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

Response ofweed infestation and grain yield to frequency oftillage and weed control - Tenaw
1998.
The treatments were: plowing frequency (no-till, 1, 2, 3,and 4 pi owings at an interval of 15
days for the repeated plowings); and weed control methods (D2.5 = Duplosan at 2.5 llha,
D2.5 +1 HW = Duplosan plus one hand weeding at 30 days after emergence (DAE); 1 HW =
one hand weeding, and 2HW = Two hand weedings at 30 and 60 DAE). The plot size was 15
rows with 0.2 m row spacing by 5 m length. Data on weed types and population m- 2 , plant
height, spike length, grains per spike, kernel weight, biomass and grain yields were taken. A
quadrat of 25 by 25 cm was used for weed count and the population was averaged over four
throws for each plot.
DMRT was used to differentiate treatment means (Gomez and Gomez, 1983). Simple
correlation and multiple regression analysis were made. The model used for mUltiple
regression analysis was:
where Y = grain yield (kg ha- I ), T = tillage frequency, and W = weed control method.
RESULTS
Moisture stress was severe during 1998 crop season with intermittent shortages of rainfall
beginning at sowing time, and this seriously affected the crop. Precipitation was plentiful in
1996 and adequate in 1997. Under the moisture stress conditions of 1998, plots plowed three
and four times had relatively better growth and grain yield, possibly due to conservation of
soil moisture and reduced weed competition.
Weed type and population density: Broadleafweeds dominated and comprised about 73%
of the total weed population. The major weeds observed were Galinsoga parvijlora, Bidens
pilosa and Nicandra physalodes (Table 1). Weed population varied behveen the two years of
this study. The reduction in weed density with increased tillage was significant in 1997. The
respective mean increases of weed population in zero-till and two plowings over four times
were 79 and 59%. Four plowings had the lowest weed infestation in each level of weed
control. Frequency of plowing is negatively correlated with weed population (Fig. 1). The
lowest weed population density was observed on plots weeded twice. Weed density was 49
and 24% more in plots treated with Duplosan (D2.5 and D2.5 + IHW) as compared with two
weeding, respectively (Fig. 4).
Plant height (cm): Plant height increased as the number of piowings increased, and the mean
height was 16 and 6 cm more with four piowings as compared to two and three, respectively.
This was consistent across seasons and is attributed to better seedbed preparation and reduced
weed competition in all growing seasons. Plant height had a positive and significant
association with spike length, biomass and grain yields but a negative correlation with density
of weeds (Table 2). With greater plant height, spikes were longer and more biomass was
produced.
Spike length (cm): In 1997 and 1998, spike length increased with the number of plowings.
The mean spike length was 42, 33 and 14% greater for four pIowings as compared to no-till,
one and two plowings, respectively (Fig. 2).
372