Materials and Methods

Growth stages of major weeds in cereals of the Setif high plains (North-East, Algeria) were recorded for 5 years: 1994/1995, 1996/1997, 1998/1999, 2000/2001, and 2004/2005. The field experiment is located 2 km south of Setif city, at an altitude of 1100 m. The soil is clay loam, the pH (1:5 H20) is 7.9, and the percentage of the organic matter is 0.45. Setif region climate is characterized by a cold and wet winter, a hot summer, generally very dry. The climatic area is semi-arid.

Climatic characteristics of 5 years of observations, compared with the average period of 1981/2005, are reported in Table 41.1. We noted that 1999 and 2001 are relatively warm and dry. Their average temperatures exceed that of the 1981/2005 period, successively, by 1 and 1.1 °C. The total of monthly average temperatures of these 2 years exceeds that of the 1981/2005 period of 11.7 and 13.2°C, respectively.

Table 41.1 Climatic characteristics of 5 years of observations.

Years characteristics

1995

1997

1999

2001

2005

1981/2005

Annual average

14.4

15.1

15.5

15.6

14.5

14.5

temperatures (°C)

Sum of monthly average

172.2

181.6

186.0

187.5

173.8

174.3

temperatures (°C)

Rainfall (mm)

422.4

402.4

384.0

251.7

373.8

403

Observations were made since the sowing of durum wheat (Triticum durum Desf.) until its stage of maturation, at 5-8 day intervals, in four plots of 25 m2. Sowing took place during the 5 years of experimentation between November 1 and 20. Weed species were identified following the "Nouvelle flore d'Algérie" of Quezel and Santa (1962-63). Phenological stages of these species were recorded according to the BBCH scale (Lancashire et al., 1991) as first leaf, vegetative development (development of harvestable vegetative plant parts), flowering maturity of seed (ripening of fruit and seed), and senescence (leaves change color and fall).

The models developed on the basis of heat units expressed as degree-days have been widely used for predicting growth and development weeds (Forcella, 1998, Baker and Reddy, 2001). In order to determine relations between phenological cereal weeds and climatic variations, degree-days were computed using the following equation:

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