Use of sorghum allelopathic properties to control weeds in irrigated wheat in a semi arid region of Punjab

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1 Agriculture, Ecosystems and Environment 79 (2000) 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 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.: ; fax: 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 intensive. 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 previously susceptible weeds has been reported (Putwain, /00/$ see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S (99)

2 106 Z.A. Cheema, A. Khaliq / Agriculture, Ecosystems and Environment 79 (2000) ). This suggests the need to search for new techniques/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 bicolor) is well recognised for its allelopathic effects on other crops (Putnam and DeFrank, 1983). Mature sorghum plants posses a number of (nine) water soluble allelochemicals which are phytotoxic to the growth of certain weeds such as Phalaris minor Retz., Chenopodium album L., Rumex dentatus L. and Convolvulus arvensis L. (Cheema, 1988). Incorporation of sorghum roots suppressed the weed biomass by 25 50% and increased wheat yields by 7 8% (Cheema, 1988). A single spray of 5% sorgaab 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 dependent (Rice, 1984). The general objective of this research was to explore 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 technique 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 Research 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 Yermosols 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 obtained 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 (m 2 ) from each experimental 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 samples taken from each plot. Fertile tillers per unit area (m 2 ) 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 experimental 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) Experiment 1: effect of sorghum stalk and sorgaab on weeds and wheat Allelopathic effects of sorghum stalk incorporation into soil and sorgaab foliar spray along with chemical and cultural weed control methods were studied on the growth of different rabi (winter) weeds and on the growth and yield of wheat during The treatments were control (unweeded check), sorghum stalk soil incorporation at 2, 4 and 6 Mg ha 1, one sorgaab

3 Z.A. Cheema, A. Khaliq / Agriculture, Ecosystems and Environment 79 (2000) 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 complete 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 single 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 respective 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 Experiment 2: effect of concentration and frequency of sorgaab spray on weeds and wheat The effects of concentration (5 and 10%) and frequency of sprays of sorgaab on the growth of weeds and wheat during 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), sorgaab 1 : 10 and 1 : 20 ratio each sprayed 30, and 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 1 each sprayed 30 DAS. Spray volume was calibrated as in Experiment 1 and spraying was also done in the same way 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 mortality of 20, 21 and 23%, respectively. Sorghum stalk soil incorporation at rates of 4 and 6 Mg ha 1 resulted in higher weed mortality (29.2 and 40.8%, respectively). Both hand weeding and sorghum stalks incorporation at 6 Mg ha 1 resulted 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 inhibiting 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). Total weed dry weight was significantly reduced by all treatments over control (Table 1). Soil incorporation of sorghum stalks at 2, 4 and 6 Mg ha 1 reduced weed dry weight by 42, 48 and 56%, respectively. Sorgaab spray reduced weed dry weight by 35 38%. The suppression in weed dry weight by soil incorporation of sorghum stalks and sprays of sorgaab suggested the

4 108 Z.A. Cheema, A. Khaliq / Agriculture, Ecosystems and Environment 79 (2000) Table 1 Effect of various weed control methods on weed density and dry weight in Experiment 1 Treatment Weed density (number of plants per m 2 ) Weed dry weight (g m 2 ) Control 63.7 a a 19.6 a Sorghum stalks (soil incorp.) at 2 Mg ha b (20.2) b 11.3 bcd (42.0) Sorghum stalks (soil incorp.) at 4 Mg ha c (29.2) 10.0 cde (48.0) Sorghum stalks (soil incorp.) at 6 Mg ha 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 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) a Means with different letters in a column differed significantly (5% level). b In 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 weeding was 51%. Maximum weed inhibition was obtained with the herbicide (chlorotoluron + MCPA). Sorghum stalks incorporated into soil at 2, 4, and 6Mgha 1 and sorgaab spray at 30 DAS and 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 derived 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 being the most economical treatment with maximum net benefits. All other weed control methods employed in this study produced lower benefits Experiment 2: effect of concentration and frequency of sorgaab spray on weeds and wheat Total weed population was significantly reduced by all the treatments as compared to control (Table 5). One, two or three sprays of sorgaab (1 : 10 ratio) provided similar weed suppression as three sprays of sorgaab (1 : 20 ratio) on 90 DAS while, one or two sorgaab (1 : 20 ratio) sprays were relatively less effective. Difference in the extent of weed suppression by different concentrations of sorgaab suggests such effects to be concentration dependent (Rice, 1984). Hand weeding gave 50% weed suppression while 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 b a d 8.4 d 39.2 d 38.0 e 2.9 b Sorghum stalks (soil incorp.) at 2 Mg ha c cd 9.7 bc 40.3 cd 39.1 de 3.1 ab (6) b Sorghum stalks (soil incorp.) at 4 Mg ha c bc 10.3 abc 41.3 bc 42.5 ab 3.4 ab (16) Sorghum stalks (soil incorp.) at 6 Mg ha d ab 10.5 ab 42.2 abc 43.0 ab 3.4 ab (17) Sorgaab spray (1 : 20) 30 DAS 89.4 c bcd 9.5 c 41.3 bc 40.13cd 3.2 ab (11) Sorgaab spray (1 : 20) 30 and 60 DAS 88.5 c c 10.0 bc 43.0 ab 42. abc 3.3 ab (15) Chlorotoluron + MCPA at 2.5 kg ha a 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) a Means with different letters in a column differed significantly (5% level). b In parenthesis % increase compared with control, DAS: days after sowing, soil incorp.: soil incorporated.

