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a Departamento de Biología y Producción de los Vegetales, University of Extremadura, Ctra. de Cáceres s/n, 06071 Badajoz, Spain
b Departamento de Ciencias y Recursos Agrícolas y Forestales, University of Córdoba, Córdoba, Spain
c Departamento de Producción Vegetal y Tecnología Agraria, University of Castilla-La Mancha, Ciudad Real, Spain
* Corresponding author (rjlobe{at}unex.es)
Received for publication August 1, 2002.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Abbreviations: HI, harvest index • NHI, nitrogen harvest index • NUtE, nitrogen utilization efficiency • TDM, total dry matter • TSW, thousand-seed weight
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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In Mediterranean areas, legume crops are suitable alternatives in rainfed systems but are rarely used. The value of grain legumes as a preceding crop is well known, especially in rotations with cereals (Pahl, 2001). The water and N contents of the soil are the main factors affected by rotation with legumes (Papastylianou, 1993). López-Bellido et al. (2000) showed, in a long-term experiment, the strong response of wheat yield after faba bean compared with fallow, chickpea (Cicer arietinum L.), sunflower (Helianthus annuus L.), and continuous wheat. Faba bean consistently fixed more N than either pea (Pisum sativum L.) or chickpea, even under drought conditions. The incorporation of harvest residues results in a significant net increase in soil N, provided there are no major nutrient constraints (Carranca et al., 1999). Faba bean is rarely the main crop in a farming system, and it is seldom grown continuously on the same land. The most common practice is rotation of faba bean with cereals.
Farmers used and still use faba bean as a low-input break crop in a cereal–sunflower rotation under rainfed conditions. Faba bean is generally a rainfed crop grown in areas receiving more than 400 mm of rainfall, but in drier regions, it is generally irrigated (Saxena, 1985). Faba bean has a shallow root system with little osmoregulation and is very sensitive to high temperatures and water stress, particularly during anthesis and pod filling (Grashoff and Verkerke, 1991; Bond et al., 1994; Xia, 1994). For this reason, faba bean is often grown under irrigation in many dry parts of the world and until recently was only considered suitable for production in Mediterranean-type environments with high rainfall (>400 mm yr-1) (Walton and Trent, 1988; ICARDA, 1994). However, Siddique et al. (1993) and Loss and Siddique (1997) reported that faba bean is adapted to low-rainfall regions.
According to Papendick et al. (1988), successful production of faba bean, and indeed any legume, in dry areas depends on the feasibility of obtaining economic yields with a limited water supply. Management systems should consider (i) matching crops and cropping sequences with seasonal rainfall, (ii) crop practices designed to maximize water conservation, (iii) soil management to prevent compaction and the formation of tillage pans, (iv) adequate control of pests, (v) appropriate seedbed preparation and fertilization, and (vi) timely planting. These objectives can be accomplished using conservation tillage systems, improved systems of fertilization and exploitation of N fixation, and appropriate mechanization.
The high interseasonal variability of faba bean yields is caused mainly by suboptimal environmental conditions (Thompson and Taylor, 1982). Variations in water availability are one of the major causes of yield variation in faba bean (Day and Legg, 1983). Soil water shortage has been identified as a major constraint in increasing faba bean production (De Costa et al., 1997a). In this sense, sowing soon after the first autumn rains generally results in increased seed yield potential compared with delayed sowing because of more available water, higher biomass production, early anthesis, and increased harvest index (HI) (Loss and Siddique, 1997). Another strategy used with the same objective is conservation tillage. This practice is being adopted by an increasing number of farmers worldwide as a means of enhancing water conservation as well as controlling erosion and reducing farm energy requirements. Most attention in terms of conservation production systems has focused on cereal crops, and more consideration must be given to legume cropping (Papendick et al., 1988). Abdel-Daiem et al. (1988) claimed that no-tillage increased average seed and straw yields of faba bean after cotton (Gossypium hirsutum L.) or maize (Zea mays L.). Short-term studies using no-tillage for legume production showed that faba bean under no-tillage could generate yields similar to those obtained under conventional tillage (Izaurralde et al., 1993). However, Izaurralde et al. (1995) reported that higher yields under deep tillage rather than no-tillage conditions were associated with improved rooting conditions and water extraction.
