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Agronomy Journal 92:200-205 (2000)
© 2000 American Society of Agronomy

FORAGES

Growth and Yield of White Lupin Under Mediterranean Conditions

Effect of Plant Density

Luis López-Bellidoa, Mariano Fuentesa and Juan E. Castilloa

a Dep. de Ciencias y Recursos Agrícolas y Forestales, Univ. de Córdoba, P.O. Box 3048, Córdoba, Spain

cr1lobel{at}uco.es


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 Materials and methods
 Results and discussion
 REFERENCES
 
In a species with a well-defined growth pattern such as lupin, changes in plant density alter the structure and size of the canopy and affect grain yield components. A 4-yr study of autumn-sown white lupin (Lupinus albus L.) was conducted under rainfed Mediterranean conditions in southern Spain to determine the influence of plant density on biomass and grain yield. Three plant densities (20, 40, and 60 plants m-2) were tested in a randomized complete block design with four replications. Between-year variation in rainfall during the growing season had more marked effects on growth indices than on grain yield. Dry matter accumulation, leaf area index, and leaf area duration were directly related to plant density; however, leaf senescence was higher with increased density. While grain yield exhibited no significant differences among the densities studied, the harvest index decreased with increasing plant density. With increasing plant density, the number of pods per plant decreased, whereas number of seeds per pod and mean seed mass remained unaltered. Path coefficient analysis showed that pods per plant and per unit area had most important direct and indirect effects on grain yield. The high plasticity of the canopy structure offset changes in grain yield components of lupin which resulted from differences in plant density and led to a constant grain yield. This feature can be turned to advantage under the extremely variable conditions of the Mediterranean climate.

Abbreviations: DM, dry matter • HI, harvest index • LAD, leaf area duration • LAI, leaf area index


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
Materials and methods
 Results and discussion
 REFERENCES
 
THE EFFECTS OF INTRASPECIFIC plant-to-plant competition in plants on biomass and production, as well as on the organs that govern crop profitability, have been demonstrated previously (Clements et al., 1929). Models that relate yield and plant density have also been available (Bleasdale and Nelder, 1960; Willey and Heath, 1969). Lupin has an indeterminate growth pattern, and so competition among plants results in changes in the lateral branching structure. A number of authors have examined the influence of plant density on growth and grain yield in L. angustifolius L. (French et al., 1994; Herbert and Hill, 1978; Palta and Ludwig, 1998; Withers, 1975) and L. albus L. under temperate climatic conditions (Duthion et al., 1994; Herbert, 1977b; Huyghe, 1991; Shield et al., 1996). The effects of plant density on autumn-sown white lupin have been studied to a much lesser extent, particularly under Mediterranean conditions.

Increasing plant density in lupin decreases both branching and accumulation of dry matter (DM) per plant. Increasing plant density also leads to increasing dry weight per unit area, although this is dependent on species, density, and environmental conditions (Herbert, 1977b; Withers, 1975). Leaf area index (LAI) and leaf area duration (LAD) also tend to increase with increased plant density, but leaves senescence more rapidly after flowering compared with low plant densities (Barradas and Pinto, 1994; Fuentes, 1985; Herbert, 1977a).

Generally, the literature on lupin supports the assumption that plant density has a more marked effect on DM accumulation than on grain yield. Lupin crops are highly plastic morphologically; the plant structure adapts itself to the growing conditions and alters its size and canopy structure according to environment, season, and plant density (Greenwood et al., 1975; Herbert, 1979; Huyghe, 1993). For this reason, the relationships among grain yield, yield components, and plant density have traditionally been controversial subjects in agronomic studies (Duthion et al., 1994; Withers, 1975). According to Herbert (1977a, 1977b), Postiglione (1983), and Shield et al. (1996), increasing the seeding rate in L. albus and L. angustifolius increases grain yield. By contrast, Plancquaert (1982) ascribed the absence of an effect of plant density on grain yield to the number of pods per unit area obtained at high densities being offset by the increased number of pods per plant at low densities. Other authors have confirmed that increasing the seed rate results in high plant mortality in dense populations, an effect that also tends to equalize yields (Pate et al., 1985; Withers et al., 1974). According to Fuentes (1985), the variable influence of plant density on grain yield arises from environmental conditions; thus, a high seed rate is the most suitable choice under growth-restricting conditions (e.g., late sowing) and the opposite holds true under favorable conditions. As a result, the optimum plant density for different lupin crop species can easily range from 20 to 120 plants m-2.

