Use of sorghum allelopathic properties to control weeds in irrigated
wheat in a semi arid region of Punjab
Z.A. Cheema
∗, A. Khaliq
Department of Agronomy, University of Agriculture, Faisalabad-38040, Pakistan
Received 16 July 1998; received in revised form 18 May 1999; accepted 22 October 1999
Abstract
Conventional methods of weed control are weather dependent, costly and labour intensive. Indiscriminate use of chemicals for controlling weeds may pose environmental problems. Sorghum allelopathy is a new technique, which has been tested for controlling weeds of wheat (Triticum aestivum L.) as a substitute for chemical herbicides to reduce environmental pollution. Mature sorghum herbage contains a number of water-soluble secondary chemical substances (allelochemicals). Sorghum allelopathy can be used as sorgaab (water extract of mature Sorghum bicolor L. Moench plants obtained after soaking in water for 24 h and sprayed as a natural herbicide), sorghum mulch, sorghum soil incorporation and in crop rotation. Two experiments were conducted. In Experiment 1, allelopathic effects of sorghum stalk incorporation into soil and sorgaab foliar spray along with chemical and cultural weed control methods on the growth of different rabi (winter) weeds and on the growth and yield of wheat were studied. In Experiment 2, the effects of concentration (5 and 10%) and frequency of sprays of sorgaab on the growth of weeds and wheat were compared with hand weeding and chemical herbicides. Sorgaab controlled up to 35–49% weeds and increased wheat yield by 10–21%. Mature sorghum chopped herbage (2–6 Mg ha−1) incorporated in the soil at
sowing controlled up to 40–50% weeds and increased wheat yield by 15%. Two foliar sprays of 10% sorgaab at 30 and 60 days after sowing was the most economical method for controlling weeds in wheat with maximum net benefits and 535% marginal rate of return. Weed control through hand weeding and/or chemical herbicides was found to be uneconomical due to higher costs involved in both the cases. Sorgaab can be used as a natural weed inhibitor in wheat. © 2000 Elsevier Science B.V. All rights reserved.
Keywords: Sorgaab; Sorghum allelopathy; Weed control; Wheat
1. Introduction
Weed infestation is the main cause of low yields in wheat in Pakistan and probably reduces yields by 25–30% (Nayyar et al., 1994). Weeds compete with crop plants for different factors (Anderson, 1983) and sometime interfere with crop growth by releasing toxic substances in the rhizosphere (Rice, 1984). Apart from direct effects, weeds may also serve as alternate host
∗Corresponding author. Tel.:+92-413-0281; fax:+92-413-0679.
for insect pests. According to Baloch (1993) grain yield in Pakistan may be increased by up to 37% if weeds are properly controlled.
Traditional methods for controlling weeds are time consuming, weather dependent and labor inten-sive. Unwise use of herbicides in tropical agriculture can create environmental hazards and their safety is also uncertain (Kasasian, 1971). Herbicides can affect nutritive value of certain crops (Saghir and Bhatti, 1970). Moreover herbicide resistance in previ-ously susceptible weeds has been reported (Putwain,
1982). This suggests the need to search for new tech-niques/approaches of weed control which may be inexpensive, easy-to-use and helpful in conserving the ecosystem.
Allelopathy is a natural and environment-friendly technique which may prove to be a unique tool for weed control and thereby increase crop yields (Purvis et al., 1985; Cheema, 1988). Sorghum (Sorghum bi-color) is well recognised for its allelopathic effects on other crops (Putnam and DeFrank, 1983). Ma-ture sorghum plants posses a number of (nine) wa-ter soluble allelochemicals which are phytotoxic to the growth of certain weeds such as Phalaris mi-nor Retz., Chenopodium album L., Rumex dentatus L. and Convolvulus arvensis L. (Cheema, 1988). In-corporation of sorghum roots suppressed the weed biomass by 25–50% and increased wheat yields by 7–8% (Cheema, 1988). A single spray of 5% sor-gaab solution applied 30 days after sowing increased wheat yields by 14% and suppressed weed biomass by 20–40% (Cheema et al., 1997). The effects of sorghum allelochemicals are selective and concentration depen-dent (Rice, 1984).
