Adaptation of indeterminate faba beans to weather and management under a Mediterranean climate

Field Crops Research 66 (2000) 81±99

Adaptation of indeterminate faba beans to weather and management under a Mediterranean climate Federico Saua,*, M. IneÂs MõÂnguezb a

Depto. de ProduccioÂn Vexetal, Escola PoliteÂcnica Superior, University of Santiago de Compostela, 27002 Lugo, Spain b Depto. de ProduccioÂn Vegetal: Fitotecnia, Escuela TeÂcnica Superior de Ingenieros AgroÂnomos, Technical University of Madrid, 28040 Madrid, Spain Received 24 April 1999; received in revised form 7 January 2000; accepted 7 January 2000

Abstract The response and adaptation of faba bean to terminal drought was studied during two growing seasons differing in radiation, rainfall and vapour pressure de®cit. Field experiments were carried out under irrigated and rainfed conditions, using highly productive, indeterminate cultivars sown at various densities. Water relations, crop evapotranspiration, dry matter production and partitioning, yield components and root development were monitored. During the ®rst year, a strong water de®cit developed, leaf midday and predawn water potentials decreased and stomatal resistance increased sharply during pod ®lling. Water de®cit developed gradually during the second year and stomatal resistance increased progressively during the reproductive period. In both years, faba bean adopted water conservation mechanisms that delayed dehydration mainly through stomatal closure at relatively high water potential. No signi®cant osmotic adjustment was observed. The two water stress patterns, plant densities and spatial distribution produced different water-use ef®ciencies. These differences disappeared when corrected for vapour pressure de®cit. Maximum grain yield, over 6000 kg haÿ1, was obtained with irrigation at plant densities of 20 and 33 plants mÿ2. In irrigated plots, where the density was increased to 33 plants mÿ2, greater biomass production was not associated with greater yield, because of low mobilisation (re¯ected by a decrease in harvest index). High yields were also obtained under rainfed conditions at a density of 25 plants mÿ2 when moist conditions prevailed in spring. A combination of dry spring and low plant density (20 plants mÿ2) produced the smallest yield (ca. 3900 kg haÿ1). No differences due to nitrogen application or inoculation were found. Root length densities did not vary signi®cantly among treatments, at most sampling dates and among the experiments, but indirect estimation of root/shoot ratio indicated an increase in rainfed treatments. Indeterminate cultivars proved to be suitable in this region of highly variable spring water supply. A density of 25 plants mÿ2 is appropriate for the area whereas higher plant density (33 plants mÿ2) and non-limiting water conditions can lead to excessive vegetative growth and smaller harvest indices in these cultivars. # 2000 Elsevier Science B.V. All rights reserved. Keywords: Vicia faba L.; Water de®cit; Irrigation; Water-use ef®ciency; Yield components; Root-length density Abbreviations: cv., Cultivar; DAS, Days After Sowing; ETc, Crop Evapotranspiration; ET0, Reference Evapotranspiration; HI, Harvest Index; I, Irrigated Treatments; Kc, Crop Coef®cient; LAI, Leaf Area Index; ÿN, Inoculated Treatments; ‡N, Nitrogen Fertilised Treatments; R, Rainfed Treatments; Rsm, Midday Stomatal Resistance; Rs, Stomatal Resistance; S.E., Standard Error of Mean; SR, Solar Radiation; * Corresponding author. Tel.: ‡34-982-25-23-03, ext: 23112; fax: ‡34-982-24-18-35. E-mail address: [email protected] (F. Sau)

0378-4290/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 4 2 9 0 ( 0 0 ) 0 0 0 6 7 - 8

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F. Sau, M. IneÂs MõÂnguez / Field Crops Research 66 (2000) 81±99

VPD, Vapour Pressure De®cit; WUE, Water-use Ef®ciency; WUEb, Water-use Ef®ciency Related to Biomass; WUEy, Water-use Ef®ciency Related to Grain Yield; Cd, Predawn Water Potential; Cl, Leaf Water Potential; Cm, Midday Water Potential

1. Introduction Faba bean (Vicia faba L.) is one of the most important legume crops in the Mediterranean basin (FAO, 1997). In West Asia and North Africa, it is grown for both human and animal consumption, whereas in Europe it is used as pig and poultry fodder (Duc, 1997). Faba bean is generally a rainfed crop grown in areas receiving more than 400 mm of rainfall but in drier regions, e.g. Egypt, it is generally irrigated (Saxena, 1985). Studies on water use in faba bean have been carried out in temperate (Grashoff, 1990a,b; Husain et al., 1990; Rengasamy and Reid, 1993) and in arid and semiarid environments (Silim and Saxena, 1993; ICARDA, 1994; Loss et al., 1997; Manschadi et al., 1998a,b; Leport et al., 1998). Other ®eld experiments have shown the ability of faba bean to produce high seed yields compared to other grain legumes, under rainfed conditions in Mediterraneantype environments (Siddique et al., 1993; Thomson and Siddique, 1997). Thomson and Siddique (1997) associated the high dry-matter production of Vicia faba and Pisum sativum relative to other species, e.g. Lupinus albus and Lupinus angustifolius, with their ability to grow and produce rapid ground cover during the early part of the growing season when soil water is readily available and vapour pressure de®cit is low. On the other hand, decreasing the rate of leaf area expansion and increasing root growth have been described as potentially advantageous adaptations of faba bean to water de®cit (Husain et al., 1990). Furthermore, Reid (1990) demonstrated, through a modelling approach, that increased root growth was the more important of the above-mentioned mechanisms in adaptation to water de®cit. Nevertheless, Manschadi et al. (1998a) reported that under semiarid conditions, root growth was signi®cantly reduced when compared with the well watered treatments. The study reported here is part of a research project, carried out over two growing seasons, to investigate the response of faba bean with indeterminate growth to irrigation and rainfed conditions, under management practices applied by farmers in southern Spain. Farm-

