Effect of Weed Management Practices on Weed Dynamics, Nutrient Depletion, Productivity and Profitability of Summer Mungbean (Vigna radiata) under Zero Tillage Condition

Agriculture contributes about 17.0% of national GDP and about 70% of the population is dependent on agriculture and allied activities for their livelihood (Anonymous, 2019a). Pulses, being a rich resource of proteins (20-25%) contribute about 14% of total protein supplementation in Indian dietary requirements. As per recommendation of Indian Council of Medical Research (ICMR) the minimum requirement of pulse is 70 g/capita/day but still the availability is only 35.8 g/person/day (Chopra, 2018). Pulses are mainly grown as crop, cover crop, catch crop, inter crop and green manure crop that able to fix atmospheric nitrogen as well as improves soil fertility.
       
Mungbean (Vigna radiata) a short duration leguminous crop is grown over an area of 3.64 Mha with productivity of 8.72 q/ha (Anonymous, 2019b). Its cultivation is mainly confined in Rajasthan, Andhra Pradesh, Maharashtra, Tamil Nadu, Madhya Pradesh, Gujarat, Haryana and Bihar. In Haryana, total production of mungbean is 0.024 MT from an area of 0.029 Mha with productivity of 8.24 q/ha (Anonymous, 2019a). It serves as very important source of protein, vitamins and minerals predominantly in developing countries. Mungbean contains about 51.6% carbohydrate, 26 to 27% protein, 4 to 5% minerals and 3 to 4% vitamins (Kaul, 1982).
       
Weeds are one of the most important factors causing significant yield reduction in mungbean grown during summer and rainy season (Gupta et al., 1990). Heavy weed competition during the initial 25-30 days (Raghvani et al., 1985) causes yield reduction to the tune of 50-90% depending upon the cultivars (spreading or erect type), weed flora and density, soil moisture level, soil types and other environmental conditions (Kumar et al., 2006; Ali et al., 2011 and Choudhary et al., 2016). Hence, there is a need to find out the successful weed management strategies to realize better growth and higher yield. Mechanical practices including hand weeding (HW) and inter culture operations are good enough to keep the weed infestation under check but the timely availability and labour costs and incessant rains many a times hampers the field operations (Nath et al., 2016). The progressive transformation of agriculture concerning intensive use of herbicides is gaining importance in recent years due to ease in application, cost-effective with better efficacy (Butter et al., 2008). Therefore, chemical weeding under such situation turn out to be indispensible and can be the good alternative to HW. Chemical weed controls an excellent alternative to manual as well as mechanical weeding and supply weed-free environment during early growing stage up to 30-35 days (Dungarwal et al., 2003; Das and Yaduraju, 2011, 2012). Therefore, keeping above facts in view, the present study was undertaken to assess the effect of different weed management practices in zero tilled mungbean in summer season with better efficacy, higher productivity and profitability margins.

The field experiment was conducted at the Agronomy Research Farm, ICAR-National Dairy Research Institute, Karnal, Haryana, located at 29^o41' N latitude and 76^o58' E longitude with an altitude of 245 m above mean sea level in Trans Indo-Gangetic Plain of India. The experiment was laid out in Randomized Block Design consisting of eight treatments and three replications. Treatments include T₁-Weedy check, T₂ - Weed free, T₃ - Pendimethalin (pre-emergence, PE) @ 0.75 kg/ha, T₄ - Pendimethalin @ 0.75 kg/ha fb HW 20 days after sowing (DAS), T₅ - Imezathyper (post-emergence, POE) @ 75 g/ha 20 DAS, T₆ - Shaked (Propaquizafop + Imezathyper) @ 2 L/ha as POE, T₇ - Pendimethalin @ 0.75 kg/ha fb Imezathyper @ 75 g/ha 20 DAS and T₈ - Pendimethalin @ 0.75 kg/ha fb Quizolofop ethyl  @ 50 g/ha 20 DAS. The soil of experiment field was clay loam in texture having neutral pH (7.3), low in KMnO₄ Oxidizable nitrogen (164 kg/ha), medium in Walkley-Black organic carbon (0.5%), 0.5 M NaHCO₃-extractable phosphorus (20 kg/ha) and 1N NH₄OAC extractable potassium (228 kg/ha). The recommended dose of fertilizers 20 kg N (urea), 30 kg P₂O₅ (di-ammonium phosphate) and 40 kg K₂O (muriate of potash) was applied at the time of sowing (20:30:40 kg NPK/ha). Rhizobium and phosphorus solubilising bacterial (PSB) inoculated 20 kg seed of mungbean (Variety: MH 421) was sown with zero-till drill machine at 30 cm row spacing. Later on, desirable plant population was maintained by thinning out extra plants and maintaining 10 cm plant spacing.
       
