Nitrogen dynamics in agroforestry systems. A review

Abstract

Agroforestry is an agricultural diversification practice that purposefully grows trees together with crops and/or animals. Nitrogen (N) plays a pivotal role in the sustainability and productivity of these systems. In this study, we synthesize our current understanding and data availability of N dynamics in agroforestry systems, providing the first comprehensive synthesis on major N pathways in agroforests. We review five categories of N pools and fluxes: N input, internal N cycle, N sequestration, N loss, and N output. Within these categories, we compile data from worldwide measurements of N input and N gaseous emissions. The N inputs among agroforestry systems are from N 2 fixation through leguminous trees (global average: 240 kg N ha -1 yr -1 ), organic amendments and inorganic fertilizers (36 kg N ha -1 yr -1 ), and, possibly, undocumented N deposition. Various pathways are identified in internal N cycles: direct transfer of fixed N from tree to crop, N mineralization of organic matter originating from trees, pumping up subsoil N by tree roots, and ammonia captured by trees. Agroforestry practices almost consistently show reductions in N loss, via soil erosion, runoff, and leaching. Agroforestry systems release gaseous N as nitrous oxide (N 2 O) (~4.7 kg N 2 O-N ha -1 yr -1 ) and nitric oxide (NO). While N 2 O emissions in agroforestry are either higher (improved fallows) or lower (riparian buffers) in comparison to monocropping, NO emissions are similar in agroforestry (improved fallows) and monocropping. The N sequestration rates in agroforestry soil pools (98-154 kg N ha −1 yr −1 ) are three times higher than biomass pools (36-43 kg N ha −1 yr −1 ). Since agroforestry practices can increase crop yield and N content in crops, this translates into higher N output in agroforestry systems. Studies are required to accurately quantify sub-components of N pools and fluxes and identify mitigation measures to manage N loss in agroforestry systems.

Le statut organique des sols à Saint-Raphaël : quels mécanismes, quelles pratiques agricoles et quels indicateurs ?

“…En conséquence, plus la proportion en carbone organique associée aux particules fines est forte, plus le COS sera considéré comme stable (Barré et al, 2020). Nos résultats ont montré, en raison de sa plus forte concentration en COS, que le système agroforestier peut augmenter la production agricole, améliorer le stockage et la séquestration du carbone organique et du coup atténuer les émissions de gaz à effet de serre, réduire l'érosion des sols, conserver la biodiversité et améliorer la fertilité des sols et la sécurité alimentaire en Haïti (Tsonkova et al, 2014 ;Torralba et al 2016 ;Kim et Isaac, 2022, Dorvil et al, 2023. Enfin, l'agroforesterie est donc une pratique pouvant concilier performance agronomique/fertilité et préservation de l'environnement à Saint-Raphaël.…”

Planting patterns in rubber agroforestry (Hevea brasiliensis) developed by the communities of Menggala Mas Village, Lampung Province, Indonesia

“…Furthermore, well-managed agroforestry practices can boost crop productivity by creating a favourable micro-climate, controlling pest outbreaks, improving soil structure, fertility and soil water content, enhancing crop pollination and providing habitat (Bentrup et al 2019;Kim and Isaac 2022). Agroforestry also has many benefits for the society, especially in improving the economy and food security (Herwanti et al 2022).…”

Nutrient Contribution and Carbon Sequestration of an Agroforestry System of Coffea canephora Cultivated by Conventional and Organic Management in the Ecuadorian Amazon

“…Thevathasan et al [53] indicate that when biomass is produced in an agroforestry system, nutrient cycling can, over time, promote the accumulation of N in the soil. Schroth [54] mentions that coffee and cocoa plantations under leguminous shade provide 3 and 14 t ha −1 yr −1 of biomass, containing 60 and 340 kg of N, while, in alley cropping with perennial herbaceous and woody crops in rotation (Quercus rubra and Carya illinoinensis), the amount of N in the biomass was 86, 233, 6.3, and 1.9 kg ha −1 [55]. In this study, it was determined that AFSs provided a higher N supply than monocultures, which is in agreement with Schroth [54], who mentions that the amount of biomass produced by N-fixing trees has higher concentrations of this element than that produced by non-fixing species, where the amount of N depends mainly on the phenological stage (senescence or fruiting).…”