ers used and still use faba beans as a low-input break crop in a cereal/sun¯ower rotation under rainfed conditions (Guerrero, 1987). Faba bean seed prices have always been high, so a low seeding density is used (ca. 20 plants mÿ2), fertiliser is not applied and weeds are partly controlled mechanically to minimise herbicide use (Guerrero, 1987). Canopy development, radiation interception and radiation-use ef®ciency were discussed in a previous paper (MõÂnguez et al., 1993) that highlighted the impact of the water regime on vegetative growth and radiation interception. The large leaf area indices (LAI) obtained under irrigation brought into question the suitability of indeterminate cultivars. Water availability plays a major role in faba bean assimilate partitioning, and in this paper we examine the water relations, water-use ef®ciency (WUE), root distribution and grain yield components of two indeterminate faba bean cultivars grown under two water regimes (irrigated and rainfed), nitrogen fertilised or inoculated and at different plant densities. 2. Material and methods The ®eld experiments were carried out at the Agricultural Research Centre in CoÂrdoba, in the Guadalquivir Valley, southern Spain, during 1986± 1987 (Exp. 1) and 1987±1988 (Exps. 2A and 2B). The ®rst experiment followed the management practices in the area, such as the use of low densities, mechanical weed control, and when applied, furrow irrigation. The low sowing densities were also those used in the area (20 plants mÿ2) (Guerrero, 1987). In 1987±1988, plant densities were increased and distance between rows decreased, still allowing furrow irrigation (Exp. 2A). In the rainfed treatments, distance between rows was halved, but mechanical weed control was still practiced during the two months after sowing (Exp. 2B). 2.1. Climate and soil conditions Mean daily solar radiation (SR), maximum and minimum temperatures, vapour pressure de®cit

F. Sau, M. IneÂs MõÂnguez / Field Crops Research 66 (2000) 81±99

83

Table 1 Mean daily solar radiation (SR), mean daily maximum (Tmax) and minimum (Tmin) temperatures, mean daily reference evapotranspiration (ET0), vapour pressure de®cit, and cumulative rainfall measured for 10±11 days interval between December and June in 1986±1987 and 1987± 1988 growing seasons Period

December 1±10 December 11±20 December 21±31 January 1±10 January 11±20 January 21±31 February 1±10 February 11±20 February 21±28 29 March 1±10 March 11±20 March 21±31 April 1±10 April 11±20 April 21±30 May 1±10 May 11±20 May 21±31 June 1±10 June 11±20 June 21±30

1986±1987

1987±1988

SR Tmax (MJ mÿ2) (8C)

Tmin (8C)

ET0 (mm)

VPD (kPa)

Rainfall (mm)

SR Tmax (MJ mÿ2) (8C)

Tmin (8C)

ET0 (mm)

VPD (kPa)

Rainfall (mm)

8.7 7.0 9.0 9.1 8.8 7.4 9.6 11.3 12.4 15.5 16.3 16.7 14.9 23.6 21.0 27.0 25.0 24.8 30.3 29.3 27.0

4.4 4.5 0.1 1.2 0.2 7.9 5.9 5.8 5.1 8.8 7.0 6.9 9.6 8.8 11.3 11.0 11.6 11.9 14.3 13.9 19.0

2.0 1.8 1.5 1.6 1.5 1.8 1.8 1.4 2.1 2.7 1.7 1.5 1.8 2.5 4.3 5.6 6.1 6.7 7.0 6.9 8.4

0.37 0.22 0.31 0.35 0.34 0.28 0.29 0.37 0.40 0.70 0.66 0.62 0.40 0.88 1.08 1.26 1.11 1.29 1.83 1.31 2.34

14.7 16.3 0.8 14.8 65.4 46.7 42.8 25.2 24.1 0.0 0.0 11.7 64.7 0.0 0.3 0.0 1.7 3.0 0.0 0.3 0.0

5.9 5.4 8.7 8.2 5.8 7.0 9.4 12.8 14.7 15.1 17.7 20.1 16.6 20.2 21.3 16.6 22.7 26.2 23.9 21.1 21.9

8.7 12.0 5.8 4.2 7.4 8.6 4.9 5.8 3.9 3.6 5.3 6.9 7.0 12.7 9.4 12.2 11.7 13.6 15.5 14.2 16.9

2.1 2.1 2.3 2.2 1.7 2.0 2.0 2.6 2.5 2.7 3.4 3.5 2.4 3.4 4.2 4.1 4.8 5.8 6.3 6.1 5.8

0.20 0.15 0.26 0.24 0.18 0.20 0.27 0.41 0.49 0.59 0.77 0.75 0.57 0.89 0.76 0.57 0.78 1.22 1.11 0.85 0.97

95.2 134.9 8.6 10.6 56.9 32.2 4.6 10.7 0.1 0.3 1.1 9.1 31.3 3.0 11.9 16.9 20.2 0.0 4.1 6.9 17.4

16.2 14.0 13.4 14.4 11.2 16.1 16.5 15.3 16.4 24.5 20.4 19.7 18.8 25.7 26.3 28.4 25.9 29.0 32.0 30.2 36.3

(VPD), daily reference evapotranspiration (ET0) and cumulative rainfall (recorded every 10±11 days), for both growing seasons are presented in Table 1. ET0 was calculated using the method of Hargreaves and Samani (1982) as recommended by Mantovani et al. (1992) for the Guadalquivir Valley. Spring VPD was higher during the ®rst year and consequently a larger ET0 was registered. Also SR was higher during Exp. 1 from May 1 till harvest. ET0 from April 11 to June 10 in 1987 was 328 mm and in 1988, 291 mm, while rainfall was 5 and 56 mm, respectively. The soil was a Typic Xero¯uvent, deep alluvial with sandy loam texture and was at ®eld capacity in December, when the faba beans were sown. The water-holding capacity of the soil to 2.0 m depth was 150 mm mÿ1 in Exp. 1 and 178 mm mÿ1 in Exps. 2A and 2B. The upper and lower limits of available water were 0.22 and 0.07 m3 mÿ3 (Exp. 1), and 0.27 and 0.09 m3 mÿ3 (Exp. 2) and were determined by

15.5 17.1 15.6 14.3 13.0 15.0 15.0 17.3 16.2 18.5 24.1 24.5 19.1 25.4 22.6 21.9 23.7 29.4 29.2 26.1 28.3

neutron probe. Soil analyses were made before the experiments commenced and the soil was fertilised accordingly with ample amounts of P and K (65 kg P haÿ1 as superphosphate, 62 kg K haÿ1 as potassium sulphate) to remove any limitation from these two nutrients. At both sites, soil pH in water was 7.1. 2.2. Field experiments and treatments The treatments were based on the levels of water supply: irrigated (I) or rainfed (R), two types of nitrogen nutrition: N fertilised (‡N) or inoculated (ÿN), and faba bean cultivars. The inoculant was provided by the Experimental Station at La Rinconada, Seville, Spain. The cultivars (Alameda and Brocal) used in these experiments were obtained at the Legume Unit of the Agronomy and Breeding Department of the Agriculture Research Centre in CoÂrdoba and were both commercially available. They are both classi®ed as