The general objective of this research was to ex-plore the possibility of using mature sorghum stalks and sorgaab as natural weed control technique in wheat grown in a semi-arid environment. Prevailing cropping system of the region is mixed cropping with wheat, sugarcane (Saccharum officinarum L.) and maize (Zea mays L.) as major crops. The specific objectives were to compare the efficacy and economics of this tech-nique with traditional weed control methods such as hand weeding and also chemical weed control.
2. Materials and methods
2.1. General procedures
Field experiments were conducted to study the effectiveness of sorghum allelopathic properties for weed control in wheat grown at the Agronomic Re-search Area, University of Agriculture, Faisalabad, Pakistan. The soil belongs to Lyallpur soil series (Aridisol-fine-silty, mixed, hyperthermic Ustalfic, Haplargid in USDA classification and Haplic Yer-mosols in FAO classification scheme). The pH of saturated soil paste (pHs) and electrical conductivity
(EC) of the saturation extract (ECe) were 7.9 and 0.41 dS m−1, respectively. Sorghum plant herbage was harvested at maturity, dried, chaffed with fodder cutter into 2 cm pieces and kept under cover to avoid possible leaching by rain water. Chaffed sorghum material was either soil incorporated to a depth of 3–5 cm at sowing or soaked in distilled water in 1 : 20 ratio (Hussain and Gadoon, 1981) for 24 h at room temperature to prepare sorgaab. The latter was ob-tained by filtering the mixture (herbage and water) through a screen. Sorgaab was either used fresh or frozen at –15◦C for subsequent use.
Seedbed was prepared by giving three cultivations and plankings. Wheat was sown manually on a moist seedbed by a single row hand drill in 25 cm apart rows. In addition to soaking, irrigation was applied at tillering, stem elongation, booting, anthesis and grain development stages. Soaking irrigation and each of the subsequent irrigation comprised of 4 and 3 ha cm, respectively.
Data on weed density and weed biomass were recorded on 60 or 90 days after sowing (DAS) from two randomly selected quadrates (m2) from each ex-perimental plot. Weed dry weight was recorded after drying the weeds in an oven at 70◦C for 72 h. Data
on wheat plant height, spike length and, grains per spike were recorded from 10 randomly selected sam-ples taken from each plot. Fertile tillers per unit area (m2) were recorded from two randomly selected sites from the experimental plot. A random sample was obtained from each plot to take 1000-grain weight. Grain yield was recorded on plot basis and converted into Mg ha−1. Weed species observed in the experi-mental field were Fumaria indica Hauskn., P. minor Retz., R. dentatus L. and C. album L. Data collected were analyzed statistically by using the MSTAT C program (Freed and Eisensmith, 1986).
2.2. Experiment 1: effect of sorghum stalk and sorgaab on weeds and wheat
spray (30 DAS), two sorgaab sprays (30 and 60 DAS), chlorotoluron+MCPA (Dicuran M.A., 60 WP) spray at 2.5 kg ha−1 (30 DAS) and one hand weeding (30 DAS). The volume of sorgaab spray (300 l ha−1) was calibrated using ordinary water.
The experiment was laid out in a randomized com-plete block design with four replications in plots 7.5 m×1.5 m. Wheat variety Pasban was planted on 21 November 1996 in 25 cm spaced rows with a sin-gle row hand drill using the seed rate of 45 kg ha−1. An application of 120 kg N and 37 kg P ha–1 in the form of urea and diammonium phosphate was applied and normal irrigation was given to crop. The chaffed sorghum stalks were soil-incorporated to a depth of 3–5 cm at the time of seedbed preparation in the re-spective plots. Sorgaab and chlorotoluron+MCPA were applied in the respective plots using a knapsack hand sprayer using T-jet nozzle. Hand weeding was done with a hand hoe.
