The Eleventh Regional Wheat Workshop For Eastern ... - Cimmyt

Response ofweed infestation and grain yield to frequency oftillage and weed control- Tenaw
superior root growth, which indirectly increased grains/spIke, biomass and grain yields.
Repeated tillage stimulates weed seed germination before the final tillage and reduces the
seed bank and subsequent weed densities (Johnson et aI, 1989). The findings of Dorado et al.
(1998), Thompson and Whitney (1998) and ICARDA (1984) showed that weed density was
more in no-till plots than from repeated plowings. Weed infestation due to repeated tillage
was reduced by more than 50% compared with zero tillage (ICARDA, 1984).
The result achieved by Thompson and Whitney (1998) showed poor crop stands from no-till
plots. Similarly, Kreuz (1993) in his investigation has obtained lower seedling density,
number of spikes m- 2 , and straw yields from zero-till plots. Wallace and Bellinder (1989)
found decreased potato stand by 16% with reduced tillage when averaged over seasons. The
report of the above-mentioned researchers showed that the yield of potato in reduced plots
decreased an average of 22% compared to yields in conventionally tilled plots while in other
years no difference was detected between tillage systems. On the contrary, reduced tillage
and zero-till can produce a similar yield as that of repeated tillage provided that straw mulch
is applied. Aulakh and Gill (1988) reported that zero tillage, due to retention of crop residue
on top of the soil, had more yield and lower bulk density than conventional tillage. Zero
tillage applied with straw mulch had more grains/spike and gave similar grain yields of wheat
as compared to repeated tillage of 6 to 8 plowings (Majid et al. (1988). The reason for the
better performance of zero till was due mainly to uniform placement of seeds, which resulted
in better plant emergence and less weed infestation than the conventional. Brecke and
Shilling (1996) indicated higher yield from zero till due to reduced weed competition. Stobbe
(1989) and Jongdee (1994) advocated the importance of straw mulch in minimum (zero)
tillage for better performance and grain yield of wheat. Other researchers (Aulakh and Gill,
1988) also confirmed that due to retention of crop residue on the soil, yields from zero tillage
were higher and soil bulk density was lower than the conventional tillage.
Minimum tillage can cost less since the power and time requirement is minimal (Dawelbeit
and Salih, 1994; Stobbe, 1989). In addition, minimum tillage allows earlier plahting, reduces
soil erosion and there can be less potential for pesticide contam~nation of surface water
(Brecke and Shilling, 1996). The result achieved by Macharia et al. (1997) showed that
significant difference was not detected on wheat yield due to tillage systems in the first three
consecutive seasons. Kamwaga (1989) found no significant variation in yield between the
conventional and other tillage practices for two years at various locations because of well
distributed precipitation. He noted that with erratic rainfall, minimum tillage could produce
higher grain yield of wheat.
The overall objective of this study was, therefore, to investigate the effect of repeated tillage
and weed control on weed infestation, growth and grain yield of wheat.
MATERIALS AND METHODS
The study was conducted at Arsi Negelle in the Southern Region of Ethiopia for three
consecutive years, 1996-98. The wheat variety, Dashen, was sown at a seed rate of 125 kg
ha- I . Diammonium phosphate was applied at planting to supply 18 and 20 kg ha- I nitrogen
and phosphorus, respectively. Tillage was with the traditional ox-drawn plow. Glyphosate
was applied at 4.5 I ha- 1 15 to 20 days before sowing for the zero-tillage plots. Seed was
drilled with 20 cm row spacing. For the zero-tillage, seed was sown in furrows made using
hoes, and fertilizer was side banded. Planting dates were 22 July 1996 and 1997, and 4 Aug.
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