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Herbicides tank-mixes effects on weeds and productivity and profitability of chilli (Capsicum annuum L.) under conventional and zero tillage
Scientia Horticulturae 198 (2016) 191–196
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Herbicides tank-mixes effects on weeds and productivity and profitability of chilli (Capsicum annuum L.) under conventional and zero tillage Abdolhamid Hajebi a,1 , T.K. Das a,∗ , Ajay Arora b , Shashi Bala Singh c , Fatemeh Hajebi d a
Division of Agronomy, Indian Agricultural Research Institute, New Delhi 110 012, India Division of Plant Physiology, Indian Agricultural Research Institute, New Delhi 110 012, India c Division of Agricultural Chemicals, Indian Agricultural Research Institute, New Delhi 110 012, India d Agricultural and Natural Resources Engineering Organization of Hormozgan, Hormozgan, Iran b
a r t i c l e
i n f o
Article history: Received 5 September 2015 Received in revised form 11 November 2015 Accepted 13 November 2015 Keywords: Ascorbate peroxidase Chilli Imazethapyr Tank-mix herbicides Weed Zero tillage
a b s t r a c t Weeds heavily infest chilli and cause significant yield losses. Herbicide mixtures control diverse weeds better and prevent/delay weed shift and resistance. They have been hardly studied in chilli under conservation agriculture. Pendimethalin is the prevalent herbicide used in chilli, but not effective against nutsedge. Oxyfluorfen and quizalofop-p-ethyl also have negligible/no effect on nutsedge. Imazethapyr is a post-emergence herbicide and more effective against nutsedge, but its pre-emergence activity against nutsedge/weeds and selectivity to chilli have not been studied. In this study, these herbicides were tankmixed or sequentially applied to expand the weed spectrum being currently controlled. Our objective was to compare herbicide mixes to improve weed control, especially with nutsedge. We observed that the pre-emergence tank-mix application of pendimethalin 0.75 kg ha−1 + imazethapyr 0.075 kg ha−1 resulted in significantly higher weed control efficacy (∼86%) and leaf chlorophyll, but lower ascorbate peroxidase activity, suggesting that imazethapyr was selective to chilli. In this treatment, the yield and gross returns were 2% lower, but the net returns and net returns:cost were higher by 3% and 20%, respectively compared to weed-free check that included the costs of hand weeding. The zero tillage with residue (ZT + R) did not affect herbicide activity. The pendimethalin + imazethapyr tank-mix treatment with ZT + R would provide higher yield and income through better weed management and less/no chances for nutsedge insurgence, which usually occurs due to continuous use of herbicides with limited efficacy on nutsedge. It would reduce application cost by 50%, and doses and residues of these herbicides by 25% in agro-ecosystems. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Chilli (Capsicum annuum L.) is an important commercial spice/vegetable crop in India, grown on a wide range of soils and altitudes up to 2000 m above mean sea level. Chilli fruits are a source of vitamin C, E, provitamin A, and carotenoids, known for their antioxidants properties (Chatterjee et al., 2007; Deepa et al., 2007). Chilli is grown in wide rows and has initial slow growth, which favour huge weed infestation, comprising of grasses, broad-leaves
∗ Corresponding author. Fax: +91 1125842283. E-mail addresses: hamid [email protected] (A. Hajebi), [email protected] (T.K. Das). 1 Present address: Department of Natural Resources, Agricultural and Natural Resources Research Center of Hormozgan, Hormozgan, Iran. http://dx.doi.org/10.1016/j.scienta.2015.11.020 0304-4238/© 2015 Elsevier B.V. All rights reserved.
and sedges. Weeds can reduce chilli yield by 60–70% (Patel et al., 2004). Generally, the critical period for weed competition in chilli (Frank et al., 1988) is 30–60 days after transplanting (DAT). In India, weeds in chilli are controlled mainly by manual weeding, which is labor-extensive and expensive. Herbicide could be a cost-effective alternative. The selectivity of herbicide limits the choice of herbicides in chilli. Conventional single herbicidebased weed control is not adequate for controlling all weeds, having diverse morphology and physiology, and emerging at different stages. This can cause weed shift and hastens resistance in weeds. In this context, herbicide mixtures (ready-mixes/premixes or tank-mixes) can be useful (Das, 2008), which would provide better broad-spectrum weed control vis-à-vis prevent weed shift/insurgence and delay resistance. Ready-mixes are very few and have inherent limitations in fixing the required quantities of component herbicides for desired levels of weed control efficacy. In contrast, tank-mixes can readily be prepared by the
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farmers in fields just before application by physical mixing of components herbicides, usually at lower doses than recommended. The tank-mixes can reduce the expense of application cost and may be synergistic to improve herbicide efficacy. There are chances of more selectivity when applied at pre-emergence, and crop can germinate in weed-free situations, which favours faster seedling establishment (Das, 2008; Younesabadi Masoumeh et al., 2013; Susha et al., 2014). Besides, less quantity of the specific herbicide would enter into the environment due to lower doses used through tank-mix combinations. Pendimethalin is recommended for chilli. It is exclusively a pre-emergence, broad-spectrum herbicide (Kulshrestha et al., 2000), and is effective against annual weeds, mainly grasses, but not effective against nutsedge. Oxyfluorfen is a broad-spectrum herbicide and applied as pre- and post-emergence. Quizalofop-pethyl is an acetyl CoA carboxylase (ACCase) inhibitor herbicide, narrow-spectrum, controlling only grasses, and applied as postemergence. Imazethapyr is a post-emergence broad-spectrum herbicide, mainly recommended for soybean and groundnut, and is effective against nutsedge (Kumar et al., 2012). Its application may prevent nutsedge insurgence in future, which is of common occurrence in crops that are continuously applied with herbicides having limited efficacy on nutsedge. We used oxyfluorfen and quizalofopp-ethyl at pre-emergence, their usual time of application, but imazethapyr as pre-emergence as against post-emergence. The doses of oxyfluorfen, quizalofop-p-ethyl and imazethapyr were reduced by 40, 50 and 25%, respectively (∼being 0.250, 0.050 and 0.100 kg ha−1 as the recommended doses) in the tank-mix with 25% (0.75 kg ha−1 instead of 1.00 kg ha−1 ) lower than recommended dose of pendimethalin towards achieving greater selectivity and better weed control. Crops respond to herbicides in physiological ways that can be measured. Pendimethalin can affect chlorophyll content in crop leaves (Tuti and Das, 2011; Younesabadi Masoumeh et al., 2013). Also herbicides can stimulate production of oxidant compounds • [such as superoxide ion (O2 − ), hydrogen peroxide (H2 O2 )] by inhibiting biosynthetic pathways (Arora et al., 2002). These compounds are related to stress levels that crop experiences, and crop responds by producing anti-oxidant enzymes, namely, superoxide dismutase (SOD), catalase (CAT) or ascorbate peroxidase (APX) that scavenge the stress-effects (Arora et al., 2002; Yamamoto et al., • 2003; Guo et al., 2004). The SOD accelerates the conversion of O2 − to H2 O2 , while CAT, APX and a variety of other peroxidases catalyze the breakdown of H2 O2 (Balestrasse et al., 2006). These enzymes can be measured, and may provide an assessment of potential crop injury/selectivity by a herbicide. One possible test is measuring the activity of APX. These defence mechanisms may operate in chilli, but have not been studied. Studying the APX activity can reveal this. Conservation agriculture (CA), involving zero tillage with residue retention may provide greater adaptation and mitigation to climate change through better crop growth and yield (Das et al., 2014) and improving soil health (Bhattacharyya et al., 2013; Das et al., 2013; Monsefi et al., 2014). It has enough scope for adoption in spices/vegetables like chilli, but is hardly studied. The crop residue on the soil surface does intercept herbicide sprays. The residue, depending on the amount and the positioning/alignment, whether standing erect after combine harvesting or lying on the surface due to applied after whole crop harvesting, can intercept and prevent herbicides from reaching to soil and interfere/reduce their effects on weeds. Increasing the volume rate (∼water quantity) of spraying or using foot sprayer, having higher water requirement may reduce the negative effect of residue to a great extent. Irrigating the field immediately after herbicide application can nullify the interference of residue retained. Besides, it is actually the combined effect of tillage, crop residue and herbicide that would impact on weed interference/dynamics over the years (Peachey et al., 2004;