84

F. Sau, M. IneÂs MõÂnguez / Field Crops Research 66 (2000) 81±99

Vicia faba L., intermediate types of botanical varieties major and equina (Muratova, 1931; Cubero, 1974; Lawes et al., 1983) and have indeterminate growth patterns. Experiment 1. Only one cultivar (cv. Alameda) was sown. Treatments were assigned in a split-plot factorial arrangement in a randomised complete-block design with the two water treatments representing whole plots and the two nitrogen sources as subplots. Treatments were replicated four times. Seed was hand-sown on 10 December 1986. Individual plots were 8 m long, orientated East±West and comprised eight rows 0.70 m apart. The average density reached was around 19 plants mÿ2 (see Table 2). Where applicable, plots were irrigated at 96, 110, 131, 145 and 149 days after sowing (DAS), i.e. 16 March, 30 March, 20 April, 4 and 8 May, respectively. Furrow irrigation was carried out to avoid predawn water potentials dropping below ÿ0.25/ÿ0.3 MPa. The amounts of water applied at each irrigation ranged from 30 to 60 mm and the total amount was ca. 265 mm. Previous neutron probe measurements indicated the amount of water necessary to reach ®eld capacity. Three applications of urea supplied a total of 200 kg N haÿ1 to the fertilised treatments: 100 kg at sowing and 50 kg each at the beginning and end of bloom. The (ÿN) treatments were inoculated. The irrigated and rainfed plots were harvested on 8 June (180 DAS) and 19 May (160 DAS) 1987, respectively. A sample of 8 m2 was harvested from the central rows for dry grain yield and biomass, and a subsample of 1.5 m2 was used for analysis of grain yield components. Designs were modi®ed in the second year because results from Exp. 1 suggested that plant densities had been too low and that, in rainfed conditions, mechanical weed control was carried out at high cost to radiation interception (MõÂnguez et al., 1993). Two experiments were carried out during the 1987±1988 season. Experiment 2A was a maximum yield assay (Thomson and Taylor, 1982) with all treatments furrow irrigated. The two cultivars (Alameda and Brocal) were hand-sown on 24 December 1987 at 33 plants mÿ2 (see Table 3). The experimental design was a randomised block in four replicates with cultivars and nitrogen sources as treatments. Individual plots comprised eight rows, 8 m long, and 0.60 m apart to allow for furrow irrigation and mechanical weed control and

with a North±South orientation. Plots were irrigated at 78, 95, 118, 147 and 159 DAS (11 March, 28 March, 20 April, 19 and 31 May, respectively) and followed the same criteria as in Exp. 1. Total irrigation was ca. 250 mm. In the fertilised treatments, 300 kg N haÿ1 was supplied, as urea, in three applications (100±100± 100 kg at the same times as in Exp. 1). The remainder of the plots was inoculated. Harvesting was carried out on 10 June (169 DAS), as described for Exp. 1. In Exp. 2B, the two cultivars were hand-sown on 24 December 1987 and the crops were rainfed. The experimental design was a randomised block in four replicates with cultivars and nitrogen sources as treatments as in Exp. 2A. Nitrogen and inoculation were applied as in Exp. 2A. Individual plots comprised eleven rows, 8 m long and 0.35 m apart, with a North±South orientation. Plant density was 26 plants mÿ2 (see Table 3). Harvesting was carried out on 26 May 1988 (154 DAS), as described in Exp. 1. 2.3. Dry matter partitioning and height of the canopy Dry matter contents of stems, petioles, leaves, ¯owers and pods were measured and leaf area recorded at intervals of about 15 days after collecting 0.35±0.37 m2 of plant material from each plot. A three-plant subsample was taken and separated into stems, petioles, leaves, ¯owers and pods. All the subsample components and remaining plants were dried separately to constant weight, in a convective oven at 708C for more than 48 h. Leaf area was determined with a LI-COR planimeter Model LI3000. Crop height (tip of the upper leaf of a plant) was measured four times in each plot every 5±10 days. 2.4. Water relations measurements Predawn (Cd) and midday (Cm) leaf water potentials were measured on fully expanded leaves, with a pressure chamber (Soil Moisture, Equipment Corporation, Santa Barbara, CA, USA) following the recommendations of Tyree and Hammel (1972). In 1987, leaf water potentials were estimated at 8±15 day intervals between 79 and 162 DAS (27 February and 21 May, respectively), while in 1988, the measurements were carried out between 56 and 159 DAS (18 February and 31 May, respectively). Midday leaf water potentials were always measured around solar

Treatments

Variable No. of plants mÿ2

I‡N 17.5 a IÿN 18.0 a R‡N 19.1 a RÿN 18.9 a Significance of effectsb W n.s. N n.s. WN n.s. a

(2.1) (0.7) (1.2) (0.9)

No. of pods per plant

No. of seeds per pod

Seed weight (g)

Grain yield (g mÿ2)

HI

14.6 13.1 11.4 11.8

2.2 2.3 2.2 2.3

1.22 1.22 0.88 0.87

685.4 626.4 393.6 398.5

0.59 0.62 0.58 0.58

* n.s. n.s.

a (1.1) ab (2.2) b (1.2) b (0.9)

n.s. n.s. n.s.

a a a a

(0.1) (0.1) (0.1) (0.1)

** n.s. n.s.

a (0.06) a (0.09) b (0.11) b (0.06)

*** n.s. n.s.

a (53.4) a (60.4) b (61.3) b (33.3)

n.s. n.s. n.s.

b (0.02) a (0.02) b (0.02) b (0.02)

Biomass at harvest (g mÿ2)

No. of seeds mÿ2

No. of Pods mÿ2

1168.5 a (109.2) 1007.7 a (116.0) 684.1 b (121.7) 683.8 b (77.5)

561.8 514.5 445.5 459.9

252.2. a (18.1) 223.6 ab (43.2) 203.6 b (11.1) 203.8 b (20.8)

** n.s. n.s.

* n.s. n.s.

a (57.0) ab (69.1) b (35.0) b (61.9)

n.s. n.s. n.s.

