Brazilian agriculture plays a major role in the world’s grain production, as the country has rapidly ascended to the position of 2nd largest soybean producer and 3rd largest maize producer. A large part of this success is due to the country’s large area where soybeans and another crop (generally maize) can be planted consecutively in the same year, termed double-cropping systems. However, climate change poses a major threat to these systems, especially in the country’s latest agricultural frontier.
Over the course of a few decades, soybeans in Brazil evolved from being a localized crop, with planting suitable only in higher latitude regions, to being the most cultivated crop countrywide. This happened gradually after the 1970s thanks to the development of varieties that were more adapted to the conditions of central and northern Brazil. One of the most important developments was the removal of the photoperiod (duration of the day) dependence of the soy plants. This allowed the expansion of the crop to regions more to the north where days are never too long, but also had a side effect. As the plant stopped needing longer days, it could be planted in a wider time window in the higher latitudes (Figure 1).
Figure 1: Estimates of the limiting factors for soybeans in a double-cropping system by latitude. Solid, thick lines represent the planting date windows considering the photoperiod limitations of the varieties available during the selected harvest years. As less photoperiod-dependent varieties were developed, planting could happen in a wider window in higher latitudes. The blue horizontal bars represent the climatological range of the beginning of the rainy season (20th, 50th, and 80th percentiles). Shaded regions represent soy planting windows that are able to accommodate a second crop (e.g. maize) in the same rainy season. (Republished with permission from Elsevier)
We combined estimates of this photoperiod dependence with another important limiting factor for planting in Brazil: the rainy season. In many regions, the rainy season was large enough for planting two crops if the first one could be planted early, and the removal of the photoperiod limitation allowed the large-scale adoption of those systems after the 1990s. Today, more than half of Brazilian maize is planted as a second crop after soy, and adoption of these systems is still growing rapidly.
However, the dependence on a long rainy season is still an issue for double-cropping, especially in a large region in northeastern Brazil, dubbed MATOPIBA after its states’ acronyms, which is one of the world’s most active agricultural frontiers and where these systems are quickly expanding. The study shows that climate change caused both by GHG emissions and the deforestation of Brazilian biomes, is likely to harm Brazil’s double cropping potential. Under the pessimistic (but currently most realistic) climate change scenario developed by the International Panel on Climate Change (IPCC), the RCP 8.5, the area where double cropping is possible in central Brazil where most of the production is would shrink ~17% by 2050. In MATOPIBA, where currently large investments are being made in agricultural expansion, this reduction would be of around 60%, more than halving the area where these highly profitable systems would be possible. Technological improvements will likely play a role in offsetting these effects but are unlikely to solve the problem.
We evaluated whether soy and maize varieties that are able to yield well with a very short development cycle of 90 days, that currently do not exist, would make it possible to squeeze two crops in the likely shorter rainy seasons of the future. Using these hypothetical varieties would still lead to a reduction of the area where double cropping is possible of 4-7% in central Brazil, and a still high 30% in MATOPIBA.
Such large changes in double cropping potential will likely lead to a reduction in land prices, severe damages to the economy of some recently (and still poorly) developed regions, and increased pressure for further deforestation of both the cerrado biome, which MATOPIBA is part of and the neighboring Amazon. Although the last years have seen governmental and private measures to protect the Amazon being successful to some extent, the cerrado biodiversity hotspot is still largely unprotected.
Figure 2: Historical changes in double cropping suitability due to the development of new varieties. Note the major changes in central Brazil until the 1990s (Republished with permission from Elsevier)
Figure 3: Historical and projected total area where double cropping (DC) is possible. SB: Southern Brazil; CB: Central Brazil; MT: state of Mato grosso, the country’s largest soybean producer. (Republished with permission from Elsevier)
These findings are described in the article entitled Evolution of rain and photoperiod limitations on the soybean growing season in Brazil: The rise (and possible fall) of double-cropping systems, recently published in the journal Agricultural and Forest Meteorology. This work was conducted by Gabriel M. Abrahão and Marcos H. Costa from the Federal University of Viçosa.