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<p>The integration of pigeon pea as a leguminous shrub into agroforestry systems (AFS) is expected to enhance soil nitrogen and its availability for associated crops. This study aimed to estimate, over a three-month period, the atmospheric nitrogen fixation rate (%Ndfa) by two-year-old pigeon pea (<i>Cajanus cajan</i>) grown as a sole crop and in association with cassava (<i>Manihot esculenta</i>), and the transfer of N from pigeon pea to cassava (%Ndft) in the mixed pigeon pea-cassava plots. The <sup>15</sup>N isotope dilution method was used with six-month-old sole cassava crops as reference. Nine plots (three replicates per treatment) were randomly selected in farmers’ fields. A 100&#xa0;m<sup>2</sup> area was delimited in each plot for <sup>15</sup>N soil labeling using 98 atom% <sup>15</sup>N-NH<sub>4</sub> solution. Plant samples were collected from both species for isotopic analysis. Results showed that %Ndfa was 100% in both pigeon pea systems. Considering %Ndfa of 100% from planting date, the quantity of N fixed was twice as high in sole pigeon pea (19.7&#xa0;kg&#xa0;N&#xa0;ha<sup>−1</sup>) as in mixed pigeon pea-cassava (7.4&#xa0;kg&#xa0;N&#xa0;ha<sup>−1</sup>). This finding was consistent with the 2.8 times higher planting density in sole pigeon pea plots compared to mixed pigeon pea-cassava plots. Nitrogen transfer from pigeon pea to cassava was greater (73.9%) when the cassava plant was positioned between pigeon pea rows (in the middle) rather than adjacent to them (42.8%). Our results suggest that integrating pigeon pea into semi-arid AFS could enhance the nitrogen status of the associated crop, particularly in unfertilized AFS.</p>

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High rates of nitrogen fixation and transfer by pigeon pea (Cajanus cajan) to associated crops in a semi-arid agroforestry system

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年5月26日

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  • Sarah Rakotozafy,
  • Bruno Bordron,
  • Tantely Razafimbelo,
  • Malalatiana Razafindrakoto,
  • Kirsten vom Brocke,
  • Hajasoa Mosa Redida,
  • Jean-Pierre Bouillet

摘要

The integration of pigeon pea as a leguminous shrub into agroforestry systems (AFS) is expected to enhance soil nitrogen and its availability for associated crops. This study aimed to estimate, over a three-month period, the atmospheric nitrogen fixation rate (%Ndfa) by two-year-old pigeon pea (Cajanus cajan) grown as a sole crop and in association with cassava (Manihot esculenta), and the transfer of N from pigeon pea to cassava (%Ndft) in the mixed pigeon pea-cassava plots. The 15N isotope dilution method was used with six-month-old sole cassava crops as reference. Nine plots (three replicates per treatment) were randomly selected in farmers’ fields. A 100 m2 area was delimited in each plot for 15N soil labeling using 98 atom% 15N-NH4 solution. Plant samples were collected from both species for isotopic analysis. Results showed that %Ndfa was 100% in both pigeon pea systems. Considering %Ndfa of 100% from planting date, the quantity of N fixed was twice as high in sole pigeon pea (19.7 kg N ha−1) as in mixed pigeon pea-cassava (7.4 kg N ha−1). This finding was consistent with the 2.8 times higher planting density in sole pigeon pea plots compared to mixed pigeon pea-cassava plots. Nitrogen transfer from pigeon pea to cassava was greater (73.9%) when the cassava plant was positioned between pigeon pea rows (in the middle) rather than adjacent to them (42.8%). Our results suggest that integrating pigeon pea into semi-arid AFS could enhance the nitrogen status of the associated crop, particularly in unfertilized AFS.