Two values followed by the same letter in the same column are not signi®catively different at 0.05 level. Each value is the mean of four replicates. *, ** and *** indicate signi®cance at 0.05, 0.01 and 0.001 levels, respectively, for water treatments (W), nitrogen source (N) and their interaction; (n.s.) indicates differences were not signi®cant at 0.05 level. b

F. Sau, M. IneÂs MõÂnguez / Field Crops Research 66 (2000) 81±99

Table 2 Averagea and standard error of mean (in brackets) of yield components, harvest index (HI) and biomass at harvest of irrigated-N fertilised (I‡N), irrigated-inoculated (IÿN), rainfed-N fertilised (R‡N) and rainfed-inoculated (RÿN) treatments in Exp. 1

85

86 Table 3 Averagea and standard error of mean (in brackets) of yield components, harvest index (HI) and biomass at harvest of irrigated-N fertilised (‡NI), irrigated- inoculated (IÿN), rainfed-N fertilised (R‡N) and rainfed-inoculated (RÿN) treatments in Exps. 2A and 2B Treatments

No. of plants mÿ2

No. of pods per plant

No. of seeds per pod

Seed weight (g)

Grain yield (g mÿ2)

HI

32.3 30.4 33.3 36.0

9.5 9.9 8.1 7.6

2.3 2.4 2.3 2.4

0.94 0.88 0.98 0.89

656.4 628.5 601.4 598.4

0.52 0.50 0.49 0.47

a a a a

(5.2) (2.5) (2.0) (2.8)

a a a a

(1.0) (1.53) (1.49) (1.6)

Significance of effectsb C n.s. N n.s. CN n.s.

n.s. n.s. n.s.

n.s. n.s. n.s.

Exp. 2B Alameda R‡N Alameda RÿN Brocal R‡N Brocal RÿN

12.9 a (2.3) 11.4 a (2.1) 11.8 a (2.6) 7.8 b (1.3)

2.2 2.1 2.2 2.4

* * n.s

n.s. n.s. n.s.

23.4 27.9 22.6 30.8

b (1.4) a (1.7) b (2.2) a (3.5)

Significance of effectsb C n.s. N ** CN n.s. a

a a a a

(0.2) (0.3) (0.2) (0.1)

a a a a

(0.04) (0.02) (0.09) (0.06)

n.s. n.s. n.s. a a a a

(0.2) (0.1) (0.1) (0.2)

1.01 0.97 1.05 1.09 n.s. n.s. n.s.

a a a a

(33.8) (113.2) (56.3) (66.6)

n.s. n.s. n.s. a a a a

(0.07) (0.06) (0.10) (0.05)

646.9 637.2 582.1 601.7 n.s. n.s. n.s.

a a a a

(0.02) (0.03) (0.02) (0.04)

n.s. n.s. n.s. a a a a

(79.7) (39.5) (49.6) (31.3)

0.63 0.61 0.61 0.57 ** ** n.s.

a (0.02) a (0.01) a (0.02) b (0.02)

Biomass at harvest (g mÿ2)

No. of seeds mÿ2

No. of pods mÿ2

1274.2 1248.0 1240.2 1289.4

700.7 719.2 615.5 671.0

305.6 300.7 268.3 274.7

a a a a

(81.9) (161.4) (104.6) (151.9)

n.s. n.s. n.s.

n.s. n.s. n.s.

1033.6 a (149.8) 1049.1 a (77.1) 960.1 a (93.3) 1061.4 a (24.7)

637.0 658.9 554.1 552.0

n.s. n.s. n.s.

* n.s. n.s.

a a a a

(61.4) (97.4) (88.2) (59.5)

a a a a

(48.4) (60.5) (42.2) (31.9)

n.s. n.s. n.s. a a a a

(60.1) (18.4) (34.8) (41.6)

294.4 322.6 257.1 233.0

ab (30.9) a (24.6) ab (31.5) b (13.2)

* n.s. n.s.

Two values followed by the same letter in the same column are not signi®catively different at 0.05 level. Each value is the mean of four replicates. *, ** and *** indicate signi®cance at 0.05, 0.01 and 0.001 levels, respectively, for cultivar (C), nitrogen source (N), and their interactions; (n.s.) indicates differences were not signi®cant at 0.05 level. b

F. Sau, M. IneÂs MõÂnguez / Field Crops Research 66 (2000) 81±99

Exp. 2A Alameda I‡N Alameda IÿN Brocal I‡N Brocal IÿN

Variable

F. Sau, M. IneÂs MõÂnguez / Field Crops Research 66 (2000) 81±99

noon on clear sunny days (12:30±13:30) on upper expanded leaves immediately following measurements of stomatal resistance (Rsm) with an automatic transient porometer (Delta-T Devices, model Mk3). Duplicate measurements of stomatal resistance and leaf water potential were taken in each plot. In addition, leaf water potential (Cl) and stomatal resistance measurements (Rs) were made throughout an entire day in all treatments on ®ve occasions: 3 days in 1987 (124, 135 and 146 DAS; 13 April, 24 April and 5 May) and 2 days in 1988 (149 and 158 DAS; 21 May and 30 May). Finally, osmotic potentials of completely rehydrated leaves were measured three times: twice in 1987 (104 and 137 DAS; 24 March and 26 April) and once in 1988 (127 DAS; 29 April). Two leaves from each individual plot were sampled before dawn and immediately rehydrated to full turgor by inserting the petioles into deionised water, cutting them below water level and maintaining the leaves in dark, humid conditions for 2 h. Leaves were then wrapped in aluminium foil and immediately frozen. Leaves were thawed in their wrappings at 258C for 1 h and then pressed with a hydraulic press (Campbell, J-14). Osmotic potential of expressed sap was measured by vapour pressure osmometry with Wescor C-52 sample chambers, used as dew point hygrometers, connected to a Wescor HR-33T dew-point microvoltimeter (Savage et al., 1983). 2.5. Soil water content and ETc Access tubes were installed in individual plots, to a depth of 180 cm. Measurements were made using a Campbell Paci®c Model 503 neutron probe at intervals of 10±20 days throughout the growing season, starting at 61 and 49 DAS (9 February and 11 February) in 1987 and 1988, respectively. Readings were taken at 30 cm intervals in the soil pro®le to a depth of 180 cm. On the same days, soil samples were taken from the upper 15 cm, weighed, oven-dried for more than 48 h at 1108C and weighed again to estimate water content. Between sowing and the ®rst neutron probe measurement, crop evapotranspiration (ETc) was calculated as described by Doorenbos and Pruitt (1977) for when evaporation dominates ETc. Because root sampling showed that the roots of the crop reached a depth of more than 1 m in all treatments (see Section 3.4),