2.3. Experiment 2: effect of concentration and frequency of sorgaab spray on weeds and wheat
The effects of concentration (5 and 10%) and fre-quency of sprays of sorgaab on the growth of weeds and wheat during 1996–97 were compared with hand weeding and chemical herbicides. The experimental procedures were same as in Experiment 1, except that sorgaab was also prepared in 1 : 10 ratio in addition to 1 : 20 ratio. Same procedures were adopted to grow wheat in plots measuring the same size as in Study 1. The treatments were control (unweeded check), sor-gaab 1 : 10 and 1 : 20 ratio each sprayed 30, 30+60 and 30+60+90 DAS, one hand weeding (30 DAS), two hand weedings (30 and 60 DAS, respectively), chlorotoluron+MCPA (Dicuran M.A., 60WP) at 2.5 kg ha−1, bromoxynil+MCPA (Buctril M, 40EC) at 1.2 l ha−1 and isoproturon (Tolkan, 50WP) at 2.0 kg ha−1each sprayed 30 DAS. Spray volume was calibrated as in Experiment 1 and spraying was also done in the same way.
2.4. Economic analysis
Total cost for all the experimental treatments was calculated after determining the field prices of all inputs. Costs that vary (Variable cost) are the costs
(per ha) of purchased inputs, labour, and machinery that vary between experimental treatments (Byerlee, 1988). Average yield was adjusted downward (10%) to reflect the difference between the experimental yield and the yield farmer could expect from the same treatment. Net benefits were calculated by subtracting the total variable cost from the gross benefits for each treatment. Dominance analysis was carried out by first listing the treatments in the order of increasing variable costs. Any treatment that had net benefits that were less than or equal to those of a treatment with lower variable cost was taken to be dominated. Finally marginal rate of return (MRR) was calculated by dividing the marginal net benefits (change in net benefits) by the marginal cost (change in cost) and expressed as a percentage.
3. Results and discussion
3.1. Experiment 1: effect of sorghum stalk and sorgaab on weeds and wheat
Total weed population was significantly reduced by all the treatments compared to control (Table 1). Sorghum stalks soil incorporation at 2 Mg ha−1 and one and two sprays of sorgaab gave similar weed mor-tality of 20, 21 and 23%, respectively. Sorghum stalk soil incorporation at rates of 4 and 6 Mg ha−1resulted in higher weed mortality (29.2 and 40.8%, respec-tively). Both hand weeding and sorghum stalks incor-poration at 6 Mg ha−1resulted in high weed mortality compared to control. Chemical weed control resulted in 81.8% weed mortality. Sorgaab reduced the weed population either by killing the existing weeds or in-hibiting the germination of weeds after the application of sorgaab (allelopathic effect). Weed suppression by sorghum stalk incorporation into soil also suggested the release of sorghum allelochemicals into the soil as already reported (Bhowmik and Doll, 1984; Cheema et al., 1997; Narwal et al., 1990).
Table 1
Effect of various weed control methods on weed density and dry weight in Experiment 1
Treatment Weed density (number of plants per m2) Weed dry weight (g m−2)
Control 63.7 aa – 19.6 a –
Sorghum stalks (soil incorp.) at 2 Mg ha−1 50.9 b (20.2)b 11.3 bcd (42.0) Sorghum stalks (soil incorp.) at 4 Mg ha−1 45.0 c (29.2) 10.0 cde (48.0) Sorghum stalks (soil incorp.) at 6 Mg ha−1 37.7 d (40.8) 8.6 e (56.0)
Sorgaab spray (1 : 20) 30 DAS 50.0 b (21.6) 12.6 b (35.4)
Sorgaab spray (1 : 20) 30 and 60 DAS 49.0 bc (23.1) 12.0 bc (38.7)
Chlorotoluron+MCPA and 2.50 kg ha−1 11.6 e (81.8) 2.3 f (88.0)
Hand weeding 32.6 d (48.9) 6.6 dc (51.0)
L.S.D (0.05) 4.9 2.12
aMeans with different letters in a column differed significantly (5% level).
