Toward a sustainable farming model

terça-feira, 28 de junho de 2016
China, despite only having some 9 percent of the world’s farming lands — as farming land per capita here is less than 40 percent of the global average — is a net exporter of food and successfully feeds 21 percent of the world’s population through intensive agriculture. But this tremendous achievement comes at a cost.

Chinese agriculture, like intensive agricultural systems in many parts of the world, faces major environmental challenges. Soil erosion, soil pollution, water scarcity and loss of agricultural biodiversity are widely reported.

Intensive agricultural practices around the world are currently unsustainable. Under this system, crop yields are maintained through heavy fertilizer applications, which are unsustainable because these require high energy inputs to supply inorganic nitrogen (this process consumes 5 percent of the world’s natural gas production and 2 percent of the world’s annual energy supply).

It also depends on the mining of non-renewable rock phosphorus, diminishing stocks of which will become increasingly difficult to extract in the coming decades as the easiest-to-access ore with high phosphorus content has already been mined.

Further, it allows nutrients to wash out and pollute fresh and coastal waters, causing algal blooms and lethal oxygen depletion, as well as dispersing nutrients in the ocean.

Despite these high environmental costs of conventional intensive agriculture, and the widespread application of crop-breeding programs, we have been unable to improve the yields of several major crops, which have stagnated in the past 15 years.

China’s rapid industrialization has given rise to concerns over soil pollution. An official report by the country’s Ministry of Environmental Protection and the Ministry of Land and Resources found pollutants in 20 percent of arable land, exceeding national standards. Such land can be rehabilitated but this requires taking that land out of food production, with possible consequences for food security.

Other threats come from soil erosion: A government report published in 2008 estimated that 100 million Chinese could lose the land they live on within 35 years if soil erosion continued at the current rate.

While experts cited farming and forestry as the main causes, contributing to over a third of the area affected, the research team said erosion was damaging industrial areas and cities as well as remote rural land.

Water is an increasing issue in China too — water shortages, water pollution and flooding are all impacting growth and affecting public health and welfare in many parts of the country.

In 2011, China switched from being a predominantly rural society to one in which more than half the population live in cities. At the end of 2014, some 54 percent of the population lived in cities, up from 36 percent in 2000, according to World Bank data.

New intensive model

In a recent paper, the Grantham Centre for Sustainable Futures, a collaboration in the United Kingdom between the University of Sheffield and the Grantham Foundation for the Protection of the Environment, set out a model for a system of intensive agriculture that would address the needs of growing populations and developing economies in a sustainable way.

This model combines the lessons of history with the benefits of modern biotechnology, to redesign intensive agriculture.

Modern varieties of crops used in many intensive agricultural systems have been optimized for a system of high-nutrient artificial inputs and chemical control of pests and diseases. These crops have consequently lost their natural reliance on the microbes in soil which, in native varieties, enable plants to extract complex nutrients from the soil and to defend themselves against natural enemies.

Soil is thus becoming a hydroponic system: A physical substrate to support plants, but providing little else. In particular, deep ploughing has caused a decline of soil organic carbon, reducing the soil’s abilities to retain water and supply nutrients, and a loss of structure that allows rapid soil erosion.

As soil is lost rapidly but only replaced over millennia, this represents one of the greatest global threats for agriculture. It is the degraded state of our agricultural soils that appear responsible, at least in part, for the plateauing in yield for many of our crops.

In the 19th century, farmers in the UK had little access to artificial fertilizers, and consequently had to manage the soil well. Soil management combined the application of manures and the rotation of annual crops with grass and nitrogen-fixing legume cover crops which recharged soil carbon and nutrients as well as rebuilding soil’s physical structure.

These conservation-agriculture methods are today practiced in organic agriculture, where the resultant benefits of increased organic matter for soil structure, water-holding abilities, and nutrient availability are well established.

However, organic systems do not utilize advances made in agrichemistry inputs, meaning that yields are limited, thus rendering organic agriculture unsustainable in terms of feeding a growing global population.

Historically, good soil management was supplemented by the collection and application of “night soil” (human excrement), a practice that continued into the 20th century. In a historical example of the circular economy, this closed the nutrient loop, recycling organic nitrogen and phosphorus back into soil.

Modern approach

Additional benefits for soil organic matter are achieved in modern agriculture from the “no-till” method, where direct drilling is used to sow seeds, and cover crops and weeds are removed using herbicides, and ploughing is not needed. This approach reduces the oxidation of soil organic matter, conserving the soil structure.

This echoes China’s traditional farming practices which stretch back some 4,000 years. For most of this time, it used no chemical fertilizers or pesticides, yet supported small-scale intensively managed farms which maximized land productivity.

As with Europe in the 19th century, traditional Chinese practices included legume crops for nitrogen fixation, and the use of diverse crop varieties in rotation. Human, animal and crop wastes were also systematically recycled to maintain soil fertility.

Many of these successful Chinese agricultural practices were described by the American agronomist Franklin Hiram King in his book, Farmers of Forty Centuries, published shortly after his death in 1911. He said the key to 4,000 years of land fertility was the practice of “agriculture without waste”, with no use of external inputs.

While the enhanced use of cover crops almost certainly requires an increase in the land area used in agriculture, there is potential for less land to be in active cultivation at any one point in time.

A sustainable model for intensive agriculture could combine the lessons of Chinese and European history with the benefits of modern biotechnology, and is founded on three principles:

First, managing soil by direct manure application, the rotation of annual and cover crops, and practicing no-till agriculture.

Second, using biotechnology to wean crops off the artificial world we have created for them, enabling plants to initiate and sustain symbioses with soil microbes.

Third, this involves the recycling of nutrients from sewage, in a modern example of the circular economy. Inorganic fertilizers could be manufactured from human sewage in biorefineries operating at industrial or local scales.

Enhancing the biological functionality of soils allows it to store more water and nutrients, and support microbial communities that can boost plant health through direct suppression of soil-borne diseases and priming plant immune systems.

Of course no one model equally fits all problems, different agricultural scenarios (geography, climate, crop) will benefit from this approach more than others.

Redesigning the agricultural system would not be straightforward but, in doing so, we could reduce our dependence on energy-intensive and non-renewable inorganic fertilizer, reduce fertilizer pollution of watercourses, and create a soil fit for future generations.

Colin Osborne is associate director at the Grantham Centre for Sustainable Futures at the University of Sheffield in the UK.

Duncan Cameron is professor of plant and soil biology and co-director at the Plant Production and Protection (P3) centre for translational agricultural technologies at the University of Sheffield.

Mark Sinclair is the director of Science and Innovation Partnerships for Energy2050 at the University of Sheffield, on secondment from the UK government’s Foreign & Commonwealth Office Science & Innovation Network.

Fonte: China Daily Asia