The treatment-wise herbicide application was done using knapsack sprayer fitted with a flat-fan nozzle with water volume of 400 L/ha. One hand weeding was done at 20 days after sowing as per treatment. Adequate measures to taken to control the insects-pests and disease. A total six irrigations were given to the crop at 4, 17, 24, 38, 50 and 62 DAS. Data on species-wise weed count and weeds dry weight were recorded at 30 DAS and at harvest using a quadrate measuring 25 × 25 cm in each plot. For dry weight, the weed samples were first sun-dried and then in an oven at 70^oC temperature for 72 hrs. Five plants for each treatment were randomly selected for recording the growth and yield attributes. Nutrient uptake by weeds was computed by multiplying the weeds dry weight (kg/ha) with their respective nutrient content (%).
   
Various indices are used to assess the effectiveness of weed management practices viz., weed control efficiency % (WCE) Mani et al., (1973), weed control index (WCI) Mishra and Tosh, 1979, weed index (WI) Gill and Kumar (1969). The economics of treatments was computed on the basis of prevailing market price of input and outputs for each treatment. Net returns and B: C ratio was calculated by following formulas.
   
Data on yield attributes like (no. of branches/plant, no. of pods/plant, no. of seeds/pod and test weight) and yield were recorded as per standard process at the time of harvesting from five plants for each treatment. Data on weed parameters, growth parameters and yield parameters were subjected to analysis of variance (ANOVA) technique for randomized block design given by Gomez and Gomez (1984). Since data recorded on weed density and weed dry weight do not follow normal distribution, so the data were transformed using square root √x + 0.5 transformation and then statistically analyzed.

Weed dynamics
 
The field trial was attentively monitored during crop growth stages to look the presence of different weed species at the particular stage (Fig 1). It was observed that three types of weeds were present in experimental field i.e. monocot (narrow leaved), dicot (broad leaved) and sedge weeds. A total of 11 weed species including 4 grasses, 2 sedges and 5 broadleaf weeds were observed. Among the grassy weeds Cynodon dactylon and Panicum repens were the most prominent weeds. The broadleaf weed viz., Amarnthus viridis, Digera arvensis, Trianthema portulacastrum and Portulaca oleracea were prominent. Cyperus rotundus was the prominent sedge. Similar botanic compositions of weeds were also reported by Poornima et al., (2018) and Kumar et al., (2006). The share of monocot, broad leaf and sedge weeds of total weeds were 36.36, 45.46 and 18.18%, respectively.
 

 
Monocot weeds
 
At 30 DAS and harvest, weed free followed by Propaquizafop + Imezathyper recorded lowest grassy weeds (1.2, 1.5 and 1.9, 2.3, respectively) which were at par with Pendimethalin (PE) fb Quizolofop ethyl (2.3 and 2.5). The monocot weed population at 30 DAS and harvest (Table 1), was recorded lower by 77.4 and 81.0% respectively, under weed free followed by 64.2 and 70.9% respectively, under Propaquizafop + Imezathyper as compare to weedy check. Applications of Propaquizafop + Imezathyper and Pendimethalin (PE) fb Quizolofop ethyl herbicides were most effective in controlling the grassy weeds. Pendimethalin having broad spectrum activity on weeds, control all type of weed during initial growing period of crop and later on Quizolofop ethyl control most of grassy weeds. Shaked (Propaquizafop + Imezathyper) hinders amino acid synthesis (protein synthesis) and also fatty acid synthesis. This leads to disruption of the DNA synthesis and cell growth and ultimately the weeds get killed similar result was also recorded by Kundu et al., (2009).
 

 
 
Dicot weeds
 
At 30 DAS, weed free was recorded minimum dicot weed population (1.3) which was at par with Pendimethalin as PE fb one HW at 20 DAS (1.6) followed by Propaquizafop + Imezathyper (2.7). At harvest lowest dicot weed population was recorded under weed free (1.9) followed by Propaquizafop + Imezathyper (2.9) which was at par with Pendimethalin as PE fb one HW at 20 DAS (3.2). Weedy check was recorded significantly highest dicot weeds at all the crop growth stages (Table 1). The dicot weed population at 30 DAS and harvest was recorded lower by 74.3 and 71.2% respectively, under weed free followed by 46.2 and 56.8% respectively, under Propaquizafop + Imezathyper as compare to weedy check. Weed free recorded minimum dicot weeds throughout growing period because of repeated HW at different stages of crop growth, kept field free from weeds. Same time excellent reductions in dicot weed population by combination of chemical and manual weeding and broad-spectrum activity of Shaked (Propaquizafop + Imezathyper). Imezathyper inhibit the growth of dicot weeds due to membrane disruption due to solutes leakage from cells with some synergic effects with Propaquizafop.
 
