Enhancing the competitive ability of crops - Ecological Management of Agricultural Weeds - page 286

from horse-drawn to tractor-drawn cultivators allowed reduction in row
spacing from 1 m or more to around 0.75 m. More recently, herbicides have
allowed much narrower row spacings, particularly in soybean where narrow
inter-rows often increase yields substantially even in weed-free conditions
(Cooper, 1977; Parker, Marchant & Mullinix, 1981; Beatty, Eldridge &
Simpson, 1982; Boquet, Koonce & Walker, 1982). Most of the work on row
spacing postdates the widespread use of herbicides, and much of this work
was stimulated by liberation from the planting constraints imposed by tradi-
tional inter-row cultivation methods. However, the advent of improved tech-
nology for mechanical weed management, including a new generation of
harrows, and cultivator guidance systems coupled with tools that work close
to crop rows, has opened possibilities for cultivation of narrowly spaced rows.
To avoid crushing part of the crop with tractor tires during cultivation, the
planter needs to leave wider inter-rows in the drive tracks. However, for wide
planters and cultivators, the drive track inter-rows constitute a small percent-
age of the field. Adapting cultivation systems to narrow rows is as yet largely
unexplored.

Effects of row orientation on light penetration into crop
canopies
Row orientation in orchards and row crops affects the percentage of
incident light that penetrates through crop canopies, particularly when the
canopy is not closed.Because a variety of factors including row spacing,height
and shape of the canopy, leaf area density, and time of year affect light inter-
ception, most of the work to date has emphasized mathematical modeling
rather than empirical measurements. Several of these models agree in
showing that throughout most of the temperate growing season light inter-
ception in orchards and row crops is greater when rows run N-S rather than
E-W (Cain, 1972; Jackson & Palmer, 1972; Mutsaers, 1980; Palmer, 1989).
Depending on the shape of the row canopy, the effects can be substantial (e.g.,
47% vs. 38% interception - Palmer, 1977). Late in the temperate growing
season, E-W-oriented rows intercept more light. A model by Schnieders et al .
(1999) showed that a hypothetical crop in the Netherlands was most produc-
tive when rows were oriented NW-SE because this put rows perpendicular to
the sun during the time of day when combined direct and indirect light inten-
sity was highest.
As latitude decreases from 55 , the benefit of N-S row orientation

increases (Cain, 1972; Jackson & Palmer, 1972; Mutsaers, 1980; Palmer, 1989).
From 25

° to 25 °

the difference between N-S and E-W orientation near the
summer solstice decreases with latitude, but the portion of the year during

° to 5 °