Norsworthy and Oliveira, 2007; Anderson, 2009, 2010; Susha et al., 2014), and result in an integrated weed management. Therefore, this study was undertaken to evaluate the individual and combined effects of tillage/residue and herbicide tank-mixes on weeds, chilli yield and economics. 2. Materials and methods 2.1. Experimental sites The experiments were carried out on a fixed lay-out in the field, maintained for two years at the Indian Agricultural Research Institute, New Delhi during the rainy-seasons of 2012 and 2013. The site was irrigated and irrigation was provided through surface check basin method. The field was no-till fallow during the previous winter seasons, 2011–12 and 2012–13. In both years, chilli seedlings were transplanted and the respective herbicide/herbicides tankmixes applied to the respective treatment plots. New Delhi is situated at 28◦ 35 N latitude and 77◦ 12 E longitude at an elevation of 229 m above mean sea level. Soil was alluvium (Typic Ustochrepts; Order Inceptisol) and sandy-loam with 63% sand, 17% silt and 20% clay. It had 0.54% organic C and pH 7.6. The available P (19 kg P ha−1 ) and K (191 kg K ha−1 ) were medium, but available N (275 kg N ha−1 ) was low. 2.2. Treatments/herbicides Two tillage levels, viz., conventional tillage (CT) and zero tillage with residue (ZT + R) were the main plot treatments. Seven weed control treatments such as pendimethalin 1.0 kg ha−1 pre-emergence (PE); pendimethalin 0.75 kg ha−1 + oxyfluorfen 0.15 kg ha−1 tank-mix PE; pendimethalin 0.75 kg ha−1 + imazethapyr 0.075 kg ha−1 tank-mix PE; pendimethalin 0.75 kg ha−1 PE followed by (fb) quizalofopp-ethyl 0.025 kg ha−1 at 30 day after transplanting (DAT); pendimethalin 0.75 kg ha−1 PE fb hand pulling at 30 DAT; weedy check (WC); and weed-free check (WFC) were the sub-plots treatments. These treatments were laid out in a split plot design with three replications. In the ZT plots, glyphosate at 1.0 kg ha−1 was applied 7–10 days before transplanting of chilli to control existing weeds. In these plots, the residue of Sesbania aculeata L. (Dhaincha) grown in the previous summer season was retained @ 10 t ha−1 fresh biomass (∼1.4–2.0 t ha−1 dry weight) on the surface of zero-till plots as mulch. In CT, three ploughings (one disking and two harrowing) and one levelling were done for land preparation. The areas of main and sub-plots were 37.5 m by 3.0 m and 4.5 m by 3.0 m, respectively. The net plot size (area actually considered for chilli fruit yield) was 3.6 m by 1.8 m. The first irrigation was given immediately after the transplanting of chilli seedlings in respective plots. The preemergence applications of pendimethalin alone or the tank-mixes (pendimethalin + imazethapyr/oxyfluorfen) were made two days after transplanting (DAT) or irrigation. For the tank-mix treatments, component herbicides at required quantities were mixed in the spray-tank just before spraying. Quizalofop at required quantity was applied as post-emergence at 30 DAT. For the pre- and post-emergence applications of respective herbicides, a knapsack sprayer fitted with a flat fan nozzle (Sukun Agencies India, Mumbai, Maharashtra) was used with a volume rate of 400 L water ha−1 . Weed-free check plots were kept free from weeds throughout growing season by hand pulling of weeds. 2.3. Agronomic practices Healthy seedlings (35 days old) of chilli cv. ‘Pusa Sadabahar’ (Indian Agricultural Research Institute, New Delhi), raised in a
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self-managed nursery in this research farm, were transplanted at 60 × 45 cm in the first week of August in both years. Chilli was fertilized with 100 kg N, 50 kg P2 O5 and 50 kg K2 O ha−1 through urea, diammonium phosphate, and muriate of potash, respectively. Half dose of N and full doses of P and K were applied at the time of transplanting. The remaining N was top-dressed in two equal splits at 45 and 60 DAT after one day of irrigation applied through check basin method.
2.4. Sampling techniques and observations 2.4.1. Agronomic observations A quadrat (0.5 × 0.5 m) was randomly placed in each plot at 60 DAT and individual weed species were counted, collected, sundried for 2 days and kept in an oven at 70 ± 5 ◦ C for 48 h for recording dry weight. At 15 days after herbicides application, per cent weed control efficacy and per cent injury to chilli plants were visually judged and rating was made on a scale from 0 to 100% (control/phytotoxicity) scale. Green chilli fruits were picked manually from the net plot area (3.6 m by 1.8 m) in every plot for determining yield. There were six pickings of green chilies in every cropping season.
2.4.2. Physiological/biochemical observations At 60 DAT, random sampling of chilli leaves was done from each treatment for determining the chlorophyll a and b and total chlorophyll contents by dimethylsulfoxide method (Hiscox and Israelstam, 1979). Fifty milligram chilli fresh leaf discs were added to 10 mL dimethyl sulfoxide (DMSO) in test tubes for extracting the pigments. Tubes were kept in dark for 4 h at 65 ◦ C. The absorbance was recorded at 663 and 645 nm using DMSO as blank. Leaf soluble protein was determined from the absorbance of blue colour developed by the reaction of Folin–Ciocalteau reagent by the amino acids tyrosine and tryptophan in the protein (Lowry et al., 1951). Ascorbate peroxidase (APX) activity was assayed by recording the decrease in optical density due to ascorbic acid at 290 nm by a spectrophotometer (Nakano and Asada, 1981).
2.5. Chilli cultivation economics The costs prevailing in the experimental years (2012 and 2013) of all inputs required were used for calculating the cost of chilli production. The market prices of green chilli fruits during these two years were used for calculating the gross returns (GR). Weed-free check required 60 mandays ha−1 for four hand pulling of weeds and incurred INR (∼Indian National Rupee) 13,200 ha−1 , considering the wages of 220.00 per manday. The net returns (NR) was worked out by deducting the cost of cultivation from the GR. The net returns:cost (NR:C) was calculated from the NR divided by the cost of production.
2.6. Statistical analysis All data on weed and chilli were subjected to analysis of variance (ANOVA) using the PROC GLM procedure of SAS (SAS Institute, 2003). The two-year data were subject to pool analysis to visualize the variations of particular crop/weed parameters between the years, treatments, and the year × treatment interactions, which were mostly non-significant at P ≤ 0.05. The significance was tested by variance ratio (i.e., F value) at P ≤ 0.05 (Gomez and Gomez, 1984). Standard error (SE) and least significant difference (LSD) were worked out for each parameter of weed and chilli studied for comparing the treatment means.
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Table 1 Rating on chilli crop phytotoxicity and weed control efficacy (WCE) at 15 days after herbicide application across the treatments (pooled means of two years). Treatment
Tillage level CT ZT + R SE (D.F. 4*) LSD (P ≤ 0.05) Weed management Pendimethalin Pendimethalin + oxyfluorfen Pendimethalin + imazethapyr Pendimethalin fb quizalofop Pendimethalin fb hand pulling WC WFC SE (D.F. 48) LSD (P ≤ 0.05)
Weed control efficacy (WCE)a
Chilli crop phytotoxicity (CCP)a
62 65 9 NS
7 7 1 NS**
70 80 86 56
9 22 7 5
53
4
0 100 14 40
0 0 2 5
*D.F.—degrees of freedom; **NS—non-significant. a Rating on crop phytotoxicity and weed control efficacy were based on visual observations in the plots/treatments across replications on a scale from 0 (zero) to 100, where 0 means 0% phytotoxicity/weed control and 100 means 100% phytotoxicity/weed control.
