It’s all in the mix: Diverse ecosystems are more efficient – this principle of nature can apparently also be transferred to the field, a study documents. Mixed cultures from different crops can therefore yield more yields than monocultures. By breeding optimized plant varieties and using specialized harvesting machines, the cultivation of mixed crops could be worthwhile in the future, say the scientists.
Only one crop grows as far as the eye can see: Large-scale monocultures shape modern agriculture. The uniformity is practical because it simplifies many cultivation methods – but the monotony also has disadvantages: the soil is emaciated on one side and pathogens can spread easily, as all plants are equally susceptible. This is one of the reasons for the great need for pesticides in conventional agriculture. This is why the advantages of mixed culture are already being used, especially in organic vegetable growing and in private gardens: Rows of carrots, onions, lettuce and the like alternate – several types of crops or varieties are grown side by side.
Is diversity worthwhile in the field?
A natural principle comes into play here: ecosystems can perform their functions better and produce more biomass if the biodiversity is great. The positive effect on plant productivity is already known in the case of agricultural ecosystems: “Research in agricultural meadows has shown that more diverse meadows are more productive than those made up of just one or a few sown species,” says Christian Schöb from the Swiss Federal Institute of Technology in Zurich. So far, however, there have hardly been any comparable studies for arable farming. That is why Schöb and his colleagues have now investigated to what extent mixed cultures also have a beneficial effect on the cultivation of plants in which the seed yield is in the foreground.
For this purpose, the scientists created two experimental cultivation areas: one in Switzerland and another in the dry and warmer Spanish province of Extremadura. For their experiments, they grew mixtures of two or four different crops. These were wheat, oats, coriander, quinoa, lentils, lupine, flax and a relative of rapeseed. These plants were sown alternately in parallel strips twelve centimeters apart. No pesticides were used in the experiments.
The comparison with the seed yields of the same plant species in monoculture showed that even from mixtures of two species it rose by three percent in Spain and by 21 percent in Switzerland. If the researchers sowed four species side by side, the additional yield was as much as 13 and 44 percent in Spain and Switzerland. The researchers attribute the additional yield achieved to the biodiversity effect. It is therefore becoming apparent that the diversity of these arable crops enables better utilization of the available resources and, above all, better, natural control of harmful pathogens.
The bottom line is more seed yield
As the researchers also report, the mixed culture also had a surprising effect: the plants form more leaves and longer stems than in monoculture. Overall, this resulted in more biomass. However, the following applies: The investment in the vegetative parts of the plant tends to be at the expense of seed production. Nevertheless, due to the overall stronger growth, the advantage remains, emphasizes Schöb: “In spite of everything, the mixed culture led to a higher seed yield than the monoculture”.
According to the researchers, the effect that the plants invested more energy in the development of vegetative biomass could also be a side effect of the breeding of the varieties used. Because their yield was only optimized with growth among their peers. Conversely, it seems possible that the potential for additional yield can be better exploited with seeds that are adapted to mixed crops, say the scientists. At the moment, however, there are no seed producers who offer varieties specifically for use in mixed cultures. The researchers are therefore now planning to develop appropriate plants or seeds. “We would like to repeat our experiments with these self-produced seeds to see whether the selection in a mixed culture bears fruit in the truest sense of the word,” says Schöb.
In order for the mixed culture to prevail in cultivation, another aspect is also important, the researchers emphasize in conclusion: Machines are necessary that can simultaneously harvest different crops and separate the crop. “Such machines already exist, but they are still the exception and expensive, probably because there has been little demand for them so far,” says Schöb. By combining optimized seeds with suitable machines, however, the cultivation of mixed crops could ultimately be worthwhile for many farmers, believes the agricultural researcher.
Source: Swiss Federal Institute of Technology Zurich, specialist article: Nature Plants, doi: 10.1038 / s41477-021-00948-4