Weed dynamics
The field trial was conscientiously monitored throughout crop growth stages and the presence of the following three types of weeds was found in the field
i.e.
Echinochloa cruss-galli, Echinochloa colona and
Leptochloa chinensis among grassy weed;
Cyperus iria and
Cyperus difformis among sedges;
Ammania baccifera and
Alternanthera sessilis among broadleaf weeds. Similar composition of weed flora in direct-seeded rice was also reported by
Singh et al., (2017) and
Kashyap et al., (2019).
Weed density and weed dry matter
In our study, integrated weed management (IWM) practices had a remarkable influence on total weed density and weed dry weight at 40 and 60 DAS (Table 1). The highest and lowest weed density and dry weight at both stages were observed under weedy check and weed free conditions, respectively. However, among the integrated management of weeds, recommended practice
i.e. PE fb PoE fb 1 HW at 20 cm row spacing resulted in the lowest weed density (no./m
2) and dry weight (g/m
2) during 40 DAS (10.7 and 8.8, respectively) and 60 DAS (7.1 and 12.3, respectively, which was on par with SSB fb PE of pendimethalin fb 1 HW at 30 DAS.
At 60 DAS, stale seedbed fb PE of pendimethalin fb 1MW fb 1HW at 45 DAS resulted in the lowest weed density among IWM practices and was similar to recommended practice under 25 cm spacing. While in both stages weed population and dry matter accumulation were statistically at par under remaining integrated weed management practices except in stale seedbed along with either alone post-emergence application of penoxsulam and SSB fb PE of pendimethalin fb 1 HW at 30 DAS. A similar result was also reported by
Singh et al., 2007 in which mulching of previous wheat crop residue at 4 t/ha reduced annual and broadleaved weed densities in dry-DSR compared with no mulch and
Sesbania co-culture in rice reduced broadleaf and grass weed density by 76-83% and 20-33% respectively, and total weed biomass by 37-80% compared to the sole rice crop. Also, the brown leaves of
Sesbania after the herbicide application served the purpose of mulch as well as smothering effect on the weed flora of rice
(Gopal et al., 2010). Also, stale seedbed with shallow tillage was found effective in controlling all early flush of weed seedlings above and below the soil surface (Singh
et al., 2018).
Weed control efficiency, weed control index and weed index
Weed control efficiency and weed control index varied with different weed management practices at 60 DAS (Table 2). Maximum and minimum WCE and WCI recorded in weed free and weedy check plots respectively. Among the weed management pendimethalin fb penxosulam fb 1 HW at 45 DAS with row spacing 20 cm recorded highest WCE (96.8%) and WCI (93.9%), but, the weed index was 15.9% which pointed out the relative yield loss over weed free, as a result of competition caused by closer spacing. These results were agreed with the findings of Kokilam
et al., (2020). Stale seedbed fb application of pendimethalin fb mechanical weeding and hand weeding at 45 DAS recorded similar WCE, WCI and WI (93.7, 90.2 and 2.9, respectively) as that of the recommended practice of weed management with row spacing 25 cm.
Crop yield
The data perusal on grain yield (Table 2) showed that weed free recorded the highest grain yield (4.4 t/ha) which was at par with the following treatments; recommended practice with 25 cm row spacing, SSB fb application of pendimethalin fb 1 mechanical weeding at 25 DAS fb 1 HW at 45 DAS (4.3 t/ha), mulching with the application of penoxsulam (PoE) at 22.5 g/ha fb 1 HW at 45 DAS (4.1 t/ha), line sown
Sesbania + application of pendimethalin (PE) fb 1 MW fb 1 HW (4.0 t/ha) and SSB with line sown
Sesbania fb application of pendimethalin fb application of 2,4-D (PoE) fb 1 HW at 45 DAS (4.0 t/ha). Grain: straw ratio and harvest index of rice were not significantly influenced by the integrated weed-control treatments. This might be because of efficient weed control due to the integration of cultural, mechanical and chemical methods along with hand weeding which finally influenced weed population their biomass accumulation and yield. The similar result were also suggested by
Gaire et al., 2013 that
Sesbania co-culture with rice helped in lowering the weed population by nearly about 50% with a supplementary effect on rice yield. Also addition of mechanical weeding by conoweeder to weed control option provided better weed control in inter rows as well as aeration to soil root zone ensuing superior crop yield
(Kumar et al., 2012). A negative correlation of the weed density and dry matter with the yield of rice was obtained (Fig 1 and 2). It implies that the grain yield of direct-seeded rice decreased proportionally with the increase in interference of weed and vice-versa. Comparable result between weeds and crop was also reported by
Ganai et al., (2014), that high weed density and biomass resulted in significant reductions in the crop yield.