Besides many other factors limiting wheat yield, weed infestation had emerged as one of the major factors causing reduction in yield. Weeds are known to be plants of negative value, which compete with main crop for space, water, nutrients and carbon dioxide for photosynthesis. Weeds decrease yield up to 17.2% (Bareradia et al., 1993) and in most serious cases may lead to complete failure of crop (Gill and Wallia, 1979). It has been reported that the crops yield may be increased by about 37% by complete eradication of weeds (Jalis and Shah, 1982). Moreover, the weed problem is getting from bad to worst in irrigated areas where cropping intensity is rapidly increasing with the result that weed management through fallowing, hoeing, harrowing and cultivation practices has become impossible and use of weedicides has become inevitable for obtaining higher yield and better quality produce.
Agrawal and Singh (1985) stated that nitrogen requirements of wheat could be reduced by 67% to produce the same yield if weeds were controlled by applying 1.4 kg ha‾1 Tribunil at pre-emergence stage. Hooda et al. 1986 studied nutrient uptake by weeds in wheat as influenced by three weed control treatments and two nitrogen rates. Semenov and Goncharaov (1985) studied the effect of application of 0.3 kg ha‾1 Simazine reemergence and 30-180 kg ha‾1 each of NPK and reported that Simazine treatment in plots fertilized @ 120 kg ha‾1 gave the highest yield. Velva (1989) reported that cholorotoluron and nitrogen fertilizer had a synergistic effect on the growth and yield of wheat. The best result was obtained with a single application of N @ 180 kg ha‾1 coupled with Milron 75 [email protected] 1.25 kg ha‾1 favorably affected all the yield components like fertile tillers m‾2, number grains per spike, 1000-grain weight and subsequently gave the highest grain yield 48.55 q ha‾1 in wheat.
Yadav et al. (1995) evaluated the herbicide and fertilizer compatibility for weed control in wheat under different levels of nitrogen and four methods of isoproturon application. Pre-emergence spraying of isoproturon effectively controlled weeds upto 64 percent and increased yield of wheat which was attributed to increase in number of grains per spike and 1000-grain weight. Pandey et al. (1998) applied 50, 57 and 100 kg N ha‾1 to wheat. The crop was hand weeded 30 days after sowing or was treated with pendimethalin and isoproturon. Singh and Prasad (1998a) applied 0-80 kg N ha‾1 to wheat and treated it with 1.0 kg fluchloralin ha‾1 (pre-emergence) and/or 1.0 kg isoproturon ha‾1 (post-emergence). Nitrogen application significantly increased weed dry matter and grain yield as compared with the control. Weed control treatments reduced weed infestation by 27-58% compared with the unweeded control. Kumar (1998) treated wheat with tralkoxydium by weeds was highest in untreated weedy control.
The present study was therefore conducted to investigate the effect of herbicide doses at different levels of nitrogen on wheat growth and yield under agro-climatic conditions of Faisalabad.
Materials and Methods
The study to evaluate the effect of different nitrogen levels and herbicide doses on wheat yield and weed control in wheat was carried out at the research area of Agronomy department, University of Agriculture, Faisalabad during the year 2001-2002. A commercial wheat variety Chenab-2000 was used as a test crop and was sown on 7th November, on a well prepared seed bed. With the help of single row hand drill in 25 cm apart rows using a seed rate of 125 kg ha‾1. A basal dose of phosphoric fertilizer @ 100 kg ha‾1 was applied at the applied at the time of sowing. The experiment was laid out in randomized complete block design (RCBD) with split plot arrangement, having four replications. The main plot treatments included the application of 100 kg N ha‾1 (N1) and 125 kg N ha‾1 (N2) and sub plot treatments were weedy check (D0 ), Topik (Clodinofop 15 WP) @ 200 g ha‾1 and Topik (Clodinofop 15 WP) @ 300 g ha‾1 (D2). The net plot size measured 2x5 m. All other treatments including irrigation were kept constant. The crop was harvested on 20th April. From each plot a unit area of one square metre was taken at random to record observations on number of tillers per unit area (m2), spike length (cm) number of grains per spike, 1000-grain weight, grain yield (t ha‾1) and weed biomass per unit area (g m‾2) by following the standard procedure. Data collected were analyzed statistically using least significance difference test at 0.05 probability level (Steel and Torrie, 1984).