In lupin, number of lateral branches and pods per plant are grain yield components most markedly affected by changes in plant density; in fact, both decrease with increasing number of plants per unit area (Herbert, 1977a; Palta and Ludwig, 1998; Withers, 1984). According to Herbert (1977b), the number of pods per plant markedly influences yield formation and has the highest positive correlation with yield. On the other hand, the number of seeds per pod and mean seed mass are scarcely influenced by plant density. However, there may be differences in the latter two components between the main stem and lateral branches; low densities result in more balanced values in both, among different branching orders (Herbert, 1977b; Withers, 1984).

Our objective was to relate trends for yield components with plant density to growth and yield in white lupin (L. albus L.) sown in autumn at different plant densities under rainfed Mediterranean conditions.


   Materials and methods
TOP
 ABSTRACT
 INTRODUCTION
 Materials and methods
Results and discussion
 REFERENCES
 
Field experiments were conducted over a period of 4 yr (1987–1988, 1989–1990, 1990–1991, and 1991–1992) in Córdoba, southern Spain (37°51' N), on a loamy-clay Haploxeralt soil with pH of 6.2 to 6.8, CaCO3 of 0 to 8 g kg-1, available P of 3.5 to 5 mg kg-1, and available K of 166–207 mg kg-1.

Each year, sweet white lupin (cv. Multolupa) was sown at three plant densities (20, 40, and 60 plants m-2). The sowing dates were 6 Oct. 1987, 2 Nov. 1989, 20 Nov. 1990, and 12 Nov. 1991. The experiment was a randomized complete block with four replications. Each plot contained four 15-m rows, with an interrow spacing of 60 cm. Sowing was done by hand, using twice as many seeds as needed at each plant density to ensure the desired stand. The actual average number of plants at harvest in each treatment was 20.3, 38.2, and 54.6 plants m-2, respectively (Table 1) .


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  		Table 1 Average actual plant density at harvest for grain lupin in a 4-yr experiment at Córdoba, Spain

 
Phenological growth stages were estimated (Fig. 1) . The growth stages identified, following López-Bellido and Fuentes (1990), were emergence (V0); first flower on the main stem (R1); full flowering in the main order of branches, equivalent to the first flower on the second order of branches (R3); end of flowering and beginning of pod filling (R4); and harvest maturity (R8).



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  		Fig. 1 Phenological growth stages in grain lupin (L. albus L.) at Córdoba, Spain, according to years. S, sowing; R1, first flower main stem; R4, last flower and beginning of pod filling; R8, harvest maturity. Arrows indicate plant sampling dates

 
Plants were sampled from 0.5-m lengths of row throughout the growth period, starting when plants had 10 leaves (V10) (Fig. 1). Samples were taken from each of the two central rows in each plot. Total DM was determined by drying the plants at 80°C to constant weight and DM accumulation was calculated. Leaf areas were measured on a LI-3000 portable electronic area meter (Li-Cor, Lincoln, NE), and the LAI was calculated. Leaf area duration was determined by considering the LAI values from all the samplings and the time elapsed between them, according to Evans (1972). Grain yield was determined over an 8-m length of the two central rows in each plot. At harvest, the plant density in the central rows were verified and identified in advance and six plants were taken at random from each main plot to determine the yield percentage of the main stem and yield components (pods m-2, pods plant-1, seeds pod-1, and mean seed mass).

The data were subjected to analysis of variance (ANOVA) using a randomized complete block design combined over years, according to McIntosh (1983). Difference between means was determined with an LSD test. A linear correlation analysis was applied pairwise to all the parameters studied. Yield and yield components were also subjected to path coefficient analysis (Li, 1955). According to Fraser and Eaton (1983), path coefficient analysis allows one to examine the complex relationships between yield and yield components in greater detail and depth on the basis of cause and effect; both direct and indirect (the component influences yield and yield components through others) effects were assessed.


   Results and discussion
TOP
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
REFERENCES
 
Weather Conditions
The weather conditions for the period over which the study was conducted are summarized in Fig. 2 . As is typical of the Mediterranean climate, quantity and distribution of rainfall were highly variable throughout the growth period. The 1987–1988 and 1989–1990 periods had the highest rainfall (689 and 686 mm, respectively, and both above the 584 mm average for the area). On the other hand, the 1990–1991 and 1991–1992 periods had below-average rainfall (511 and 516 mm, respectively). Temperature was not limiting for lupin growth; the values recorded over the active growth period (from initiation of flowering to pod filling, between March and May) were especially favorable in the 1987–1988 period. Differences in actual plant density between years were significant (Table 1). Higher plant density values were observed for the earlier sowing dates. Higher plant losses were observed for the higher plant densities, in agreement with results of Pate et al. (1985).