Nitrogen is seldom limiting if the legumes are well nodulated with effective strains of Rhizobium. Many studies on the effects of N fertilizer on field-grown faba bean have shown that no fertilizer N is needed to attain either large yields or high seed protein concentrations (Bond et al., 1985). Even larger applications of N fertilizer reduced seed yield but increased the dry weight of straw (Abdel-Daiem et al., 1988). Addition of inorganic fertilizer N to soil reduces the N2 fixation rate (Mahler et al., 1988). According to Mahler et al. (1988), soil applications of inorganic N fertilizers have inconsistent effects on faba bean yields. However, sometimes even with apparently satisfactory nodulation, it is possible to obtain significant yield responses to fertilizer N (Papendick et al., 1988). In these cases, a starter application of 15 to 20 kg N ha-1 is beneficial, presumably by ensuring rapid seedling establishment before the symbiotic system becomes effective.
Most previous research on faba bean has focused on the effect of water stress, adaptation of different genotypes, N2 fixation, sowing date, and plant density. There is little published information on the effect of tillage systems. The aims of the present study were to examine, within the scope of a long-term experiment started in 1986, the effects of tillage systems and soil residual N on seed yield, seed yield components, and N uptake of faba bean in rotation with wheat under rainfed Mediterranean conditions.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Initially, only the influence of tillage systems on faba bean yield was studied over an 11-yr period (1987–1988 to 1991–1992, 1993–1994 to 1997–1998, and 2000–2001). The effect of fertilizer N was included as factor during the past 4 yr. In these years, a study was performed to evaluate effects of tillage system and fertilizer N applied to wheat on faba bean seed yield, yield components [HI, pods per square meter, seeds per pod, and thousand-seed weight (TSW)], N uptake (seed, straw and total), seed protein content, N utilization efficiency (NUtE), and N harvest index (NHI) over the last 4 yr of the study. Nitrogen utilization efficiency (kg kg-1) was calculated as the ratio of seed yield to total plant N uptake while NHI (%) was calculated as the ratio of N in seed to total plant N uptake. Moreover, in 4 yr (1995–1996, 1996–1997, 1997–1998, and 1999–2000), the authors studied the effect of the same treatments on wheat grain yield and soil nitrate.
No-tillage plots were seeded with a no-till seed drill. Weeds were controlled with glyphosate [N-(phosphonomethyl)glycine] + MCPA [(4-chloro-2-methylphenoxy)acetic acid] at a rate of 0.5 + 0.5 L a.i. ha-1 before planting. Conventional tillage treatment included moldboard plowing and disk harrowing and/or vibrating tine cultivation to prepare a proper seedbed. During the faba bean growing season, weeds were controlled by means of cyanazine [2-(4-chloro-6-ethylamino-1,3,5-triazin-2-yl-amino)-2-methyl propionitrile] at 2 L a.i. ha-1. Glyphosate was applied at a rate of 0.065 L a.i. ha-1 as a postemergence spray on faba bean plots when broomrape (Orobanche crenata Forsk) was about 0.5 to 1 cm high (García-Torres et al., 1987). Within the wheat-growing season, weeds were controlled with specific herbicides: diclofop methyl {2-[4-(2,4-dichlorophenoxy)phenoxy]propanoic methyl} + tribenuron {methyl-2-[[[[(N-4-methoxy-6-methyl-1,3,5-triazin-2-yl)-N-methylamino]carbonyl]amino]sulphonyl]benzoate} at 0.9 and 15 g a.i. ha-1, respectively.
