Soil damage, climate change, water and energy availability are all challenges for farming
S&T have made key contributions to increasing food production, but new strategies are needed
Sustainable agriculture can benefit from 'system' approaches and farmers' participation
Farming must feed more people more sustainably. Zareen Bharucha looks at scientific approaches past and present.
Advances in agricultural science and technology (S&T) have contributed to remarkable increases in food production since the mid-twentieth century. Global agriculture has grown 2.5–3 times over the last 50 years. [1] This has let food production keep pace with human population growth so that, overall, there are enough calories produced per capita. However, progress toward reducing hunger is variable across the world (see figure 1). Copyright: FAOFigure 1. 2012 Global Hunger Index scores [2] Click on the image above to enlargeHunger and malnutrition affect every aspect of human development and persist for various reasons including unequal access to land, to sufficient and nutritious food, and to other productive resources. Adequate food production is necessary but insufficient to ensure national nutritional security. In India, for example, millions of households suffer from chronic undernourishment and malnutrition despite the fact that favourable years produce more than enough grain, and there is a public distribution system designed to supply poor households with subsidised grain. [3]
Agricultural production needs to increase to address this unequal access to food and resources, and to meet the needs of a growing world population. It may need to increase by an estimated 70 per cent globally and by 100 per cent in developing countries by 2050 in order to keep pace with population growth and shifting diets.
Reformed agrifood systems will also need to navigate complex resource limits imposed, in part, by environmental degradation to which modern agriculture has contributed.
So the challenge for agriculture is three-fold: to increase agricultural production, especially of nutrient-rich foods, to do so in ways which reduce inequality, and to reverse and prevent resource degradation. S&T can play a vital role in meeting these challenges — for example, by developing innovations that smallholders with limited resources can afford and use.
Land and water pressures
About 12 per cent (1.6 billion hectares) of the world's land area is used for agriculture. Land degradation, or the loss of land's productive capacity, is a global problem (figure 2), but especially in dryland regions, a quarter of which are devoted to agriculture. [4] Drylands also support over 30 per cent of the world's population. [5]
Copyright: ISRICFigure 2. Global loss of Net Primary Productivity in degrading areas, 1981–2003 [6] Click on the image above to enlargeWater management is another major challenge. Agriculture accounts for 70 per cent of all water taken from aquifers, streams, rivers and lakes. [1] To meet projected demands, the efficiency of water use (crop produced 'per drop') will need to improve in both irrigated and rainfed zones.
Forty per cent of global increases in food production have come from irrigated areas. By 2050, the area under irrigation is projected to increase by six per cent over 2009 levels, and agricultural water withdrawals will need to increase by ten per cent over current levels. [1]
Rainfed systems are the world's largest agricultural system, taking up 80 per cent of cultivated land area and producing 60 per cent of the world's crops. In Africa, rainfed agriculture produces 97 per cent of staples. [1] Rainfed zones overlap with regions where risks of land degradation are highest, and wheresmallholder farming predominates. Yet, these are the very regions which will need to play a bigger role in providing food in the future — because the world's capacity to expand irrigation is limited, and the damage caused by over-irrigation and large-scale irrigation projects (such as land degradation and habitat loss) is now widely recognised.
Region
Yield gap* (%) in 2005
East Asia
11
Southeast Asia
32
Northern America
33
Western and Central Europe
36
Australia and New Zealand
40
Western Asia
49
Southern America
52
South Asia
55
Pacific Islands
57
Northern Africa
60
Eastern Europe and Russian Federation
63
Central Asia
64
Central America and Caribbean
65
Sub-Saharan Africa
76
*The difference between optimal and actual yield affected by real-life conditions and challenges such as environmental degradation or poor management.
Table 1: Yield gaps for cereals, roots and tubers, pulses, sugar crops, oil crops and vegetables in 2005 [1]
Soil health
Crop productivity is also constrained by land management practices that lead to erosion, waterlogging and salinization (salt build-up), and loss of nutrients from soils. Overgrazing, over-irrigation, using too much or too little inorganic fertilizer, ploughing and other mechanical disturbance all contribute to poor soils. Soil degradation is a particular problem in tropical developing countries, where soil is often less 'forgiving' of poor management. Across Africa, for example, agriculture that removes soil nutrients such as nitrogen, potassium and phosphorus without replenishing them (sometimes termed nutrient mining) contributes to low crop productivity. Phosphorus availability is a key concern. Phosphorus is essential for plant growth and, unlike nitrogen fertilizers, cannot be produced artificially. Phosphorus is mined from finite deposits that are expected to be depleted in 70-125 years. [7] Strategies for dealing with this include managing soil phosphorus by judiciously applying inorganic fertiliser, preventing soil erosion, recycling nutrient-rich biodegradable waste (a traditional source of soil nutrients across much of the developing world) and crop improvements which modify plant roots to enable them to better absorb available soil phosphorus.
Energy and climate change
Another key constraint is energy availability, specifically of fossil fuels. Modern agriculture is energy intensive — tractor and transport fuel, producing agri-chemicals and storing and processing food all depend on affordable fossil fuels. So there are growing concerns about the carbon footprint of the agrifood sector.
Agriculture contributes around 13.5 per cent of global greenhouse gas emissions as a result of cultivation practices and the expansion of agricultural land into forest areas, releasing stored carbon from above and below ground.
And there are complex, context-specific impacts associated with climate change. Delayed or early onset of seasons, more variable precipitation and temperatures, and increasing incidence of climate 'shocks' — such as unpredictable dry spells — can all affect plant growth. To adapt to these changes farmers will need knowledge, financial and social support and a package of context-specific technologies (some old, some new).
Fundamental transformation
These challenges and constraints call for a fundamental transformation in agriculture across the world. Increasing food production could follow either extensification (converting forests, grasslands and other 'natural' ecosystems into cropland) or intensification (increasing the amount produced per hectare within existing cropland). Intensification is generally preferred as it spares other ecosystems from agricultural use.
To meet food demands, intensified agriculture will need to close so-called 'yield gaps' — the difference between current yields and those obtainable under optimal management — in ways that prevent, or in some cases reverse, environmental harm. Table 1 shows global yield gaps for key agricultural commodities.
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