Sedge weeds
 
At 30 DAS, significantly lowest sedge weeds population was recorded under weed free treatment (1.1) followed by Pendimethalin (PE) fb HW (2.6). At harvest, significantly lowest sedge weeds population was recorded under weed free treatment (1.9) followed by Pendimethalin fb Imezathyper (3.2). Unweeded control recorded maximum sedge weeds population at all stages of crop growth. The sedge weed population at 30 DAS and harvest, was recorded lower by 79.0 and 74.3% respectively, under weed free followed by 33.3 and 48.6% respectively, under Propaquizafop + Imezathyper as compare to weedy check (Table 1). HW was effectively control sedge weed over chemical control because of successfully destroying the rhizome of sedge. The rhizome of sedge not suppressed by herbicides but same time by HW uprooted the whole weed plant entirely. Ultimately this leads to kept minimum sedge population throughout growing period. The extraordinary reduction in sedge weed population at different stages might be due to efficient weed control in particular treatments either manual or chemical or both. These results were harmonies with findings of Kaur et al., (2009).
 
Total weed population
 
Significantly lower total weed population (Table 1) at 30 DAS was recorded under weed free situations (1.9) followed by pendimethalin fb one HW (3.7). At harvest lowest, total weed population was recorded lowest under weed free (2.9) followed by Propaquizafop + Imezathyper as POE (4.5). The total weed population at 30 DAS and harvest, was recorded lower by 78.9 and 76.8% respectively, under weed free followed by 46.3 and 64.6% respectively, under Propaquizafop + Imezathyper as compare to weedy check. The extraordinary reduction in weed population at different stages might be due to broad spectrum activity of Propaquizafop + Imezathyper particular on established plants of both grasses and broad leaf weeds helps to kept field free from all types of weed. Propaquizafop inhibit ACCase enzyme at the initial stage of fatty acid synthesis this leads to killing most of grasses weeds same time Imezathyper control dicot weeds by inhibiting of acetolactate synthase (ALS) and this leads to death of weeds. The similar results were also reported by Kaur et al., (2009), Kataria et al., (2018) and Kumar et al., (2018).
 
Weed dry weight (g), weed control efficiency, weed control index and weed index
 
It was noticed that there was continuous increase in total weed dry weight from sowing to harvesting (Table 2). Significantly lowest weeds dry weight at 30 DAS and harvest was recorded under weed free (1.1 and 1.9, respectively) followed by Pendimethalin (PE) fb one HW 20 DAS (3.8 and 5.3, respectively) which was at par with Propaquizafop + Imezathyper (3.9 and 5.8, respectively) and Pendimethalin fb Imezathyper (4.1 and 6.8, respectively). Weedy check recorded huge weed dry weight at 30 DAS (6.5) and harvest (10.7). The weed dry weight at 30 DAS and harvest, was recorded lower by 83.0 and 82.2% respectively, under weed free followed by 40.0 and 45.7% respectively, under Propaquizafop + Imezathyper as compare to weedy check. The progressive increase in weed population and weed dry weight under weedy check might be due to continuous growth of weeds throughout the crop season attached with more competitive capability than crop that was approximately entirely smother due to accelerated growth of weeds. HW was recorded better weeds control due to uprooting of weeds and thus reducing the dry weight. These results were in harmony with Venkata et al., (2017) findings.
 

       
WCE varied with time in different treatments (Table 2). At 30 DAS the maximum WCE of (96.3%) was observed with weed free followed by Pendimethalin fb one HW (83.5). At harvest the maximum WCE of (94.9%) was observed under weed free followed by Shaked (Propaquizafop + Imezathyper) as POE at 20 DAS (84.3%). Application of Pendimethalin as PE was recorded lowest WCE after weed check. Pendimethalin as PE fb one HW was recorded highest WCE might be because of pendimethalin records lowest weed population during initial growing period and HW records lowest weed population at critical crop-weed competition as compared to all other treatments.
       
At 30 DAS and harvest the maximum WCI of 98.5 and 97.3%, respectively was observed under weed free followed by Pendimethalin as PE fb one HW (66.6 and 75.9%, respectively). Like WCE, highest WCI was recorded by application of Pendimethalin as PE fb one HW. This might be due to lowest weed dry weight at 30 DAS and harvest as compared to other treatments. Kumar et al., (2017) were also found similar results.
       