3. Results 3.1. Weed control efficacy and chilli crop phytotoxicity Eleven weed species, 6 monocots and 5 dicots, belonging to 7 botanical families were present in chilli. Monocot weeds were: Acrachne racemosa (Heyne ex Roem and Schult) Ohwi, Cyperus rotundus (L.), Dactyloctenium aegyptium (L.) P. Beauv. Willd., Commelina benghalensis (L.), Digitaria sanguinalis (L.) Scop. and Echinochloa colona (L.). Dicot weeds were: Trianthema portulacastrum (L.), Digera arvensis (L.) Forsk., Phyllanthus niruri (L.), Convolvulus arvensis (L.), and Parthenium hysterophorus (L.). Monocots were more dominant than dicots. The most important monocots were A. racemosa and C. rotundus, whereas the most important dicots were T. portulacastrum and D. arvensis. The pre-emergence tank-mix application of pendimethalin + imazethapyr reduced weed density and dry weight by 93 and 89%, respectively, compared with WC, and increased WCE by 86% (Table 1). This resulted in lowest weed density and dry weight (Table 2), which were significantly lower than those in other treatments. The pre-emergence tank-mix application of pendimethalin + oxyfluorfen resulted in similar/comparable WCE, but caused significantly higher CCP (∼22%) than that observed in the pendimethalin + imazethapyr. At 15 days after herbicide treatment, pendimethalin alone (1.0 kg ha−1 ) gave higher WCE, but caused greater CCP than those in pendimethalin (0.75 kg ha−1 ), applied in combination with post-emergence quizalofop or hand pulling. We observed that herbicide efficacy was not reduced due to zero tillage with residues (ZT + R) lying on the soil surface. The ZT + R resulted in similar weed control efficacy (WCE) and chilli crop phytotoxicity (CCP) (Table 1), and weed density and dry weight (Table 2) with that of CT. 3.2. Chilli leaf chlorophyll and soluble protein and ascorbate peroxidase activity The chlorophyll a and b and total chlorophyll (Table 3), soluble protein and ascorbate peroxidase (APX) activity (Table 4) in chilli leaves did not differ significantly between CT and
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Table 2 Total weed density and weed dry weight in chilli at 60 DAT as influenced by tillage and herbicide application (pooled means of two years). Treatment Tillage level CT ZT + R SE (D.F. 4*) LSD (P ≤ 0.05) Weed management Pendimethalin Pendimethalin + oxyfluorfen Pendimethalin + imazethapyr Pendimethalin fb quizalofop Pendimethalin fb hand pulling WC WFC SE (D.F. 48) LSD (P ≤ 0.05)
Table 4 Leaf soluble protein and ascorbate peroxidase (APX) activity of chilli at 60 DAT as influenced by tillage and herbicide application (pooled means of two years).
Total weed density (no m−2 )
Total weed dry weight (g m−2 )
Treatment
61 54 3 NS
68 65 3 NS**
30 37 15 48
51 61 24 75
55
42
216 0 3 8
214 0 3 9
Leaf soluble protein (mg g−1 fresh weight)
APX activity (mole ascorbate oxidized min−1 g−1 fresh weight at 25 ◦ C)
Tillage level CT ZT + R SE (D.F. 4*) LSD (P ≤ 0.05)
25.3 24.2 0.4 NS
1.6 1.4 0.04 NS**
Weed management Pendimethalin Pendimethalin + oxyfluorfen Pendimethalin + imazethapyr Pendimethalin fb quizalofop Pendimethalin fb hand pulling WC WFC SE (D.F. 48) LSD (P ≤ 0.05)
30.8 21.4 28.7 19.8 23.0 25.6 24.2 0.7 2.0
1.2 2.5 1.2 1.3 0.8 2.7 1.2 0.1 0.2
*D.F.—degrees of freedom; **NS—non-significant.
*D.F.—degrees of freedom; **NS—non-significant.
ZT + R, but differed significantly between the herbicidal treatments. Significantly higher values of chlorophyll a and b and total chlorophyll and leaf soluble protein were observed in the pendimethalin alone compared to all other treatments, except the pendimethalin + imazethapyr. The pendimethalin + imazethapyr resulted in significantly higher values of these variables than those in pendimethalin + oxyfluorfen, and the sequential application of pendimethalin fb quizalofop or hand pulling. The APX activity in chilli leaves (Table 4) due to this tank-mix treatment was significantly lower than those in pendimethalin + oxyfluorfen, and weedy check, indicating that chilli was less stressed in this treatment.
3.3. Chilli fruit yield and economics All herbicide treatments resulted in significantly higher chilli yield, gross returns (GR), net returns (NR) and net returns:cost (NR:C) than those in weedy check (Table 5), but the pendimethalin + imazethapyr was most superior. The pendimethalin + imazethapyr was on par with WFC, with 2% lower yield and GR, but 3% higher NR than that of WFC. The NR:C obtained in this tank-mix was 20% higher than that in WFC. Both CT and ZT + R
were statistically on par, although the latter treatment resulted in 5, 5 and 7% higher chilli fruit yield, GR and NR, respectively. 4. Discussion This study showed that imazethapyr when tank-mixed with pendimethalin at pre-emergence was selective to chilli and had the highest 86% weed control efficacy (Table 1) through significant reduction in weed population by 93% and dry weight by 89% (Table 2). This greater efficacy could be mainly due to better compatibility of imazethapyr with pendimethalin in the tank mixture. Similar compatibility of these two herbicides has been reported in maize (Susha et al., 2014) and soybean (Younesabadi Masoumeh et al., 2013). Arnold et al. (1993) observed greater effects from the ready-mixes of imazethapyr against Solanum nigrum (black nightshade), Kochia scoparia (kochia), Salsola iberica (Russian thistle), Amaranthus blitoides and Amaranthus retroflexus (prostrate and redroot pigweed) in Pinto bean. Tank-mixing these herbicides improved weed control by expanding the weed spectrum being controlled. Possible synergism upon tank-mixing of imazethapyr and pendimethalin cannot be ruled out since weed control effects were similar or better even though the doses of both herbicides were reduced by 25% than the recommended doses. This tank-mix
Table 3 Chlorophyll ‘a’and ‘b’ and total chlorophyll content in leaves of chilli at 60 DAT as influenced by tillage and herbicide application (pooled means of two years). Treatment Tillage level CT ZT + R SE (D.F. 4*) LSD (P ≤ 0.05) Weed management Pendimethalin Pendimethalin + oxyfluorfen Pendimethalin + imazethapyr Pendimethalin fb quizalofop Pendimethalin fb hand pulling WC WFC SE (D.F. 48) LSD (P ≤ 0.05)
Chlorophyll ‘a’ (mg g−1 fresh weight)
Chlorophyll ‘b’ (mg g−1 fresh weight)
Total chlorophyll (mg g−1 fresh weight)
2.2 2.3 0.04 NS
0.3 0.4 0.01 NS
2.5 2.7 0.04 NS**
2.6 1.9 2.5 2.0
0.4 0.3 0.4 0.3
3.0 2.2 2.8 2.3
2.2
0.3
2.5
2.1 2.4 0.06 0.18
0.3 0.4 0.01 0.03
2.4 2.8 0.07 0.19
*D.F.—degrees of freedom; **NS—non-significant.
