Concentration of seagulls in the Chafarinas Islands (three semi‐arid North African islets) induce... more Concentration of seagulls in the Chafarinas Islands (three semi‐arid North African islets) induces profound changes in soil properties including eutrophication, salinization, acidification and nutrient imbalances. Soils of heavily seabird‐affected sites have significantly higher soluble K and NO3 levels (>20‐fold), Zn and Fe availability (>5‐fold), water‐retention capacity (>40% increase) and 15N enrichment, compared with control sites. These seabird‐induced soil changes are paralleled by (i) different patterns of abundance of the two main chenopod shrubs: Suaeda vera abundance is higher (>30‐fold) in seabird‐affected sites while Salsola oppositifolia largely dominates in low‐affected areas. No differences were found for Atriplex halimus. The abundance of the first two species may be largely explained by changes in soil soluble K‐to‐available Ca ratio whose value depends of the interaction between seabird products and soil constituents; (ii) significant increases in leaf...
The quantification of labile and recalcitrant fractions of organic C could provide valuable infor... more The quantification of labile and recalcitrant fractions of organic C could provide valuable information in the study of soil organic carbon (SOC) changes in agrosystems. Few studies have determined the effects of farming practices on the recalcitrant and labile fractions of SOC at depth in a Mediterranean Vertisol. Our objective was to determine the effects of tillage, crop rotation and N fertilization on labile and recalcitrant SOC fractions and characterize d 13 C in a soil profile (0-120 cm) from a long-term experiment established in 1986 on rainfed Mediterranean Vertisols in southern Spain. The following treatments were studied: conventional tillage (CT) vs. no-tillage (NT); three crop rotations (wheat [Triticum aestivum L.]-chickpea [Cicer arietinum L.], wheat-sunflower [Helianthus annuus L.] and wheat-faba-bean [Vicia faba L.]); and two N fertilizer application rates (0 and 100 kg N ha À1). The SOC contents of the soil samples from five soil layers (0-15, 15-30, 30-60, 60-90 and 90-120 cm) were determined. Throughout the experiment, the SOC content was greater in surface than in deep layers. The NT resulted in a greater SOC content than CT (10.7 Mg ha À1 and 8 Mg ha À1 , respectively) in the most superficial soil layer. The SOC content was greater in the recalcitrant fraction than in the labile fraction (62% and 38% of total SOC, respectively). The recalcitrant SOC fraction was greater under CT than under NT. In the uppermost 15 cm, the labile organic C fraction was greater in the NT treatments than in the CT treatments because tillage resulted in a greater mineralization of the least stable forms of SOC. The influence of N rate and crop rotation on SOC was very low. The stable C isotopic composition (d 13 C) was greater at depth than at the surface for both total SOC and the recalcitrant fraction. The labile fraction had more 13 C than the recalcitrant fraction. The d 13 C value was greater under CT than under NT for both soil fractions. Tillage system exerted a notable influence in both soil fractions and therefore in the organic matter quality since the labile fraction is an indicator of this quality.
... Ramón Redondo a , Corresponding Author Contact Information , E-mail The Corresponding Author ... more ... Ramón Redondo a , Corresponding Author Contact Information , E-mail The Corresponding Author and Javier G. Yélamos b. ... is the molar ratio of the heavy to light isotope, 13 C/ 12 C. International agreement recognised a fossil in calcium carbonate, the Pee Dee Belemnite (PDB ...
