Research points to advantages of intercropping sorghum with tropical grasses

Growing two crops in the same area enhances land-use efficiency while boosting atmospheric carbon sequestration and soil nutrient cycling.

By Karina Toledo  |  Agência FAPESP – Intercropping of sorghum with tropical perennial grasses can be both economically advantageous and beneficial for the environment, according to a series of studies conducted at São Paulo State University’s Botucatu School of Agricultural Sciences (FCA-UNESP) in Brazil.

Some of the most recent results, obtained with support from FAPESP, were published in Agronomy Journal.

“Our research shows that intercropping not only doesn’t interfere with grain yield but also enhances land-use efficiency by providing pasture of excellent quality during the dry season. This can help avoid livestock weight loss, as well as increasing carbon sequestration and soil nutrient cycling,” said Carlos Alexandre Costa Crusciol, a professor at FCA-UNESP and coordinator of the research.

Over the past 15 years, with support from FAPESP, Crusciol’s group has focused on studying the benefits of intercropping grain crops such as corn, soybeans and sorghum with tropical grasses such as palisade grass (Urochloa brizantha) and guinea grass (Panicum maximum). One of their aims is to propose integrated crop-livestock systems as an alternative for the rehabilitation of degraded areas and a means of optimizing agricultural land use.

Their results have already been published in the European Journal of Agronomy, Crop & Pasture Science and Crop Science. They previously published several articles in Agronomy Journal, in 2012, 2013 and 2015, among other publications.

Recent studies performed in PhD research by Gustavo Pavan Mateus at the São Paulo State Agribusiness Technology Agency (APTA/Andradina) and Nídia Raquel Costa at FCA-UNESP analyzed sorghum intercropping with palisade grass compared to guinea grass. Researchers at UNESP’s Botucatu School of Veterinary Medicine & Animal Science (FMVZ), the US Department of Agriculture (USDA) and North Carolina State University (NC State) collaborated.

In these studies, the researchers set out to determine which grass species performed best in terms of nutrient competition, grain yield, forage dry matter, and land-use efficiency.

According to Crusciol, the experiments showed that palisade grass competes less with sorghum for nutrients and improves grain yield. “In this case, the yield was similar to that of sorghum alone [monocropped],” he said. “Guinea grass is more aggressive: it competes more for nutrients and reduces grain yield even when nitrogen fertilizer is used.” 

The experiments also showed that to obtain the best results it is necessary to increase the top-dressing nitrogen fertilizer rate by at least 50% compared with the rate recommended for monocropped sorghum by the São Paulo State Agronomy Institute (IAC) in Technical Bulletin 100. No parameters for sorghum intercropping nitrogen use have previously been published in the scientific literature.

Methodology

In the methodology tested by Crusciol’s group, sorghum is sown in November at a depth of 4 centimeters (cm), and grass seeds are sown with fertilizer at a depth of 7 cm.

“The sorghum emerges between seven and ten days before the grass and therefore dominates competition for nutrients. The grass is shaded by the sorghum canopy and develops slowly because it receives less light,” Crusciol said.

The grain is harvested after approximately 120 days. The sorghum plants reach the end of their lifecycle and then begin to dry up and wither. The grass then becomes fully developed and covers the entire area, which can be used for grazing.

“It’s normally possible to use the area as pasture about 30-40 days after the grain harvest. The livestock can graze there throughout the dry season in fall and winter, when pasture production falls sharply in Brazil owing to lack of rain. The grass is young and has roots that go down as far as 2 meters, so it’s more drought-tolerant,” Crusciol explained.

At the start of spring, animals should be withdrawn from the area, and the farmer should wait 20 days for the pasture to grow back. A herbicide can then be applied to desiccate the plants.

“The grass dies and becomes straw, which helps the soil retain moisture. It also contains nutrients that will be returned to the soil via recycling. This is a way of bringing to the surface the nutrients that are wasted deeper underground. The roots of sorghum plants aren’t as deep as the roots of these grass species. [With the intercropping process] you reduce nutrient leaching and avoid contaminating the water table. This system also protects the soil against erosion and prevents silting of rivers,” Crusciol said.

After the grass has desiccated, the cycle resumes with no-tillage planting of grain crops. “These [crops] could be sorghum again in November, but also kidney beans, soybeans, corn, rice or cotton,” Crusciol said.

The system could work well in several regions of São Paulo State, he added, such as Araraquara, Araçatuba, Bauru, Marília, Presidente Prudente, Ribeirão Preto and São José do Rio Preto. It would also succeed throughout the Cerrado and in many African countries with climates similar to Brazil’s.

“These two species of perennial grass originated in Africa, and the production system would certainly work well there,” he said. “Another factor that makes intercropping an attractive proposition for Africa is that sorghum is part of many people’s everyday diet there. In Brazil, it’s mainly for animal feed, just as it is in the rest of South America, North America, Europe and Australia.”

Crusciol also believes other parts of the world with a tropical or subtropical climate, such as Australia and the southern United States, could benefit from this sorghum intercropping system. In terms of production and acreage, sorghum is the world’s fifth most important cereal crop, after corn, rice, wheat and barley. Among its advantages over corn and soybeans, for example, is greater tolerance to water stress and less fertile soil.

Repercussions

After publication of the article in Agronomy Journal, the group’s findings were also highlighted by CSA News, the official magazine of the American Society of Agronomy (ASA), the Crop Science Society of America (CSSA) and the Soil Science Society of America (SSSA). It became UNESP’s first study to be published as a “web story” – a news story posted on their websites. According to Crusciol, it was also publicized by media linked to the US agricultural sector.

Although this type of intercropping system is well known and fairly widely practiced in Brazil, it is considered innovative in the US.

“People used to fear that grasses would compete with grain crops and turn into weeds,” Crusciol said. “We’ve shown that this competition can be greatly reduced and that you can produce grain and pasture on the same acreage. Or you can use this biomass to generate bioenergy. In any event, the farmer makes the area productive during a period when it would normally be fallow.”