Abstract

Summary: Soil research has been a prominent part of the agroforestry research agenda from the start of the current World Agroforestry Centre as ICRAF in 1978 with a focus on new answers to land degradation problems. Early hopes that, in order to be widely adopted, agroforestry primarily lacked policy support and effective extension rather than research, proved to be too simple. While policy attention was drawn to the need for soil replenishment in Africa and for alternatives to slash-and-burn throughout the humid tropics, the specific ways to achieve these goals in the local context were under investigation. A research agenda was framed that saw trees on farms and in agricultural landscapes as ways to conserve and improve soil carbon (C) stocks, add nitrogen (N) by use of N2-fixing trees, mobilize poorly available phosphorous (P) sources and capture deep soil nutrient stocks and mobile nutrients on the way out by leaching. Simultaneously the trees should be a source of valuable products (such as firewood, timber, fodder, fruits, medicinal bark and roots), a regulator of (micro)climate and watershed functions, and a provider of supportive functions for crops and animals. In doing so the experience with bottom-up approaches showed that local ecological knowledge of soils included classifications and functional insights complementary to what formal science had as yet explored. A phase of research on hypotheses at process level, analyzing the various tree-soil-crop interactions one by one, was followed by the construction of synthetic simulation models. Meanwhile, the early use of plot level experimentation, inherited from agronomic traditions, proved to be a challenge as lateral tree roots were difficult to control unless plot sizes were large and replicated trials huge. Beyond plotlevel experiments, research shifted from characterizing to managing lateral resource flows and filter functions, reinterpreting the earlier erosion control emphasis at hill-slope and landscape scales. Dynamics of soil water led to quantification of soil structure and its dependence on root-based carbon inputs, old tree root channels and earthworms. Further soil biological work was focused on mycorrhiza, rhizobia, nematodes and other soil biota. The more fundamental understanding of soil biology, led to early work on soil carbon dynamics and greenhouse gas emissions from tropical land use, especially in humid tropical forest margins. Reducing and avoiding below- and aboveground emissions were combined in the search for alternatives to slash and burn. Understanding the underlying principles required for sustainable and profitable land use, with or without trees, contributed to a general trend where promises of packaged technology evolved into supporting farmer knowledge and decisions. Agroforestry practices aimed at soil fertility improvement were extensively tested on farms, which led to a better understanding of the risks and benefits under different conditions. A focus on the diverse realities on farm meant that laboratory methods for soil characterization had to be scaled up and simplified. The use of soil spectral properties proved to be efficient in dealing with the spatial diversity of soils in both landscape and farm level applications. However, at the end of the day, our funders and investors want to see and be assured of pathways to development impact, and demonstrating that through changes in soil quality over the long-term and over large extents requires wider application of these methods. The concepts of soil function in multifunctional landscapes, the interdisciplinary integration of tools and approaches, and the direct linkage of growing knowledge and increased action will continue to evolve, but can be rooted in a rich tradition and are on solid ground.

Keywords

agroforestry, multifunctionality

Published in

ICRAF Working Paper
2015, number: 200, pages: 1-25
Publisher: World Agroforestry Centre (ICRAF)

SLU Authors

• Öborn, Ingrid

  • Department of Crop Production Ecology, Swedish University of Agricultural Sciences
    
  • World Agroforestry Centre (ICRAF)

UKÄ Subject classification

Soil Science
Environmental Sciences related to Agriculture and Land-use


Publication identifier

DOI: https://doi.org/10.5716/WP15023.PDF

Permanent link to this page (URI)

https://res.slu.se/id/publ/72296