Efficacy of Herbicides on Weed Control in Zero-tilled Wheat (Triticum aestivum L.) in the Eastern Indo-gangetic Plains

Wheat is one of the most important winter cereals and is the backbone of food security. India, contributing approximately 30-35% of total food grain production in our country. Production of wheat during 2019-20 is estimated at record 106.21 million tonnes. It is higher by 2.61 million tonnes as compared to wheat production during 2018-19 and is higher by 11.60 million tonnes than the average wheat production of 94.61 million tonnes (Anonymous, 2020). India ranks second in the world after china and its total crop production is 87 million tonnes in the world. Its share in the world is 11.7% (Wadhwa, 2019). Weed interference is one of the most important, but less understood factors, contributing to lowering the yields of wheat (Hassan and Marwat, 2001). Weeds reduce yield of the crop, deteriorate the quality of the farm produce and trim down the market value of wheat. An estimated yield loss of about 10% in the less developed countries and 25% in the least developed countries is caused by weeds (Akobundu, 1987). Heavy infestation of weeds alone causing 33% reduction in yield is a serious constraint in sustaining productivity of wheat. Yield losses of wheat crop estimated to vary between 30-50% based on weed infestation (Pandey et al.,1997). 
       
Zero tillage technique (Fig 1) not only ameliorates the problem of delayed sowing but also reduces the incidence of most problematic weeds like Phalaris minor in wheat. Weed flora of wheat differ from field to field, depending on environmental conditions, irrigation, fertilizer use, soil type, weed control practices and cropping sequences. Among grassy weeds, P. minor and among broad-leaved weeds, Rumex dentatus and Medicago denticulata are of major concern in irrigated wheat under rice-wheat sequence in India (Balyan and Malik 2000; Chhokar et al., 2006).
 

       
Herbicide use has increased in both conventional tillage and zero tillage systems because it provides effective and economical weed control and saves labour power (Rao et al., 2007). The broad-leaf weeds in zero tillage system can be controlled effectively with the application of 2,4-D, but leaf deformities in wheat is a major concern associated with its application (Balyanand Malik, 2000). Metsulfuron methyl is very effective herbicide for controlling broad- leaved weed species (Saha and Rao, 2010).  Metsulfuron 5 g ha^-1 at 30-35 DAS provides effective control of Rumex spinosus along with other broad-leaved weeds, as 2,4-D do not control this weed. In fields where both grass and broad-leaved weeds are present, one post-emergence application of Sulfosulfuron + Metsulfuron at 30 g at 30-35 DAS is quite effective.

The experiments/on farm trial (OFT) were conducted at Farmers field in village Hasanchak and Agwanpur under the ICAR- Krishi Vigyan Kendra, Barh, Patna during the winter season (Rabi), 2014- 2015. The experiment was laid in Randomized Block design (RBD) replicated 4 times (Farmers field) with 5 treatments viz., 2, 4-D, ethyl ester 2.00 kg ha^-1 at 25 days after sowing fb one hand weeding at 55 days after sowing (Farmer practices), Sulfosuluron 75% WP + Metsulfuron 20% WP @ 40 g ha^-1 at 25 days after sowing, Sulfosulfuron 75% WP 25 g ha^-1, Metsulfuron 20% WP @ 20 g ha^-1 at 25 days after sowing and control (Unweeded). The soil of the experiment field was clay loam in texture with 7.6 soil pH. The value of other soil properties in the experimental fields was medium organic carbon 0.62%, low available N 216. kg ha^-1, low available P 10.5 kg ha^-1 and low available K 175.0 kg ha^-1. Available soil N, P, K and other parameters like pH and organic carbon were estimated as per standard procedure. Soil pH was determined by glass electrode method in 1:2 soil: water suspension (Jackson, 1965). Organic carbon was determined by rapid titration method of walkley and black as described by Jackson (1965). Available nitrogen in soil samples was determined by adopting the alkaline permanganate method (Subbiah and Asija, 1956). The phosphorus content of soil was estimated by colourimetric procedure described by Olsen et al., (1954). The available potassium was extracted by neutral normal ammonium acetate and estimated by using flame photometer (Muhr et al., 1963). Fertilizer was supplied to the crop through urea, diammonium phosphate and Muriate of potash and were applied in the ratio of 120:60:60 kg ha^-1 of N, P₂O₅ and K₂O respectively. Time to time irrigation was given to the crop and need based intercultural and plant protection measures were adopted. The spray of herbicides was done with knapsack sprayer fitted with flat fan nozzle with discharge rate of 250 litres ha^-1. Sowing of PBW-343 variety of wheat was done on Oct. 20, 2014 at seed rate of 100 kg ha^-1 sowing is done with zero till drill. Sowing of zero till plots was made after sickle harvest of Rice. Weed control efficiency (WCE) of different treatments was calculated on the basis of reduction in dry weight of weeds weighed in treated plots over the control (Unweeded) and expressed as percentage. Formula of Mani et al., 1973) was adopted for computing the weed control efficiency.
   
Where,
WDC= Weed dry weight in control plot (g/m²).
WDT= Weed dry weight in treated plot (g/ m²). The analysis of variance was done using CPCS software.

