Food Security Discussion Series
Summary by Dr Jane O'Sullivan
8 September 2016
“Food security: some challenging thoughts about current developments from a soil management perspective”
When we get down to the roots of sustainability issues of farming systems, they are in the soil. Gunnar Kirchhof shared insights from many years of working with farmers in both developed and developing countries, addressing challenges in soil degradation and soil remediation.
Conservation Agriculture (CA) is the term used by the FAO (Food and Agriculture Organisation of the United Nations) for a suite of practices intended to minimise damage to soil, and to remediate damaged soil. Its main approaches include:
- Continuous minimisation of mechanical disturbance,
- Permanent organic cover of soil surface, and
- Diversification of crop species grown in sequence and/or association.
In practice, minimum tillage is supported by other inputs, including herbicides to control weeds and fertilisers to achieve surface cover of plants. While the complexity of this technology “package” has been a barrier to uptake in some instances, it has been described as a “three-legged stool”, which does not function without each of its parts.
Its claimed benefits include increased carbon sequestration, increased or more stable yield, reduced soil compaction, increased soil available water, increased water infiltration and consequent reduction in erosion. In reality, the latter is the most consistent and most important outcome. The other impacts are more site-dependent and many farmers may not achieve them. For example, in NSW black vertisols, conversion to CA greatly increased saturated hydraulic conductivity (i.e. water penetration and drainage) but on grey vertisols, there was little change. On some soils, there is a yield penalty after conversion to CA, but it may improve over time and outperform conventional tillage in the longer term. Impacts on organic carbon are variable and depend on starting condition: on previously depleted soils, there is more chance of increasing soil carbon. On many soils, CA may simply slow the loss of soil carbon rather than achieve net sequestration. A meta-analysis of 69 studies found no increase in soil carbon in most cases.
Despite not living up to many of its claimed soil-related benefits for farmers, CA has been widely adopted and persisted with by farmers in developed countries. This appears to be largely due to the cost saving from minimum tillage, enabled by a fall in price of herbicide while fuel prices rose during the early 1990s. But subsistence farmers do not experience the same incentives. Uptake in different countries has depended on political support.
Problems encountered by CA adopters include pest and disease management (resulting from leaving crop residues in the field) and herbicide resistance (where herbicide use is frequent, resulting in a need for occasional tillage for weed control). On hard-setting soils in the west African Guinea savannah, CA may take a long time to remediate the root zone, to restore yield to the level farmers expect following tillage. Alternatively, by starting with a one-off aggressive tillage to incorporate organic material, subsequent CA management may be beneficial.
Gunnar felt that the wholesale push for CA adoption in sub-Saharan Africa, by UN agencies and aid organisations, risked disenchantment through over-promising and could spoil its potential to reduce soil degradation when used appropriately. A more pragmatic approach would see targeted CA promotion in the agro-ecological zones where success rates are expected to be high.
CA is part of a wider FAO agenda for agro-ecology, defined as “an ecological approach to agriculture that views agricultural areas as ecosystems and is concerned with the ecological impact of agricultural practices”. In practise this title encompasses a range of approaches with widely varying levels of scientific backing, from agroforestry and integrated pest management to organic farming, use of biochar and bans on genetically modified organisms (GMOs). The promotion of organic agriculture in particular has become pervasive through non-scientific channels. They largely originated in Europe where organic farming was a convenient response to the problem of manure disposal, in a context of subsidised intensive animal production, and where the upstream impacts of the fodder and animal enterprises are not included in the footprint of the “organic” product. However, a back-of-envelope calculation shows that the nitrogen needs for global cereal production alone can’t be met from legume crops and the manure from the world’s livestock. The global food system depends on synthetic nitrogen fertiliser. Yet in developing countries, beliefs are now entrenched about chemical fertilisers making unhealthy food, poisoning the soil or causing infertility in women, and that soil microbes can make all the nutrients crops need. Likewise, there is widespread awareness of biochar and its claimed benefits despite their lack of substantiation and the high environmental impact of biochar production.
Some of the real solutions lie in promoting CA where it is likely to succeed, rainwater harvesting (but issues of infrastructure maintenance and malaria breeding must be managed) and innovative agroindustries which coordinate, resource and train smallholders to produce at a high commercial standard.
Our discussion explored the power of an established mindset to resist education and evidence intended to dispel myths. Bias exists not only among students but among researchers and journal editors, readily accepting positive claims and sceptical of negative findings in relation to such topics as CA, organics or biochar. The Australian government’s promotion of “carbon farming” is based on highly selective case studies. But people may do the right thing for the wrong reasons – we need to consider what incentives may motivate them.
Browse other summaries from the Food Security Discussion Series here.