Page 247 - Environment: The Science Behind the Stories

methods on over half their farmland. According to U.S. govern-
1 Cut furrow ment figures, erosion rates in the United States declined from
9.1 tons/ha (3.7 tons/acre) in 1982 to 5.9 tons/ha (2.4 tons/acre)
in 2003, thanks to conservation tillage and other soil conserva-
tion measures.
No-till and conservation tillage methods were pio-
neered in the United States and the United Kingdom, but are
now most widespread in subtropical and temperate South
America. In Brazil, Argentina, and Paraguay, over half of all
cropland is now under no-till cultivation. In this part of the
world, heavy rainfall promotes erosion, causing tilled soils
to lose organic matter and nutrients, and hot weather can
overheat tilled soil. Thus, the no-till approach is especially
helpful here, and results have exceeded those in the United
2 Drop seed 3 Close furrow States: Crop yields increased (in some cases they nearly
in furrow over seed doubled), erosion was reduced, soil quality was enhanced,
and pollution declined, all while costs to farmers dropped
by roughly 50%.
Figure 9.16 Farmers practice no-till farming with a no-till Critics of no-till farming in the United States note that
drill. The drill 1 cuts a furrow through the soil surface, 2 drops this approach often requires heavy use of chemical herbi-
in a seed, and 3 closes the furrow over the seed. cides (because weeds are not physically removed from fields)
and synthetic fertilizer (because non-crop plants take up a
significant portion of soil nutrients). In many industrialized
adding organic matter to the soil, no-till farming captures car- countries, this has indeed been the case. Proponents, however,
bon that otherwise would make its way to the atmosphere and point out that in developing regions of South America, farm-
instead stores it in the soil. In addition, because no-till farming ers have departed from the industrialized model by relying
reduces tractor use, the farmer burns less gasoline. Some farm- more heavily on green manures (dead plants as fertilizer)
ers have even received money from carbon offsets (p. 531) for and by rotating fields with cover crops, including nitrogen-
using no-till methods. Researchers today are debating just how fixing legumes. The manures and legumes nourish the soil,
much impact no-till farming can have on carbon sequestra- and cover crops reduce weeds by taking up space the weeds
tion (see THe SCieNCe beHiND THe STOrY, pp. 248–249). might occupy.
In the United States today, nearly one-quarter of farm- Critics counter that green manures are generally not
land is under no-till cultivation, and over 40% is farmed using practical for large-scale intensive agriculture. Certainly,
conservation tillage (Figure 9.17). Forty percent of soybeans, conservation tillage methods work better in some areas than
21% of corn, and 18% of cotton receive no-till treatment. Iowa in others, and better with some crops than with others. Farm-
ranks second only to Illinois in total area under no-till farming, ers will do best by educating themselves on the options and
but its rate of no-till farming (23%) is close to the national aver- choosing what is best for their particular crops on their own
age. Tennessee, Virginia, Maryland, and Kentucky use no-till land.

WeIGHING THe ISSUeS

HoW WoULD yoU FARm? You are a farmer owning land on
Table 9.1 benefits of No-Till Farming both sides of a steep ridge. You want to plant a sun-loving
• Reduces erosion crop on the sunny, but very windy, south slope of the ridge and
• Helps soil retain moisture a crop that needs a great deal of irrigation on the north slope.
• Enhances soil structure What farming techniques might best conserve your soil? What
• Reduces soil compaction factors might you want to know about before you decide to
commit to one or more methods?
• Stores carbon in soil, lessening its release to the atmosphere
• Improves biological activity in soil
• Helps soil retain nutrients
• Cuts down on water and air pollution Plant cover is the key to erosion control
• Requires less time and labor
Farming methods to control erosion make use of the general
• Decreases fossil fuel use and costs
principle that protecting and restoring vegetative cover will
• Minimizes wear and tear on equipment
protect soils, and this principle is applied widely beyond
• Tends to increase long-term soil productivity, crop yields, farming. When grazing livestock, people try to move animals
and farming profit from place to place before the plant cover in any one area is
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