Mohammadi, G.R. and Amiri, F.
(2011)
Critical period of weed control in soybean (Glycine max) as influenced by starter fertilizer.
Australian Journal of Crop Science, 5 (11).
pp. 1350-1355.
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Abstract
The critical period of weed control (CPWC) in crops depends on many factors including supply and availability of nutrients. In order
to investigate the effect of starter fertilizer on the CPWC in soybean a field experiment in a randomized complete block design with
four replications in a factorial arrangement was conducted at the Agricultural Research Farm of Razi University, Kermanshah, Iran.
Two factors were examined: the first factor was the starter fertilizer levels (0 and 25 kg ha-1) applied in the form of monoammonium
phosphate and the second factor was the different weed interference periods. Results indicated that soybean seed yield and yield
components were significantly decreased when the weed interference period was increased. Weedy condition for the entire growing
season reduced seed yield by 36% as compared with full season weed free condition. In order to prevent > 5% seed yield loss
soybean field must be kept weed-free from the V1 to R1 (9-47 days after crop emergence (DAE) or 111.20 to 743.05 accumulated
thermal units (ATU) and between the V7 and R3 (26-52 DAE or 374.55 to 832.75 ATU) at 0 and 25 kg.ha-1 of starter fertilizer level,
respectively. Generally, the use of starter fertilizer slightly delayed the end of the CPWC (by 5 days), but this condition shortened the
CPWC by 12 days because of the later beginning of the CPWC (by 17 days). Practical implication of this finding is that application
of monoammonium phosphate as starter fertilizer can reduce the time needed for weed control in soybean field and consequently lead
to less herbicide application and cultivation.
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