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  		Fig. 2 Monthly average temperature and precipitation at Córdoba, Spain (1987–1992)

 
The influence of the weather on growth indices and grain yield varied markedly between years (Table 2) . Thus, in 1987–1988 and 1989–1990, growth indices and grain yield were much higher than in the other years and very similar to each other (Tables 3 and 4) , with average total DM 1810 g m-2, LAI 6, LAD 550 d, and grain yield 3480 kg ha-1. On the other hand, the 1990–1991 and 1991–1992 periods provided poor conditions for lupin growth (Tables 3 and 4) and both gave similar values, with average total DM 570 g m-2, LAI 3, LAD 195 d, and grain yield 1530 kg ha-1. A comparison between both groups of values reveals that climate differences between years had a less marked effect on grain yield (roughly twice as high in the first 2 yr) than on total DM (three times higher for the same period). The harvest index (HI) values obtained (average of 20 and 40% for the first and second period, respectively) are consistent with this differential effect of the climate on lupin growth and confirm the ability of lupin to adapt itself to Mediterranean conditions, as well as a low efficiency in yield development under favorable growth conditions as previously shown by Fuentes (1985).


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  		Table 2 Mean squares of ANOVA for lupin growth indices, grain yield, and yield components as affected by plant density in a 4-yr experiment at Córdoba, Spain.{dagger}

 

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  		Table 3 Lupin growth indices as affected by plant density in a 4-yr experiment at Córdoba, Spain

 

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  		Table 4 Lupin grain yield and yield components as affected by plant density in a 4-yr experiment at Córdoba, Spain

 
Growth Analysis
Dry matter accumulation per unit area increased with increasing plant density; however, the differences between the results obtained with 60 and 40 plants m-2 were not always significant (Fig. 3) , nor were those in total DM (Table 3). These results are in partial agreement with those of Herbert (1977a) for L. albus and those of Withers (1975) for L. angustifolius, both sown in spring, and contradict those reported by Fuentes (1985), who found no differences for DM among plant densities under Mediterranean conditions. Withers (1984) ascribed a differential response to the environmental conditions during the growing season (when favorable, such conditions lower the plant density required to ensure optimal results).



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  		Fig. 3 Accumulation of total dry matter in grain lupin (L. albus L.) at Córdoba, Spain, according to years and plant density. Vertical bars indicate LSD (0.05)

 
Leaf area index followed the same trend as DM accumulation; LAI increased with increasing plant density, but the 60 and 40 plants m-2 densities were not always significantly different (Fig. 4) . Also, the maximum LAI increased with increasing plant density, but significantly only in 2 of 4 yr (Table 3). The highest LAI values were obtained at the end of flowering (mid-May), after which leaf senescence occurred due to high temperatures and soil water deficits. Leaf senescence was greater at the two higher plant densities than at the lowest (Fig. 4), consistent with the results of Barradas and Pinto (1994), Fuentes (1985), and Herbert (1977a). In any case, LAD always increased with increasing plant density, but no significant differences were observed between 40 and 60 plants m-2 for the 4 yr on average (Table 3). The LAD values obtained in all experiments were markedly higher than those reported by Greenwood et al. (1975), and Herbert and Hill (1978) for L. angustifolius, and by Herbert (1977b) and Vavilov and Gautalina (1982) for L. albus; however, they are consistent with the values obtained by Fuentes (1985) under Mediterranean conditions (Table 3). According to Barradas and Pinto (1994), obtaining increased leaf areas and optimizing growth under Mediterranean conditions entails exploiting the relationship between the indeterminate growth pattern of lupin and plant density.



