Agriculture Reference
In-Depth Information
to germinate. At the same time, local equipment manufacturers developed cheap,
locally adapted seed drills that performed well when planting wheat into unplowed
rice paddies. The result has been a rapid increase in no-till wheat area. By 2005,
between 3 and 4 million ha of wheat were sown using no till (Erenstein et al., 2007).
Scientists in Asia are now examining ways to grow both rice and wheat with no
till. At present, rice is grown after puddling the soil (wet plowing), a practice that
destroys much of the benefit obtained by using no till for wheat. A no-till rice-wheat
rotation has the potential to substantially reduce water use in rice production, very
important for water-scarce areas (Tang et al., 2004). Successful use of no till in rice,
however, requires that weed control issues be resolved. Use of herbicide-tolerant
transgenic rice may be the answer, although public concerns about transgenic plants
and their effect on landless labor still need to be addressed.
Apart from reducing erosion, saving energy, reducing production costs, and
(sometimes) increasing yields, CA often has other benefits. These include more effi-
cient use of water, nutrients, and fossil fuel; lower greenhouse gas (GHG) emis-
sions; less soil disturbance; improved soil biology (by promoting the growth of soil
organisms); and improved soil physical conditions (improved soil structure, water
infiltration, root penetration, and so on). Improved soil health facilitates nutrient
cycling and fosters natural biological control of insect and disease pathogens. CA
relies on soil organisms such as earthworms and fungal hyphae for natural tillage.
These develop networks of channels within the soil for aeration and new root growth.
There is evidence that a more diverse biological population helps restrict the activ-
ity of pathogenic fungi like
Fusarium
. Residue retention promotes a better habitat
for beneficial insects that help control crop pests like rice stem borer (Hobbs 2007,
Hobbs et al., 2008).
CA reduces GHG emissions by reducing the use of diesel fuel in land preparation
and pumping water. Diesel savings can be as much as 50 to 60 L/ha in rice-wheat
areas. By switching to nonpuddled, aerobic rice, methane emissions can also be sig-
nificantly reduced. There is still a need to reduce nitrous oxide emissions through
more efficient utilization of nitrogenous fertilizers. GHG emissions and climate
change are further discussed in Chapter 16.
At times, concern is expressed that the use of zero tillage requires that herbicides be
used instead of tillage for controlling weeds. In some instances, this may be true but in
others not. In rice-wheat systems of South Asia, zero tillage led to a reduction in herbi-
cide use (Singh et al., 2002). In these systems, wheat season and rice season weeds are
very different. Such weeds as
Phalaris minor
only germinate in the cool temperatures
of winter—and when seeds are brought to the surface by tillage. Data from South Asia
indicate that fewer weeds grow under zero tillage than in plowed fields. Furthermore,
after 3 to 5 years of using zero tillage (with the new herbicides), weed populations are
reduced to the point at which farmers can grow wheat with no herbicides whatsoever.
As noted, however, weed control in no-till rice is more of a problem. The extent to
which herbicides are needed in no-till systems is location specific.
Widespread adoption of CA is heavily dependent on the local availability of suit-
able, reasonably priced implements capable of effective no-till sowing under local
conditions. Very different kinds of implements are needed for systems powered by
large tractors, small tractors, animal traction, and human labor. Note that no-till