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Table 5 Green chilli yield, gross returns (GR) and net returns (NR) and net returns:cost (NR:C) of chilli production as influenced by tillage and herbicide application (pooled mean of two years). Treatment
Green chilli yield (t ha−1 )
Cost of production ( × 103 ) ha−1 **
GR ( × 103 ) ha−1 **
NR ( × 103 ) ha−1 **
NR:C
Tillage level CT ZT + R SE (D.F. 4*) LSD (P ≤ 0.05)
7.7 8.1 0.1 NS
52.1 53.1 – –
162.4 170.7 2.8 NS
110.2 117.5 2.8 NS
2.1 2.2 0.1 NS***
Weed management Pendimethalin Pendimethalin + oxyfluorfen Pendimethalin + imazethapyr Pendimethalin fb quizalofop Pendimethalin fb hand pulling WC WFC SE (D.F. 48) LSD (P ≤ 0.05)
8.6 8.6 10.1 7.2 6.9 3.6 10.3 0.2 0.5
50.6 51.5 52.2 51.5 53.3 48.4 61.0 – –
181.0 181.8 213.0 151.7 144.6 76.1 217.4 3.8 10.8
130.4 130.3 160.8 100.2 91.3 27.6 156.3 3.9 10.9
2.6 2.5 3.1 1.9 1.7 0.6 2.5 0.1 0.2
*D.F.—Degrees of freedom; **1.0 US$ = (INR) 60.95; ***NS—Non-significant; The common cost (excluding treatment cost) was 44,803; cost of tillage (for CT) 3045; cost of residue (for ZT) 4050; cost of laborers (for weed-free check) 12,750 (mean of two years). Herbicide treatments costs varied from 2272 (in pendimethalin 1.0 kg ha−1 ) to 3840 (in pendimethalin 0.75 kg ha−1 + imazethapyr 0.075 kg ha−1 ). The market price for chilli fruits was 21,000 per tonne.
also reduced application cost by 50% (∼ 500 per ha) compared with applying these herbicides separately but in sequence to achieve similar weed control. Herbicide input into the environment can be reduced by 25% by tank-mixing herbicides with lower rates. Pendimethalin led to significantly higher values of chlorophyll “a” and total chlorophyll (Table 3) of chilli leaves in the pendimethalin alone treatment. Similar effect of pendimethalin has been observed in soybean (Tuti and Das, 2011; Younesabadi Masoumeh et al., 2013). Results of Shabana et al. (2001), showing increases in protein and carbohydrate contents in the alga treated with pendimethalin corroborate this. Higher activity of ascorbate peroxidase (APX) implies greater stresses (Table 4) in plants (Arora et al., 2002; Wang and Zhou, 2006). In chilli leaves, a significant decrease in APX activity due to the tank-mix application of pendimethalin + imazethapyr indicated that chilli plants were less/not stressed and tolerant to imazethapyr. A very low phytotoxicity (7%) to chilli plants observed in this treatment could substantiate this (Table 1). Besides, the lower stress can be partially related to lower weed interference because of these herbicides being more effective. In contrast, higher APX activity observed in the pendimethalin + oxyfluorfen (Table 4) indicated more stresses, leading to higher phytotoxicity to chilli by 22% (Table 1). Under situations of abundance of chlorophylls in leaves, all chlorophylls may not equally contribute to photosynthesis, and their number may not have direct relation with the rate of photosynthesis (Khan et al., 2006). This could be a reason why pendimethalin alone with higher chlorophyll and leaf soluble protein resulted in lower yield compared to pendimethalin + oxyfluorfen with lowest chlorophyll content. Younesabadi Masoumeh et al. (2013) observed similar results. This study revealed that, due to four manual weeding given, the WFC was costlier by almost 9000 ha−1 than pendimethalin + imazethapyr tank-mix treatment. As a result, WFC, although gave highest chilli yield and GR (Table 5), the pendimethalin + imazethapyr was superior to it by giving 3% higher NR and 20% higher NR:C. This tank-mix gave similar chilli yield, but incurred lower cost than that of WFC. Singh et al. (2011) reported similar higher net income due to applying butachlor 1.0 kg ha−1 , followed by weed-free check in rainfed chilli. The effect of ZT + R was not significantly different from that of CT, which could be due to the short time span of two years with this study. A little impact of ZT + R, however, was visualized in the form of slightly greater reductions in weed density (∼12%) and dry weight (∼5%) (Table 2), higher WCE (∼3%) (Table 1), and higher chlorophyll content (Table 3) that culminated into slightly higher
yield (∼5%), NR (∼7%), and NR:C (Table 5). An additional benefit of crop/Sesbania residue on the soil surface is that weed seedling establishment may be reduced (Kumar et al., 2012; Ramachandran et al., 2012; Das, 2014). Statistically non-significant, but a 12% lower APX activity observed in this treatment indicated lower stresses to maize plants. The moderation/mitigation effects of residue to moisture and temperature stresses might play a role. The ZT+R incurred slightly higher cost by 1000 ha−1 than that of CT (Table 5), but higher chilli yield by 0.4 t ha−1 obtained in this treatment compensated this and increased the GR and NR by 8300 ha−1 and 7300 ha−1 , respectively. This study recommended a pendimethalin + imazethpyr tankmix application for better weed control in chilli, but remained inconclusive on the effect of tillage/residue. The duration of experiment should be longer, and the amount of residue may be increased/optimized for better results. The results would likely be reproducible under similar soil and climatic conditions, yet replicate trials across sites would lead to more validation of the effects of both herbicides and tillage/residue. Besides, experimenting on a chilli crop-based cropping system for whole year in a fixed layout under conservation agriculture would lead to higher yield and income. 5. Conclusion This study indicated that imazethapyr applied at pre-emergence was selective to chilli due to lower ascorbate peroxidase activity and less/negligible negative effects on chlorophyll and leaf soluble protein in chilli. The pre-emergence tank-mix application of pendimethalin 0.75 kg ha−1 + imazethapyr 0.075 kg ha−1 resulted in better weed control, higher chilli yield, net returns and net returns:cost. The tillage systems did not significantly affect herbicide efficacy. Zero tillage with residue was similar with conventional tillage on weed control, chilli yield and income. Therefore, a combination of the pendimethalin 0.75 kg ha−1 + imazethapyr 0.075 kg ha−1 tank-mix and zero tillage with residue may be recommended for better weed management and higher chilli productivity and profitability. Acknowledgements The authors sincerely acknowledge the necessary services and supplies provided by the Indian Agricultural Research Institute during the course of investigation. They are also thankful to the Agricultural and Natural Resources Research Center of Hormoz-
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Hiscox, J.D., Israelstam, G.F., 1979. A method for the extraction of chlorophyll from leaf tissue without maceration. Can. J. Bot. 57, 1332–1334. Khan, M.S., Chaudhry, Y.P., Wani, P.A., Zaidi, A., 2006. Biotoxic effects of the herbicides on growth, seed yield, and grain protein of greengram. J. Appl. Sci. Environ. Manag. 10 (3), 141–146. Kulshrestha, G., Singh, S.B., Lal, S.P., Yaduraju, N.T., 2000. Effect of long term field application of pendimethalin: enhanced degradation in soil. Pest Manag. Sci. 56, 202–206. Kumar, M., Das, T.K., Yaduraju, N.T., 2012. An integrated approach for management of Cyperus rotundus (purple nutsedge) in soybean-wheat cropping system. Crop Prot. 33 (4), 74–81. Lowry, O.H., Rosebrough, N.J., Farr, A.L., Randall, R.J., 1951. Protein measurement with folin phenol reagent. J. Biol. Chem. 193 (1), 265–275. Monsefi, A., Sharma, A.R., Rang Zanc, N., Behera, U.K., Das, T.K., 2014. Effect of tillage and residue management on productivity of soybean and physico-chemical properties of soil in soybean-wheat cropping system. Int. J. Plant Prod. 8 (3), 429–440. Nakano, Y., Asada, K., 1981. Hydrogen peroxide is scavenged by ascorbate-specific peroxidase in spinach chloroplasts. Plant Cell Physiol. 22 (5), 867–888. Norsworthy, J.K., Oliveira, M.J., 2007. Tillage and soybean canopy effects on common cocklebur (Xanthium strumarium) emergence. Weed Sci. 55 (5), 474–480. Patel, R.B., Barevadia, T.N., Patel, B.D., Meisuriya, M., 2004. Effect of cultural and chemical methods on weed and fruit yield of green chilli. Indian J. Weed Sci. 36 (3&4), 300–301. Peachey, R.E., William, R.D., Mallory-Smith, C., 2004. Effect of no-till or conventional planting and cover crops residues on weed emergence in vegetable row crop. Weed Technol. 18 (4), 1023–1030. Ramachandran, A., Veeramani, A., Prema, P., 2012. Effect of brown manuring on weed growth, yield and economics of irrigated maize. Indian J. Weed Sci. 44 (3), 204–206. SAS Institute, 2003. SAS/STAT. User’s Guide. Version 9.1. SAS Inst. Inc., Cary, NC. Shabana, E.F., Battah, M.G., Kobbia, I.A., Eladel, H.M., 2001. Effect of pendimethalin on growth and photosynthetic activity of Protosiphon botryoides in different nutrient states. Ecotoxicol. Environ. Saf. 49 (2), 106–110. Singh, U., Hiremath, S.M., Halikatti, S.I., Shashidhara, G.B., Patil, P.L., 2011. Evaluation of herbicides for weed control in rainfed transplanted chilli (Capsicum annuum L.). Karnataka J. Agric. Sci. 24 (2), 125–128. Susha, V.S., Das, T.K., Sharma, A.R., Nath, C.P., 2014. Carry-over effect of weed management practices of maize (Zea mays) on weed dynamics and productivity of succeeding zero and conventional till wheat (Triticum aestivum). Indian J. Agron. 59 (1), 41–47. Tuti, M.D., Das, T.K., 2011. Sequential application of metribuzin on weed control, growth and yield of soybean (Glycine max). Indian J. Agron. 56 (1), 57–61. Wang, M., Zhou, Q.X., 2006. Effects of herbicide chlorimuron-ethyl on physiological mechanisms in wheat (Triticum aestivum). Ecotoxicol. Environ. Saf. 64 (2), 190–197. Yamamoto, Y., Kobayashi, Y., Ramadevi, S., Rikiishi, S., Matsumoto, H., 2003. Oxidative stress triggered by aluminium in plant roots. Plant Soil 255, 239–243. Younesabadi Masoumeh, Das, T.K., Sharma, A.R., 2013. Effect of tillage and tank-mix herbicide application on weed management in soybean (Glycine max). Indian J. Agron. 58 (3), 372–378.
