Results and Discussion

The 5-year study involved 14 species belonging to 12 plant families. Prevalent families were Brassicaceae and Apiaceae. Some families give few species of weeds, but very noxious (Convolvulaceae and Polygonaceae). The most abundant species were Veronica hederifolia, Papaver rhoeas, Vaccaria pyramidata, Fu-mariaparviflora, and Polygonum aviculare.

Species are classified in Tables 41.2 and 41.3 according to the date of flowering. The earliest flowering recorded was for Ranunculus arvensis and V. hederifolia, with degree-days accumulation of 316 and 426, respectively, and the latest was for Scolymus hispanicus and P. aviculare with degree-days accumulation of 2021 and 1297, respectively.

Just after the first rains of autumn, weed seeds inflate and germinate; these two processes take place during December. The first leaf appears for the majority of species at the end of December and beginning of January. It is only from the stage vegetative development that we can notice differences between species phenology. Those which have weak thermal requirements achieve their stages of vegetative development quickly and arrive in first at stage of flowering (March-beginning of April); it was the case with V. hederifolia and R. arvensis, and they are winter-spring species. Most of their cycles of development take place in winter. They reach the maturity of seed with less than 600 degree-days. Species which require higher temperatures require more time in their development and reach their stages of flowering from May to June; it was the case of Diplotaxis virgata, V. pyramidata, and P. aviculare. These are spring-summer species whose stage of vegetative development is spread out until spring. They require between 1900 and 2300 degree-days to mature their seeds (Table 41.2). Between the two preceding groups of species, we have an intermediate group composed of F. parviflora, Rapistrum rugosum, Galium tricorne, Bifora testiculata, Turgenia latifolia, Vicia monantha, Papaver rhoeas, and Bromus rubens; these are characteristic species of the cereals weed flora in North Africa and they require temperature between 800 and 1200°C to mature their seeds.

The analysis of the variance showed that the year of observation had no significant effect on the sum of degree-days required by every species to carry out its life cycle or to carry out its phenological stages. The sum of degree-days required by every species was almost constant during the 5 years of observation; it was the same during relatively warm years (such as on 1999 and 2001) or during the three other normal years. According to McCarty (1986), each plant operates under a specific set of thermal requirements that determine time of germination, emergence, and subsequent developmental stages. Thus, the apparent variation in times of occurrence from year to year of various phenological stages may be based on some specific sets of weather conditions like temperature.

Until senescence the species which had the shortest cycle and which lasted less than 160 days were R. arvensis and V. hederifolia, these species emerged early and started quick growth during relatively cool temperatures, utilizing the normally abundant winter rainfall and available soil water. Species which have the longest cycle and which lasted more than 240 days were S. hispanicus and P. avi-culare (Table 41.3). These species spend the winter as rosettes and show active growth in the spring.

Table 41.2 Degree-days accumulation by phenological stages of each species (average of 5 years).

Phenological stages First Vegetative Flowering Maturity Senescence

Table 41.2 Degree-days accumulation by phenological stages of each species (average of 5 years).

Phenological stages First Vegetative Flowering Maturity Senescence

Weed species

leaf

development

of seed

Ranunculus arvensis L.

120^

87

109

149

311

207(2)

316

465

776

Veronica hederifolia L.

108

100

218

137

155

208

426

563

718

Fumaria parviflora Lamk.

120

245

120

375

366

365

485

860

1226

Rapistrum rugosum (L.)All.

133

211

166

458

497

344

510

968

1465

Galium tricorne Witth.

120

245

212

284

366

365

577

861

1227

Bifora testiculata Hoffm.Roth.

147

368

91

431

519

515

606

1037

1556

Turgenia latifolia Hoffm.

120

396

201

321

519

516

717

1038

1557

Vicia monantha Retz.

120

396

330

192

519

516

846

1038

1557

Papaver rhoeas L.

120

441

348

302

620

561

909

1211

1831

Bromus rubens L.

120

441

348

215

656

561

909

1124

1780

Diplotaxis virgata DC.

120

597

494

346

447

717

1211

1557

2004

Vaccaria pyramidata Medik.

133

712

366

173

509

845

1211

1384

1893

Polygonum aviculare L.

133

712

452

595

410

845

1297

1892

2302

Scolymus hispanicus L.

160

1396

465

223

200

1556

2021

2244

2444

(1) Counted from December 1

(2) Cumulate

(2) Cumulate

Table 41.3 Dates and durations (days) of phenological stages of major cereal weeds in Setif region (average over 5 years).

Weed species

First leaf

Vegetative development

Flowering

Maturity of seed

Senescence

Ranunculus arvensis L.

12-

25 / 1-5(1)

1-5 / 3-1

3-1 / 3-20

3-20 / 4-10

4-10 / 5-10

36(2)

54 (90) (3)

19 (109)

20 (129)

30 (159)

11.81(4)

13.09

8.04

27.61

18.40

Veronica hederifolia L.

12

-20 / 1-1

1-1 / 3-1

3-1 / 4-5

4-5 / 4-20

4-20 / 5-5

32

59 (91)

35 (126)

15 (141)

15 (156)

10.95

6.88

5.38

17.54

20.05

Fumaria parviflora

12

-20 / 1-5

1-5 / 3-25

3-25 / 4-10

4-10 / 5-15

5-15 / 6-10

Lamk.

36

78 (114)

15 (129)

35 (164)

25 (189)

11.30

15.28

8.10

14.61

15.34

Rapistrum rugosum

1-

1 / 1-10

1-10 / 3-25

3-25 / 4-15

4-15 / 5-25

5-25 / 6-25

(L.)All.