A prerequisite for the calculation of the proportion of a legume’s nitrogen derived from the atmo... more A prerequisite for the calculation of the proportion of a legume’s nitrogen derived from the atmosphere (%Ndfa) using the 15N natural abundance technique (NA) is the determination of the B value (δ15N value for a legume when completely dependent on N2 fixation for growth). With this objective, Kabuli-type chickpea seeds were inoculated with Mesorhizobium ciceri, strain ISC-6, and an indigenous strain mixture (ISM) from the Guadalquivir Valley (southern Spain); and mayor-equina-type faba bean seeds were inoculated with Rhizobium leguminosarum strain ISL-19. Both legumes were grown in perlite with an N-free nutrient solution and in a growth chamber; uninoculated plants were also grown under the same conditions. Samples of the inoculated plants were collected at full flowering and maturity, analyzing total N and 15N content of the nodules, root, shoot and seeds. The seeds sown and uninoculated plants at wilting were also analyzed. The uninoculated chickpea and faba bean plants showed strong 15N discrimination in the remobilization of reserve proteins from the cotyledons to the shoot. Only 52% of the 15N from the chickpea seed and 46% from the faba bean seed were translocated to the shoot. The Bwhole plant value for both inoculated species (−1.44‰ in chickpea and −1.33‰ in faba bean) demonstrated the existence of a significant isotopic discrimination of N in the fixation of atmospheric N2. The Bshoot value did not show significant differences between full flowering and seed maturity for either species, which allowed field sampling to be performed for the calculation of %Ndfa between both growth stages. Each species presented different 15N discrimination for the different parts analyzed. In chickpea, strong discrimination was observed between the nodules (+3.11‰) and the rest of the plant (−1.67‰); this discrimination was less pronounced in faba bean and always with negative values between the underground parts (nodules and root, with a mean value of −0.75‰) and the shoot (−1.71‰). The Bshoot value obtained was −1.80‰ in chickpea and −1.71‰ in faba bean. However, given the importance of the amount of seed N in chickpea and faba bean, seed 15N contribution should be considered in the calculation of the Bshoot value using a mass balance model which considers 50% of this amount. In this case, the adjusted Bshoot values would increase to −2.05‰ and −1.89‰ in chickpea and faba bean, respectively.
A 3-year field experiment in rainfed Vertisol was designed to study the effects of timing and spl... more A 3-year field experiment in rainfed Vertisol was designed to study the effects of timing and splitting of N fertilizer on the efficiency of nitrogen in wheat (Triticum aestivum L.). A single rate of 150 kg N ha À1 was used, different fractions being applied at sowing, tillering and stem elongation. The experiment was designed as a randomized complete block with four blocks. At the same time, a 15 N experiment was conducted within the main experiment area, with microplots, to quantify N uptake from fertilizer and soil. Mean wheat use of N fertilizer ranged from 14.1% when applied at sowing to 54.8% when applied as a top dressing at the beginning of stem elongation. The mean annual contribution of soil residual N and mineralization was 152 kg N ha À1 , representing a considerable proportion of total wheat N uptake, ranging from 83.2% when N fertilizer was applied in the fall to 49.4% when it was applied at stem elongation. This would account for the poor and inconsistent response of grain yield and N efficiency indices, and for the importance of soil N in Vertisols for predicting wheat N fertilizer requirements, due to the carryover effect. Application of N fertilizer to wheat preferably as a top dressing, between tillering and stem elongation, is a strategy to be recommended from the standpoint both of the environment and of farmer returns. #
A prerequisite for the calculation of the proportion of a legume’s nitrogen derived from the atmo... more A prerequisite for the calculation of the proportion of a legume’s nitrogen derived from the atmosphere (%Ndfa) using the 15N natural abundance technique (NA) is the determination of the B value (δ15N value for a legume when completely dependent on N2 fixation for growth). With this objective, Kabuli-type chickpea seeds were inoculated with Mesorhizobium ciceri, strain ISC-6, and an indigenous strain mixture (ISM) from the Guadalquivir Valley (southern Spain); and mayor-equina-type faba bean seeds were inoculated with Rhizobium leguminosarum strain ISL-19. Both legumes were grown in perlite with an N-free nutrient solution and in a growth chamber; uninoculated plants were also grown under the same conditions. Samples of the inoculated plants were collected at full flowering and maturity, analyzing total N and 15N content of the nodules, root, shoot and seeds. The seeds sown and uninoculated plants at wilting were also analyzed. The uninoculated chickpea and faba bean plants showed strong 15N discrimination in the remobilization of reserve proteins from the cotyledons to the shoot. Only 52% of the 15N from the chickpea seed and 46% from the faba bean seed were translocated to the shoot. The Bwhole plant value for both inoculated species (−1.44‰ in chickpea and −1.33‰ in faba bean) demonstrated the existence of a significant isotopic discrimination of N in the fixation of atmospheric N2. The Bshoot value did not show significant differences between full flowering and seed maturity for either species, which allowed field sampling to be performed for the calculation of %Ndfa between both growth stages. Each species presented different 15N discrimination for the different parts analyzed. In chickpea, strong discrimination was observed between the nodules (+3.11‰) and the rest of the plant (−1.67‰); this discrimination was less pronounced in faba bean and always with negative values between the underground parts (nodules and root, with a mean value of −0.75‰) and the shoot (−1.71‰). The Bshoot value obtained was −1.80‰ in chickpea and −1.71‰ in faba bean. However, given the importance of the amount of seed N in chickpea and faba bean, seed 15N contribution should be considered in the calculation of the Bshoot value using a mass balance model which considers 50% of this amount. In this case, the adjusted Bshoot values would increase to −2.05‰ and −1.89‰ in chickpea and faba bean, respectively.