87

water balance between two neutron probe measurements was carried out in rainfed treatments, assuming that all water removed, above a depth of 1 m, had been used by the crop. In irrigated treatments, one neutron probe measurement was made just before watering, and another 2 days later. Estimation of ETc between the two neutron probe measurements made before and after watering was made using crop coef®cients (Kc) values of 1.0 and 1.15 for before and after the crop had reached full cover, respectively. Calculation of ETc between the neutron probe measurement made 2 days after irrigation (1) and that made just before the next irrigation (2) was calculated by subtracting the water content above 1 m depth found at time (2) from time (1) and adding rainfall. 2.6. Soil sampling for root length density Root length density (RLD) in various soil layers was determined using a modi®ed Newman method (Newman, 1966), as described by Alvarez de Toro (1987). Samples were taken with a 4 cm diameter, hand-operated soil corer, during the vegetative period, at bloom and at harvest in both experiments. In Exp. 1, the ®rst samples were collected at 71 DAS (19 February) in two cores (A and B) in each individual plot. Core A was situated in the plant row close to the plants and soil samples were collected each 15 cm down the pro®le to 60 cm. Core B was situated at a distance of 17.5 cm from A, perpendicular to the row of plants. In core B, only two 15 cm layers were collected, i.e. down to 30 cm. The second set of core samples was taken at 103 DAS (23 March). Cores A and B were situated as before, while an additional core (C) was taken 35 cm from A, perpendicular to and half way between rows. At all sample sites, soil was collected at 15 cm intervals to a depth of 75 cm. The third set of core samples in Exp. 1 was taken at harvest time, and consisted of three cores (A, B and C) as at the second sampling with two extra samples each of 30 cm depth taken in each core, so that the sampling reached 135 cm depth. In Exps. 2A and 2B, soil samples were taken in a similar way at 71 DAS (4 March), 146 DAS (18 May) and at harvest. Total root length per soil surface at bloom and harvest was calculated assuming that the mean root density in each sampled soil layer was similar to the mean obtained from the A, B and C cores.

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2.7. Statistical analysis Results obtained for the various parameters were subjected to analysis of variance (SAS for Windows). A least signi®cant difference (p0.05) test method was applied, where appropriate, to determine differences among means. 3. Results 3.1. Water potential and stomatal resistance In both years, irrigated plants maintained predawn water potentials (Cd) above ÿ0.3 MPa until the beginning of senescence (Fig. 1a and b). In Exp. 1 midday water potentials (Cm) decreased throughout the crop cycle, while in Exp. 2A, they were more stable (Fig. 1a and b). Midday stomatal resistance (Rsm) in both experiments was around 100 smÿ1 until senescence (Fig. 1c and d). The onset of water de®cits in the rainfed treatments in Exp. 1, appeared at around 95 DAS (15 March); this stress increased gradually until 125 DAS (14 April), then a recovery was observed due to rainfall (Table 1). After 125 DAS there was a sharp drop in both Cd and Cm. Thelatter fell toÿ1.6(R‡N)andÿ1.7(RÿN) MPa, while in irrigated plots the values did not fall below ÿ1.2 MPa. As a result, a signi®cant increase in Rsm was measured from 125 DAS. Within 10 days, Rsm increased from around 100 smÿ1 to above 400 smÿ1 (Fig. 1c). In Exp. 2B (rainfed), Cd and Cm decreased steadily from 85 DAS (18 March) but did not fall below the lowest values observed in Exp. 1. This was re¯ected in the changes in Rsm and the values reached were lower than in Exp. 1 (Fig. 1c and d). In all experiments, for the same level of water supply, there were no signi®cant differences between ‡N and ÿN treatments for Cd, Cm and Rsm. Changes in Cl and Rs were measured throughout two entire days in Exp. 1 and it was found that Rs increased sharply with both nitrogen treatments, when Cl dropped below ÿ1.2 MPa (135 DAS, 24 April) and ÿ1.5 MPa (146 DAS, 5 May). At 146 DAS, the response curve (Rs vs. Cl) was more scattered because some leaves of ‡N plants maintained relatively open stomata at very low Cl (ÿ2.2 MPa). Similar results were obtained in Exp. 2B.

Osmotic potentials of completely rehydrated leaves were similar in all treatments and at each sampling time. In Exp. 1 the average and standard error of mean (S.E.) of osmotic potentials measured were ÿ0.71 (S.E.ˆ0.065) and ÿ0.85 (S.E.ˆ0.085) MPa at 104 DAS (24 March) and 137 DAS (26 April), respectively. In Exps. 2A and 2B, the average was ÿ0.99 (S.E.ˆ0.135) MPa (127 DAS; 29 April). No signi®cant differences were found in osmotic potential due to water, nitrogen source or cultivar. 3.2. Crop height, dry matter production and water use Main-stem elongation rates were calculated and paired with corresponding average values of Cd. In all treatments and experiments, the elongation rate decreased signi®cantly when predawn water potentials fell below ÿ0.25 MPa. Total biomass at harvest, grain yield and harvest index (HI) were plotted against maximum crop height (Fig. 2). For these indeterminate cultivars and environmental conditions, yield stabilised and HI decreased when crop height exceeded 1.20 m. Progressive aboveground biomass production is plotted against accumulated evapotranspiration (ETc) in Fig. 3a for all experiments. Differences in ETc between irrigated and rainfed treatments in Exp. 1 were larger than the differences between Exps. 2A and 2B. Most of the water-use ef®ciencies, measured as aboveground biomass/ETc (WUEb), were greater in Exps. 2A and 2B than in Exp. 1 (Fig. 3a). For the same amount of water applied, WUEb tended to be greater in ‡N than in ÿN treatments (Fig. 3a). When biomass was plotted against ETc/VPD, no differences were found between experiments or growing season and a linear regression with high r2 (ca. 0.92) was obtained (Fig. 3b). ETc, WUEb and water-use ef®ciency related to grain yield (WUEy) from emergence to harvest are shown in Table 4. Evapotranspiration of rainfed treatments was similar in both years (ca. 350 mm) while in irrigated treatments ETc was slightly greater in Exp. 1 (ca. 585 mm) than in Exp. 2A (ca. 530 mm). Nitrogen supply did not affect WUEb and WUEy in any of the experiments. In Exp. 1, WUEb and WUEy were not affected by water supply. WUEb tended to be greater in Exp. 2B (rainfed and low density) than in Exp. 2A

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Fig. 1. Changes in predawn (& , &) and midday (*, *) water potential during Exp. 1 (a), Exps. 2A and 2B (b), and changes in midday stomatal resistances (D, ~) during Exp. 1 (c), Exps. 2A and 2B (d). Open and solid symbols correspond to irrigated and rainfed treatments respectively. Each point is the mean of 8 and 16 replicates in Exp.1 and Exps. 2A and 2B, respectively.