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Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti
Herbicides tank-mixes effects on weeds and productivity and profitability of chilli (Capsicum annuum L.) under conventional and zero tillage Abdolhamid Hajebi a,1 , T.K. Das a,∗ , Ajay Arora b , Shashi Bala Singh c , Fatemeh Hajebi d a
Division of Agronomy, Indian Agricultural Research Institute, New Delhi 110 012, India Division of Plant Physiology, Indian Agricultural Research Institute, New Delhi 110 012, India c Division of Agricultural Chemicals, Indian Agricultural Research Institute, New Delhi 110 012, India d Agricultural and Natural Resources Engineering Organization of Hormozgan, Hormozgan, Iran b
a r t i c l e
i n f o
Article history: Received 5 September 2015 Received in revised form 11 November 2015 Accepted 13 November 2015 Keywords: Ascorbate peroxidase Chilli Imazethapyr Tank-mix herbicides Weed Zero tillage
a b s t r a c t Weeds heavily infest chilli and cause significant yield losses. Herbicide mixtures control diverse weeds better and prevent/delay weed shift and resistance. They have been hardly studied in chilli under conservation agriculture. Pendimethalin is the prevalent herbicide used in chilli, but not effective against nutsedge. Oxyfluorfen and quizalofop-p-ethyl also have negligible/no effect on nutsedge. Imazethapyr is a post-emergence herbicide and more effective against nutsedge, but its pre-emergence activity against nutsedge/weeds and selectivity to chilli have not been studied. In this study, these herbicides were tankmixed or sequentially applied to expand the weed spectrum being currently controlled. Our objective was to compare herbicide mixes to improve weed control, especially with nutsedge. We observed that the pre-emergence tank-mix application of pendimethalin 0.75 kg ha−1 + imazethapyr 0.075 kg ha−1 resulted in significantly higher weed control efficacy (∼86%) and leaf chlorophyll, but lower ascorbate peroxidase activity, suggesting that imazethapyr was selective to chilli. In this treatment, the yield and gross returns were 2% lower, but the net returns and net returns:cost were higher by 3% and 20%, respectively compared to weed-free check that included the costs of hand weeding. The zero tillage with residue (ZT + R) did not affect herbicide activity. The pendimethalin + imazethapyr tank-mix treatment with ZT + R would provide higher yield and income through better weed management and less/no chances for nutsedge insurgence, which usually occurs due to continuous use of herbicides with limited efficacy on nutsedge. It would reduce application cost by 50%, and doses and residues of these herbicides by 25% in agro-ecosystems. © 2015 Elsevier B.V. All rights reserved.
1. Introduction Chilli (Capsicum annuum L.) is an important commercial spice/vegetable crop in India, grown on a wide range of soils and altitudes up to 2000 m above mean sea level. Chilli fruits are a source of vitamin C, E, provitamin A, and carotenoids, known for their antioxidants properties (Chatterjee et al., 2007; Deepa et al., 2007). Chilli is grown in wide rows and has initial slow growth, which favour huge weed infestation, comprising of grasses, broad-leaves
∗ Corresponding author. Fax: +91 1125842283. E-mail addresses: hamid [email protected] (A. Hajebi), [email protected] (T.K. Das). 1 Present address: Department of Natural Resources, Agricultural and Natural Resources Research Center of Hormozgan, Hormozgan, Iran. http://dx.doi.org/10.1016/j.scienta.2015.11.020 0304-4238/© 2015 Elsevier B.V. All rights reserved.
and sedges. Weeds can reduce chilli yield by 60–70% (Patel et al., 2004). Generally, the critical period for weed competition in chilli (Frank et al., 1988) is 30–60 days after transplanting (DAT). In India, weeds in chilli are controlled mainly by manual weeding, which is labor-extensive and expensive. Herbicide could be a cost-effective alternative. The selectivity of herbicide limits the choice of herbicides in chilli. Conventional single herbicidebased weed control is not adequate for controlling all weeds, having diverse morphology and physiology, and emerging at different stages. This can cause weed shift and hastens resistance in weeds. In this context, herbicide mixtures (ready-mixes/premixes or tank-mixes) can be useful (Das, 2008), which would provide better broad-spectrum weed control vis-à-vis prevent weed shift/insurgence and delay resistance. Ready-mixes are very few and have inherent limitations in fixing the required quantities of component herbicides for desired levels of weed control efficacy. In contrast, tank-mixes can readily be prepared by the
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farmers in fields just before application by physical mixing of components herbicides, usually at lower doses than recommended. The tank-mixes can reduce the expense of application cost and may be synergistic to improve herbicide efficacy. There are chances of more selectivity when applied at pre-emergence, and crop can germinate in weed-free situations, which favours faster seedling establishment (Das, 2008; Younesabadi Masoumeh et al., 2013; Susha et al., 2014). Besides, less quantity of the specific herbicide would enter into the environment due to lower doses used through tank-mix combinations. Pendimethalin is recommended for chilli. It is exclusively a pre-emergence, broad-spectrum herbicide (Kulshrestha et al., 2000), and is effective against annual weeds, mainly grasses, but not effective against nutsedge. Oxyfluorfen is a broad-spectrum herbicide and applied as pre- and post-emergence. Quizalofop-pethyl is an acetyl CoA carboxylase (ACCase) inhibitor herbicide, narrow-spectrum, controlling only grasses, and applied as postemergence. Imazethapyr is a post-emergence broad-spectrum herbicide, mainly recommended for soybean and groundnut, and is effective against nutsedge (Kumar et al., 2012). Its application may prevent nutsedge insurgence in future, which is of common occurrence in crops that are continuously applied with herbicides having limited efficacy on nutsedge. We used oxyfluorfen and quizalofopp-ethyl at pre-emergence, their usual time of application, but imazethapyr as pre-emergence as against post-emergence. The doses of oxyfluorfen, quizalofop-p-ethyl and imazethapyr were reduced by 40, 50 and 25%, respectively (∼being 0.250, 0.050 and 0.100 kg ha−1 as the recommended doses) in the tank-mix with 25% (0.75 kg ha−1 instead of 1.00 kg ha−1 ) lower than recommended dose of pendimethalin towards achieving greater selectivity and better weed control. Crops respond to herbicides in physiological ways that can be measured. Pendimethalin can affect chlorophyll content in crop leaves (Tuti and Das, 2011; Younesabadi Masoumeh et al., 2013). Also herbicides can stimulate production of oxidant compounds • [such as superoxide ion (O2 − ), hydrogen peroxide (H2 O2 )] by inhibiting biosynthetic pathways (Arora et al., 2002). These compounds are related to stress levels that crop experiences, and crop responds by producing anti-oxidant enzymes, namely, superoxide dismutase (SOD), catalase (CAT) or ascorbate peroxidase (APX) that scavenge the stress-effects (Arora et al., 2002; Yamamoto et al., • 2003; Guo et al., 2004). The SOD accelerates the conversion of O2 − to H2 O2 , while CAT, APX and a variety of other peroxidases catalyze the breakdown of H2 O2 (Balestrasse et al., 2006). These enzymes can be measured, and may provide an assessment of potential crop injury/selectivity by a herbicide. One possible test is measuring the activity of APX. These defence mechanisms may operate in chilli, but have not been studied. Studying the APX activity can reveal this. Conservation agriculture (CA), involving zero tillage with residue retention may provide greater adaptation and mitigation to climate change through better crop growth and yield (Das et al., 2014) and improving soil health (Bhattacharyya et al., 2013; Das et al., 2013; Monsefi et al., 2014). It has enough scope for adoption in spices/vegetables like chilli, but is hardly studied. The crop residue on the soil surface does intercept herbicide sprays. The residue, depending on the amount and the positioning/alignment, whether standing erect after combine harvesting or lying on the surface due to applied after whole crop harvesting, can intercept and prevent herbicides from reaching to soil and interfere/reduce their effects on weeds. Increasing the volume rate (∼water quantity) of spraying or using foot sprayer, having higher water requirement may reduce the negative effect of residue to a great extent. Irrigating the field immediately after herbicide application can nullify the interference of residue retained. Besides, it is actually the combined effect of tillage, crop residue and herbicide that would impact on weed interference/dynamics over the years (Peachey et al., 2004;
Norsworthy and Oliveira, 2007; Anderson, 2009, 2010; Susha et al., 2014), and result in an integrated weed management. Therefore, this study was undertaken to evaluate the individual and combined effects of tillage/residue and herbicide tank-mixes on weeds, chilli yield and economics. 2. Materials and methods 2.1. Experimental sites The experiments were carried out on a fixed lay-out in the field, maintained for two years at the Indian Agricultural Research Institute, New Delhi during the rainy-seasons of 2012 and 2013. The site was irrigated and irrigation was provided through surface check basin method. The field was no-till fallow during the previous winter seasons, 2011–12 and 2012–13. In both years, chilli seedlings were transplanted and the respective herbicide/herbicides tankmixes applied to the respective treatment plots. New Delhi is situated at 28◦ 35 N latitude and 77◦ 12 E longitude at an elevation of 229 m above mean sea level. Soil was alluvium (Typic Ustochrepts; Order Inceptisol) and sandy-loam with 63% sand, 17% silt and 20% clay. It had 0.54% organic C and pH 7.6. The available P (19 kg P ha−1 ) and K (191 kg K ha−1 ) were medium, but available N (275 kg N ha−1 ) was low. 2.2. Treatments/herbicides Two tillage levels, viz., conventional tillage (CT) and zero tillage with residue (ZT + R) were the main plot treatments. Seven weed control treatments such as pendimethalin 1.0 kg ha−1 pre-emergence (PE); pendimethalin 0.75 kg ha−1 + oxyfluorfen 0.15 kg ha−1 tank-mix PE; pendimethalin 0.75 kg ha−1 + imazethapyr 0.075 kg ha−1 tank-mix PE; pendimethalin 0.75 kg ha−1 PE followed by (fb) quizalofopp-ethyl 0.025 kg ha−1 at 30 day after transplanting (DAT); pendimethalin 0.75 kg ha−1 PE fb hand pulling at 30 DAT; weedy check (WC); and weed-free check (WFC) were the sub-plots treatments. These treatments were laid out in a split plot design with three replications. In the ZT plots, glyphosate at 1.0 kg ha−1 was applied 7–10 days before transplanting of chilli to control existing weeds. In these plots, the residue of Sesbania aculeata L. (Dhaincha) grown in the previous summer season was retained @ 10 t ha−1 fresh biomass (∼1.4–2.0 t ha−1 dry weight) on the surface of zero-till plots as mulch. In CT, three ploughings (one disking and two harrowing) and one levelling were done for land preparation. The areas of main and sub-plots were 37.5 m by 3.0 m and 4.5 m by 3.0 m, respectively. The net plot size (area actually considered for chilli fruit yield) was 3.6 m by 1.8 m. The first irrigation was given immediately after the transplanting of chilli seedlings in respective plots. The preemergence applications of pendimethalin alone or the tank-mixes (pendimethalin + imazethapyr/oxyfluorfen) were made two days after transplanting (DAT) or irrigation. For the tank-mix treatments, component herbicides at required quantities were mixed in the spray-tank just before spraying. Quizalofop at required quantity was applied as post-emergence at 30 DAT. For the pre- and post-emergence applications of respective herbicides, a knapsack sprayer fitted with a flat fan nozzle (Sukun Agencies India, Mumbai, Maharashtra) was used with a volume rate of 400 L water ha−1 . Weed-free check plots were kept free from weeds throughout growing season by hand pulling of weeds. 2.3. Agronomic practices Healthy seedlings (35 days old) of chilli cv. ‘Pusa Sadabahar’ (Indian Agricultural Research Institute, New Delhi), raised in a
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self-managed nursery in this research farm, were transplanted at 60 × 45 cm in the first week of August in both years. Chilli was fertilized with 100 kg N, 50 kg P2 O5 and 50 kg K2 O ha−1 through urea, diammonium phosphate, and muriate of potash, respectively. Half dose of N and full doses of P and K were applied at the time of transplanting. The remaining N was top-dressed in two equal splits at 45 and 60 DAT after one day of irrigation applied through check basin method.
2.4. Sampling techniques and observations 2.4.1. Agronomic observations A quadrat (0.5 × 0.5 m) was randomly placed in each plot at 60 DAT and individual weed species were counted, collected, sundried for 2 days and kept in an oven at 70 ± 5 ◦ C for 48 h for recording dry weight. At 15 days after herbicides application, per cent weed control efficacy and per cent injury to chilli plants were visually judged and rating was made on a scale from 0 to 100% (control/phytotoxicity) scale. Green chilli fruits were picked manually from the net plot area (3.6 m by 1.8 m) in every plot for determining yield. There were six pickings of green chilies in every cropping season.
2.4.2. Physiological/biochemical observations At 60 DAT, random sampling of chilli leaves was done from each treatment for determining the chlorophyll a and b and total chlorophyll contents by dimethylsulfoxide method (Hiscox and Israelstam, 1979). Fifty milligram chilli fresh leaf discs were added to 10 mL dimethyl sulfoxide (DMSO) in test tubes for extracting the pigments. Tubes were kept in dark for 4 h at 65 ◦ C. The absorbance was recorded at 663 and 645 nm using DMSO as blank. Leaf soluble protein was determined from the absorbance of blue colour developed by the reaction of Folin–Ciocalteau reagent by the amino acids tyrosine and tryptophan in the protein (Lowry et al., 1951). Ascorbate peroxidase (APX) activity was assayed by recording the decrease in optical density due to ascorbic acid at 290 nm by a spectrophotometer (Nakano and Asada, 1981).
