Enhancing the competitive ability of crops - Ecological Management of Agricultural Weeds - page 305

Conclusions
The several cultural practices discussed in this chapter are based on
common underlying general principles.
First, the presence of weeds changes the cultural conditions that result in maximum
crop yield . The optimal choice for crop density, cultivar and planting date very
often depend on whether or not the grower can expect significant weed com-
petition with the crop. If the grower has a management program that reduces
weed pressure to negligible levels in most years,then recommendations based
on weed-free field studies may be optimal.However, weeds often significantly
affect crop productivity due to a difficult-to-control species, lack of adequate
herbicides for the particular crop, reluctance to use herbicides, or unpredict-
able effects of weather. In these situations, a moderate increase in planting
density is likely to be beneficial, and cultivar, planting date, and plant
arrangement may need to be adjusted as well.
Second, crop yield in the presence of weeds increases with the difference in the height,
biomass, and leaf area of the crop relative to that of the weeds at the onset of competition .
Factors such as increased planting density, larger seeds or transplants, larger
or more rapidly growing cultivars, and planting dates that maximize early
season growth of the crop all give the crop a head start relative to the weeds.
Consequently, when the crop and the weeds grow into competitive contact,
these factors lead to greater proportional occupation of the soil surface by crop
shoots and the soil volume by crop roots. Taller stature gives the crop an even
greater advantage over the weeds due to the asymmetric nature of competi-
tion for light. As discussed in Chapters 2 and 5, agricultural weeds are sensi-
tive to both shade and nutrient stress. To the extent the crop is in a better
position to shade the weeds and deplete water and nutrients in the rhizo-
sphere of the weeds at the onset of competition,the less it will suffer yield loss
from competition with weeds.
REFERENCES
Ahmed, N.U., & Hoque, M.Z.(1981).Plant height as a varietal characteristic in reducing
weed competition in rice. International Rice Research Newsletter ,6(3), 20.
Akobundu, O., & Ahissou,A.(1985).Effect of inter-row spacing and weeding frequency on
the performance of selected rice cultivars on hydromorphic soils of West Africa.
Crop Protection ,4, 71-6.
Alessi, J., & Power, J.F.(1970).Influence of row spacing, irrigation, and weeds on dryland
flax yield, quality, and water use. Agronomy Journal ,62, 635-7.
Ambe, J.T. (1995).Effect of plant population density of sweet potato ( Ipomoea batates (L.)
LAM) on weed incidence and severity in Cameroon. International Journal of Pest
Management ,41, 27-30.