought-tolerant for-
age species that are very successful under drier conditions.
In a world in which increasing consumption of animal
products and ecologically inefficient and degrading meth-
ods of raising livestock represent some of the most serious
threats to the integrity and long-term productivity of our
food systems, many traditional and managed grazing sys-
tems in low-rainfall regions stand as good examples of
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