Erratum to ''Faba bean nitrogen fixation in a wheat-based rotation under rainfed Mediterranean co... more Erratum to ''Faba bean nitrogen fixation in a wheat-based rotation under rainfed Mediterranean conditions: Effect of tillage system'' [Field Crops Res. 98 (2006) 253-260]
A field experiment was conducted during a 2-year period (2001-2002 and 2002-2003) in Córdoba (Sou... more A field experiment was conducted during a 2-year period (2001-2002 and 2002-2003) in Córdoba (Southern Spain) on a rainfed Vertisol, within the wheat-faba bean rotation framework of a long-term experiment started en 1986, to determine the effects of tillage systems [no tillage (NT) and conventional tillage (CT)], on faba bean N 2 fixation. Fixation was calculated using the 15 N dilution and 15 N natural abundance methods using wheat as reference crop. Nitrogen derived from the atmosphere (Ndfa) percentages ranged between 70 and 96%, and N 2 fixed between 39 and 144 kg N ha À1 . The N balance was positive for all years and treatments, with a mean value of 18.3 kg N ha À1 and a maximum of 40 kg N ha À1 , in terms of above-ground biomass only. No significant difference was recorded between faba bean N 2 fixation values as calculated by the 15 N enriched (ID) method and the 15 N natural abundance (NA) method. The effect of tillage system on %Ndfa and the amount of N 2 fixed was not significant, possibly due to the negligible difference in soil NO 3 À -N content between the two systems. #
Efficient management of legumes in order to maximize benefits depends on a correct field assessme... more Efficient management of legumes in order to maximize benefits depends on a correct field assessment of N2 fixation. A field experiment was conducted during a 6-year period (2001–2002 to 2006–2007) in Córdoba (Southern Spain) on a rainfed Vertisol within the wheat-chickpea and wheat-faba bean rotation framework of a long-term experiment started in 1986. The aim was to determine the effect
A 3-year field experiment in rainfed Vertisol was designed to study the effects of timing and spl... more A 3-year field experiment in rainfed Vertisol was designed to study the effects of timing and splitting of N fertilizer on the efficiency of nitrogen in wheat (Triticum aestivum L.). A single rate of 150 kg N ha À1 was used, different fractions being applied at sowing, tillering and stem elongation. The experiment was designed as a randomized complete block with four blocks. At the same time, a 15 N experiment was conducted within the main experiment area, with microplots, to quantify N uptake from fertilizer and soil. Mean wheat use of N fertilizer ranged from 14.1% when applied at sowing to 54.8% when applied as a top dressing at the beginning of stem elongation. The mean annual contribution of soil residual N and mineralization was 152 kg N ha À1 , representing a considerable proportion of total wheat N uptake, ranging from 83.2% when N fertilizer was applied in the fall to 49.4% when it was applied at stem elongation. This would account for the poor and inconsistent response of grain yield and N efficiency indices, and for the importance of soil N in Vertisols for predicting wheat N fertilizer requirements, due to the carryover effect. Application of N fertilizer to wheat preferably as a top dressing, between tillering and stem elongation, is a strategy to be recommended from the standpoint both of the environment and of farmer returns. #
The quantification of the below-ground N of legumes is a key to understand its effect on soil N f... more The quantification of the below-ground N of legumes is a key to understand its effect on soil N fertility and the N economy of subsequent legume-based rotations. Significant amounts of the N fixed by legumes are incorporated into the soil as fallen leaves and stems. However, the N from roots, nodules and root exudates has rarely been quantified under field conditions, nor have the management effects been evaluated. This study measured the effects of tillage system [no-tillage (NT) and conventional tillage (CT)] on N rhizodeposition in faba bean (Vicia faba L.) and chickpea (Cicer arietinum L.) during a 3-year period ) in a Vertisol under rainfed Mediterranean conditions. Faba bean and chickpea plants were labelled in situ with 15 N using stem feeding and leaf feeding, respectively. NT increased the N derived from rhizodeposition (NdfR) with respect to CT (135 vs. 68 kg N ha −1 in faba bean and 115 vs. 97 kg N ha −1 in chickpea). Such differences between tillage methods can be attributed to the more favourable conditions for root growth produced by NT. NdfR was significantly influenced by depth; in faba bean, the greatest amount (70%) was found in the 0-30 cm layer, whereas in chickpea, 41% of the NdfR was concentrated in the 30-60 cm depth. The 54% and 61% of total plant N was NdfR (in faba bean and chickpea, respectively) representing 90% of the below-ground plant N in both crops. Our results show that the N derived from rhizodeposition is an important source for N balance and is a key to soil fertility in rain-fed Mediterranean cropping systems.
