Nowadays, single cultivation occupies the dominant position of arable land, and large areas of land are occupied by single, promising fine varieties with high yield. However, arable land growing only one crop has its disadvantages: these areas can easily be targeted by fungi and pests and pose a threat to crops. In order to control pests, farmers have to use insect-resistant varieties and various insecticides.
Mixed cultures provide a potential option for single cultures. Instead of planting only one species or variety on a large area of land, multiple species or varieties are sown side by side. However, because there are few studies on this method, especially from an agricultural point of view, mixed cultures are rare in cultivable agriculture.
A team led by Professor Christian at the Federal Institute of Technology in Zurich now reveals that mixed cultures actually produce higher yields than single cultures in cultivable agriculture. Their study was recently published in the journal Nature Plants.
Mixed culture draws on the ecological principle that ecosystems can more effectively function in places where biodiversity is high. These functions include regulating water balance, maintaining soil fertility and improving plant productivity.
This also applies to agroecosystems: "Studies of grasslands used in agriculture have shown that areas with more plant mixes are more productive than areas with only one or several plants," Schb says.
So far, almost no similar study has focused on cultivable agriculture. That's why, he and his colleague start investigating whether such basic ecological mechanisms can also have an impact on arable land, particularly in terms of yield.
The researchers created two test gardens: one at the University of Zurich's Irchell Campus in Switzerland and the other in Estremadura Province in Spain. The latter climate is much drier and warmer than Zurich, which allows researchers to study how these crops grow under possible future climatic conditions.
In their experiment, the researchers selected two or four different crops from eight selected crops, including wheat, oats, quinoa, lentils, lentils, flax, and pseudoflax (a rapeseed rapeseed) as well as coriander. Only seeds of different species were used. These crops were sown in alternating parallel rows at 12 cm intervals.
The researchers compared seed quality between mixed-cultivated crops and monoculture crops. They also measured plant biomass based on plant growth on the ground.
The results were self-evident: even mixed cultivation of both crops increased yield by 3% in Spain and 21% in Switzerland compared with single cultivation. Where the researchers sown the four crops simultaneously, yield increases were as high as 13% and 44% in Spain and Switzerland, respectively.
The researchers explain that this additional yield is mainly due to biodiversity effects: more plant species can better utilize existing resources and more effectively control natural pests, and experiments are performed without the use of pesticides.
However, the researchers also point out that mixed-cultivated plants grow more leaves or stems than single-cultivated ones. In other words, plants invest more energy and material in producing vegetative biomass, while correspondingly less in producing seeds. Schb explained that plants have to make compromises: the more energy they invest in plant biomass, the less energy they use for seeds. “Nevertheless, in equilibrium, these plants still produce more seeds than single cultivation,” the agricultural researcher said.
He attributed the fact that plants invested more energy in creating vegetative biomass to the variety used in the experiment. “These seeds are exclusively bred for a single variety. This means that these plants perform best when they are grown in other conspecifics.”
Schb believes that seeds suitable for mixed cultivation may have greater potential for additional yield.
Over time, people have changed most crops to produce fruits and higher yields under monoculture conditions. Compared to wild tomatoes, tomatoes grown today are huge, and the fruits of wild tomatoes are blueberry sized. In order to obtain the best possible yield from mixed cultivation, current breeding methods, targeted cultivation with single cultivation, must be slightly adjusted.
As far as the present situation is concerned, no seeds are produced or sold specifically for mixed cultures. Therefore, researchers are busy harvesting and testing their own experimental seeds. “We want to repeat our experiments with these self-produced seeds so that we can test whether selection in mixed cultures really produces results.”
However, agricultural practices need to be changed if mixed cultures are to make progress. In addition to this, machines need to be able to harvest different crops simultaneously and separate different harvest products. “These machines do exist, but the numbers are small, let alone expensive." There is currently too little need for them. Combined with optimized seeds and correct machines, mixed cultures will provide a real opportunity for the future of farmers.
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