41

73 (114)

20 (134)

40 (174)

30 (204)

9.87

11.41

7.74

12.60

25.53

Galium tricorne Witth.

12

-25 / 1-5

1-5 / 3-25

3-25 / 4-20

4-20 / 5-15

5-15 / 6-10

36

78 (114)

25 (139)

25 (164)

25 (189)

16.50

8.14

5.58

19.78

22.54

Bifora testiculata

1-

■5 / 1-15

1-15 / 4-15

4-15 / 4-25

4-25 / 5-30

6-1 / 6-30

Hoffm.Roth.

46

89 (135)

10 (145)

35 (180)

30 (210)

12.46

7.97

7.05

13.64

17.48

Turgenia latifolia

1

-1 / 1-5

1-5 / 4-15

4-15 / 5-5

5-5 / 5-30

5-30 / 6-30

Hoffm.

36

99 (135)

20 (155)

25 (180)

30 (210)

19.41

12.14

7.90

16.49

20.27

Vicia monantha Retz.

1

-1 / 1-5

1-5 / 4-15

4-15 / 5-15

5-15 / 5-30

5-30 / 6-30

36

99 (135)

30 (165)

15 (180)

31 (211)

10.25

15.35

6.60

17.51

17.57

Papaver rhoeas L.

1

-1 / 1-5

1-5 / 4-20

4-20 / 5-20

5-20 / 6-10

6-10 / 7-20

36

104 (140)

30 (170)

20 (190)

30 (220)

9.84

14.48

8.03

14.72

16.05

Bromus rubens L.

1

-1 / 1-5

1-5 / 4-20

4-20 / 5-20

5-20 / 6-5

6-5 / 7-10

36

104 (140)

30 (170)

15 (185)

35 (220)

11.10

10.05

5.64

9.12

8.61

Diplotaxis virgata DC.

1

-1 / 1-5

1-5 / 5-5

5-5 / 6-10

6-10 / 6-30

6-30 / 7-20

36

119 (155)

35 (190)

20 (210)

20 (230)

11.82

11.21

7.87

22.54

15.72

Vaccaria pyramidata

1-

-5 / 1-10

1-10 / 5-15

5-15 / 6-10

6-10 / 6-20

6-20 / 7-15

Medik.

41

124 (165)

25 (190)

10 (200)

25 (225)

14.11

13.65

6.49

12.05

21.57

Polygonum aviculare L.

1-

-5 / 1-10

1-10 / 5-15

5-15 / 6-15

6-15 / 7-15

7-15 / 7-30

41

124 (165)

30 (195)

30 (225)

18 (243)

15.36

15.70

5.27

11.78

19.63

Scolymus hispanicus L.

1-

5 / 1-20

1-20 / 6-30

6-30 / 7-20

7-20 / 7-30

7-30 / 8-7

51

160 (211)

21 (232)

10 (242)

8 (250)

10.82

12.14

4.90

25.49

17.25

(1) Dates, (2) Duration in days, (3) Cumulate in days, (4) CV % : coefficient of variation (ratio of the standard deviation to mean, reported as a percentage).

(1) Dates, (2) Duration in days, (3) Cumulate in days, (4) CV % : coefficient of variation (ratio of the standard deviation to mean, reported as a percentage).

Phenological similarities may be considered as an expression of physiological and genetic similarities of species and may be used as a measure of relationship. On the basis of duration of the vegetative cycle, the season during which most of this cycle takes place and period of flowering, species reported in Table 41.3 were grouped as winter-spring species (R. arvensis, V. hederifolia, F. parviflora, R. rugosum, G. tricorne, B. testiculata, T. latifolia, V. monantha, P. rhoeas, and B. rubens), and spring-summer species (D. virgata, V. pyrami-data, and P. aviculare). The variability which exists in each group depends on the temperature. Maturity of seeds was ranged from early April to the beginning of June for the first group, and from beginning of June to July for the second group.

S. hispanicus can be counted like summer species; its stage of development was spread out until the end of June and it flowered and matured in July. When it is present in large quantities in the fallow, it dominates the summer floristic aspects.

The results of analysis of durations (in days) of the phenological stages of all species showed that the coefficients of variation were relatively high for the stages of first leaf, vegetative development, maturity of seed, and senescence (Table 41.3). It means that the duration of these stages varied from 1 year to the next; indeed, during relatively warm years the duration of these phenological stages was short compared with normal years. So, the cereal weeds show an adaptation to the global warming by modulating the duration of their phenological phases. The lowest coefficients of variation were noted for flowering stage of all species; this phenological event was affected by the temperature and day length.

Increases in temperature due to global climate changes could significantly impact weed competitiveness and crop-weed interactions (Tungate et al., 2006). During warm years, weeds accelerate their development and become more concurrent toward cereals. It is necessary to note that they are less demanding for water than the cultivated plants and their seeds are in the ground well before the arrival of the cereals seeds; therefore they use the soil humidity to inflate and start their germination, before even the ploughing. Under these conditions, competition is really strong and early. In this order Fuhrer et al. (2006) noted that warming accelerates plant development and reduces grain-fill, reduces nutrient-use efficiency, increases crop water consumption, and favors C4 weeds over C3 crops. Overall, intensive agriculture may have the potential to adapt to changing conditions, in contrast to extensive agricultural systems or low-input systems which may be affected more seriously.

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