GLTEN Africa: Cropping system diversity, a cornerstone of sustainable intensification.

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The former Director General of the United Nations, Kofi Annan, has called for a 'uniquely African Green Revolution'. Implicit in this statement is the acknowledgement that the first Green Revolution that provided the template for the modern intensive agriculture and that dominates landscapes in Europe, much of Asia and North America may not be sustainable in the long term. This first Green Revolution that began in the 1960s, was based on the breeding of high yielding varieties of a few crops coupled with high inputs of fertilisers and crop protection products. An emerging problem with this way of farming is that the heavy reliance on inorganic fertilisers and chemical pesticides results in 'open leaky' systems with impacts on the environment including diffuse pollution and losses of biodiversity. There is also evidence that these systems may not be sustainable from a farming perspective as the health of soils declines and pests, weeds and diseases evolve resistance to pesticides. In contrast, large areas of Sub-Saharan Africa are still cropped on a much smaller scale with lower inputs and a greater diversity of crops but with much lower productivity. It can be argued, therefore that the UK and Sub-Saharan Africa are at opposite ends of the intensification spectrum but both are unsustainable (either in terms of food production or the environment).We expect that a more diverse system in terms of the number of different crops grown and variety of crop management practices used will provide food and nutrition more sustainably because different crops will be more or less affected by variability in the weather between years. Because, there are differences in how crops use nutrients from the soil, a more diverse mixture of crops would also be expected to be more efficient and reduce impacts on the environment. We will study the importance of the existing diversity in cropping systems in Sub-Saharan Africa. By doing this, we will be able to recommend ways of increasing production that retains the right level of crop and management diversity to ensure the systems are resilient. To quantify the value of diversity of cropping systems in Africa, we will use data from Long Term Experiments (LTEs) that have been running over several decades in Africa and the UK. These experiments will be used to compare how farming in different ways over many years contributes to sustainability in terms of the health of the soil, stability of food supply and use of natural resources. When considering ideas such as 'sustainability' or 'resilience' it is important to have experiments like these that do not just look at short term effects of a change of practice but are able to capture effects that are only evident over the medium to long term - as is the case for the impact of management on soil health. The results of the work on the LTEs will be combined with a survey of farms in four regions in Sub-Saharan Africa (N-Nigeria, Eastern Rwanda, parts of Malawi and Western Kenya) to collect data on the existing variety in the types of crops and ways they are grown. We will particularly interested in the local use of crops that are not grown on a wide scale. By combining this information with what we have learnt from the LTEs about the relationship between cropping system diversity and sustainability, we will be able to compare the different systems and identify the ones that strike the best balance between providing food and protecting the environment. This work will be supported by computer models that are able to predict how potentially novel combinations would deliver food and environemntal benefits.