5 Z.A. Cheema, A. Khaliq / Agriculture, Ecosystems and Environment 79 (2000) Table 3 Economic analysis of various weed control techniques in wheat in Experiment 1 Components T 1 a T 2 T 3 T 4 T 5 T 6 T 7 T 8 Total yield (Mg ha 1 ) Adjusted yield (10% less) Total income (Rs. 240/40 kg) Cost of sorghum herbage (Rs. 500 Mg 1 ) Cost of herbicide (Rs. 625 kg 1 ) 1563 Labor charges b Sprayer rental charges (Rs. 50 per spray) Variable cost c (Rupees) Net benefits (Rupees) a T 1 = control (unweeded check), T 2,T 3,T 4 = sorghum stalk soil incorporation at 2, 4, 6 Mg ha 1, respectively, T 5 = one sorgaab spray [30 days after sowing (DAS)], T 6 = two sorgaab sprays (30 and 60 DAS), T 7 = chlorotoluron + MCPA (Dicuran M.A., 60 WP) spray at 2.5 kg ha 1 (30 DAS), T 8 = one hand weeding (30 DAS). b Rs. 80 per spray, hand weeding at Rs. 80 per man per day (10 men ha 1 ), soil incorporation 4 men ha 1. c Variable 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 cost a (Rs.) Net benefits (Rs.) MRR b Control Sorgaab (1 : 20) spray 30 DAS % Sorgaab (1 : 20) sprays 30 and 60 DAS % Hand weeding 30 DAS D Sorghum stalks (soil incorp.) at 2 Mg ha D Chlorotoluron + MCPA at 2.5 kg ha D Sorghum stalks (soil incorp.) at 4 Mg ha D Sorghum stalks (soil incorp.) at 6 Mg ha D a Variable cost: the costs (per ha) of purchased inputs, labor, and machinery that vary between experimental treatments. b Marginal 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 m 2 ) 90 DAS (g m 2 )90DAS Control 18.1 a a 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 g (86.5) 3.5 f (89.5) Bromoxynil + MCPA at 1.2 l ha f (80.2) 4.7 f (86.0) Isoproturon at 2.0 kg ha fg (82.4) 4.5 f (86.7) L.S.D (0.05) a Means with different letters in a column differed significantly (5% level). b In parenthesis % decrease compared with control, DAS: days after sowing.

6 110 Z.A. Cheema, A. Khaliq / Agriculture, Ecosystems and Environment 79 (2000) 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 b a g 9.1 e 40.7 d 39.0 d 2.7 e Sorgaab (1 : 10) one spray (30 DAS) 88.0 cd 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 bcd 12.0 abc 44.8 ab 45.0 ab 3.3 abc 21 Sorgaab (1 : 10) three sprays (30, d bc 12.1 ab 45.0 ab 45.1 ab 3.3 ab 22 and 90 DAS) Sorgaab (1 : 20) one spray (30 DAS) 89.7 c 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 ef 11.4 abcd 44.0 abc 43.8 bc 3.1 bcd 14 Sorgaab (1 : 20) three sprays (30, cd ef 12.0 abc 44.3 abc 44.0 bc 3.1 bcd 15 and 90 DAS) One hand weeding (30 DAS) 93.1 ab def 10.3 d 42.0 cd 42.0 cd 2.9 de 7 Two hand weedings (30 and 60 DAS) 94.2 ab cde 10.8 cd 43.0 bcd 42.8 cd 3.1 bcd 14 Chlorotoluron + MCPA at 2.5 kg ha a a 12.7 a 46.0 a 46.7 a 3.5 a 30 Bromoxynil + MCPA)at1.2lha ab 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 ab 12.6 a 45.3 ab 46.2 a 3.3 ab 23 LSD (0.05) a Means 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 sprays (1 : 10 ratio) gave similar (49%) reductions in total weed dry weight, respectively (Table 5). A single spray of sorgaab (1 : 10 ratio) reduced total weed dry weight similar to two sprays of sorgaab (1 : 20 ratio) 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 herbage b herbicide c charges d charges cost e benefits T a T T T T T T T T T T T Remarks Mg ha 1 10% less Rs. 240/40 kg Rs. 50 per spray Rupees Rupees a T 1 = control (unweeded check), T 2,T 3 and T 4 = Sorgaab (1 : 10 ratio) sprayed 30, and days after sowing (DAS), T 5,T 6 and T 7 = Sorgaab (1 : 20 ratio) sprayed 30, and days after sowing, respectively, T 8 = one hand weeding (30 DAS), T 9 = two hand weedings ( DAS), T 10 = chlorotoluron + MCPA (Dicuran M.A., 60WP) at 2.5 kg ha 1,T 11 = bromoxynil + MCPA (Buctril M, 40EC) at 1.2 l ha 1,T 12 = isoproturon (Tolkan, 50WP) at 2.0 kg ha 1 each sprayed 30 DAS. b Sorghum herbage at Rs. 500 Mg 1. c Dicuran M.A. at Rs. 625 kg 1, Buctril M at RS. 614 l 1 and Tolkan at Rs. 420 kg 1. d Rs. 80 per spray, hand weeding at Rs. 80 per man per day(10 men ha 1 ), soil incorporation 4 men ha 1. e The costs (per ha) of purchased inputs, labor, and machinery that vary between experimental treatments, Rs.: Rupees.