bIn parenthesis % decrease compared with control, DAS: days after sowing, soil incorp.: soil incorporated, major weed flora of experimental field: Fumaria indica Hauskn., Phalaris minor Retz., Rumex dentatus L. and Chenopodium album L.
presence and effectiveness of allelochemicals in both these materials. Weed suppression with hand weed-ing was 51%. Maximum weed inhibition was obtained with the herbicide (chlorotoluron+MCPA).
Sorghum stalks incorporated into soil at 2, 4, and 6 Mg ha−1and sorgaab spray at 30 DAS and 30+60 DAS increased wheat grain yield by 6, 16, 17, 11 and 15%, respectively over control (Table 2). More grains per spike, heavier grains, enhanced spike length and reduced plant height resulted in higher grain yields on average. Cheema et al. (1997) reported a 14% increase in wheat grain yield due to sorgaab spray.
Economic analysis and marginal rates of return de-rived from various weed control methods are shown in Tables 3 and 4. One sorgaab spray at 30 DAS and two sorgaab sprays at 30 and 60 DAS resulted in 980 and 332% marginal rates of returns, two sorgaab sprays
Table 2
Effect of various weed control methods on growth parameters and yield of wheat in Experiment 1
Treatments Plant height Fertile tillers Spike length Number of grains 1000-grain Grain yield (cm) (m−2) (cm) per spike weight (g) (Mg ha−1)
Control 91.8 ba 329.1 d 8.4 d 39.2 d 38.0 e 2.9 b –
Sorghum stalks (soil incorp.) at 2 Mg ha−1 89.0 c 335.1 cd 9.7 bc 40.3 cd 39.1 de 3.1 ab (6)b Sorghum stalks (soil incorp.) at 4 Mg ha−1 88.6 c 344.1 bc 10.3 abc 41.3 bc 42.5 ab 3.4 ab (16) Sorghum stalks (soil incorp.) at 6 Mg ha−1 86.3 d 352.0 ab 10.5 ab 42.2 abc 43.0 ab 3.4 ab (17) Sorgaab spray (1 : 20) 30 DAS 89.4 c 340.1 bcd 9.5 c 41.3 bc 40.13cd 3.2 ab (11) Sorgaab spray (1 : 20) 30 and 60 DAS 88.5 c 349.1 c 10.0 bc 43.0 ab 42. abc 3.3 ab (15) Chlorotoluron+MCPA at 2.5 kg ha−1 94.8 a 365.0 a 11.0 a 43.4 a 43.7 a 3.6 a (22)
Hand weeding 92.9 ab 340.1bcd 9.5 c 40.5 cd 41.4 bc 3.2 ab (10)
LSD (0.05) 2.1 14.0 1.0 2.0 2.0 0.6
aMeans with different letters in a column differed significantly (5% level).
bIn parenthesis % increase compared with control, DAS: days after sowing, soil incorp.: soil incorporated.
being the most economical treatment with maximum net benefits. All other weed control methods employed in this study produced lower benefits.