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  		Fig. 4 Evolution of the leaf area index (LAI) in grain lupin (L. albus L.) at Córdoba, Spain, according to years and plant density. Vertical bars indicate LSD (0.05)

 
Yield and Yield Components
Grain yield did not reflect the response of DM accumulation, LAI, and LAD to plant density. Grain yield did not respond to increased plant density in 3 of 4 yr (Table 4). Similar results were reported for white lupin by Plancquaert (1982) and by Withers et al. (1974). In other studies, Duthion et al. (1994), Postiglione (1983), and Shield et al. (1996) found grain yield in L. albus to increase with increasing plant density. Pate et al. (1985) and Withers et al. (1974) claim that increasing the seeding rate results in high plant mortality; this, however, was not the case with our experiments, where differences in plant densities were maintained through harvest. The absence of a significant plant density effect on grain yield is more likely to be due to the high plasticity of the lupin plant, which adapts its structure to the growing conditions, offsetting the effects of plant density (Greenwood et al., 1975; Herbert, 1979). This is a desirable feature under Mediterranean conditions, as it promotes yield stability. According to Fuentes (1985), the lack of influence of plant density on lupin grain yield must be ascribed to differences in the environmental conditions during the growing season: when such conditions are favorable, plants tend to branch more extensively, so the optimal density is reached with a smaller number of plants; the opposite is true under restrictive conditions.

Increasing plant density had an adverse effect on HI; it was lower at the two higher densities in 2 of 4 yr and markedly different from the lowest density (Table 3). This contradicts the results of Herbert (1977b) for white lupin, where HI did not change with plant density. The limited water resources available in spring under Mediterranean conditions, unlike temperate climates, result in optimal grain yields at low plant densities despite the more favorable values of the growth indices at the higher densities. Lupin is not adapted for grain production under high plant densities.

The significance of the role of the main stem in yield increased with increasing plant density (Table 4), which is consistent with the results of Herbert (1977b) for white lupin. The differences arise from increased development of the canopy at the lower densities, which favor branching and hence increase their contribution to final yield (Huyghe, 1991).

Number of pods per plant was the most sensitive and variable yield component; it decreased markedly with increase in plant density (Table 4). This inverse relationship was previously observed in L. albus by Fuentes (1985) and Herbert (1977a), and is the result of decreased lateral branching at increased plant densities.

Number of seeds per pod also decreased with increasing plant density, but not significantly for the 4 yr as a whole (Table 4); its influence on yield was less marked than that of number of pods per plant. This is consistent with the results of Herbert (1977a), but contradicts those of Fuentes (1985), and Laconde (1984), who found number of seeds per pod to be insensitive to plant density.

Mean seed mass varied little with plant density (Table 4). Pate et al. (1985) and Withers (1984) ascribed changes in 1000-grain weight to the branching order and claimed that low densities result in a more balanced grain weight among branching orders.

Table 5 shows that plant density was not significantly correlated with grain yield; however, it was positively correlated with the growth indices studied (total DM, maximum LAI and LAD) and negatively with HI. According to Withers (1984), the grain yield–plant density relationship is highly variable, owing to the influence of environmental conditions. Number of pods per unit area also exhibited a strong positive correlation with plant density and a negative correlation with numbers of pods per plant and seeds per pod.


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  		Table 5 Correlation coefficients between plant density and growth indices, yield, and yield components in grain lupin in a 4-yr experiment at Córdoba, Spain.{dagger}

 
As can be seen from Table 6 , the direct effect of number of pods per plant as measured by path coefficient analysis is the single factor most strongly influencing yield, followed by number of plants per unit area. The direct effect of mean seed mass is much weaker and that of number of seeds per pod is negligible. This is consistent with the results of Fuentes (1985) and Herbert (1977b) for white lupin. The strongest indirect effects were also those of numbers of pods per plant and plants per unit area in all relationships, the influence of all other yield components being negligible. In a previous study of ours (López-Bellido et al., 1994) where the independent variable was the sowing season (autumn or winter), path coefficient analysis revealed the mean seed mass to exert the strongest direct and indirect effects on L. albus yield. These differences highlight the usefulness of path coefficient analysis for identifying the role of the different yield components under different growing conditions.


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  		Table 6 Path coefficient analysis for four characters in grain lupin in a 4-yr experiment at Córdoba, Spain

 
Unlike the positive response previously found in species such as L. angustifolius L. and L. luteus L. (Herbert, 1977a; Fuentes, 1985), increased grain yield in white lupin does not seem to be unequivocally related to an increased plant density. The plasticity of the morphological structure of lupin offsets differences in the number of plants per unit area. The extent of branching and the number of pods per plant tend to produce a similar number of pods per unit area whatever the plant density. Water shortage in spring and during grain formation period may also play prominent roles under Mediterranean conditions. The results suggest that the growth pattern of lupin can be used to obtain balanced grain yields over a wide range of plant densities under extremely variable climatic conditions.Vavilov Gataulina 1982

Received for publication July 27, 1998.
   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
 REFERENCES
 




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