Effect on weeds
In Table 1, given data showed that at 30 and 60 DAS minimum weed dry weight was recorded in spacing S1 (30×10 cm)
i.
e. 2.29 and 7.93 respectively, which was significantly better than other spacing. This clearly revealed that weed dry weight was lesser in narrower spacing and more in wider spacing. This is because there is higher intensity of crop-weed competition in narrower spacing than in wider spacing. Crop plants try to suppress weeds better in closer spacing than in wider spacing. At 30 and 60 DAS, treatment W2 (pendimethalin @ 1.5 kg a.i. ha
-1 at 1 DAS) was superior over all other treatments having minimum dry weight of weeds (2.32 and 7.23 g m
-2 respectively). Similar effect of pendimethalin has been reported earlier by
Singh et al., (2010). At 90 DAS, 120 DAS and at harvest, weed dry weight was found to be very less because after 90 DAS crop plant gained sufficient height and canopy so that weeds under the plants were suppressed and died (Fig 1). Also, the weed dry weight was found to be non-significant at 90, 120 DAS and at harvest under different weed management treatments. The interaction effect was found to be non-significant at all stages.
Probing ahead, data in Table 2 clearly showed that at 30 and 60 DAS, narrower spacing S1 (30×10 cm) has significantly highest weed control efficiency
i.
e. 62.44% and 24.40% respectively. Similar findings were recorded by
George et al (2009). From 90 DAS till harvest variation in weed control efficiency was found non-significant with respect to different spacings. Among weed management treatments, W2 (pendimethalin @ 1.5 kg a.i. ha
-1 at 1 DAS) was recorded significantly highest weed control efficiency
i.
e. 33.19% and 37.39% respectively. From 90 DAS till harvest weed control efficiency was found numerically too low, because of almost complete suppression of weed growth in weedy check as well, hence there were no significant differences among different weed management treatments. The interaction effect was found to be non-significant at all stages.
Growth parameters
The data embodied in Table 3, indicated that the effect of different spacing was non-significant on days taken to emergence. Almost equal days were taken by crop for emergence at different spacing. Whereas, the plant height was significantly higher in closer spacing than in wider spacing. Maximum plant height was recorded in S1 (30×10 cm)
i.
e. 218.2 cm and as the spacing decreased from S4 (50×25 cm) to S1 (30×10 cm), there was increase in plant height, which was due to closer plant to plant distance in narrower spacing. The reason behind increase in plant height at closer spacing was increased interplant competition for light, while less space available for growth of each plant. These results were found by
Singh et al., (2010) and
Sathe and Patil (2012). LAI was recorded significantly higher in S1 (30×10 cm) spacing
i.
e. 2.104 from rest of other geometries. This might be due closer spacing and denser plant population in S1. As a result LAI increased with rising plant density.
Sathe and Patil (2012) also such trends. Apart from that, the highest CGR was recorded in S4 (50×25 cm) i.e. 0.85 which was followed by S3, S2 and S1 which were also significantly different with each other. This might be due to availability of more space and less competition between crop plants in wider spacing. These results are supported by the findings of
Dhandayuthapani et al., (2015). Also primary and secondary branches were found to be maximum in S4 (50×25 cm)
i.
e. 18.2 and 13.8 per plant respectively. The number of branches decreased towards narrow spacing. Thus maximum number of branches were recorded in S4 followed by S3, S2 and S1.
Among weed management practices, the data in Table 3 showed that days taken to emergence, plant height, leaf area index (LAI), crop growth rate (CGR) and number of branches (primary and secondary) were found to be non-significant. The probable reason behind showing non-significant difference could be due to lower infestation of weeds at early stage (30 DAS). At 60 DAS, when weeds growth was at their maximum, crop plants were in their grand growth period and already gained sufficient height (more than 1.2 m) and dense canopy, so weeds could not influence growth of crop plants. Moreover at 90 DAS, due to heavy canopy and considerable plant height, weeds were highly suppressed under crop plants. Particularly, crop characteristic of self-mulching (
i.
e. shedding its leaves and cover the ground surface completely) also played an important role in weed suppression at this stage. The interaction effect was found to be non-significant at all the stages.
Yield and yield attributes
The data in given Table 4 revealed that the highest grain yield (16.29 q ha
-1) was obtained with narrower spacing S
1 (30×10 cm) which was significantly higher than wider spacing of 30×15 cm (14.13 q ha
-1), 40×15 cm (11.08 q ha
-1) and 50×25 cm (8.50 q ha
-1). It might be due to more number of plants per unit area in S1 than S2, S3 and S4. Likewise highest stover yield was recorded in spacing S1 (49.29 q ha
-1) which was significantly higher than S2 (47.95 q ha
-1), S3 (45.04 q ha
-1) and S4 (43.67 q ha
-1). This could be due to more number of plants and dry matter production per unit area. Similar results were found by
Umesh et al., (2013).
However, the maximum number of pods per plant (154.6), pod length (4.83), number of seeds per pod (3.90), 100-seed weight (7.14) were found in S4 (50×25 cm). This might be due to availability of more space and resources in wider spacing
i.
e. S4 (50×25 cm).
Khan et al., (2010) concluded that plants that absorbed more nutrients, received more light and produced more photosynthates, resulting in more seeds per pod.
Ahmad et al. (1997) reported that maximum 100-seed weight was found in wider spacing geometry. Whereas considering weed management treatments, it does not show any significant effect on yield and yield attributes. The interaction effect was also found to be non-significant.