Document Type : Research Article
Authors
Ferdowsi
Abstract
Introduction
Competition for light has been identified as the primary cause of crop yield loss in many crop–weed associations (Zimdahl, 1988). Tollenaar et al. (1994) reported that interference from mixed weeds emerging shortly after corn reduced corn biomass, harvest index, and final grain yield.
The critical period for weed control (CPWC) is a key component of an integrated weed management program. It is a period in the crop growth cycle during which weeds must be controlled to prevent yield losses.
The CPWC is useful for making decisions on the need for and timing of weed control. Zimdahl (1988) defined it as a ‘‘span of time between that period after seeding or emergence when weed competition does not reduce crop yield and the time after which weed competition will no longer reduce crop yield.’’
The purpose of this study was the effect of critical period of weed control (CPWC) on yield and yield components of corn.
Materials and methods
A field experiment was conducted at the Agricultural Research Station, of Ferdowsi University of Mashhad during 2012-2013. The experiment was laid out based on a randomized complete block design with 12 treatments and 3 replications. Two sets of weed-free and weed-infested treatments were used. At the first set of treatments, weeds were allowed to compete with maize until 19, 34, 48, 52, 59 and 123 days after emergence (weed- infested periods). Weed control was accomplished with hand weeding.
At the second one, plots were kept free of weeds until the above mentioned periods (weed- free periods). Onset and end of (CPWC) were determined based on 10% acceptable grain yield loos using Gompertz and Logistic equations. Asymptotic crop biomass accumulation was expressed with the Gompertz equation (Hunt, 1982) (Equation 1):
ln(W) 5ln(W) exp (2qexp[2kT]) max [1]
Where ln(W) is log e-transformed biomass (i.e., sum of leaf, stem, and reproductive tissues) per plant in units of mg plant-1 (all plant weights converted to milligrams so as to ensure positive values after the loge-transformation), ln(W) maxis maximum log e-transformed shoot biomass per plant in mg plant-1, T is the time from crop emergence. The coefficients q and k are constants. Studied criteria were yield components (such as row number per ear, grain number per row, grain number per ear and 100-seed weight), grain yield, biological yield and harvest index (HI).
For statistical analysis, analysis of variance and Duncan’s test were performed using Minitab ver.17.
Results and discussion
Weed species in order of dominance (dry weight basis) were Portulaca oleracea, Amaranthus retroflexus, Chenopodium album, Echinochloa crus-galli and Echinochloa crus-galli during the growing season were main dominant species. The results showed that the effect of management time and interference duration of weeds was significant on yield and yield components and HI. Maximum seed yield was obtained in 19 days weed infested and the lowest in 19 day weed control which is the whole season weed interference. Based on results critical period of control for corn in Mashhad was 22 to 61 days after plant emergence.
Conclusion
There was a reduction in seed yield with increasing duration of weed interference. Weed density and emergence determined the seed yield reduction due to weed interference duration. More work is needed on causes of variability in yield loss weed density curves, on multispecies interference, on factors other than density (timing of emergence and crop cultivar) and on comparisons of species.
References
Zimdahl, R. L. 1988. The concept and application of the critical weed-free period. Pages 145–155. In: M. A. Altieri and M. Liebman, ed. Weed Management in Agroecosystems: Ecological Approaches. Boca Raton, FL: CRC Press.
Tollenaar, M., Nissanka, S.P., Aguilera, A., Weise, S.F., and Swanton, C.J. 1994. Effects of weed interference and soil nitrogen on four maize hybrids. Agron. J., 86: 596-601.
Hunt, R. 1982. Plant Growth Curves: The Functional Approach to Growth Analysis. London: Edward Arnold. pp. 51–54, 128–135.
Keywords
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