Effects of alfalfa sowing rate and planting methods on weeds population dynamic in establishment year

Transcription

1 International Research Journal of Applied and Basic Sciences. Vol., 3 (5), , 2012 Available online at www. irjabs.com ISSN X 2012 Effects of alfalfa sowing rate and planting methods on weeds population dynamic in establishment year A.A. Yazdani 1, P. Abravan 2* & A.A. Fazeli 1- Former MSc. Student, Department of Crop Production and Plant Breeding. College of Agric., Shiraz Univ., Shiraz, Iran. 2- MSc.,.Agronomy. National Salinity Research Center. Yazd, Iran. Postal code: Former Bc. Student, Department of Crop Production and Plant Breeding. College of Agric., Shiraz Univ., Shiraz, Iran. *Corresponding Author p.abr84@gmail.com Abstract It has been hypothesized that increased sowing rate and different planting methods can increase weed suppression and thereby play a role in weed management. To assess the Effects of alfalfa sowing rate and planting methods on weeds population dynamic, field experiment was conducted in 2008 at the College of Agriculture in Shiraz University. The experimental design was a randomized complete block with four replicates in a factorial arrangement of the treatments and two factor were the planting methods (Furrow planting, Broadcasting, Row planting, and Raised bed planting) and alfalfa sowing rates (5, 10, 15, and 20 kg seed ha -1 ). Five weed species was identified by studying weed population which were mainly annual broad-leaves species. In this study, the interaction of planting methods and sowing rates on frequency percentage of Chenopodium album was different significantly. But, Alfalfa planting methods had no significant effect on weeds frequency percentage. In contrast, the effect of alfalfa sowing rates on frequency percentage of Amaranthus retroflexus and Stellaria media was significant. Results indicated that alfalfa sowing rates reduced weed frequency percentage. The effect of alfalfa sowing rates on relation density percentage (RDP) of Amaranthus retroflexus was also significant. Thus, the maximum RDP of A. retroflexus was obtained in alfalfa by 20 kg seed ha -1. Keywords: weed, planting methods, sowing rates, relative density percentage (RDP) and weed frequency percentage. Introduction Alfalfa a perennial legume is of major economic importance to farmer in the Iran. Among factors which adversely affect the crop yield, weed infestation is the most harm full for quantity and quality alfalfa yield. Weeds comprise the most undesirable aggressive and troublesome element of world's vegetation. Weeds in new alfalfa stands are a major concern. Weeds can negatively affect during establishment by competing for light, moisture, and nutrients, which can lead to reduced yield. So, weed management is important for decreasing competition with alfalfa and increasing alfalfa yield and quality during the establishment year. Effective weed management requires an understanding of weed biology and knowledge. It is also important to know the weed population dynamic because it will determine how each weed is best managed. Seeding alfalfa at the appropriate rate is critical for crop establishment, which is critical for weed management (Jahns et al. 2007). Crop density and spatial arrangement affect crop competition with weeds (Mohler 2001). Increasing crop density usually results in decreased weed biomass ( Murphy et al. 1996). A full stand of alfalfa (> 250 stems m -2 ) is competitive with weeds (Ward et al. 1990). A

2 well-prepared seedbed is important for maximizing crop emergence, which makes the crop more competitive against weeds (Jhans et al. 2007). If so, such a strategy could represent an alternative to herbicides or mechanical weed control for controlling weeds in alfalfa. The object of this study was under taken the effects of alfalfa sowing rate and planting methods on weeds population dynamic. Material and Methods The experiments were performed in 2008 at the college of agriculture in Shiraz university (29º40' N, 52º35' E). the research area is a arid and semi-arid zone, with a mean annual precipitation of 250 mm (mainly concentrated from November to May).The treatments were four crop-sowing densities (5, 10, 15 and 20 kg ha -1 ) of alfalfa and four planting methods (furrow planting, broad casting, row planting and raised bed planting). The size of each Plot was M. Hamedani alfalfa variety was planted on April 15, The experiment was fertilized at a rate of 30 kg N ha -1 as starter and 300 kg P 2 O 5 ha -1 as TSP (triple super phosphate). The quantitative survey of the farms was conducted to determine the weed frequency and relative density of each weed species using quadrate method. The quadrate size taken was 1M 1M. Ten quadrates were randomly thrown at all plots. The frequency percentage and RDP of each weed species was calculated by the following formula; The experimental design was a randomized complete block with four replicates in a factorial arrangement. Statistical analyses of treatment comparisons were conducted using the General Linear Models (GLM) procedure of the Statistical Analyses System (SAS 1996). When significant treatment means effects (P < 0.05) were found, treatment means were compared using Fisher s protected least significant difference (LSD) test. Results Weed flora During the survey, 5 weed species belonging 5 families were recorded. The major species which contributed to the weed flora of alfalfa were Amaranthus retroflexus, stellaria media, Chenopodium album, Portulaca oleraceae and Convolvulus arvensis. Weed biomass There were strong effects of sowing rate (P < 0.001) and planting methods (P = 0.001) on weed biomass. Weeds biomass decreased with increasing sowing rate (Figure 1) for all planting methods. The mean comparison of planting methods shoed that Weed biomass was lower in row planting than in other planting methods significantly (Table 1). Averaged over the four sowing rates, weed biomass was highest in the broad casting and lowest in the row planting. Weed biomass was 22% lower in the row planting than in the broad casting. Also, in this study weeds number were decreased with increasing sowing rate (Figure 2) for all planting methods. Weed frequency The results showed that effect of interaction planting methods and alfalfa sowing rate only on C. album L. frequency was significant (Table 2). But effect of sowing rates on A. retroflexus (P = 0.021) and S. media (P < 0.001) frequencies was significant. The highest frequency percentage was observed in 5 kg seed ha -1 for both weed. Also, A. retroflexus frequency percentage was higher than other weeds for all planting methods (Figure 3). Thoroughly, weed frequency percentage decreased with increasing sowing rate (Figure 4).