Erratum to ''Faba bean nitrogen fixation in a wheat-based rotation under rainfed Mediterranean co... more Erratum to ''Faba bean nitrogen fixation in a wheat-based rotation under rainfed Mediterranean conditions: Effect of tillage system'' [Field Crops Res. 98 (2006) 253-260]
A field experiment was conducted during a 2-year period (2001-2002 and 2002-2003) in Córdoba (Sou... more A field experiment was conducted during a 2-year period (2001-2002 and 2002-2003) in Córdoba (Southern Spain) on a rainfed Vertisol, within the wheat-faba bean rotation framework of a long-term experiment started en 1986, to determine the effects of tillage systems [no tillage (NT) and conventional tillage (CT)], on faba bean N 2 fixation. Fixation was calculated using the 15 N dilution and 15 N natural abundance methods using wheat as reference crop. Nitrogen derived from the atmosphere (Ndfa) percentages ranged between 70 and 96%, and N 2 fixed between 39 and 144 kg N ha À1 . The N balance was positive for all years and treatments, with a mean value of 18.3 kg N ha À1 and a maximum of 40 kg N ha À1 , in terms of above-ground biomass only. No significant difference was recorded between faba bean N 2 fixation values as calculated by the 15 N enriched (ID) method and the 15 N natural abundance (NA) method. The effect of tillage system on %Ndfa and the amount of N 2 fixed was not significant, possibly due to the negligible difference in soil NO 3 À -N content between the two systems. #
Efficient management of legumes in order to maximize benefits depends on a correct field assessme... more Efficient management of legumes in order to maximize benefits depends on a correct field assessment of N2 fixation. A field experiment was conducted during a 6-year period (2001–2002 to 2006–2007) in Córdoba (Southern Spain) on a rainfed Vertisol within the wheat-chickpea and wheat-faba bean rotation framework of a long-term experiment started in 1986. The aim was to determine the effect
The quantification of the below-ground N of legumes is a key to understand its effect on soil N f... more The quantification of the below-ground N of legumes is a key to understand its effect on soil N fertility and the N economy of subsequent legume-based rotations. Significant amounts of the N fixed by legumes are incorporated into the soil as fallen leaves and stems. However, the N from roots, nodules and root exudates has rarely been quantified under field conditions, nor have the management effects been evaluated. This study measured the effects of tillage system [no-tillage (NT) and conventional tillage (CT)] on N rhizodeposition in faba bean (Vicia faba L.) and chickpea (Cicer arietinum L.) during a 3-year period ) in a Vertisol under rainfed Mediterranean conditions. Faba bean and chickpea plants were labelled in situ with 15 N using stem feeding and leaf feeding, respectively. NT increased the N derived from rhizodeposition (NdfR) with respect to CT (135 vs. 68 kg N ha −1 in faba bean and 115 vs. 97 kg N ha −1 in chickpea). Such differences between tillage methods can be attributed to the more favourable conditions for root growth produced by NT. NdfR was significantly influenced by depth; in faba bean, the greatest amount (70%) was found in the 0-30 cm layer, whereas in chickpea, 41% of the NdfR was concentrated in the 30-60 cm depth. The 54% and 61% of total plant N was NdfR (in faba bean and chickpea, respectively) representing 90% of the below-ground plant N in both crops. Our results show that the N derived from rhizodeposition is an important source for N balance and is a key to soil fertility in rain-fed Mediterranean cropping systems.