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Fig. 2. Grain yield (& , &), biomass at harvest (D, ~) (a) and harvest index (*, *) (b) vs. maximum crop height of Exps. 1, 2A and 2B. Open and solid symbols correspond to the means of four replicates of irrigated and rainfed treatments, respectively.

(irrigated and high density) and WUEy in Exp. 2B was around 50% greater than in Exp. 2A. 3.3. Yield and yield components Yield components, yields and HI from Exps. 1, 2A and 2B are presented in Tables 2 and 3. In Exp. 1, the average grain yield for irrigated treatments was 66% greater than for rainfed. Seed weight and number of

seeds per ground area were signi®cantly reduced by water de®cit. No differences in yield were found between Exps. 2A and 2B. In Exp. 2A a smaller seed weight was compensated by more seeds per ground area. While the irrigated treatments of Exp. 1 had similar yields to those in Exp. 2A, for rainfed treatments, yields were approximately 55% greater in Exp. 2B than in Exp. 1.

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Fig. 3. Biomass production vs. accumulated crop evapotanspiration (ETc) (a) and ETc/vapour pressure de®cit (VPD) (b) in Exps.1, 2A and 2B. Nitrogen fertilised treatments (*, *) for Exp. 1 and ( , ) for Exps. 2A and 2B. Inoculated treatments (D, D) for Exp. 1 and (r, !) for Exps. 2A and 2B, respectively. Open symbols correspond to irrigated treatments and solid to rainfed ones. Each point represents the mean of four replicates in Exp. 1 and of eight replicates in Exps. 2A and 2B.

3.4. Root length densities Root length densities (RLD) at 71 DAS (19 February), 103 DAS (23 March) and at harvest are shown in Fig. 4a, b and c, respectively, for both water and nitrogen treatments in Exp. 1. During the vegetative

period (Fig. 4a), at bloom (Fig. 4b), and at harvest time (Fig. 4c), root depth reached 45, 75 and 105 cm, respectively. No signi®cant differences were found in RLD among treatments. Root length was 5.6 km mÿ2 at bloom and 7.8 at harvest. Nevertheless, the rainfed ÿN treatment had a greater RLD at bloom

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Table 4 Averagea and standard error of mean (in brackets) of crop evapotranspiration (ETc), water-use ef®ciency related to biomass (WUEb) and to grain yield (WUEy) of irrigated-N fertilised (I‡N), irrigated-inoculated (IÿN), rainfed-N fertilised (R‡N) and rainfed-inoculated (RÿN) treatments in Exps. 1, 2A and 2B Treatments

ETc (mm)

WUEb (kg (biomass) haÿ1 mmÿ1)

WUEy (kg (grain) haÿ1 mmÿ1)

Exp. 1 I‡N IÿN R‡R RÿN

588.4 578.6 358.7 347.3

19.8 17.5 19.0 19.7

11.6 10.9 10.9 11.5

Significance of effectsb W N WN

*** n.s. n.s.

n.s. n.s. n.s.

n.s. n.s. n.s.

Exp. 2A I‡N IÿN

527.9 a (47.1) 529.0 a (39.6)

24.0 a (2.4) 24.1 a (3.5)

12.0 a (1.5) 11.6 a (1.7)

Significance of effectsb N

n.s.

n.s.

n.s.

Exp. 2B R‡N RÿN

340.9 a (16.0) 354.3 a (13.5)

29.3 a (3.4) 29.8 a (1.3)

18.0 a (1.9) 17.5 a (1.2)

Significance of effectsb N

n.s.

n.s.

n.s.

a (28.7) a (40.8) b (15.3) b (12.1)

a a a a

(1.3) (2.4) (2.7) (2.3)

a a a a

(0.5) (1.3) (1.3) (1.0)

a

Two values followed by the same letter in the same column are not signi®catively different at 0.05 level. Each value is the mean of four replicates. b *, ** and *** indicate signi®cance at 0.05, 0.01 and 0.001 levels, respectively, for cultivar (C), nitrogen source (N) and their interaction; (n.s.) indicates differences were not signi®cant at 0.05 level.

and harvest in the ®rst 15 cm, than the rainfed ‡N treatment (Fig. 4b and c). Although spatial plant distribution was different, similar results were obtained in Exps. 2A and 2B, because water de®cit did not affect RLD distribution. No differences in RLD were found in the upper soil layer (0±15 cm) between ‡N and ÿN treatments of Exp. 2B (results not shown; Sau, 1989). 4. Discussion Differences in the weather in spring, 1987 (high radiation and VPD, low rainfall) and 1988 (lower radiation and VPD, higher rainfall) (Table 1), is one example of interannual variability found in the Mediterranean basin where this study was carried out. Available soil water content at sowing was near soil capacity (0.15 and 0.18 m3 mÿ3) and evaporative

demand was low during most of the winter (Table 1) so that water did not limit crop growth during most of the vegetative development. On the other hand, temperatures were mild (Table 1) and by the end of March, 2400 and 3700 kg haÿ1 of above ground biomass were obtained in Exp. 1 (low density) and Exp. 2B, respectively (Sau, 1989). The threshold temperature for growth in faba bean is considered to be 08C, which means that this crop can increase its biomass during winter if water is available (Siddique et al., 1993; Leport et al., 1998). This may lead to grain yield similar to that of the rainfed yields of Exp. 1 (3900 kg haÿ1) if pests and diseases are controlled (Table 2). Large increases in yield can be obtained when spring is wet and plant density is increased up to 25 plants mÿ2 as in Exp. 2B (6000 kg haÿ1) (Table 3). In other Spanish areas, such as the Central Plateau, mean winter temperature is approximately 48C lower and crop growth almost ceases from December until

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93

Fig. 4. Root-length density distribution during the vegetative period (a), at bloom (b) and at harvest (c) of cv. Alameda, in various soil layers and at various distances from the plant row. In Exp. 1, core A: on the row line (*); core B: 17.5 cm from the row (&); core C: 35.5 cm from the row ( ). Treatments: I‡N: irrigated and N fertilised; IÿN: irrigated and inoculated; R‡N: rainfed and N fertilised; RÿN: rainfed and inoculated.

mid-February. Early sowing (at the beginning of November) in these areas allows these faba bean cvs. to reach equivalent standing biomass at the end of winter (de Oliveira, 1995; Ridao et al., 1996) for experiments with 25 plants mÿ2 plant density.