3.2. Experiment 2: effect of concentration and frequency of sorgaab spray on weeds and wheat
Table 3
Economic analysis of various weed control techniques in wheat in Experiment 1
Components T1a T2 T3 T4 T5 T6 T7 T8
Total yield (Mg ha−1) 2.9 3.1 3.4 3.4 3.2 3.3 3.6 3.2
Adjusted yield (10% less) 2.6 2.8 3.0 3.1 2.9 3.0 3.2 2.9
Total income (Rs. 240/40 kg) 15 768 16 524 18 090 18 360 17 388 18 036 19 170 17 280 Cost of sorghum herbage (Rs. 500 Mg−1) – 1000 2000 3000 20 40 – –
Cost of herbicide (Rs. 625 kg−1) – – – – – – 1563 –
Labor chargesb – 320 320 320 80 160 80 800
Sprayer rental charges (Rs. 50 per spray) – – – – 50 100 50 –
Variable costc(Rupees) – 1320 2320 3320 150 300 1693 800
Net benefits (Rupees) 15 768 15 204 15 770 15 040 17 238 17 736 17 477 16 480
aT
1=control (unweeded check), T2, T3, T4=sorghum stalk soil incorporation at 2, 4, 6 Mg ha−1, respectively, T5=one sorgaab spray [30 days after sowing (DAS)], T6=two sorgaab sprays (30 and 60 DAS), T7=chlorotoluron+MCPA (Dicuran M.A., 60 WP) spray at 2.5 kg ha−1 (30 DAS), T8=one hand weeding (30 DAS).
bRs. 80 per spray, hand weeding at Rs. 80 per man per day (10 men ha−1), soil incorporation 4 men ha−1.
cVariable cost: the costs (per ha) of purchased inputs, labor, and machinery that vary between experimental treatments.
Table 4
Marginal rates of return for various weed control techniques in wheat in Experiment 1
Treatments Variable costa (Rs.) Net benefits (Rs.) MRRb
Control – 15768 –
Sorgaab (1 : 20) spray 30 DAS 150 17238 980%
Sorgaab (1 : 20) sprays 30 and 60 DAS 300 17736 332%
Hand weeding 30 DAS 800 16480 D
Sorghum stalks (soil incorp.) at 2 Mg ha−1 1320 15204 D
Chlorotoluron+MCPA at 2.5 kg ha−1 1693 17477 D
Sorghum stalks (soil incorp.) at 4 Mg ha−1 2320 15770 D Sorghum stalks (soil incorp.) at 6 Mg ha−1 3320 15040 D
aVariable cost: the costs (per ha) of purchased inputs, labor, and machinery that vary between experimental treatments. bMarginal rate of return; Rs.: Rupees, D: Dominated, soil incorp.: soil incorporated.
Table 5
Effect of frequency and concentration of sorgaab spraying on weed dynamics in wheat in Experiment 2
Treatments Weed Density (number of Weed dry weight
plants per m2) 90 DAS (g m−2) 90 DAS
Control 18.1 aa – 34.0 a
Sorgaab (1 : 10) one spray (30 DAS) 9.8 cd (46.0)b 21.3 c (37.4)
Sorgaab (1 : 10) two sprays (30 and 60 DAS) 10.1 c (44.2) 17.4 d (49.0) Sorgaab (1 : 10) three sprays (30, 60 and 90 DAS) 9.8 cd (45.5) 17.2 d (49.0)
Sorgaab (1 :20) one spray (30 DAS) 11.4 b (37.0) 25.5 b (25.0)
Sorgaab (1 : 20) two sprays (30 and 60 DAS) 11.2 b (39.0) 21.7 c (36.0) Sorgaab (1 : 20) three sprays (30, 60 and 90 DAS) 10.2 c (43.7) 21.7 c (36.1)
One hand weeding (30 DAS) 8.9 de (50.0) 22.6 c (33.4)
Two hand weedings (30 and 60 DAS) 9.1 de (50.0) 10.0 e (71.0)
Chlorotoluron+MCPA at 2.5 kg ha−1 2.4 g (86.5) 3.5 f (89.5)
Bromoxynil+MCPA at 1.2 l ha−1 3.6 f (80.2) 4.7 f (86.0)
Isoproturon at 2.0 kg ha−1 3.2 fg (82.4) 4.5 f (86.7)