Concentration of seagulls in the Chafarinas Islands (three semi‐arid North African islets) induce... more Concentration of seagulls in the Chafarinas Islands (three semi‐arid North African islets) induces profound changes in soil properties including eutrophication, salinization, acidification and nutrient imbalances. Soils of heavily seabird‐affected sites have significantly higher soluble K and NO3 levels (>20‐fold), Zn and Fe availability (>5‐fold), water‐retention capacity (>40% increase) and 15N enrichment, compared with control sites. These seabird‐induced soil changes are paralleled by (i) different patterns of abundance of the two main chenopod shrubs: Suaeda vera abundance is higher (>30‐fold) in seabird‐affected sites while Salsola oppositifolia largely dominates in low‐affected areas. No differences were found for Atriplex halimus. The abundance of the first two species may be largely explained by changes in soil soluble K‐to‐available Ca ratio whose value depends of the interaction between seabird products and soil constituents; (ii) significant increases in leaf...
The quantification of labile and recalcitrant fractions of organic C could provide valuable infor... more The quantification of labile and recalcitrant fractions of organic C could provide valuable information in the study of soil organic carbon (SOC) changes in agrosystems. Few studies have determined the effects of farming practices on the recalcitrant and labile fractions of SOC at depth in a Mediterranean Vertisol. Our objective was to determine the effects of tillage, crop rotation and N fertilization on labile and recalcitrant SOC fractions and characterize d 13 C in a soil profile (0-120 cm) from a long-term experiment established in 1986 on rainfed Mediterranean Vertisols in southern Spain. The following treatments were studied: conventional tillage (CT) vs. no-tillage (NT); three crop rotations (wheat [Triticum aestivum L.]-chickpea [Cicer arietinum L.], wheat-sunflower [Helianthus annuus L.] and wheat-faba-bean [Vicia faba L.]); and two N fertilizer application rates (0 and 100 kg N ha À1). The SOC contents of the soil samples from five soil layers (0-15, 15-30, 30-60, 60-90 and 90-120 cm) were determined. Throughout the experiment, the SOC content was greater in surface than in deep layers. The NT resulted in a greater SOC content than CT (10.7 Mg ha À1 and 8 Mg ha À1 , respectively) in the most superficial soil layer. The SOC content was greater in the recalcitrant fraction than in the labile fraction (62% and 38% of total SOC, respectively). The recalcitrant SOC fraction was greater under CT than under NT. In the uppermost 15 cm, the labile organic C fraction was greater in the NT treatments than in the CT treatments because tillage resulted in a greater mineralization of the least stable forms of SOC. The influence of N rate and crop rotation on SOC was very low. The stable C isotopic composition (d 13 C) was greater at depth than at the surface for both total SOC and the recalcitrant fraction. The labile fraction had more 13 C than the recalcitrant fraction. The d 13 C value was greater under CT than under NT for both soil fractions. Tillage system exerted a notable influence in both soil fractions and therefore in the organic matter quality since the labile fraction is an indicator of this quality.
... Ramón Redondo a , Corresponding Author Contact Information , E-mail The Corresponding Author ... more ... Ramón Redondo a , Corresponding Author Contact Information , E-mail The Corresponding Author and Javier G. Yélamos b. ... is the molar ratio of the heavy to light isotope, 13 C/ 12 C. International agreement recognised a fossil in calcium carbonate, the Pee Dee Belemnite (PDB ...
