Long-term experiments show that ecological intensiﬁcation stores carbon and restores soil health

New evidence suggests that climate change can be mitigated by using some ecologically-sound farming practices. Long-term experiments, of 10 years or more, in Africa and Europe, show that yields of maize and other key crops are improved when farmers use ecological intensification practices. These include crop diversity (such as intercropping and crop rotation), planting fertility-improving crops (especially legumes), and applying manure or other organic fertilizer. Ecological intensification can be high yielding, while saving on mineral fertilizer, especially nitrogen, reducing greenhouse gas emissions.

Conservation (Left) vs. conventional (Right) agriculture during El Niño. ©Christian Thierfelder / CIMMYT.

Agriculture needs long-term experiments to assess the consequences of farming practices over time. It only takes a few years to destroy soil health, but much more time to rebuild it. Because of annual variations in the weather, trials must be repeated for several years. Painstaking, quantitative research over many years by CIMMYT has shown that in the long-run, farmers can increase their harvests, while reducing greenhouse gas emissions. With ecological intensification, agriculture does not have to be a cause and a casualty of climate change.

Agriculture contributes to climate change, which also makes farming more difficult.

Fortunately, some of the practices that help farmers adapt to climate change also mitigate its effects. Excessive soil tillage, pesticides and mineral fertilizers increase carbon emissions, so curbing their use could help global agriculture to return to a “safe operating space,” according to work by CIMMYT.

CIMMYT scientists contributed to a study on long-term experiments in Europe and Africa, published in Nature Sustainability. Data from more than 30 experiments show that ecological intensification (crop diversity, fertility-improving crops and organic fertilizer) increases the yields of maize, wheat and other staple crops, especially when mineral nitrogen fertilizer is used at low rates. Ecological intensification may take some years to show its benefits, so long-term experiments are crucial for measuring their value over time.

Diversifying farms, with intercropping or crop rotation, reduces weed pressure, pests and diseases, lowering the demand for chemical pesticides. Fields of diverse crops yield more than monocrops, and provide a buffer against the negative effects of extreme weather.

Excessive nitrogen application does not necessarily increase yields as it may be washed away if the soils are too depleted. In Africa, such soils have sometimes been called “non-responsive soils” and there is no easy fix to bring them back into production. However, adding crop residues and animal manure at the soil surface increases soil carbon, which holds more nutrients and makes them available over time, as plants need them. This also restores the soil’s health and biodiversity.

Aerial view of long-term trials. ©Christian Thierfelder / CIMMYT.

Results from the long-term experiments show that increased tillage does not raise yields, but it often leads to soil erosion, depletion and compaction, suggesting that plowing can be reduced, saving on fuel expenses.

Conservation agriculture, one strategy of ecological intensification, is based on the three principles of crop diversification, keeping the ground covered with crop residues and minimizing soil disturbance. At long-term experiments at six research locations in four countries (Zimbabwe, Zambia, Mozambique and Malawi) yields of maize varieties were significantly higher when all three principles of conservation agriculture were applied, especially when the crops were diversified with legumes. Moderate rates of nitrogen fertilizer can enhance yields in conservation agriculture.

“These long-term experiments show that it is possible to sequester more carbon into the soil, although it requires sufficient amounts of crop residues and a conducive diversification strategy. This has beneficial effect on our climate as less greenhouse gases, especially carbon dioxide, are being emitted,” says Christian Thierfelder, a principal cropping systems agronomist at CIMMYT in Zimbabwe, who has led the long-term experiments in southern Africa.

Conservation agriculture three principles

Minimizing
soil
disturbance

Crop
diversification

Keeping
the ground
covered with
crop residues

Farmers in Asia, Africa and Latin America can harvest more maize and other staple food crops while lowering their production costs and improving soil health. It has been important to gather data over several years, because it takes time for ecological intensification and conservation agriculture to bear fruit. It is also necessary to assess these systems under a changing climate as cropping seasons become increasingly variable. Conservation agriculture is especially beneficial in areas with low or moderate rainfall. So, ecological intensification and conservation agriculture can help farmers adapt to climate change while keeping their soil fertile.

Organic fertilizer and rotations with fertility- improving crops improve maize yields and sequester carbon. ©Christian Thierfelder / CIMMYT.

Agriculture needs long-term experiments to assess the consequences of farming practices over time.

Adding crop residues and animal manure at the soil surface increases soil carbon, which holds more nutrients and makes them available over time, as plants need them.