Nutrient acquisition strategies in agroforestry systems

Abstract

Background Disentangling nutrient acquisition strategies between trees and crops is central to understanding positive nutrient interactions in agroforestry systems for improved low-input agriculture. However, as plants are responsive to a complex soil matrix at multiple scales, generalizable diagnostics across diverse agroforests remains challenging. Scope We synthesize research at various scales of the tree-crop interface that are cumulatively hypothesized to underpin nutrient acquisition strategies in agroforestry systems. These scales span the whole root system to fine-scale sites of acquisition actively engaged in biological and chemical interactions with soil. We target vertical and horizontal dimensions of acquisition patterns; localized root-soil dynamics including biological associations; root-scale plasticity for higher acquisition; and nutrient additions via biological nitrogen fixation and deep soil nutrient uplift. We consolidate methodological advances and the effects of environmental change on wellestablished nutrient interactions. Conclusions Root distribution patterns remain one of the most universal indicators of nutrient acquisition strategies in a range of agroforestry systems, while root functional traits are emerging as an effective root-scale indicator of nutrient acquisition strategy. We validate that in agroforestry systems crop root functional traits reveal bivariate trade-offs similar to, but weaker than, crops in monoculture, with mechanistic links to nutrient acquisition strategies. While interspecific root overlap may be associated with nutrient competition, clear cases of enhanced chemically and microbially meditated processes result in species-and management-specific nutrient facilitation. We argue for agroforestry science to use distinct and standardized nutrient acquisition indicators and processes at multiple scales to generate more nuanced, while also generalizable, diagnostics of tree-crop interactions. And extensive research is needed on how agroforestry practices stabilize key nutrient acquisition patterns in the face of environmental change.

Climate change adaptation in and through agroforestry: four decades of research initiated by Peter Huxley

“…Recent advances and perspectives on belowground functioning of AF systems (Cardinael et al 2020) include, beyond the water and nitrogen cycle, advances on functional trait classifications of roots (Isaac and Borden 2020;Borden et al 2020) and an understanding of how competition with winter crops induces deeper rooting of walnut trees in a Mediterranean alley-cropping AF system (Cardinael et al 2015a, b). Further progress on tree root system is in recognition of the soil binding and soil anchoring functions that together reduce landslide risks on sloping land, subject to high-intensity rainfall events (Hairiah et al 2020a, b).…”

Agroforestry Benefits and Challenges for Adoption in Europe and Beyond

“…Due to the diversity of crop and tree species in AFS, yields are more stable in cases of adverse climatic conditions [141,142], reducing the risk exposure for the farmers. Further, there is better nutrient cycling due to the complementarity in time and space in resource use between the crop and tree species, enhancing the resource use and cycling [143] within the production system. AFS are not without challenges due to various reasons.…”

Influence of Duration of Agroforestry on Physico-Chemical Soil Quality Parameters in Machakos County, Kenya

“…In this case, the cover function involves reducing raindrop impact and wind action on soil particles by increasing soil cover through litter and pruning. The most widely held view is that trees in agroforestry systems can improve soil quality mainly by biological nitrogen (N) fixation and increasing the amounts of aboveground and belowground organic matter inputs (Isaac & Borden, 2019;Sarabia et al, 2020). There are a number of benefits that are directly related to soil quality including preventing soil erosion through surface litter cover and under story vegetation (Akdemir et al, 2016;Béliveau et al, 2017), improving water infiltration (Sahin et al, 2016), increasing soil moiture (Cardinael et al, 2017;Feliciano et al, 2018), maintaining soil fertility (Liu et al, 2018), enhancing water dynamics (Ling et al, 2017;Hasselquist et al, 2018), conserving soil biodiversity (Torralba et al, 2016), improving soil microbial biomass (Buyer et al, 2017) and mitigation of climate change by carbon sequestration (Newaj et al, 2016;Hasselquist et al, 2018).…”