A prerequisite for the calculation of the proportion of a legume’s nitrogen derived from the atmo... more A prerequisite for the calculation of the proportion of a legume’s nitrogen derived from the atmosphere (%Ndfa) using the 15N natural abundance technique (NA) is the determination of the B value (δ15N value for a legume when completely dependent on N2 fixation for growth). With this objective, Kabuli-type chickpea seeds were inoculated with Mesorhizobium ciceri, strain ISC-6, and an indigenous strain mixture (ISM) from the Guadalquivir Valley (southern Spain); and mayor-equina-type faba bean seeds were inoculated with Rhizobium leguminosarum strain ISL-19. Both legumes were grown in perlite with an N-free nutrient solution and in a growth chamber; uninoculated plants were also grown under the same conditions. Samples of the inoculated plants were collected at full flowering and maturity, analyzing total N and 15N content of the nodules, root, shoot and seeds. The seeds sown and uninoculated plants at wilting were also analyzed. The uninoculated chickpea and faba bean plants showed strong 15N discrimination in the remobilization of reserve proteins from the cotyledons to the shoot. Only 52% of the 15N from the chickpea seed and 46% from the faba bean seed were translocated to the shoot. The Bwhole plant value for both inoculated species (−1.44‰ in chickpea and −1.33‰ in faba bean) demonstrated the existence of a significant isotopic discrimination of N in the fixation of atmospheric N2. The Bshoot value did not show significant differences between full flowering and seed maturity for either species, which allowed field sampling to be performed for the calculation of %Ndfa between both growth stages. Each species presented different 15N discrimination for the different parts analyzed. In chickpea, strong discrimination was observed between the nodules (+3.11‰) and the rest of the plant (−1.67‰); this discrimination was less pronounced in faba bean and always with negative values between the underground parts (nodules and root, with a mean value of −0.75‰) and the shoot (−1.71‰). The Bshoot value obtained was −1.80‰ in chickpea and −1.71‰ in faba bean. However, given the importance of the amount of seed N in chickpea and faba bean, seed 15N contribution should be considered in the calculation of the Bshoot value using a mass balance model which considers 50% of this amount. In this case, the adjusted Bshoot values would increase to −2.05‰ and −1.89‰ in chickpea and faba bean, respectively.
A 3-year field experiment in rainfed Vertisol was designed to study the effects of timing and spl... more A 3-year field experiment in rainfed Vertisol was designed to study the effects of timing and splitting of N fertilizer on the efficiency of nitrogen in wheat (Triticum aestivum L.). A single rate of 150 kg N ha À1 was used, different fractions being applied at sowing, tillering and stem elongation. The experiment was designed as a randomized complete block with four blocks. At the same time, a 15 N experiment was conducted within the main experiment area, with microplots, to quantify N uptake from fertilizer and soil. Mean wheat use of N fertilizer ranged from 14.1% when applied at sowing to 54.8% when applied as a top dressing at the beginning of stem elongation. The mean annual contribution of soil residual N and mineralization was 152 kg N ha À1 , representing a considerable proportion of total wheat N uptake, ranging from 83.2% when N fertilizer was applied in the fall to 49.4% when it was applied at stem elongation. This would account for the poor and inconsistent response of grain yield and N efficiency indices, and for the importance of soil N in Vertisols for predicting wheat N fertilizer requirements, due to the carryover effect. Application of N fertilizer to wheat preferably as a top dressing, between tillering and stem elongation, is a strategy to be recommended from the standpoint both of the environment and of farmer returns. #
A prerequisite for the calculation of the proportion of a legume’s nitrogen derived from the atmo... more A prerequisite for the calculation of the proportion of a legume’s nitrogen derived from the atmosphere (%Ndfa) using the 15N natural abundance technique (NA) is the determination of the B value (δ15N value for a legume when completely dependent on N2 fixation for growth). With this objective, Kabuli-type chickpea seeds were inoculated with Mesorhizobium ciceri, strain ISC-6, and an indigenous strain mixture (ISM) from the Guadalquivir Valley (southern Spain); and mayor-equina-type faba bean seeds were inoculated with Rhizobium leguminosarum strain ISL-19. Both legumes were grown in perlite with an N-free nutrient solution and in a growth chamber; uninoculated plants were also grown under the same conditions. Samples of the inoculated plants were collected at full flowering and maturity, analyzing total N and 15N content of the nodules, root, shoot and seeds. The seeds sown and uninoculated plants at wilting were also analyzed. The uninoculated chickpea and faba bean plants showed strong 15N discrimination in the remobilization of reserve proteins from the cotyledons to the shoot. Only 52% of the 15N from the chickpea seed and 46% from the faba bean seed were translocated to the shoot. The Bwhole plant value for both inoculated species (−1.44‰ in chickpea and −1.33‰ in faba bean) demonstrated the existence of a significant isotopic discrimination of N in the fixation of atmospheric N2. The Bshoot value did not show significant differences between full flowering and seed maturity for either species, which allowed field sampling to be performed for the calculation of %Ndfa between both growth stages. Each species presented different 15N discrimination for the different parts analyzed. In chickpea, strong discrimination was observed between the nodules (+3.11‰) and the rest of the plant (−1.67‰); this discrimination was less pronounced in faba bean and always with negative values between the underground parts (nodules and root, with a mean value of −0.75‰) and the shoot (−1.71‰). The Bshoot value obtained was −1.80‰ in chickpea and −1.71‰ in faba bean. However, given the importance of the amount of seed N in chickpea and faba bean, seed 15N contribution should be considered in the calculation of the Bshoot value using a mass balance model which considers 50% of this amount. In this case, the adjusted Bshoot values would increase to −2.05‰ and −1.89‰ in chickpea and faba bean, respectively.