Effect of herbicide on Weeds dry weight and WCE
 
Weed control methods caused significant reduction in weed density over control (Unweeded) Table 1. Dry weight of weed both grassy and broad leaf weed was maximum in under 2,4-D ethyl ester 2.00 kg ha^-1 after first irrigation (25 days after sowing) (Conventional tillage- Farmers practices) it was recorded 254 gm^-2 followed by sulfosulfuron 75% WP @ 25 g ha^-1 25 days after sowing (101 gm^-2), Metsulfuron 20% WP 20 g ha^-1 (91 gm^-2), Sulfosulfuron 75% WP+ Metsulfuron 20% WP @ 40 g ha^-1 (38 gm^-2) and control (Unweeded) (415 g m^-1). These findings are in close conformity with those reported by Sareta et al., (2016). The dry matter of grassey weeds in the wheat crop treated with sulfosulfuron 75% WP @ 25 g ha^-1 25 days after sowing was found to be lower and dry matter of broad leaf weeds was found to be higher than the control (Unweeded). Similarly, dry matter of grassey weeds in the wheat crop treated with Metsulfuron 20% WP 20 g ha^-1 was found to be higher and dry matter of broadleaf weeds was found to be lower than the control (Unweeded). Combined application of Sulfosulfuron 75% WP+ Metsulfuron 20% WP @ 40 g ha^-1 provided very effective control of grassy and broadleaf weeds as the dry matter accumulation by weeds in this treatment was found to be lower than all other treatments. Similar results have been reported by Walia et al., (2005). Weed control efficiency (WCE) was recorded highest (91%) under sulfosulfuron 75% WP+ Metsulfuron 20% WP @ 40 g ha^-1. Among herbicides, application of 2,4-D, ethyl ester (Conventional tillage- Farmers practices) recorded lowest (39%) WCE as compared to other treatments. Similar result conformity also recorded by Singh et al., (2017). In areas, where P. minor has evolved resistance to Isoproturon, application of sulfosulfuron 25 g, Clodinafop 60 g, Fenoxaprop 100 g ha at 30-35 DAS of wheat provided effective control of Phalaris minor and Avena ludoviciana in ZT wheat. In case of broad-leaved weeds like Chenopodium album, Anagallis arvensis, Medicago denticulata, Coronopus didymus, Rumex dentatus etc., 2,4-D sodium salt or 2,4-D ethyl ester at 400-500 g ha^-1 at 35-45 DAS when wheat is sown at normal time and at 45- 55 DAS in late sown crop (December) are effective. Metsulfuron 5g ha^-1 at 30-35 DAS provides effective control of Rumex spinosus along with other broad-leaved weeds, as 2,4-D do not control this weed. In fields where both grass and broad-leaved weeds are present, one post-emergence application of Sulfosulfuron + Metsulfuron at 30 g ha^-1 at 30- 35 DAS is effective Singh et al., (2015).
 

 
Effect on growth, yield attributes and yield
 
Yield is considered to be a function of various growth and yield attributing characters like plant height, effective tillers m^-2, grains ear head^-1 and Test weight. In weed management treatments, the highest plant height (108 cm), effective tillers m^-2 (679), no. of grains per spiklets (3.10) and test weight (46.70 g) was found under the  Sulfosulfuron 75% WP+ Metsulfuron 20% WP @ 40 g ha^-1 followed by Sulfosulfuron 75% WP @ 25 g ha^-1 25 days after sowing, Metsulfuron 20% WP 20 g ha^-1, 2,4-D ethyl ether (Conventional tillage-Farmers practices) and Control (Unweeded). Higher yield attributing characters might be due to a result of low weed population under this treatment. Similarly, (Walia et al., 2005) and Kumar et al., 2019) reported  weed control treatments resulted in significant increase in growth and yield attributing characters as compared to unweeded crop.             
       
Amongst weed management Table 2 and Fig 2, Sulfosulfuron 75% WP+ Metsulfuron 20% WP @ 40 g ha^-1 recorded significantly highest grain (4280 kg ha^-1) and biological yield (10950 kg ha^-1) yield of wheat as compared to all other treatments. Significantly lowest grain (1800 kg ha^-1) and biological (4800 kg ha^-1) yield of wheat was recorded under the Control (Unweeded). Study of data further revealed that grain (4002 kg ha^-1) and biological (9860 kg ha^-1) yield under Metsulfuron 20% WP @ 40 g ha^-1 was on par with Sulfosulfuron 75% WP @ 25 g ha^-1 25 days after sowing and significantly superior over 2,4-D ethyl ether (conventional tillage-Farmers practices) and Control (Unweeded). This could be attributed to efficient control of weeds grassy and broadleaf weed as evidenced by lowest density of weeds and higher weed control efficiency. Similar results have been reported by Balyan and Malik (2000) and Mishra and Singh (2012).
 

 

 
Effect on economics
 
The practical utility of any weed control measure can be best judged on the basis of net return Table 2 and Fig 3. Among the weed management practices, net income were highest (₹ 48145 ha^-1) with application of Sulfosulfuron 75% WP+ Metsulfuron 20% WP @ 40 g ha^-1 followed by Metsulfuron 20% WP 20 g ha^-1, Sulfosulfuron 75% WP @ 25g ha^-1 25 days after sowing, 2,4-D ethyl ether (conventional tillage-Farmers practices) and Control (Unweeded). This is might be due to lower cost of cultivation and highest grain yield obtained under this treatments. Similar results have been reported by Saha and Rao (2010) and Singh et al., (2015). B: C ratio were also found significantly highest (2.93) with the application of Sulfosulfuron 75% WP+ Metsulfuron 20% WP @ 40 g ha^-1 as compared to all other treatments. Irreversible of the herbicide treatments lowest B:C ratio were recorded under Control (Unweeded). Similar results have been reported by Sareta and Begna (2016).
 

On the basis of experimental findings, it is concluded that wheat sown under Zero-till drill with combined application of Sulfosulfuron 75% WP+ Metsulfuron 20% WP @ 40 g ha^-1  at 25 DAS shows lowest weed dry weight, highest WCE and obtained higher grain yield, net return and B:C ratio under rice-wheat cropping system of Eastern Indo-Gangetic plains India.

Authors express their gratitude to Indian Council of Agricultural Research (ICAR), New Delhi for providing fund for present study On Farm Trials (OFT).