Effect of critical period of weed control on growth indices of corn

Document Type : Research Article




Physiological growth analysis is the most important in prediction of plant growth and yield. Growth analysis is an approach to evaluate what events occurs during plant growth. Total dry matter trend (TDM), Crop growth rate (CGR) and relative growth rate are the most important characteristics in plant growth analysis. Growth analysis is a suitable technique for plant response to different environmental conditions and agricultural management during plant life (Tesar, 1984).
Competition for light has been identified as the primary cause of crop yield loss in many crop–weed associations. Tollenaar et al. (1994) reported that interference from mixed weeds emerging shortly after corn reduced its growth and yield.
The purpose of this study was the effect of critical period of weed control (CPWC) on physiological growth indices 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 done based on a randomized complete block design with 12 treatments and three replications. Two sets of weed-free and weed-infested treatments were used. At the first set of treatments, weeds were allowed to compete with corn 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). Dry matter (DM), leaf area index (LAI), crop growth rate (CGR) and relative growth rate (RGR) of corn were measured and calculated accordingly. The areas of green leaves were measured using a Delta-T leaf area meter. The samples including stems and leaves were dried in a forced-air oven and after total dry matter (TDM) was measured. The leaf area data was divided to ground area and the leaf area index (LAI) was obtained. The sigmoid equation (Eq. 1) was fitted to the TDM data and by derivation from this equation, the crop growth rate (CGR) (Eq. 2) and relative growth rate (Eq. 3) were obtained (Steinmaus and Norris, 2002):
W (t) = a / 1+ exp {-b (t-m)} [Eq. 1]
CGR = b. w (t) {1-(w (t)/a)} [Eq. 2]
RGR = b {1-(w (t)/a)} [Eq. 3]
Where t is the time (day), W(t), dry matter at time t; a, the maximum total dry matter; b, the slope of increasing the dry matter; m, the time that corn had the maximum growth rate and CGR is crop growth rate. The regression analysis was performed by SAS 9.1 and the graphs were prepared by Excel.

Results and discussion
The results showed that during the days after planting in all treatments leaf area index first increased until 62 days after planting and then it had a descending trend. By increasing in duration of weed control, dry matter accumulation was enhanced. The highest dry matter was observed in weed control at all the growing season and the lowest was for weed control until 19 days after emergence. Crop growth rate (CGR) in all treatments first increased slightly and then increased more quickly until 70 days after planting. Then CGR decreased with a sharp slope. The maximum and the minimum crop growth rate were observed in control during all the growing season (31.14 g.m-2.day) and weed control until 19 days after emergence (31.80 g.m-2.day).

There was a reduction in growth indices with increasing duration of weed interference. Weed density and emergence determined the growth indices reduction due to weed interference duration. It was suggested that weed interference will not reduce growth indices of corn if weeds are controlled in a timely manner with hand weeding.


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Articles in Press, Accepted Manuscript
Available Online from 01 January 2024
  • Receive Date: 06 May 2017
  • Accept Date: 06 May 2017
  • First Publish Date: 27 November 2020