Erratum to ''Faba bean nitrogen fixation in a wheat-based rotation under rainfed Mediterranean co... more Erratum to ''Faba bean nitrogen fixation in a wheat-based rotation under rainfed Mediterranean conditions: Effect of tillage system'' [Field Crops Res. 98 (2006) 253-260]
A field experiment was conducted during a 2-year period (2001-2002 and 2002-2003) in Córdoba (Sou... more A field experiment was conducted during a 2-year period (2001-2002 and 2002-2003) in Córdoba (Southern Spain) on a rainfed Vertisol, within the wheat-faba bean rotation framework of a long-term experiment started en 1986, to determine the effects of tillage systems [no tillage (NT) and conventional tillage (CT)], on faba bean N 2 fixation. Fixation was calculated using the 15 N dilution and 15 N natural abundance methods using wheat as reference crop. Nitrogen derived from the atmosphere (Ndfa) percentages ranged between 70 and 96%, and N 2 fixed between 39 and 144 kg N ha À1 . The N balance was positive for all years and treatments, with a mean value of 18.3 kg N ha À1 and a maximum of 40 kg N ha À1 , in terms of above-ground biomass only. No significant difference was recorded between faba bean N 2 fixation values as calculated by the 15 N enriched (ID) method and the 15 N natural abundance (NA) method. The effect of tillage system on %Ndfa and the amount of N 2 fixed was not significant, possibly due to the negligible difference in soil NO 3 À -N content between the two systems. #
Efficient management of legumes in order to maximize benefits depends on a correct field assessme... more Efficient management of legumes in order to maximize benefits depends on a correct field assessment of N2 fixation. A field experiment was conducted during a 6-year period (2001–2002 to 2006–2007) in Córdoba (Southern Spain) on a rainfed Vertisol within the wheat-chickpea and wheat-faba bean rotation framework of a long-term experiment started in 1986. The aim was to determine the effect
A 3-year field experiment in rainfed Vertisol was designed to study the effects of timing and spl... more A 3-year field experiment in rainfed Vertisol was designed to study the effects of timing and splitting of N fertilizer on the efficiency of nitrogen in wheat (Triticum aestivum L.). A single rate of 150 kg N ha À1 was used, different fractions being applied at sowing, tillering and stem elongation. The experiment was designed as a randomized complete block with four blocks. At the same time, a 15 N experiment was conducted within the main experiment area, with microplots, to quantify N uptake from fertilizer and soil. Mean wheat use of N fertilizer ranged from 14.1% when applied at sowing to 54.8% when applied as a top dressing at the beginning of stem elongation. The mean annual contribution of soil residual N and mineralization was 152 kg N ha À1 , representing a considerable proportion of total wheat N uptake, ranging from 83.2% when N fertilizer was applied in the fall to 49.4% when it was applied at stem elongation. This would account for the poor and inconsistent response of grain yield and N efficiency indices, and for the importance of soil N in Vertisols for predicting wheat N fertilizer requirements, due to the carryover effect. Application of N fertilizer to wheat preferably as a top dressing, between tillering and stem elongation, is a strategy to be recommended from the standpoint both of the environment and of farmer returns. #
The quantification of the below-ground N of legumes is a key to understand its effect on soil N f... more The quantification of the below-ground N of legumes is a key to understand its effect on soil N fertility and the N economy of subsequent legume-based rotations. Significant amounts of the N fixed by legumes are incorporated into the soil as fallen leaves and stems. However, the N from roots, nodules and root exudates has rarely been quantified under field conditions, nor have the management effects been evaluated. This study measured the effects of tillage system [no-tillage (NT) and conventional tillage (CT)] on N rhizodeposition in faba bean (Vicia faba L.) and chickpea (Cicer arietinum L.) during a 3-year period ) in a Vertisol under rainfed Mediterranean conditions. Faba bean and chickpea plants were labelled in situ with 15 N using stem feeding and leaf feeding, respectively. NT increased the N derived from rhizodeposition (NdfR) with respect to CT (135 vs. 68 kg N ha −1 in faba bean and 115 vs. 97 kg N ha −1 in chickpea). Such differences between tillage methods can be attributed to the more favourable conditions for root growth produced by NT. NdfR was significantly influenced by depth; in faba bean, the greatest amount (70%) was found in the 0-30 cm layer, whereas in chickpea, 41% of the NdfR was concentrated in the 30-60 cm depth. The 54% and 61% of total plant N was NdfR (in faba bean and chickpea, respectively) representing 90% of the below-ground plant N in both crops. Our results show that the N derived from rhizodeposition is an important source for N balance and is a key to soil fertility in rain-fed Mediterranean cropping systems.
Erratum to ''Faba bean nitrogen fixation in a wheat-based rotation under rainfed Mediterranean co... more Erratum to ''Faba bean nitrogen fixation in a wheat-based rotation under rainfed Mediterranean conditions: Effect of tillage system'' [Field Crops Res. 98 (2006) 253-260]
A field experiment was conducted during a 2-year period (2001-2002 and 2002-2003) in Córdoba (Sou... more A field experiment was conducted during a 2-year period (2001-2002 and 2002-2003) in Córdoba (Southern Spain) on a rainfed Vertisol, within the wheat-faba bean rotation framework of a long-term experiment started en 1986, to determine the effects of tillage systems [no tillage (NT) and conventional tillage (CT)], on faba bean N 2 fixation. Fixation was calculated using the 15 N dilution and 15 N natural abundance methods using wheat as reference crop. Nitrogen derived from the atmosphere (Ndfa) percentages ranged between 70 and 96%, and N 2 fixed between 39 and 144 kg N ha À1 . The N balance was positive for all years and treatments, with a mean value of 18.3 kg N ha À1 and a maximum of 40 kg N ha À1 , in terms of above-ground biomass only. No significant difference was recorded between faba bean N 2 fixation values as calculated by the 15 N enriched (ID) method and the 15 N natural abundance (NA) method. The effect of tillage system on %Ndfa and the amount of N 2 fixed was not significant, possibly due to the negligible difference in soil NO 3 À -N content between the two systems. #
Efficient management of legumes in order to maximize benefits depends on a correct field assessme... more Efficient management of legumes in order to maximize benefits depends on a correct field assessment of N2 fixation. A field experiment was conducted during a 6-year period (2001–2002 to 2006–2007) in Córdoba (Southern Spain) on a rainfed Vertisol within the wheat-chickpea and wheat-faba bean rotation framework of a long-term experiment started in 1986. The aim was to determine the effect
The quantification of the below-ground N of legumes is a key to understand its effect on soil N f... more The quantification of the below-ground N of legumes is a key to understand its effect on soil N fertility and the N economy of subsequent legume-based rotations. Significant amounts of the N fixed by legumes are incorporated into the soil as fallen leaves and stems. However, the N from roots, nodules and root exudates has rarely been quantified under field conditions, nor have the management effects been evaluated. This study measured the effects of tillage system [no-tillage (NT) and conventional tillage (CT)] on N rhizodeposition in faba bean (Vicia faba L.) and chickpea (Cicer arietinum L.) during a 3-year period ) in a Vertisol under rainfed Mediterranean conditions. Faba bean and chickpea plants were labelled in situ with 15 N using stem feeding and leaf feeding, respectively. NT increased the N derived from rhizodeposition (NdfR) with respect to CT (135 vs. 68 kg N ha −1 in faba bean and 115 vs. 97 kg N ha −1 in chickpea). Such differences between tillage methods can be attributed to the more favourable conditions for root growth produced by NT. NdfR was significantly influenced by depth; in faba bean, the greatest amount (70%) was found in the 0-30 cm layer, whereas in chickpea, 41% of the NdfR was concentrated in the 30-60 cm depth. The 54% and 61% of total plant N was NdfR (in faba bean and chickpea, respectively) representing 90% of the below-ground plant N in both crops. Our results show that the N derived from rhizodeposition is an important source for N balance and is a key to soil fertility in rain-fed Mediterranean cropping systems.
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