Results and Discussion
The maximum number of productive tillers per unit area (454.50 m‾2) were produced by the application of 125 kg N ha‾1 (N2) which were statistically higher than that of 100 kg N ha‾1 (N1) application rate (Table 1). Among herbivide doses maximum number of productive tillers per unit area (467.75m2) were produced by the application of Topik @ 300 g ha‾1 (D2) where as minimum number of productive tillers per unit area (392 m-2) were produced where no weeds were controlled (D0). As regard the interaction of nitrogen and herbicide maximum numbers of productive tillers per unit area (512.25 m‾2) were obtained by the application of treatment combination of N2D2 which were statistically higher from all other treatments under study.
Minimum numbers of productive tillers per unit area (388.25 m-2) were obtained by N1D0 which were statistically similar to N2D0 these results are in agreement with those of Iqbal (1991) who reported that application of 185kg N ha‾1 coupled with herbicide (Milron 75 WP @ 1.25 kg ha‾1) favourably affected all the yield components like number of fertile tillers, spike length, number of grains per spike etc.
As regards ear length, maximum ear length (15.14 cm) was obtained with N2 which was statistically higher than N1. Among herbicide doses maximum ear length (15.81 cm) was produced by D2 where minimum ear length (12.24 cm) was produced where no weeds were controlled D0. The interactive effect of nitrogen and herbicide was non significant. These results are in confirmation with those of Velva (1989) and Iqbal (1991). The number of grains per ear were also affected significantly due to different levels of nitrogen application. Maximum numbers of grains per ear (53.58) were obtained by N2 which were statistically higher than N1. Among herbicide doses maximum number of grains per ear (51.37) were produced by D2 which were statistically similar D1 Minimum numbers of grains per ear (44.50) were produced whereno weeds were controlled (D0). Numbers of grains per ear were not affected significantly for the interaction between nitrogen and herbicide. These results are in the line with those of Agrawal and Singh (1985), Hooda et al. (1986), Velva (1989) and Yadav et al. (1995).
Different levels of nitrogen exhibited non significant effect on 1000-grain weight. Among herbicide doses maximum 1000-grain weight (48.92 g) was obtained by D2 while minimum 1000-grain weight (38.09 g) was produced with D0. The 1000-grain weight was not affected significantly by the interaction between nitrogen and herbicide.
|Table 1:||Effect of nitrogen levels and herbicide doses on weed growth and yield
These results confirm the findings of Semenov and Goncharov (1985), Velva (1989), Yadav et al. (1995), Singh and Prasad (1998b) and Kumar (1998).
Different levels of nitrogen affected the grain yield significantly and maximum grain yield (5.74 t ha‾1 ) was obtained by N2 which was significantly higher than N1. Similarly hericide doses exerted significant effect on grain yield. The data revealed that application of D2 because of effective weed control, produced maximum grain yield (6.09 t ha‾1) while minimum grain yield (5.10 t ha‾1) was produced in control treatment (D0). The interaction between nitrogen and herbicide was non significant (Table 1).
Weed biomass produced is an indicator of weed-crop competition. The effect of nitrogen on weed biomass was non significant. However, different doses of heribicide had significant effect on weed biomass at harvest. The plots where D2 was applied produced minimum weed biomass (10.20 g m‾2) which means that maximum weed control was achieved by this treatment was applied (D0). The interaction between nitrogen and hericide was non significant (Table 1).
It was concluded that the benefits of added fertilizer can only be realized if it is coupled with an appropriate weed control approach. The results also reveal that a proper dose of herbicide should be applied to control the weeds effectively which vary with the given environmental and soil conditions. Application of Topik herbicide @ 300 g ha‾1 proved to be optimum dose at the soil conditions where the study was conducted.