Nitrogen symbiotically fixed by cowpea and gliricidia in traditional and agroforestry systems under semiarid conditions

Júlio César Rodrigues Martins,Rômulo Simões Cezar Menezes,Everardo Valadares De Sá Barretto Sampaio,Ana Dolores Santiago De Freitas

doi:10.1590/s0100-204x2015000200010

Júlio César Rodrigues Martins, Rômulo Simões Cezar Menezes + Show 2 more

Open Access

https://doi.org/10.1590/s0100-204x2015000200010

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Abstract

The objective of this work was to estimate the amounts of N fixed by cowpea in a traditional system and by cowpea and gliricidia in an agroforestry system in the Brazilian Northeast semiarid. The experiment was carried out in a randomized complete block design, in a split-plot arrangement, with four replicates, in the semiarid region of the state of Paraíba, Brazil. Plots consisted of agroforestry and traditional systems (no trees), and split-plots of the three crops planted between the tree rows in the agroforestry system. To estimate N fixation, plant samples were collected in the fourth growth cycle of the perennial species and in the fourth planting cycle of the annual species. In the agroforestry system with buffel grass and prickly-pear cactus, gliricidia plants symbiotically fix high proportions of N (>50%) and contribute with higher N amounts (40 kg ha-1 in leaves) than in the traditional system (11 kg ha-1 in grain and 18 kg ha-1 in straw). In the agroforestry system with maize and cowpea, gliricidia plants do not fix nitrogen, and N input is limited to the fixation by cowpea (2.7 kg ha-1), which is lower than in the traditional system due to its lower biomass production.

Highlights

Agroforestry systems with trees or shrub alleys within annual crop fields can be an option to reduce the fragility of certain agricultural production systems (Wick & Tiessen, 2008; Foroughbakhch et al, 2009; Li et al, 2009; Kurppa et al, 2010; Sousa et al, 2010; Lima et al, 2011)
In Kenya, for instance, from 70 to 90% of the N in the biomass of Sesbania sesban and Calliandra calothyrsus was derived from symbiotically fixed N (SFN), amounting to 120 to 360 kg ha‐1 N (Stahl et al, 2002), whereas in Sudan, 48% of the N in pure stands of Acacia senegal were fixed from the atmosphere (%Ndfa), introducing 36 kg ha‐1 N per year to the agrosystem (Raddad et al, 2005)
There was no effect of the production system on the 15N concentrations of the herb reference species (A. tenella), but the reference tree species (M. glaziovii) had a lower signal value when intercropped with maize + cowpea (Table 1)

Summary

Introduction

Agroforestry systems with trees or shrub alleys within annual crop fields can be an option to reduce the fragility of certain agricultural production systems (Wick & Tiessen, 2008; Foroughbakhch et al, 2009; Li et al, 2009; Kurppa et al, 2010; Sousa et al, 2010; Lima et al, 2011) Those systems produce a considerable amount of biomass that can be incorporated into the soil, transferring nutrients from the trees to the crops (Bertalot et al, 2010; Munroe & Isaac, 2014). SFN may represent relevant N inputs to soil‐plant systems, decreasing the need of N fertilizer application, which is frequently the most expensive among commercial fertilizers

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