L.S.D (0.05) 4.1 2.1
Table 6
Effect of frequency and concentration of sorgaab spraying on growth and yield of wheat in Experiment 2
Treatments Plant height Fertile tillers Spike length Grains per 1000-grain Grain yield %±over (cm) (m−2) (cm) spike weight (g) (Mg ha-1) control
Control 92.6 ba 302.1 g 9.1 e 40.7 d 39.0 d 2.7 e –
Sorgaab (1 : 10) one spray (30 DAS) 88.0 cd 322.1 ef 11.2 bcd 43.1 abcd 42.7 cd 3.1 bcd 14 Sorgaab (1 : 10) two sprays (30 and 60 DAS) 86.2 d 337.1 bcd 12.0 abc 44.8 ab 45.0 ab 3.3 abc 21 Sorgaab (1 : 10) three sprays (30, 60
and 90 DAS)
85.7 d 338.1 bc 12.1 ab 45.0 ab 45.1 ab 3.3 ab 22
Sorgaab (1 : 20) one spray (30 DAS) 89.7 c 310.3 fg 11.0 bcd 42.8 bcd 41.4 d 3.0 cde 9 Sorgaab (1 : 20) two sprays (30 and 60 DAS) 88.5 cd 317.0 ef 11.4 abcd 44.0 abc 43.8 bc 3.1 bcd 14 Sorgaab (1 : 20) three sprays (30, 60
and 90 DAS)
88.0 cd 320.1 ef 12.0 abc 44.3 abc 44.0 bc 3.1 bcd 15
One hand weeding (30 DAS) 93.1 ab 324.1 def 10.3 d 42.0 cd 42.0 cd 2.9 de 7 Two hand weedings (30 and 60 DAS) 94.2 ab 331.0 cde 10.8 cd 43.0 bcd 42.8 cd 3.1 bcd 14 Chlorotoluron+MCPA at 2.5 kg ha−1 96.1 a 353.1 a 12.7 a 46.0 a 46.7 a 3.5 a 30 Bromoxynil+MCPA) at 1.2 l ha−1 95.2 ab 340.1 abc 11.7 abc 44.6 abc 46.6 a 3.3 abc 21 Isoproturon at 2.0 kg ha−1(30 DAS) 95.8 a 346.1 ab 12.6 a 45.3 ab 46.2 a 3.3 ab 23
LSD (0.05) 2.2 12.9 1.1 2.4 2.0 0.3
aMeans with different letters in a column differed significantly (5% level), DAS: days after sowing.
maximum weed mortality (>80%) was recorded in plots where chemical herbicides were sprayed.
Total weed dry weight was significantly reduced by all the treatments over control. Two and three sorgaab
Table 7
Economic analysis of various weed control techniques in wheat in Experiment 2
Grain Adjusted Total Cost of Cost of Labor Sprayer rental Variable Net yield yield income sorghum herbageb herbicidec chargesd charges coste benefits
T1a 2.7 2.5 14 742 – – – – – 14 742
T2 3.1 2.8 16 578 40 – 80 50 170 16 408
T3 3.3 2.9 17 658 80 – 160 100 340 17 318
T4 3.3 3.0 17 820 120 – 240 150 510 17 310
T5 3.0 2.7 15 930 20 – 80 50 150 15 780
T6 3.1 2.8 16 632 40 – 160 100 300 16 332
T7 3.1 2.8 16 740 60 – 240 150 450 16 290
T8 2.9 2.6 15 660 – – 800 – 800 14 860
T9 3.1 2.8 16 578 – – 1600 – 1600 14 978
T10 3.5 3.2 18 900 – 1563 80 50 1693 17 207
T11 3.3 3.0 17 712 – 738 80 50 868 16 844
T12 3.3 3.0 17 928 – 840 80 50 970 16 958
Remarks Mg ha−1 10% less Rs. 240/40 kg – – – Rs. 50 per spray Rupees Rupees
aT
1=control (unweeded check), T2, T3and T4=Sorgaab (1 : 10 ratio) sprayed 30, 30+60 and 30+60+90 days after sowing (DAS), T5, T6and T7=Sorgaab (1 : 20 ratio) sprayed 30, 30+60 and 30+60+90 days after sowing, respectively, T8=one hand weeding (30 DAS), T9=two hand weedings (30+60 DAS), T10=chlorotoluron+MCPA (Dicuran M.A., 60WP) at 2.5 kg ha−1, T11=bromoxynil+MCPA (Buctril M, 40EC) at 1.2 l ha−1, T12=isoproturon (Tolkan, 50WP) at 2.0 kg ha−1 each sprayed 30 DAS.