Faba bean (cv. Alameda) was planted in 50-cm-wide rows in November at 170 kg ha-1. Hard red spring wheat (cv. Cajeme) was planted in 18-cm-wide rows in December at a seeding rate of 150 kg ha-1. Nitrogen fertilizer was applied to wheat plots as ammonium nitrate. At all application rates, half was applied before sowing (incorporated by disk harrowing in conventional tillage plots and surface-broadcast in no-tillage plots). The remaining N was applied as a topdressing at the beginning of wheat tillering. Every year, wheat plots were also supplied with P fertilizer at a rate of 29 kg ha-1; the fertilizer was incorporated in conventional tillage soil and banded with drilling in no-tillage plots. Soil-available K was adequate (530 mg kg-1).
At harvest, a 1-m2 portion at the center of each faba bean subplot was sampled. From this sample, the HI [the ratio at harvest of grain dry weight to total dry matter (TDM)], pods per square meter, seeds per pod, TSW, N uptake, and seed protein content were measured. Total dry matter and seed weight were determined by drying the sampled plants at 80°C to constant weight. Nitrogen uptake was determined by analysis of N content of straw and seed, using the Dumas combustion method (Bremner, 1996), with a LECO FP-428 analyzer (LECO Corp., St. Joseph, MI). Seed protein contents were calculated by multiplying the percentage of N by 6.2. Three soil samples were collected from each wheat plot, before wheat sowing and after wheat harvesting, at a depth 0 to 90 cm, using a hydraulic sampler. The samples were subsequently mixed and homogenized to obtain a single sample per plot. The samples were air-dried, ground and sieved, and stored in plastic bags that were kept refrigerated until analysis. The soils were analyzed for nitrate content using the Griess–Illosvay colorimetric method as modified by Barnes and Folkard (1951), with a Bran+Luebbe II AutoAnalyzer (Bran+Luebbe, Norderstedt, Germany). Faba bean seed and wheat grain were harvested in early June using a Nurserymaster Elite Plot Combine (30 m2 per subplot).
The faba bean seed yield over 11 yr was subjected to an analysis of variance (ANOVA) to determine the effect of tillage system; seed yield, yield components, N uptake, seed protein content, NUtE, and NHI over the last 4 yr were analyzed to determine the joint effect of tillage system and fertilizer N rate applied to preceding wheat. Similarly, wheat grain yield and soil nitrate content over 4 yr were subjected to an analysis of variance. In all the cases, a year-combined randomized complete block design was used, in accordance with McIntosh (1983). The only significant interaction was year x tillage for seed yield (over 11 yr) and seed protein content (over 4 yr). Treatment means were compared using Fisher's protected least significant difference (LSD) test at P 
0.05. Least significant differences for main effect and interaction comparisons were calculated using the appropriate standard error terms in accordance with Gómez and Gómez (1984). Different correlations were also calculated. The Statgraphics Plus v. 7.0 software suite (Manugistics, 1993) was used for this purpose.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Faba Bean Seed Yield and Yield Components
Year Effects
All the parameters studied were significantly influenced by year (seed yield, straw yield, TDM, HI, pods per square meter, seeds per pod, and TSW) (Table 1). Over the 11-yr study period, the highest seed yield was recorded in 1989–1990 (2964 kg ha-1) while the poorest seed yield was achieved in 1988–1989 (587 kg ha-1) (Fig. 2)
. That high variability of seed yield was associated with amount and distribution of rainfall and the weather conditions during pollination. Seed yield improved as January through April rainfall increased (y = 5.73x + 410.98; r2 = 0.42,* n = 11, where * = significant at the 0.05 level). Consecutive rainy years had a negative effect on seed yield (1996–1997 and 1997–1998) due to waterlogging conditions, hindering a good crop establishment (Fig. 1 and 2). According to De Costa et al. (1997a), soil water shortage has been identified as a major constraint in increasing faba bean production.