In Exp. 2B a slight water stress developed in spring because small rainfalls were evenly distributed. ET0 was smaller and the soil water reserve was larger than in Exp. 1. Faba beans were able to maintain high mobilisation rates during the pod-®lling period as

94

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Fig. 4 (Continued ).

shown by HI and seed weight at harvest (Tables 2 and 3). HI and seed weight of cv. Alameda in the rainfed treatments of Exp. 1 (0.58 and 0.88 g per seed) were smaller than those in Exp. 2B (0.62 and 0.99 g per seed). The drier spring, higher ET0 and lower water holding capacity of the soil in Exp. 1 rapidly exhausted the water reserve, so that water stress

developed faster. After the last rainfall in April, predawn and midday water potentials dropped sharply, stomatal resistance increased (Fig. 1c) and crop height growth almost stopped at 0.85±0.90 m (Fig. 2) corresponding to 129 DAS (ca. 20 April). A relation between decrease in stomatal conductance and reduction in the photosynthesis rate

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95

Fig. 4 (Continued ).

in leaves has been reported for faba beans by Leport et al. (1998). The higher leaf resistances registered from mid-April in the rainfed plots in Exp. 1, compared to those of Exp. 2B, may have added to the effect of low density in biomass production (Fig. 1c and d). The smaller water de®cit during Exp. 2B had a slight effect on phenological development when compared with the more severe drought that occurred in the spring of 1987 (Exp. 1). In Exp. 1, harvest maturity was reached 20 days earlier in the rainfed (160 DAS; 19 May) than in the irrigated treatments (180 DAS; 8 June), while in Exp. 2B, harvest maturity was reached at 154 DAS (26 May) and 15 days later (10 June) in Exp. 2A. This re¯ects the higher stomatal resistances in the rainfed treatments in Exp. 1 that would have caused faster thermal time accumulation at higher leaf temperature (Turner, 1986). Under controlled conditions, vegetative faba beans, grown under two nitrogen nutrition regimes Ð nitrate fed (‡N) and nitrogen ®xation (ÿN) Ð were shown to adopt water conservation mechanisms that delayed dehydration without signi®cant osmotic adjustment (Sau and MõÂnguez, 1990). In these ®eld experiments,

‡N treatments were signi®cantly less nodulated than ÿN plants (Sau, 1989) suggesting a certain amount of N2 ®xation in ‡N treatments. In Exp. 1, a decrease of 0.15 MPa in osmotic potential was detected between the two sampling dates. Osmotic potential was intermediate between those measured in the growth cabinet (Sau and MõÂnguez, 1990) and those reported by Leport et al. (1998) in the ®eld. Although the osmotic adjustment of 0.1 MPa, measured as the difference between osmotic potential of leaves at full turgor from irrigated and rainfed treatments, was similar to that found by Leport et al. (1998), the differences found here were not signi®cant. Water conservation mechanisms were mainly based on stomatal closure at relatively high leaf water potential. In Exp. 1, a marked increase in stomatal resistance was observed when Cl dropped below ÿ1.1 MPa (135 DAS, 24 April) and ÿ1.4 MPa (146 DAS, 5 May). If the trend of decreasing osmotic potential was maintained beyond 137 DAS, it could explain part of the difference in the threshold leaf water potential for stomatal closure measured between 135 and 145 DAS. The threshold values were always smaller than those observed by Sau and MõÂnguez

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(1990), ÿ0.9 MPa, and similar to those reported by Leport et al. (1998). Water-use ef®ciency related to biomass at harvest (WUEb) was higher in Exps. 2A and 2B (all above 24.0 kg haÿ1 mmÿ1) than in Exp. 1 (all below 19.8 kg haÿ1 mmÿ1) (Table 4). The lower WUEb observed in irrigated ÿN treatments in Exps. 1 and 2A compared to the remaining treatments may be due to a greater dry matter partition to roots and nodules (Fig. 3a). When biomass was plotted against ETc/VPD these differences disappeared showing that faba bean behaved in a similar way when subjected to different evaporative conditions (Fig. 3b). VPD may have accounted for the differences in WUEb through changes in the ratio of ®xed CO2/transpiration over the two years (Fisher and Turner, 1978; Richards, 1991; Condon et al., 1992). While WUE related to grain yield (WUEy) was similar for irrigated treatments in Exps. 1 and 2A (ca. 11 kg haÿ1 mmÿ1), large differences between the rainfed treatments were observed (Table 4). In Exp. 2B, WUEy exceeded 17.5 kg haÿ1 mmÿ1 while in Exp. 1 WUEy was always below 11.5 kg haÿ1 mmÿ1. The differences found between the two growing seasons explained as previously for biomass vs. ETc/VPD, and also to a higher assimilate mobilisation, which is re¯ected in the larger HI of the rainfed treatments in Exp. 2B, (except similar HI in cv. Brocal rainfed ÿN) (Tables 2 and 3). In both experiments and for all the treatments, most WUEy values were higher than those obtained in Mediterranean-type environments by Silim and Saxena (1993) in Syria and Loss et al. (1997) in Australia, possibly due to higher VPD in those regions. In this study, crop height was used as an indirect measure of vegetative growth. A large amount of biomass may be produced by using irrigation and high plant density (e.g. Exp. 2A). It could then be used by farmers as an indicator of excess vegetative growth and as a criteria for selecting frequency and level of irrigation. In Exp. 2A maximum crop height was over 1.60 m (Fig. 2) and plants had to be staked to avoid lodging. Management of indeterminate cvs. should aim at a maximum crop height of 1.20 m, as above this height there was no increase in yield and there was risk of lodging. The study of yield components and their use in agronomy and crop modelling have been considered by Egli (1998). Following his approach this study