bSorghum herbage at Rs. 500 Mg−1.
cDicuran M.A. at Rs. 625 kg−1, Buctril M at RS. 614 l−1 and Tolkan at Rs. 420 kg−1.
dRs. 80 per spray, hand weeding at Rs. 80 per man per day(10 men ha−1), soil incorporation 4 men ha−1.
eThe costs (per ha) of purchased inputs, labor, and machinery that vary between experimental treatments, Rs.: Rupees.
Table 8
Marginal rates of return from various weed control techniques in wheat in Experiment 2
Treatments Variable costa (Rs.) Net benefits (Rs.) MRRb
Control – 14742
Sorgaab (1 : 20) one spray (30 DAS) 150 15780 692%
Sorgaab (1 : 10) one spray (30 DAS) 170 16408 3140%
Sorgaab (1 : 20) two sprays (30 and 60 DAS) 300 16332 D
Sorgaab (1 : 10) two sprays (30 and 60 DAS) 340 17318 535%
Sorgaab (1 : 20) three sprays (30, 60 and 90 DAS) 450 16290 D Sorgaab (1 : 10) three sprays (30, 60 and 90 DAS) 510 17310 D
One hand weeding (30 DAS) 800 14860 D
Bromoxynil+MCPA) at 1.2 l ha−1 868 16844 D
Isoproturon at 2.0 kg ha−1 970 16958 D
Two hand weedings (30 and 60 DAS) 1600 14978 D
Chlorotoluron+MCPA at 2.5 kg ha−1 1693 17207 D
aVariable cost: the costs (per ha) of purchased inputs, labor, and machinery that vary between experimental treatments. bMRR: Marginal rate of return; Rs.: Rupees, D: Dominated.
and a single hand weeding. Two hand weedings re-duced weed dry weight by 70%. Chemical weed con-trol resulted in maximum reduction in total weed dry weight (more than 80%).
Two and three sorgaab sprays (1 : 10 ratio) in-creased wheat yield by 21 and 22%, respectively (Table 6). Spraying bromoxynil+MCPA and isopro-turon increased wheat yield by 21 and 23%, respec-tively, over the control. Two or three sorgaab (1 : 20 ratio) sprays were relatively less effective and in-creased wheat yield only by 14 and 15%, respectively. Two hand weedings increased wheat yield by 14%. Chlorotoluron+MCPA showed maximum increase (30%) in wheat yield.
Economic analysis of data and marginal rates of return derived from various treatments (Tables 7 and 8) showed that single spray of sorgaab at 1 : 20 and 1 : 10 ratio and two sprays of sorgaab (1 : 10 ratio) re-sulted in 692, 3140 and 535% marginal rates of return, respectively in this experiment. Two sorgaab sprays (1 : 10 ratio) was the most economical treatment with maximum net benefits.
4. Conclusions
Following conclusions are drawn from these studies:
1. Sorgaab foliar spraying is more effective and economical than soil incorporation of sorghum stalks. Sorgaab 1 : 10 ratio is effective than 1 : 20 ratio.
2. Two foliar sprays of Sorgaab (1 : 10 ratio) at 30 and 60 DAS could substitute chemical herbicides. 3. The use of sorgaab, being a natural weed inhibitor,
would reduce the need for chemical herbicides and provide economic benefits.
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