2.5. Chilli cultivation economics The costs prevailing in the experimental years (2012 and 2013) of all inputs required were used for calculating the cost of chilli production. The market prices of green chilli fruits during these two years were used for calculating the gross returns (GR). Weed-free check required 60 mandays ha−1 for four hand pulling of weeds and incurred INR (∼Indian National Rupee) 13,200 ha−1 , considering the wages of 220.00 per manday. The net returns (NR) was worked out by deducting the cost of cultivation from the GR. The net returns:cost (NR:C) was calculated from the NR divided by the cost of production.
2.6. Statistical analysis All data on weed and chilli were subjected to analysis of variance (ANOVA) using the PROC GLM procedure of SAS (SAS Institute, 2003). The two-year data were subject to pool analysis to visualize the variations of particular crop/weed parameters between the years, treatments, and the year × treatment interactions, which were mostly non-significant at P ≤ 0.05. The significance was tested by variance ratio (i.e., F value) at P ≤ 0.05 (Gomez and Gomez, 1984). Standard error (SE) and least significant difference (LSD) were worked out for each parameter of weed and chilli studied for comparing the treatment means.
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Table 1 Rating on chilli crop phytotoxicity and weed control efficacy (WCE) at 15 days after herbicide application across the treatments (pooled means of two years). Treatment
Tillage level CT ZT + R SE (D.F. 4*) LSD (P ≤ 0.05) Weed management Pendimethalin Pendimethalin + oxyfluorfen Pendimethalin + imazethapyr Pendimethalin fb quizalofop Pendimethalin fb hand pulling WC WFC SE (D.F. 48) LSD (P ≤ 0.05)
Weed control efficacy (WCE)a
Chilli crop phytotoxicity (CCP)a
62 65 9 NS
7 7 1 NS**
70 80 86 56
9 22 7 5
53
4
0 100 14 40
0 0 2 5
*D.F.—degrees of freedom; **NS—non-significant. a Rating on crop phytotoxicity and weed control efficacy were based on visual observations in the plots/treatments across replications on a scale from 0 (zero) to 100, where 0 means 0% phytotoxicity/weed control and 100 means 100% phytotoxicity/weed control.
3. Results 3.1. Weed control efficacy and chilli crop phytotoxicity Eleven weed species, 6 monocots and 5 dicots, belonging to 7 botanical families were present in chilli. Monocot weeds were: Acrachne racemosa (Heyne ex Roem and Schult) Ohwi, Cyperus rotundus (L.), Dactyloctenium aegyptium (L.) P. Beauv. Willd., Commelina benghalensis (L.), Digitaria sanguinalis (L.) Scop. and Echinochloa colona (L.). Dicot weeds were: Trianthema portulacastrum (L.), Digera arvensis (L.) Forsk., Phyllanthus niruri (L.), Convolvulus arvensis (L.), and Parthenium hysterophorus (L.). Monocots were more dominant than dicots. The most important monocots were A. racemosa and C. rotundus, whereas the most important dicots were T. portulacastrum and D. arvensis. The pre-emergence tank-mix application of pendimethalin + imazethapyr reduced weed density and dry weight by 93 and 89%, respectively, compared with WC, and increased WCE by 86% (Table 1). This resulted in lowest weed density and dry weight (Table 2), which were significantly lower than those in other treatments. The pre-emergence tank-mix application of pendimethalin + oxyfluorfen resulted in similar/comparable WCE, but caused significantly higher CCP (∼22%) than that observed in the pendimethalin + imazethapyr. At 15 days after herbicide treatment, pendimethalin alone (1.0 kg ha−1 ) gave higher WCE, but caused greater CCP than those in pendimethalin (0.75 kg ha−1 ), applied in combination with post-emergence quizalofop or hand pulling. We observed that herbicide efficacy was not reduced due to zero tillage with residues (ZT + R) lying on the soil surface. The ZT + R resulted in similar weed control efficacy (WCE) and chilli crop phytotoxicity (CCP) (Table 1), and weed density and dry weight (Table 2) with that of CT. 3.2. Chilli leaf chlorophyll and soluble protein and ascorbate peroxidase activity The chlorophyll a and b and total chlorophyll (Table 3), soluble protein and ascorbate peroxidase (APX) activity (Table 4) in chilli leaves did not differ significantly between CT and
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Table 2 Total weed density and weed dry weight in chilli at 60 DAT as influenced by tillage and herbicide application (pooled means of two years). Treatment Tillage level CT ZT + R SE (D.F. 4*) LSD (P ≤ 0.05) Weed management Pendimethalin Pendimethalin + oxyfluorfen Pendimethalin + imazethapyr Pendimethalin fb quizalofop Pendimethalin fb hand pulling WC WFC SE (D.F. 48) LSD (P ≤ 0.05)
Table 4 Leaf soluble protein and ascorbate peroxidase (APX) activity of chilli at 60 DAT as influenced by tillage and herbicide application (pooled means of two years).
Total weed density (no m−2 )
Total weed dry weight (g m−2 )
Treatment
61 54 3 NS
68 65 3 NS**
30 37 15 48
51 61 24 75
55
42
216 0 3 8
214 0 3 9
Leaf soluble protein (mg g−1 fresh weight)
APX activity (mole ascorbate oxidized min−1 g−1 fresh weight at 25 ◦ C)
Tillage level CT ZT + R SE (D.F. 4*) LSD (P ≤ 0.05)
25.3 24.2 0.4 NS
1.6 1.4 0.04 NS**
Weed management Pendimethalin Pendimethalin + oxyfluorfen Pendimethalin + imazethapyr Pendimethalin fb quizalofop Pendimethalin fb hand pulling WC WFC SE (D.F. 48) LSD (P ≤ 0.05)
30.8 21.4 28.7 19.8 23.0 25.6 24.2 0.7 2.0
1.2 2.5 1.2 1.3 0.8 2.7 1.2 0.1 0.2
*D.F.—degrees of freedom; **NS—non-significant.
*D.F.—degrees of freedom; **NS—non-significant.
ZT + R, but differed significantly between the herbicidal treatments. Significantly higher values of chlorophyll a and b and total chlorophyll and leaf soluble protein were observed in the pendimethalin alone compared to all other treatments, except the pendimethalin + imazethapyr. The pendimethalin + imazethapyr resulted in significantly higher values of these variables than those in pendimethalin + oxyfluorfen, and the sequential application of pendimethalin fb quizalofop or hand pulling. The APX activity in chilli leaves (Table 4) due to this tank-mix treatment was significantly lower than those in pendimethalin + oxyfluorfen, and weedy check, indicating that chilli was less stressed in this treatment.
3.3. Chilli fruit yield and economics All herbicide treatments resulted in significantly higher chilli yield, gross returns (GR), net returns (NR) and net returns:cost (NR:C) than those in weedy check (Table 5), but the pendimethalin + imazethapyr was most superior. The pendimethalin + imazethapyr was on par with WFC, with 2% lower yield and GR, but 3% higher NR than that of WFC. The NR:C obtained in this tank-mix was 20% higher than that in WFC. Both CT and ZT + R
were statistically on par, although the latter treatment resulted in 5, 5 and 7% higher chilli fruit yield, GR and NR, respectively. 4. Discussion This study showed that imazethapyr when tank-mixed with pendimethalin at pre-emergence was selective to chilli and had the highest 86% weed control efficacy (Table 1) through significant reduction in weed population by 93% and dry weight by 89% (Table 2). This greater efficacy could be mainly due to better compatibility of imazethapyr with pendimethalin in the tank mixture. Similar compatibility of these two herbicides has been reported in maize (Susha et al., 2014) and soybean (Younesabadi Masoumeh et al., 2013). Arnold et al. (1993) observed greater effects from the ready-mixes of imazethapyr against Solanum nigrum (black nightshade), Kochia scoparia (kochia), Salsola iberica (Russian thistle), Amaranthus blitoides and Amaranthus retroflexus (prostrate and redroot pigweed) in Pinto bean. Tank-mixing these herbicides improved weed control by expanding the weed spectrum being controlled. Possible synergism upon tank-mixing of imazethapyr and pendimethalin cannot be ruled out since weed control effects were similar or better even though the doses of both herbicides were reduced by 25% than the recommended doses. This tank-mix
Table 3 Chlorophyll ‘a’and ‘b’ and total chlorophyll content in leaves of chilli at 60 DAT as influenced by tillage and herbicide application (pooled means of two years). Treatment Tillage level CT ZT + R SE (D.F. 4*) LSD (P ≤ 0.05) Weed management Pendimethalin Pendimethalin + oxyfluorfen Pendimethalin + imazethapyr Pendimethalin fb quizalofop Pendimethalin fb hand pulling WC WFC SE (D.F. 48) LSD (P ≤ 0.05)
Chlorophyll ‘a’ (mg g−1 fresh weight)
Chlorophyll ‘b’ (mg g−1 fresh weight)
Total chlorophyll (mg g−1 fresh weight)
2.2 2.3 0.04 NS
0.3 0.4 0.01 NS
2.5 2.7 0.04 NS**
2.6 1.9 2.5 2.0
0.4 0.3 0.4 0.3
3.0 2.2 2.8 2.3
2.2
0.3
2.5
2.1 2.4 0.06 0.18
0.3 0.4 0.01 0.03
2.4 2.8 0.07 0.19
*D.F.—degrees of freedom; **NS—non-significant.
