RA 00048.pdf - OAR@ICRISAT

utilization because water is available for continuous
transpiration and minimal heat and water
stress. Interception of radiation can be increased
with narrow rows and high plant populations
(Clegg 1971). This is a practice which is used to
obtain a more equidistant plant arrangement in
order to optimize water use (Richie and Burnett
1971; Blum and Naveh 1976; Meyers and Foale
1981). As conditions become more arid, the
radiation load is reduced by lowering plant population
and widening rows, and by using a more
rectangular plant arrangement, to optimize more
efficient water use (Blum and Naveh 1976; Meyer
and Foale 1981).
The greatest problem with narrow rows is that
mechanical cultivation is difficult and weeds need
to be controlled early. However, adequate weed
control can be obtained using herbicides (Burnside
1977).
Surface Mulch
Reduced tillage systems which leave residues on
the soil surface are gaining favor because of
better moisture conservation, improvement of soil
physical properties, and soil erosion control.
These systems also reduce tillage time and
minimize a delay in planting due to inclement
weather (Lane and Gaddis 1976).
In the more arid areas, ecofallow and no-till
fallow are becoming popular (Greb and Zimdahl
1980; Peterson and Fenster, in press). These
systems depend on contact and preemergence
herbicides to control summer weeds. With ecofallow,
some tillage is required for late summer
weed control and reduction of residues to facilitate
planting (Peterson and Fenster, in press).
Benefits of these systems are many. Loss of soil
by wind and water erosion is reduced (Lane and
Gaddis 1976; Good and Smika 1978; Peterson
and Fenster, in press). Increased water infiltration,
and reduced evaporation thereby, results in increased
water storage. Further, increased moisture
occurs in environments where winter snow is
common. The residue allows for increased snow
catchment and the stubble allows for more
efficient snowmelt storage (Nordquist and Wicks
1976; Good and Smika 1978; Peterson and
Fenster, in press). In environments which are
marginal for continuous cropping, a wheat-maize
or sorghum-fallow-wheat cropping sequence was
successful as compared with the conventional
sequence of wheat-fallow-wheat-fallow. This was
because enough moisture was stored using these
no-till or limited-till systems (Nordquist and Wicks
1976).
There are several problems inherent with leaving
residues on the soil surface. The greatest
problem is the need for special planting equipment
(Peterson and Fenster 1981). Soil temperatures
are reduced (Nordquist and Wicks 1976; Lal
1978; Unger 1978) with a temperature difference
of 5.5°C (Good and Smika 1978). This lowering of
temperature delays the time for soil to reach
favorable temperatures for seed germination (Unger
1978) and requires earlier maturing varieties or
hybrids since planting may be delayed (Nordquist
and Wicks 1976). Herbicides used for weed
control may result in carryover problems (Peterson
and Fenster, in press).
Biological Nitrogen
Fertilizer, especially nitrogen which is required in
large amounts, has been readily available in the
past at economical costs. Nitrogen costs have
increased considerably resulting in the consideration
of using cropping systems which include
biological fixed nitrogen. Maize realized approximately
90 kg/ha nitrogen following soybeans in a
maize-soybean rotation (Shrader et al. 1966).
Sorghum grown continuously over a 4-year period
with no applied nitrogen yielded an average of
4600 kg/ha as compared with a sorghum yield of
6551 kg/ha when grown in rotation with soybeans
with no applied nitrogen. The yield level
attained by sorghum in the rotation system was
equivalent to 76 kg/ha applied nitrogen (Clegg
1981). This would indicate that a significant
amount of biologically fixed nitrogen can be
obtained from cropping systems. Other benefits
of changing crops are that they aid in controlling
insect pests and diseases, and with soybeans the
fields are in excellent condition for a no-tillage
operation.
Mechanization
The labor requirement and the number of farm
workers have declined in the Great Plains of the
USA as a result of fewer but larger farms and the
development of larger tractors and machinery
(Lagrone 1979). A farmer can easily till or plant
100 ha per day.
Irrigation has developed on marginal land with
leveling and the use of center pivot irrigation
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