Weed index worked out at harvest of crop and it was recorded lowest under weed free (0%) followed by in order of Pendimethalin as PE with one HW (6.1%) > (Propaquizafop + Imezathyper) as POE (6.3%) > Pendimethalin (PE) fb Imezathyper as POE (10.5%). The highest WI was recorded under weedy check (56.1%). The lower value of weed index might be because of fact that additive effect of both manual and chemical methods, resulted in excellent weed control. PE herbicide application kept field free from weed during initial period of crop growth and HW and POE reduce crop weed competition during later stages, thus ultimately leads to higher yield and lowest weed index. Similar results were recorded by Patel et al., (2016).
 
Nutrients depletion by weeds
 
Our study revealed that weed management practices had non-significant effect on NPK uptake by weeds (Table 3). In summer season, higher weed competition resulted in significantly higher nitrogen, phosphorus and potassium removal by weeds witnessed by weedy check (44.90, 5.98 and 25.30 kg/ha, respectively). Among herbicides, application of Pendimethalin (PE) has the highest values of NPK (35.9, 5.09 and 18.85 kg/ha, respectively) removal. Weed free treatment was recorded minimum NPK uptake by weeds (0.95, 0.17 and 0.77 kg/ha, respectively) followed by Pendimethalin as PE fb one HW, which was at par with Propaquizafop + Imezathyper as POE at 20 DAS. The maximum nutrients removed by weeds under weedy check treatment could be due to vigorous weed population and their dry weight. In contrast, efficient control of weeds and weed free situations throughout the crop growing period in weed free recorded lowest might have contributed to lowest nutrients removed by weeds because of efficient control of weeds and kept field free from weed throughout the crop growing period. These results were in harmony with Kaur et al., 2010.
 

 
Effects of weed management practices on yield attributes, yield and profitability
 
The data perusal on yield attributes (Table 4) showed that weed free recorded the longest pod length, highest no. of pods per plant, no. of seeds per pod and test weight (7.9cm, 21.0, 9.7 and 43.0g) which was at par with Pendimethalin (PE) fb one HW and Shaked (Propaquizafop + Imezathyper) as POE at 20 DAS. Variation in yield attributes of mungbean could be due to difference in growth parameters such as dry matter production and weed population. The DM production was outcome of growth parameters like plant height, no. of branches/ plant, no. of leaves and LAI. 
 

       
Similarly, weed free treatment produced significantly highest seed yield (10.1 q/ha) which was at par on Pendimethalin (PE) fb one HW (9.5 q/ha) and Shaked (Propaquizafop + Imezathyper) as POE at 20 DAS (9.5 q/ha). However, both the treatments was on par with Pendimethalin (PE) fb Imezathyper (POE) at 20 DAS (9.0 q/ha). Pendimethalin (PE) fb one HW 20 DAS, Shaked (Propaquizafop + Imezathyper) as POE at 20 DAS, Pendimethalin (PE) fb Imezathyper (POE) at 20 DAS and Pendimethalin (PE) fb Quizolofop ethyl at 20 DAS were recorded lower seed yield as compare to weed free by 6.03, 6.23, 10.49 and 16.63% respectively (Table 4). Higher growth attributes lead to higher DM production ultimately leads to higher yield. This might be because of efficient weed control by herbicides when combined with HW which finally influenced growth parameters, yield attributes and yield. Raman and Krishnamoorthy (2005) were also found the similar results.
       
Significantly highest weed density, weed dry weight, minimum number of leaves, plant height and growth and yield attributes and seed yield were recorded under weedy check as compared to rest of treatments. Under weedy check vigorous weed growth resulted in more crop weed competition for nutrients, solar radiation, water and CO₂ etc. by weeds leads to lowest yield was recorded. Mungbean seed yield may be reduce up to 50-90% due to uncontrolled weeds depending upon cultivars, soil type and other environmental conditions (Kumar et al., 2006).
       
The results revealed that POE application of Propaquizafop + Imezathyper at 20 DAS was recorded highest net return (Rs 55,079) followed by weed free (Rs 54,916) and Pendimethalin (PE) fb one HW at 20 DAS (Rs 53,105). Weedy check was recorded lowest net return i.e. Rs 18,656. Similarly, the highest B:C was recorded under Propaquizafop + Imezathyper (2.8) followed by Pendimethalin (PE) fb Imezathyper (2.5), this was due to low cost of cultivation and higher economic returns over rest of the treatments.

The study results conclude that sequential application of  Imezathyper + Propaquizafop @ 2 l/ha at 20 DAS may be recommended for attaining better weed control, higher crop yields and better monetary returns in summer mungbean under zero-till condition.