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Tillage Effects
Over the 11-yr study period, the tillage system did not significantly influence faba bean seed yield. However, the year x tillage interaction was significant (Fig. 2). Significant differences in seed yield as a function of tillage system were recorded in only 4 of the 11 study years: In 1990–1991, no-tillage was more productive than conventional tillage while in 1987–1988, 1995–1996, and 1997–1998 (the last 2 yr were very rainy), the opposite was true (Fig. 1 and 2). High rainfall in 1997–1998, which had been preceded by two rainy years, had a greater negative effect on seed yield under no-tillage due to waterlogging in the early stages of crop growth. Izaurralde et al. (1993) showed that faba bean under no-tillage could generate yields similar to those achieved under conventional tillage. However, Izaurralde et al. (1995) reported more seed yield under conventional tillage than no-tillage conditions due to improved rooting conditions and water extraction. According to Abdel-Daiem et al. (1988), no-tillage increased faba bean seed yield after cotton or maize.
Over the last 4 yr of the study, seed yield, straw yield, TDM, HI, and TSW were significantly different across tillage treatment. Conventional tillage (2007 kg ha-1) was more productive than no-tillage (1737 kg ha-1) (Table 1). This was due to three very rainy years in this period. However, the result obtained over the 11-yr study period prevails above this one. Straw yield and TDM were significantly greater with conventional tillage than no-tillage. This result contrasts with the findings of Abdel-Daiem et al. (1988), who reported that no-tillage increased straw yield in faba bean. Harvest index and TSW were greater with no-tillage than with conventional tillage. No variation was observed for pods per square meter or seeds per pod. These results suggest that the higher seed yield obtained with conventional tillage was attributable to a larger number of pods per square meter and seeds per pod although these were not significant.
Nitrogen Residual Effects
The rate of fertilizer N applied to the preceding wheat crop only exerted a significant effect on seed yield and TDM (Table 1). Seed yield and TDM were lower at 0 kg N ha-1, and no significant differences were recorded at other N rates. Seed yield values were 1674, 1934, 1930, and 1950 kg ha-1 for the N rates 0, 50, 100, and 150 kg ha-1, respectively. Previous research on faba bean N fertilization has studied the effect of N fertilizer applied to faba bean, but no information is available on the effect on faba bean of the rate of fertilizer N applied to the preceding wheat. According to Abdel-Daiem et al. (1988), larger applications of N fertilizer reduce seed yield but increase the dry weight of straw. Nevertheless, these results cannot be compared with the results obtained here. Moreover, in the experiment performed by those authors, the high N rate applied may have prompted seed yield depression. Mahler et al. (1988) reported that additions of inorganic fertilizer N to soil reduce N2 fixation rate, and this may account for yield depression. Residual N could have an effect similar to that of a starter application. According to Papendick et al. (1988), it is sometimes possible to obtain significant yield responses to fertilizer N using a starter application of 15 to 20 kg N ha-1.
No significant variations were recorded for HI, pods per square meter, seeds per pod, and TSW. However, the rates 0 and 150 kg N ha-1 prompted the lowest values for these parameters. This trend could account for the lower seed yield and TDM at 0 kg N ha-1 and the marginal depressive effect on some yield components at 150 kg N ha-1.
Faba Bean Nitrogen Uptake
Year Effects
Faba bean total N uptake, seed N uptake, straw N uptake, seed protein content, NUtE, and NHI were significantly influenced by year (Table 3). Total N uptake, seed N uptake, and straw N uptake were proportional to TDM, seed yield, and straw yield, respectively. Total N uptake and seed N uptake varied between 50 and 127 and 34 and 107 kg N ha-1, respectively (Table 3) while mean straw N uptake was 17 kg N ha-1. Kaul et al. (1996) reported that the N removed from the soil by the seed was up to 200 kg N ha-1 while plant residual N was below 100 kg N ha-1. In 1997–1998, the year with lowest yield and N uptake, the authors recorded the lowest seed protein content (26.1%), the highest value was found in 1996–1997 (33.9%). According to Bond et al. (1985), seed protein concentration varies between 22 and 36%, depending on the cultivar and environmental factors. Nitrogen utilization efficiency was greater in the years with higher seed yield and N uptake (1995–1996 and 2000–2001). Nitrogen HI was lower in 1997–1998, and no significant differences were recorded in the other years. Mean NHI (82%) was similar to the value reported by Kaul et al. (1996).