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Table 5 Green chilli yield, gross returns (GR) and net returns (NR) and net returns:cost (NR:C) of chilli production as influenced by tillage and herbicide application (pooled mean of two years). Treatment
Green chilli yield (t ha−1 )
Cost of production ( × 103 ) ha−1 **
GR ( × 103 ) ha−1 **
NR ( × 103 ) ha−1 **
NR:C
Tillage level CT ZT + R SE (D.F. 4*) LSD (P ≤ 0.05)
7.7 8.1 0.1 NS
52.1 53.1 – –
162.4 170.7 2.8 NS
110.2 117.5 2.8 NS
2.1 2.2 0.1 NS***
Weed management Pendimethalin Pendimethalin + oxyfluorfen Pendimethalin + imazethapyr Pendimethalin fb quizalofop Pendimethalin fb hand pulling WC WFC SE (D.F. 48) LSD (P ≤ 0.05)
8.6 8.6 10.1 7.2 6.9 3.6 10.3 0.2 0.5
50.6 51.5 52.2 51.5 53.3 48.4 61.0 – –
181.0 181.8 213.0 151.7 144.6 76.1 217.4 3.8 10.8
130.4 130.3 160.8 100.2 91.3 27.6 156.3 3.9 10.9
2.6 2.5 3.1 1.9 1.7 0.6 2.5 0.1 0.2
*D.F.—Degrees of freedom; **1.0 US$ = (INR) 60.95; ***NS—Non-significant; The common cost (excluding treatment cost) was 44,803; cost of tillage (for CT) 3045; cost of residue (for ZT) 4050; cost of laborers (for weed-free check) 12,750 (mean of two years). Herbicide treatments costs varied from 2272 (in pendimethalin 1.0 kg ha−1 ) to 3840 (in pendimethalin 0.75 kg ha−1 + imazethapyr 0.075 kg ha−1 ). The market price for chilli fruits was 21,000 per tonne.
also reduced application cost by 50% (∼ 500 per ha) compared with applying these herbicides separately but in sequence to achieve similar weed control. Herbicide input into the environment can be reduced by 25% by tank-mixing herbicides with lower rates. Pendimethalin led to significantly higher values of chlorophyll “a” and total chlorophyll (Table 3) of chilli leaves in the pendimethalin alone treatment. Similar effect of pendimethalin has been observed in soybean (Tuti and Das, 2011; Younesabadi Masoumeh et al., 2013). Results of Shabana et al. (2001), showing increases in protein and carbohydrate contents in the alga treated with pendimethalin corroborate this. Higher activity of ascorbate peroxidase (APX) implies greater stresses (Table 4) in plants (Arora et al., 2002; Wang and Zhou, 2006). In chilli leaves, a significant decrease in APX activity due to the tank-mix application of pendimethalin + imazethapyr indicated that chilli plants were less/not stressed and tolerant to imazethapyr. A very low phytotoxicity (7%) to chilli plants observed in this treatment could substantiate this (Table 1). Besides, the lower stress can be partially related to lower weed interference because of these herbicides being more effective. In contrast, higher APX activity observed in the pendimethalin + oxyfluorfen (Table 4) indicated more stresses, leading to higher phytotoxicity to chilli by 22% (Table 1). Under situations of abundance of chlorophylls in leaves, all chlorophylls may not equally contribute to photosynthesis, and their number may not have direct relation with the rate of photosynthesis (Khan et al., 2006). This could be a reason why pendimethalin alone with higher chlorophyll and leaf soluble protein resulted in lower yield compared to pendimethalin + oxyfluorfen with lowest chlorophyll content. Younesabadi Masoumeh et al. (2013) observed similar results. This study revealed that, due to four manual weeding given, the WFC was costlier by almost 9000 ha−1 than pendimethalin + imazethapyr tank-mix treatment. As a result, WFC, although gave highest chilli yield and GR (Table 5), the pendimethalin + imazethapyr was superior to it by giving 3% higher NR and 20% higher NR:C. This tank-mix gave similar chilli yield, but incurred lower cost than that of WFC. Singh et al. (2011) reported similar higher net income due to applying butachlor 1.0 kg ha−1 , followed by weed-free check in rainfed chilli. The effect of ZT + R was not significantly different from that of CT, which could be due to the short time span of two years with this study. A little impact of ZT + R, however, was visualized in the form of slightly greater reductions in weed density (∼12%) and dry weight (∼5%) (Table 2), higher WCE (∼3%) (Table 1), and higher chlorophyll content (Table 3) that culminated into slightly higher
yield (∼5%), NR (∼7%), and NR:C (Table 5). An additional benefit of crop/Sesbania residue on the soil surface is that weed seedling establishment may be reduced (Kumar et al., 2012; Ramachandran et al., 2012; Das, 2014). Statistically non-significant, but a 12% lower APX activity observed in this treatment indicated lower stresses to maize plants. The moderation/mitigation effects of residue to moisture and temperature stresses might play a role. The ZT+R incurred slightly higher cost by 1000 ha−1 than that of CT (Table 5), but higher chilli yield by 0.4 t ha−1 obtained in this treatment compensated this and increased the GR and NR by 8300 ha−1 and 7300 ha−1 , respectively. This study recommended a pendimethalin + imazethpyr tankmix application for better weed control in chilli, but remained inconclusive on the effect of tillage/residue. The duration of experiment should be longer, and the amount of residue may be increased/optimized for better results. The results would likely be reproducible under similar soil and climatic conditions, yet replicate trials across sites would lead to more validation of the effects of both herbicides and tillage/residue. Besides, experimenting on a chilli crop-based cropping system for whole year in a fixed layout under conservation agriculture would lead to higher yield and income. 5. Conclusion This study indicated that imazethapyr applied at pre-emergence was selective to chilli due to lower ascorbate peroxidase activity and less/negligible negative effects on chlorophyll and leaf soluble protein in chilli. The pre-emergence tank-mix application of pendimethalin 0.75 kg ha−1 + imazethapyr 0.075 kg ha−1 resulted in better weed control, higher chilli yield, net returns and net returns:cost. The tillage systems did not significantly affect herbicide efficacy. Zero tillage with residue was similar with conventional tillage on weed control, chilli yield and income. Therefore, a combination of the pendimethalin 0.75 kg ha−1 + imazethapyr 0.075 kg ha−1 tank-mix and zero tillage with residue may be recommended for better weed management and higher chilli productivity and profitability. Acknowledgements The authors sincerely acknowledge the necessary services and supplies provided by the Indian Agricultural Research Institute during the course of investigation. They are also thankful to the Agricultural and Natural Resources Research Center of Hormoz-
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