International Conference on Chemical, Ecology and Environmental Sciences (ICCEES'2011) Pattaya Dec. 2011

Allelopathic Potential of Canola (Brassica napus L.) Residues on Weed Suppression and Yield Response of Maize (Zea mays L.)

Bita. Zaji and Ahmad Majd

environment, often attract or repel, nourish, or poison other Abstract— Decomposition of some crops residues release organisms. The metabolites are released into the environment secondary metabolites that exhibit phytotoxic effects on other plants. by means of four ecological processes: volatilization, In order to determine allelopathic potential of canola on maize grain leaching, decomposition of plant residues in soil, and root yield and suppression of some common weeds, a field experiment exudation [6]. was performed in 2010. Treatments were weeding in two levels (whole season weeding and whole season interference) and Reference [7] terms allelochemicals as nature's own incorporation of canola residues into the soil, in three levels (0%, herbicides. Natural products relatively have short half-life and 15% and 30%). Allelopathic effects of canola reduced density, fresh therefore considered safe of environmental toxicology weight and dry weight of weeds. In particular, Solanum nigrum L. standpoint [8]. The most practical and immediate way to use and Amarantus retroflexus L. were inhibited while maize yield was allelopathy in weed control is to use allelopathic cover crops not influenced by canola residues. in rotations, or apply residues of allelopathic weeds or crops

as mulches [9]. Reference [10] shows that cover crop residues Keywords—Allelopathy, Canola, Maize, Weed control. provided partial weed control during the early stages of crop I. INTRODUCTION growth by causing both physical and chemical interference. Brassicaceae family has allelopathy potential on the growth LLELOPATHY, the ability of plants to inhibit germination of other plants [11]. They produce glucosinolates (GSLs) that A of other plants is a resource for weed control in crops. are not biologically active. When the plant tissue is disrupted, Research efforts in the past have concentrated on the the GSLs are hydrolysed to a number of products. The main discovery and use of herbicides for weed control, but current breakdown products are Isothiocianates (ITCs) which are research has pursued the discovery and refinement of cultural phytotoxic[11]. ITCs can only be released by the breakdown and biological control techniques for use in integrated systems of the cells during decomposition of dead plant material or [1]. incorporation green plant material into the soil. Myrosinase, Due to concerns of ecological, environmental, health the enzyme responsible for catalysis of glucosinolate problems [2]and increase the number of herbicide-resistant degradation, is physically separated from glucosinolates, thus weeds in the use of synthetic herbicides [3], there have been preventing secondary glucosinolate product formation in considerable efforts in designing weed management strategies living plants [12]. Physical disruption of plant tissue through of allelopathic compounds as bioherbicides to suppress weed. grinding is necessary for further degradation of the Also biosynthesized herbicides are easily biodegradable, they glucosinolates into ITCs and other secondary products [13]. If are believed to be much safer than synthesized herbicides [2]. Brassica spp. plant tissues are incorporated into the soil, it is Controlling weeds with allelopathic crops resi dues was f i rst possible to control weeds in the following crop by ITCs postulated by Putnam and Duke [4]. Since then, efforts in released from the mulch [12]. various parts of the world have been underway to exploit the The objectives of this research were (i) to assess the allelopathic potential of different plant species for weed allelopathicP potentialP of canola residuals on suppression of control in various cropping systems [5]. some weeds and (ii) to determine the cover crop effect on Secondary plant metabolites include a variety of maizeP grainP yieldP underP fieldP conditions.P compounds that when released from plants into the

II. M1B ATERIAL AND METHODS

Bita. Zaji is now with the Department of Agriculture, Islamic Azad The field experiment on maize (Zea mays L.var. ksc 704) University-Kermanshah Branch, Kermanshah, Iran (Islamic Rep.), Postal was carried out in 2008 in Iran (at the agriculture research Code: 6718997551 (phone: 00989188366587; fax: 00988317243196; e-mail: center of Kermanshah, on a clay–loam soil [email protected]). 47°26′N, 34°8′E) Ahmad majd is now with Biology Department, Islamic Azad University, (10% sand, 53% clay and 38% silt, pH 6.8 and 1.1% organic North of Tehran Branch, Tehran, Iran (Islamic Rep.), Postal Code: matter). Based on the soil test recommendations, P and K were 1939614484 (email: [email protected]). -1 -1 applied before seed sowing at 200 kg haP P and 120 kg haP ,P