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Nitrogen Residual Effects
Fertilizer N rates applied to the preceding wheat crop only significantly influenced total N uptake and seed N uptake in faba bean (Table 3). Total N uptake and seed N uptake were lower at 0 kg N ha-1, and no significant differences were recorded at other N rates. Seed N uptake values were 76, 89, 86, and 90 kg ha-1 for the N rates 0, 50, 100, and 150 kg ha-1, respectively. Seed protein content, NUtE, and NHI showed no variation with the N rate increase. Residual N had a similar effect to a starter application, increasing yield as reported by Papendick et al. (1988), presumably by ensuring rapid seedling establishment before the symbiotic system becomes effective. Therefore, the effect of this residual N is useful at the beginning of crop growth but is useless in the final growth stages when the seed is filled and protein content is established. Consequently, the application of the optimum fertilizer rate (100 kg N ha-1) to the preceding wheat crop, as reported by López-Bellido et al. (2000) for the same experiment, has a positive effect on the following faba bean crop.
Wheat Grain Yield and Soil Nitrate
The aim of wheat analysis is to show yield and soil nitrate (at sowing and harvest) in continuous rotation with faba bean for encompassing the preceding results in the experiment as a whole. Over the 4-yr study period, grain yield differed significantly between years (1999–2000 > 1995–1996 > 1997–1998 > 1996–1997) (Table 4). The highest grain yields were recorded in the years after a dry year (1999–2000 and 1995–1996) while the lowest yields were recorded in years after a rainy year (Fig. 1 and Table 4). The influence of the tillage system, for the 4 yr as a whole, was significant; greater yield was obtained using conventional tillage. Differences in yield within years were not significant although in 1995–1996, 1996–1997, and 1997–1998, conventional tillage tended to produce higher yields than no-tillage (Table 4). However, the most effective yields recorded with conventional tillage were caused by the predominance of wet years (López-Bellido et al., 2000). Nitrogen fertilizer rates had a significant effect on grain yield in 1995–1996, 1997–1998, and 1999–2000 and for the 4-yr period (Table 4). Grain yield was optimized at 50 kg N ha-1 in 1999–2000 and 100 kg N ha-1 in 1995–1996 and 1997–1998. For the 4 yr as a whole, grain yield tended to increase as N fertilizer rates increased, with significant differences between all the rates; but the grain yield at 100 kg N ha-1 was greater than at 150 kg N ha-1. However, López-Bellido et al. (2000), for this experiment and over 11 yr of the study period, did not report any significant differences between the rates 100 and 150 kg N ha-1.
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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The fertilizer rates of 50, 100, and 150 kg N ha-1 applied to the preceding wheat crop had an effect similar to that of N starter application, increasing seed yield, TDM, and N uptake. Consequently, the optimum N rate of 100 kg ha-1 applied to a wheat crop under southern Spain conditions has a positive effect on the following faba bean crop (López-Bellido et al., 2000). Soil nitrate at wheat sowing after faba bean is not affected by the tillage system used while the effect of N rates applied to wheat 2 yr before is very reduced due to N fixed by the faba bean crop.
High biomass may be a prerequisite for achieving high faba bean seed yields. Faba bean yield components show compensation, and TSW plays a more important role than seeds per pod and pods per square meter.
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ACKNOWLEDGMENTS |
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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