focused on two yield components. The ®rst was seed number mÿ2, related to plant density and the duration of the period when the number of these sinks is determined. The second, seed weight, which is related to the duration of grain ®lling and seed growth rate (Egli, 1998). These yield components summarised and integrated the compensation effects of the other yield components (Tables 2 and 3). In Exp. 1, the yield from irrigated treatments was ca. 65% greater than in rainfed. This difference was contributed to by seed weight (ca. 40%) and seed number mÿ2 (ca. 20%) (Table 2). Water stress may have shortened the period of sink determination because the number of nodes per stem with pods was smaller in rainfed treatments, but the difference was not signi®cant (results not shown; Sau, 1989). The low maximum LAI (LAImax ca. 3.5) in the rainfed plots was always below critical LAI (i.e. when 95% photosynthetic active radiation is intercepted: LAIc ca. 5.0; MõÂnguez et al., 1993) and limited assimilation adding to the effect of water de®cit. This implied that seed size was the main yield component to be affected by water de®cit. The slight water stress developed during Exp. 2B affected canopy development (average LAImax ca. 5.0ˆLAIc), but yields (6170 kg haÿ1) were not signi®cantly different from the irrigated treatments in Exp. 2A (average LAImax ca. 8 and 6212 kg haÿ1) (Table 3). No signi®cant differences were found in either seed weight or seed number mÿ2. Irrigated highdensity treatments had more seeds mÿ2 and smaller seeds, although differences were not signi®cant. Less mobilisation in Exp. 2A was inferred from the smaller HI and also the higher ratio of biomass of {(stems‡ petioles) at harvest}/{max (stems‡petioles)}. This ratio was 0.66 (S.E.ˆ0.15) in Exp. 2A and 0.54 (S.E.ˆ0.11) in Exp. 2B, similar to those in Exp. 1: (0.53; S.E.ˆ0.10) irrigated and (0.54; S.E.ˆ0.12) rainfed treatments. When treatments were pooled it was found that this ratio differed signi®cantly in Exp. 2A from the other treatments. Lea¯ets were not included in this ratio because most had fallen to the ground at harvest. The vegetative development of the indeterminate faba beans (LAImax ca. 8.0) may have impeded ef®cient mobilisation to seeds (MõÂnguez et al., 1993). In Exp. 2A, grain yield was attained through many small seeds mÿ2. The same yields were obtained in

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irrigated treatments of Exp. 1 with fewer larger seeds. This may indicate that yield was sink limited in Exp. 1, and source limited in Exp. 2A, by low radiation during grain ®lling (Table 1) and possibly by high maintenance respiration (McCree, 1970). High radiation during May 1988 should have increased seed weight and therefore yield. Nevertheless the management practices used in Exp. 2A (33 plants mÿ2 and irrigation for maximum ETc) is not recommended for farmers because of the associated lodging problems. The greater yields in Exp. 2B as compared to the rainfed treatments of Exp. 1 re¯ected the denser crops and the milder water stress that developed during spring, that may have stimulated assimilate mobilisation to reproductive sinks. French and Turner (1991) and Grashoff (1990a,b) have shown (in lupins and in faba bean in Central Europe, respectively) that mild water de®cit changes assimilate partitioning in favour of reproductive growth. On the other hand, development rates were faster so that pod ®lling began earlier with lower evaporative demand and higher WUE. Studies carried out under rainfed conditions in contrasting environments such as England, Germany and northern Syria have shown that indeterminate cultivars yielded more than determinate cvs. In England, crops were autumn-sown to reach a density of 40 plants mÿ2 and it was found that determinacy did not increase HI, and yields were smaller Ð the maximum yield reported for the indeterminate cv. Bourbon being 6900 kg haÿ1 (Pilbeam et al., 1990). In Syria, seeding at 44 plants mÿ2 as opposed to the recommended 22 plants mÿ2 gave a non-signi®cant reduction in yield for the indeterminate cvs. but yields increased signi®cantly in the determinate types (Silim and Saxena, 1992). In Germany, spring sowings of indeterminate cvs., at densities of 18.5 and 74 plants mÿ2 yielded 4000 and 6930 kg haÿ1, respectively (StuÈtzel and Aufhammer, 1992). In this study, neutron probe measurements and RLD evaluation showed that both cultivars were able to extract water to a depth of 1 m (Fig. 4). The Spanish cultivars seemed to develop deeper root system than other faba bean cvs. described in the literature, such as ICARDA cvs. (Manschadi et al., 1998a) or European cvs. (MuÈller et al., 1985). Total root length was longer than the maximum reported by Manschadi et al. (1998a) (2.7 km mÿ2) and also by some other authors (MuÈller et al., 1985; Husain et al., 1990). These

97

differences may have been partly due to the methodology used to measure root length. On the other hand, the higher RLD detected at bloom and at harvest in the ®rst soil layer in the rainfed ÿN treatment in Exp. 1 (Fig. 4b and c), compared to all the other treatments, may be an advantage for extracting water when there is a late spring rainfall. The large water de®cit registered during spring 1987 seemed to have stimulated root development in the upper 15 cm of the soil pro®le. At other sampling dates, no differences were found in RLD between rainfed and irrigated treatments. As above ground biomass was greater in irrigated treatments, the ratio root/shoot was higher under rainfed conditions, in contrast to the ®ndings of Manschadi et al. (1998a). Previous experiments in a growth cabinet had shown that an increase in root/ shoot was a response to water stress in faba bean (Sau and MõÂnguez, 1990). The relative increase in root growth under rainfed conditions succeeded in stabilising yield when stress was mild, as in Exp. 2B. 5. Conclusions In the southern regions of Spain, management of faba bean and other winter crops already allows phenology to match the water supply. Early accumulation of dry matter (during winter), has been shown to be positively correlated to grain legume yield under rainfed conditions (Siddique et al., 1993; Leport et al., 1998). In spite of late autumn sowing, early accumulation of biomass was possible because of the mild winter temperature. Mobilisation, estimated by the decrease in the biomass of petioles‡stems and also by HI, was similar under the different experimental conditions: (Exp. 1, rainfed, 20 plants mÿ2; Exp. 2B, rainfed, 25 plants mÿ2 and Exp. 1, irrigated, 20 plants mÿ2). When water availability and plant density were high (33 plants mÿ2), as in Exp. 2A, greater biomass production was not associated with higher yield, due to low mobilisation (re¯ected by a decrease in HI). Crop yields were not affected by the nitrogen source. The different water de®cit patterns developed during the course of the experiments, as the different densities examined indicate that for minimum management input under rainfed conditions, indeterminate cvs. are appropriate and that the minimum density at which plants should be seeded is 25 plants mÿ2.

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