3 Relative density percentage There were no significantly interaction effects of planting methods and sowing rates on RDP of weeds. The effect of alfalfa sowing rates on RDP of A. retroflexus was significant (P < 0.001). The mean comparision showed that RDP of A. retroflexus increased by increasing sowing rate (Figure 5). So, the maximum RDP of A. retroflexus was obtained in alfalfa 20 kg seed ha -1. Discussion Thoroughly, increasing of weeds biomass in low alfalfa sowing rates caused of decreasing alfalfa population allow weeds to grow and occupy open spaces in the plant canopy which resulting increase in weeds biomass and number (Undersander et al., 2001). In this study, results showed that weed biomass and number were lower in row planting method. Also, in this research confirm previous studies that show weed biomass decreased with increasing in crop sowing rates (Olsen et al. 2005, Weiner et al. 2001; Korres and Froud- Williams 2002). Our results support the hypothesis that increases in sowing rate and spatial uniformity can increase weed suppression. It is obvious that Amaranthus retroflexus (broad leaved) was the most frequent weed for all planting methods. The next frequently occurring weed species were Setaria media, Portulaca oleraceae, convolvulus arvensis and Chenopodium album respectively. Concerning the density and frequency of the weeds recorded it can be concluded that Redroot pigweed (Amaranthus retroflexus) and Chich weed (Setaria media) are the most dominant weeds of alfalfa field in establishment year, respectively. This information regarding weed biology and ecology can be helpful for the selection of weed control methods. weed biomass (gr m -2 ) Furrow planting Row planting broad casting raised bed Sowing rates (kg ha -1 ) Figure 1. Effects of sowing rates on Weed biomass. Crop sown at four rates [5, 10, 15 and 20 kg seed ha -1 ] and four crop planting methods ( furrow planting, row planting,! broad casting and " raised bed).

4 Figure 2. Effects of sowing rates on Weeds number. Crop sown at four rates [5, 10, 15 and 20 kg seed ha-1] and four crop planting methods (# furrow planting, row planting, broad casting and raised bed). Table 1. Effect of planting methods on weeds biomass. Planting methods Broad casting Raised bed Furrow Row Weed biomass (gr m -2 ) a ab bc c Within row, means followed by the same letter are not significantly different (mixed procedure $ = 0.05). Table 2. Test of fixed effects on C. album based on PROC MIXED in SAS (1996). DF MS P-value Planting methods NS Sowing rates NS Replication NS Planting methods sowing rates * Error *. Significant at the 5% level and NS. Not significant.

5 Figure 3. Effects of sowing rates on Weeds frequency percentage. Crop sown at four rates [5, 10, 15 and 20 kg seed ha -1 ] and four crop planting methods (% Amaranthus retroflexus, & Chenopodium album,! Convolvulus arvensis, Setaria media, " Portulaca oleraceae).

6 Figure 4. Effects of sowing rates on frequency percentage of A. retroflexus and S. media. Crop sown at four rates [5, 10, 15 and 20 kg seed ha -1 ] ( A. retroflexus, % S. media). Figure 5. Effects of sowing rates on RDP of A. retroflexus. Crop sown at four rates [5, 10, 15 and 20 kg seed ha- 1]. References Blackshaw RE, Safflower (Carthamus tinctorius) density and row spacing effects on competition with green foxtail (Setaria viridis). Weed Sci 41: Doll H, The ability of barley to compete with weeds. Biol Agric and Hort 14: Jahns T, Hirnyck R, Downey L, Pest Management Strategic Plan for Non-Rangeland Forages (Excluding Alfalfa) in the Western States. Korres NE and Froud-Williams RJ, Effects of winter wheat cultivars and seed rate on the biological characteristics of naturally occurring weed flora. Weed Res. 42: Mohler CL, Enhancing the competitive ability of crops. In: Ecological Management of Agricultural Weeds (Eds M Liebman, CL Mohler, CP Staver), Cambridge University Press. Cambridge, UK, PP Murphy SD, Yakubu Y, Weise SF, Swanton CJ, Effect of planting patterns and inter-row cultivation on competition between corn (Zea mays) and late emerging weeds. Weed Sci 44: Olsen J, Kristensen L, Weiner J, Griepentrog HW, Increased density and spatial uniformity increase weed suppression by spring wheat. Weed Research 45: Radford BJ, Wilson BJ, Cartledge O, Watkins FB, Effects of wheat seeding rate on wild oat competition. Aust J Exp Agric and Animal Husbandry 20: Samuel AM, Guest SJ, Effect of seed rates and within crop cultivations in organic winter wheat. In: Crop Protection in Organic and Low Input Agriculture: Options for Reducing Agrochemical Usage (Ed. RJ Unwin), British Crop Protection Council. Farnham, UK, pp

7 SAS, SAS System for Mixed Models. SAS Institute, Cary, NC, USA. Undersander DJ, West DC, Casler MD, Frost seeding into aging alfalfa stands: Sward dynamics and pasture productivity. Agron J 93: Ward CE, Dowdy AK, Berberet RC, Stritzke JF, Economic analysis of alfalfa integrated management practices. South J Agric Econ 22: Weiner J, Griepentrog HW, Kristensen L, Suppression of weeds by spring wheat Triticum aestivum increases with crop density and spatial uniformity. J App Eco 38: