Growth and Productivity of Black Gram (Vigna mungo L.) as Influenced by Residual Effect of Triafamone Herbicide Applied for Transplanted Rice (Oryza sativa L.)

Today, the global agriculture facing acute labour shortage and high wages for labourers forced the farmers to use herbicidal weed management for rice grown in different establishment methods. Many rice herbicides can be accumulated in soil (Naveen et al., 2012) and some herbicides may be accumulated but their residues might be present in the soil. These herbicide residues are much beneficial to contain the non-targeted plant species and the growth and productivity of the succeeding crop will be enhanced (Balyan, 2016). However, most of the rice farmers in Tamil Nadu practicing herbicidal weed management with different time of application with new generation herbicide molecules. But, the farmers are applying herbicides without knowing the residual effect of herbicides on the succeeding crops especially pulse crops. Because, in most of the rice growing areas, the farmers are usually cultivate pulse crops viz., black gram as rice fallow crop in order to get additional income and enrich the soil fertility.  Black gram (Vigna mungo L.) is one of the important pulse crops in Tamil Nadu, grown under irrigated, rainfed and rice fallow conditions. Rice fallow black gram is grown during the month of January to March in Cauvery Delta Zone, Tamil Nadu in an area of 2.0 lakh hectares (Anonymous, 2017). It grows in the residual soil moisture, which is broadcasted 7-10 days before the harvest of paddy crop in waxy soil condition. Since black gram is grown under paddy stubbles, it has to survive in the residual nutrients and moisture present in the soil, residual herbicides present in the soil, besides frost and mist available during the period and complete the lifecycle within 65-70 days of sowing.
               
Sometimes, this practice will leads to poor germination and productivity of the pulse crop due to high accumulation of herbicides applied in the previous rice crop. The Triafamone is a new herbicide recommended for transplanted rice either as pre emergence or early post emergence of weeds. The label claim showed that, it has very good residual control of weeds to succeeding crop after transplanted rice. To keep these points in view, experiments were carried out to study the residual effect of Triafamone herbicide on black gram after harvest of the transplanted rice.

To study the residual effect of herbicides applied to rice crop, the succeeding crop of black gram (VBN 8) field experiments were conducted at Wetland Farm of Department of Farm Management, Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu, India during Kharif 2019 and Rabi, Coimbatore, 2019-20. After the harvest of rice crop, the follow up black gram crop was dibbled in rice stubbles. A seed rate of 20 kg/ha as adopted with a spacing of 30 cm × 10 cm. The other crop management practices viz, irrigation, and plant protection measures were adopted as recommended in Crop Production Guide (2019).
       
The farm is situated at 11°N latitude and 77°E longitude and at an altitude of 426.7 m above MSL. The experiment was laid out in randomized block design comprised of thirteen treatments.  The treatments were replicated thrice.
       
The soil texture of the experimental field was clay loam with low in available nitrogen (219 kg ha^-1), medium in phosphorus (15 kg ha^-1) and high in potassium contents (449.8 kg ha^-1). Black gram VBN- 8 and CO 6 varieties having duration of 75 -80 days released by Tamil Nadu Agricultural University (TNAU) was used as the test crops.  The seeds were sown in plots of size 9 m ×  2 m at spacing of 30 cm ×  10 cm with a seed rate of 20 kg ha^-1. Fertilizer nutrients at 25: 50: 25 kg NPK ha^-1 were applied in the form of urea, single super phosphate and muriate of potash, respectively. Entire dose of fertilizers were applied basally. Treatments includes spraying of 30, 40, 50 and 100 g/ha new formulation of rice herbicide Triafamone 200 SC as pre emergence on 3 days after sowing and early post emergence herbicide (2-3 leaf stage of weeds) using knapsack sprayer fitted with deflector type nozzle pre emergence herbicide Pretilachlor 50% EC 750 g/ha on 3 days after sowing and early post emergence herbicide Pyrazosulfuron ethyl 10% WP 15 ml/ha along with farmers practice (two hand weedings) and weed free and check.
 
Weed control efficiency (WCE)
 
The weed control efficiency was computed based upon the weed dry weight in the field at 21 DAS using the formula suggested by Mani et al., (1973).
   
Where,
WCE- Weed control efficiency in percentage.
WDW_c- Total dry weight of weeds in unweeded plot.
WDW_t - Total dry weight of weeds in herbicide treated plot.
 
       
The germination percentage was worked out by counting the number of black gram seeds germinated 20 days after germination. Yield attributes of black gram was recorded at harvest from already tagged five plants. The height of the green gram was recorded at 20 and 40 DAS on five tagged plants and means was worked out and expressed in cm. Grains from net plot cleaned, sun dried and weighed at 12 per cent moisture content and grain yield calculated and expressed in kg/ha.
               
The pods harvested from net plot area (8.1 m × 1.4 m) of each treatment plot were sun dried, threshed, cleaned and grain yield was recorded at a moisture level of 14%. The yield data of net plot was converted in to per hectare. The observed data were statistically analyzed based on the procedure given by Gomez and Gomez (2008) to find out the treatment differences. All statistical analyses were performed using the software AGRES developed by TNAU. Critical differences were worked out at five per cent probability level wherever the treatment differences were significant. The non-significant results were indicated as NS.

The residual effect of Triafamone herbicide application on weed control efficiency, growth and productivity of black gram were presented in the Tables 1, 2 and 3. The detailed results and discussion were made in the respective parameters.
 

 

 

 
Effect of triafamone on weed flora in black gram
 
The observation made on the common weeds of the experimental field consisted of grasses, sedges and broad leaved weeds  from unweeded check plot at 28 and 42 Days After herbicide Application (DAA). Weed flora of the experimental field predominantly consisted of three species of grasses, two species of sedges and five species of broad leaved weeds. The weed flora composition was influenced by the herbicide Triafamone in the black gram. This result is corroborated with the findings of Mansoori et al., 2015 The major grasses were Echinochloa crus-galli (L.) and E. colonum (L.) while the sedge weed included Cyperus nutans (L.). Among the broad leaved weeds Eclipta alba (L.) and Bergia ammanioides were the dominant species. The grassy weeds dominated with relative density of 87 per cent and broad leaved weeds were dominated with the relative density of 71 per cent observed in the control plot. Whereas, drastic reduction of 37 per cent of grassy weeds and 21 per cent of broad leaved weeds were observed in the Triafamone applied plots. This might be due to effective control of Triafamone herbicide on different group of weeds in the rice crop (Punia et al., 2011; Gupta et al., 2014).
 
Weed control efficiency
 
Among the different Triafamone dose applied, the weed control efficiency ranged from 43.5% to 100% at 42 DAA. Among the different dose of application of Triafamone, application of 40 g/ha as pre emergence and early post emergence application recorded highest weed control efficiency of 100, 97.7 and 99.6, 97.8 per cent at 42 days after herbicide application during both seasons of experimentation. This might be due to better control of grassy and broad leaved weeds which led to less dry matter accumulation by weeds (Choudhary et al., 2012; Punia, 2014). Further, triafamone herbicide addressed very effectively as pre emergence and early post emergence. The mode of action of this herbicide was played role to prevent the weed seed germination during pre-emergence application and at the time early post emergence application, it was killed the weeds within the shorter period of time. This might be due to the quick translocation to the site of action (Verma et al., 2020). Lowest weed control efficiency was registered by the treatment consisting of EPOE Pyrazosulfuron ethyl at 15 g/ha with values of 43.4 and 40.8 % at 25, 50 and 75 DAT, respectively.
 
Germination of black gram
 
The different level of Triafamone herbicide application did not affect the germination percentage of succeeding green gram crop.  The germination percentage ranged between 79 to 96 per cent. The left over residue of Triafamone herbicide controlled the weeds and not influenced the germination process of black gram. But, the unweeded control plot registered lower germination percentage than other plots during both seasons. This might be due to heavy infestation of weeds in the main crop (transplanted rice) might have influenced the early competition for the black gram seed germination (Singh et al., 2014).
 
Growth and productivity of black gram
 
All the weed management practices imposed on rice significantly altered the plant height of black gram at 20 and 40 DAS. All the weed control treatments behaved similarly in influencing the plant height of succeeding green gram. Significantly higher plant height was observed in all the weed control treatments except Triafamone at higher doses (100 g/ha) at 40 DAS indicating reduction in plant height of black gram at higher doses and which was recovered during the crop growth.
 
Grain and haulm yield
 
Weed management practices adopted for rice had significant influence on the grain yield of succeeding black gram. Highest grain yield (455 and 476 kg/ ha) was recorded with council prime at 40 g/ha during rabi 2018-19 and (510 and 533 kg/ha) during Khairf 2019 this was comparable with PE pretilachlor at 0.75 kg/ha, This might be due to effective weed control (Rathi et al., 2004 and Chhodavadiya et al., 2013) as a result, the conducive environment for good crop growth and effective translocation of assimilates happened from source to sink which leads to higher productivity of black gram. Similar environment also helped to obtained higher haulm yield also. Significant difference in haulm yield was observed on the succeeding crop of black gram. Invariably pre and early post emergence application of Triafamone at 40 g/ha) higher doses recorded higher haulm yield than other herbicidal treatments (Chand et al., 2004; Singh, 2011; Shashidhar et al., 2020).

Application of Triafamone at the rate of 40 g/ha either as pre emergence or early post emergence application for the transplanted rice as main crop significantly recorded higher weed control efficiency,  growth and higher productivity yield of black gram. This shows that, the herbicide and application cost for black gram is reduced in spite of higher weed control efficiency and monetary return.

None.