457 International Conference on Chemical, Ecology and Environmental Sciences (ICCEES'2011) Pattaya Dec. 2011

TABLE I . respectively Nitrogen was applied at three phases: at plantig EFFECT OF CANOLA INCORPORATION DENSITIES ON FRESH WEIGHT, DRY time as side dressing, at the 6-leaf stage and tassel emergence WEIGHT AND DENSITIES OF WEEDS as a top dressing. Control 15% 30% The experimental site was ploughed and subsequently disc- Weed fresh weight 9.127 b 5.490 c harrowed and smoothing with land leveler in late of spring. In −2 12.743 a 2 (kg m ) (28.4) (56.9) each main plot, four subplots of 3×4m were created (each one Weed dry weight 4.861 b 3.142 b 7.946 a including four rows of maize) and all subplots were separated (kg m−2) (38.8) (60.5) by a 0.75 m wide alley. Then the shoots of canola (Brassica Weeds density 20.34b 2 46.67a 27.66b (40.7) napus L. var. Opera) which had been planted in another area (Number of plant per m ) (56.4) in august were cut off (2-4 cm above soil level) at the full Means with different letters in a column differed significantly (5% level).In parenthesis % decrease compared with control. bloom stage. The residual of canola were chopped into 5 cm pieces. Then pieces of canola were weighed in certain ratios residues of celery (Apium graveolens L.) on growth of several and incorporated 10 cm deep into the soil uniformly. weeds and crop species. Spiny amaranth (Amaranthus Experimental design was split plot-factorial in complete spinosus L.) was found to be the most sensitive to celery root randomized blocks with four replications. Treatments were residues followed by barnyardgrass (Echinochloa crus-galli weeding in two levels (whole season weeding and whole (L.) Beauv.), wild mustard (Brassica kaber (DC.) L.C. season interference) in main plots and densities of canola Wheeler) and black nightshade (Solanum nigrum L.). mulch (0, %15 and %30) are incorporated in subplots. One week after canola incorporation, maize seeds were planted in 16 the soil with residuals and without residuals of canola as a 0 15% 30% control. Irrigation and other common cultural practices were performed whenever as needed. Densities, fresh weight and dry weight of common weeds 12 including redroot amaranth (Amaranthus retroflexus L.), rough cocklebur (Xanthium strumarium L.), field bindweed 8 (Convolvulus arvensis L.), black nightshade (Solanum nigrum L.), Johnson grass (Sorghum halepense (L.) Pers.) and Curly dock (Rumex crispus L.) were determined at physiological plant/m2 of No. maturity of maize in each sampling. Data were analyzed with 4 the Statistical Analysis System (SAS) program and the means were separated by Duncan's Multiple Range Test. 0 A. C. arvensis R. crispus S. halepense S. nigrum X. rxuxetrofle strumarium

III. RESULTS AND DISCUSSION Fig. 1 Effect of canola incorporation at different densities on number Our experiments clearly demonstrate that canola residues of individual weed species incorporation in different densities had significantly (p≤0.05) affected on density, fresh weight and dry weight. Growth of Crop residues can provide selective weed control through weeds was reduced by increasing of canola density (Table 1). their physical presence on the soil surface and through the Weed assessment based on the density of individual weed release of allelochemicals [16]. Effect of allelochemicals species also show significant differences amongst treatments. contributed from crop residues also depends on the soil

However, weed density in the maize was reduced compared texture and substratum ecology [17]. weedy plots without incorporation of canola. In particular, Reference [18] shows that when fall-planted rapeseed density of redroot amaranth, black nightshade and curly dock residues were incorporated in the spring and then potatoes was inhibited at the highest density of canola incorporation were planted into these residues, mid-season weed density 84.74, 77.97 and 72.22%, respectively (Fig. 1). This result is was decreased by 73–85% and the potato plants were not similar to the reference [12]. Dry weight of individual weed harmed by the residues. It is found that decomposition of canola species as affected by the treatments also varied in the manner residues release secondary metabolites that exhibit phytotoxic consistently treated with density. Similarly the residues of effects on other plants [12]. There is a high probability that canola displayed a loss of biomass on individual weed dry ITCs are responsible for suppression of weed germination weight special a near 100% loss in redroot amaranth (Fig 2). after incorporation of green canola mulch into the soil. This effect can be used for the following crop, especially when The si mi l ar ef f ects of the Brassica and non-brassi ca residues on establishment contradict results from several other planting is done without tillage. Then it is likely that less or no field studies, which suggest that the i mpacts of Brassi ca on additional herbicides are necessary[12]. In another experiment [19], green bean ( weed suppression are greater than those provided by other Phaseolus vulgaris L.), redroot pigweed and a mi xture of the two speci es were cover crops [14]. Reference [15] investigates the effect of root planted into plots that grew and received incorporated residues

458 International Conference on Chemical, Ecology and Environmental Sciences (ICCEES'2011) Pattaya Dec. 2011 of canola and yellow mustard. Although the biomass val ues of 20 Weeding both green bean and redroot pigweed were often lower interference following the brassica cover crops, and lowest following the high glucosinolate mustard, differences were not significant. 16 These results suggest that the observed weed suppression by brassi ca resi duas i n the f i el d [14]. Reference [20] discusses the question whether 100% weed control can be achieved by 12 using cover crops or crop residues. However, results [14]

shows that some weed species still germinate after 8 incorporation of green Brassica mulch, and as a consequence, Yield (ton/ha) additional weed control methods are required [10]. The 4 potential phytotoxicity is dependent on numerous factors that together govern the rate of residue decomposition, the net rate of active allelochemical production and the subsequent 0 degrees of phytotoxicity. These factors can be basically 0 15% 30% classified into three main categories: amount and composition of plant residues, the environment in which plant residues are Fig. 3 Effect of canola incorporation densities on yield of maize in decomposing, and management practices [21]. weeding and interference plots

5 0 15% 30% REFERENCES [1] R. E. Hoagland, "Microbial Allelochemicals and Pathogens as Bioherbicidal Agents 1," Weed Technology, vol. 15, pp. 835 857, 2001. 4 [2] F. Dayan, J. Romagni, M. Tellez, A. Rimando, and S. Duke, "Managing weeds with bio-synthesized products," Pestic. Outl, vol. 10, pp. 185-188, 1999. 3 [3] P. J. Tranel and T. R. Wright, "Resistance of weeds to ALS-inhibiting herbicides: what have we learned?," Weed science, vol. 50, pp. 700-712, 2002. 2 [4] A. R. Putnam and W. B. Duke, "Biological suppression of weeds: evidence for allelopathy in accessions of cucumber," Science, vol. 185, p. 370, 1974.

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459 International Conference on Chemical, Ecology and Environmental Sciences (ICCEES'2011) Pattaya Dec. 2011

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