7 Z.A. Cheema, A. Khaliq / Agriculture, Ecosystems and Environment 79 (2000) Table 8 Marginal rates of return from various weed control techniques in wheat in Experiment 2 Treatments Variable cost a (Rs.) Net benefits (Rs.) MRR b Control Sorgaab (1 : 20) one spray (30 DAS) % Sorgaab (1 : 10) one spray (30 DAS) % Sorgaab (1 : 20) two sprays (30 and 60 DAS) D Sorgaab (1 : 10) two sprays (30 and 60 DAS) % Sorgaab (1 : 20) three sprays (30, 60 and 90 DAS) D Sorgaab (1 : 10) three sprays (30, 60 and 90 DAS) D One hand weeding (30 DAS) D Bromoxynil + MCPA)at1.2lha D Isoproturon at 2.0 kg ha D Two hand weedings (30 and 60 DAS) D Chlorotoluron + MCPA at 2.5 kg ha D a Variable cost: the costs (per ha) of purchased inputs, labor, and machinery that vary between experimental treatments. b MRR: Marginal rate of return; Rs.: Rupees, D: Dominated. and a single hand weeding. Two hand weedings reduced weed dry weight by 70%. Chemical weed control resulted in maximum reduction in total weed dry weight (more than 80%). Two and three sorgaab sprays (1 : 10 ratio) increased wheat yield by 21 and 22%, respectively (Table 6). Spraying bromoxynil + MCPA and isoproturon increased wheat yield by 21 and 23%, respectively, over the control. Two or three sorgaab (1 : 20 ratio) sprays were relatively less effective and increased 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) resulted 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. References Anderson, W.P., Weed-crop competition. Weed Science Principles, 2nd Edition. West Pub. Co., St. Paul Minn., USA, pp Baloch, G.M., Biological control of weeds. Progressive Farming, PARC, Islamabad, 3, pp Bhowmik, P.C., Doll, J.D., Allelopathic effects of annual weed residues on growth and nutrient uptake of corn and soybeans. Agron. J. 76, Byerlee, D., From Agronomic Data to Farmer Recommendation: An Economics Training Manual. CIMMYT, Mexico, D.F., pp Cheema, Z.A., Weed control in wheat through sorghum allelochemicals. Ph.D. Thesis, Agronomy Department, University of Agriculture, Faisalabad, Pakistan. Cheema, Z.A., Luqman, M., Khaliq, A., Use of allelopathic extracts of sorghum and sunflower herbage for weed control in wheat. J. Animal Plant Sci. 7,

8 112 Z.A. Cheema, A. Khaliq / Agriculture, Ecosystems and Environment 79 (2000) Freed, R.D., Eisensmith, S.P., MSTAT Microcomputer Statistical Program. Michigan State University Michigan, Lansing, USA. Hussain, F., Gadoon, M.H., Allalopathic effects of Sorghum bicolor. Oecologia (Berl). 51, Kasasian, L., The place of herbicides and weed research in tropical agriculture. Pest Articles and News Summaries, Tropical Pesticides Research Headquarters and Information Unit, London, 17, Narwal, S.S., Gupta, K., Pahuja, S.S., Allelopathic effects of aqueous stubble extract of sorghum on the seed germination and seedling growth of winter crops. Indian J. Econ. 17, Nayyar, M., Shafi, M.M., Shah, M.L., Mahmood, T., Weed eradication studies in wheat. Absts. 4th Pakistan Weed Sci. Conf., UAF. Purvis, C.E., Jessop, R.S., Lovett, J.V., Selective regulation of germination and growth of annual weeds by crop residues. Weed Res. 25, Putnam, A.R., DeFrank, J., Use of phytotoxic plant residues for selective weed control. In: Proc. Br. Crop Prot. Conf. Weeds 2, Putwain, P.D., Herbicide resistance in weeds an inevitable consequence of herbicide use. In: Proc. Br. Crop Prot. Conf. Weeds 2, Rice, E.L., Allelopathy, 2nd edition. Academic Press, Orlando, FL, USA. Saghir, A.R., Bhatti, M.S., The influence of herbicides on the chemical composition of soybean seed. In: Proc. 10th Br. Weed Control Conf. 1,