Can crop planting also be done by men and women, so that work is not tiring? - Interplanting doubles the yield

Produced by | Science Popularization China

Produced by Lei Kexin (Journalism, Chongqing University), Zhao Xumao (Young Researcher, Lanzhou University)

Producer | China Science Expo

As the saying goes, "When men and women work together, work is not tiring." In primitive society, due to differences in physiology and other aspects between men and women, a clear social division of labor naturally emerged: men farmed and women wove. This form of cooperation greatly improved the work efficiency of the society at that time.

In fact, this "matching" method of human society is also applicable to crop production, but it has a new name - intercropping. Let's take a look at how they divide the work and cooperate.

What is an intercropping system

As early as the first century BC, in order to improve land productivity, humans invented a planting method called "intercropping" in which two or more crops were planted alternately in rows or strips on the same field during the same growing season.

Intercropping is a common diversified cropping system that is widely used in sustainable farmland production. Studies have shown that this planting method improves the productivity of intercropping systems by utilizing ecological principles to enhance positive interactions and complementarity between plants and reduce interspecific competition intensity.

However, although humans have a long history of using interspecies technology, there has long been a lack of understanding of how the interactions between different plant species in semi-arid agricultural ecosystems affect land productivity.

A close-up shot of ripe wheat next to a green soybean field. Source: veer

However, a recent research result by Chinese scientists may help solve this mystery.

On May 10, 2022, the School of Ecology of Lanzhou University, in collaboration with the State Key Laboratory of Grassland Agro-Ecosystems, published a research result titled "Water use of intercropped species: Maize-soybean, soybean-wheat and wheat-maize" in the famous journal Agricultural Water Management. The research results clarified that the rational allocation of diversified planting patterns with water complementary characteristics in semi-arid areas will help to exert positive interactions between plant species and improve land productivity.

How does intercropping increase land productivity?

In the "Gongsun Chou Chapter and Verses" of "Mencius", it is mentioned that "take advantage of the situation and wait for the right time, and you can achieve twice the result with half the effort", which emphasizes that we should learn to take advantage of favorable situations to achieve double the achievements.

According to the principle of intercropping, if plants can properly utilize positive interactions and compensation mechanisms, they can gain advantages in nutrient enrichment, resource sharing, niche complementarity and reduced interspecific competition in their growth.

Based on the above background, this study was carried out to address the water shortage problem in the arid areas of northwest my country. By setting up corn-soybean, wheat-soybean and corn-wheat intercropping systems in the field, the inter-species competition trajectories and soil moisture dynamics of different intercropping combinations, the photosynthetic physiological characteristics and growth rates of different intercropping combinations were studied, and the effects of inter-species water complementarity on the productivity of intercropping systems in semi-arid areas were explored.

“Survival of the fittest”. Any two different species will compete for the same resources. Especially when the living habits of the two competing species are more similar, the competition will be more intense, and the winner is often clear. In the face of resource scarcity in semi-arid areas, competition is more significant, and species diversity is particularly lacking.

However, the study found that compared with the monocropping system, intercropping with soybeans can significantly increase the biomass and maximum growth rate (Imax) of corn and wheat.

Soybean and corn crops | Source: veer

That is to say, in the combination of corn-soybean and soybean-wheat, corn and wheat have similar temperaments to soybeans, and they make progress together under the "incentive effect" of soybeans throughout the growth period, rather than the survival of the fittest.

Soybeans are like selfless elders who serve without asking for anything in return. While promoting the growth of wheat and corn, the biomass and growth rate of soybeans are not significantly affected.

Not only that, by studying the photosynthetic characteristics of each species during the symbiotic period and the compensatory growth period, it was found that intercropping with soybeans also significantly increased the nitrogen content, chlorophyll content and photosynthetic rate of corn and wheat leaves, making corn and wheat grow more vigorously and produce more and fuller fruits.

Soybeans mature near corn fields in spring | Source: veer

However, wheat and corn are a pair of "enemies" who never give in to each other. Not only that, wheat is slightly more competitive than corn.

In the wheat-corn intercropping model, wheat's biomass and growth rate in the early stage of symbiosis are much higher than corn. Although corn recovers and gradually surpasses wheat in the compensatory growth period after wheat harvest, the inhibitory effect of intercropping with wheat on corn growth cannot be denied.

At the same time, due to the "suppression" of wheat, the nitrogen accumulation, chlorophyll content and photosynthetic rate of corn leaves also decreased significantly, which resulted in the inability of corn to recover within the compensation period, greatly reducing corn yield.

Three crops compete for water

We can see that with the help of soybeans, soybeans, corn and wheat all obtain sufficient nutrition. However, just "eating" without "drinking water" is not enough, especially in the semi-arid northwest region where water resources are scarce.

So, how do the three intercropping combinations of soybean-wheat, soybean-corn, and wheat-corn perform in terms of water resource competition?

First, intercropping with soybeans significantly increased soil moisture content in the 0-100 cm range in both maize and wheat strips throughout the growing period.

But in July, wheat matured and consumed a lot of water. As the dominant species in all layers, it absorbed soil moisture from soybean and corn strips for compensatory utilization, resulting in a significant decrease in soil moisture content in soybean and corn strips.

After wheat was harvested in mid-to-late July, soybeans and corn entered the compensatory growth period, and it was not until mid-September that water was basically replenished.

Soybean and corn fields mature in spring | Source: veer

Mencius emphasized that "on the road to success, the right time, the right place and the right people are the three essential elements, which cover everything on the road to success."

In nature, "the right time and the right place" are the environmental conditions for crop production, and "harmony between people" represents the artificial species configuration. The research results show that crop diversity depends on species configuration and environmental conditions to form intercropping species combinations with complementary advantages. For example, the soybean-wheat and soybean-corn intercropping systems are beneficial to improving crop productivity.

Therefore, rationally configuring the traits of intercropping species and selecting intercropping combinations with water complementarity and utilization advantages for application in semi-arid areas will help improve water resource utilization efficiency and promote crop yields through underground niche complementarity.

In the later stage, the research will continue to rationally combine and configure the traits of intercropping species according to environmental conditions, thereby improving interspecies complementarity while reducing their competition intensity.

Win-win cooperation is a great magic weapon for human beings to gain a foothold in society, and this magic weapon is also applicable to nature. Scientists work together to complement the advantages of intercropping systems. Under such concerted efforts, even in extremely harsh environments, fruits that can nourish the local area can be grown.

Wang Wei, a doctoral student in ecology at the School of Ecology, Lanzhou University, is the first author of the article, and Professor Xiong Youcai is the corresponding author. The research was supported by the National Natural Science Foundation of China's International Cooperation Key Project, the Gansu Province Key R&D Project, and the Gansu Academy of Sciences Application Development Project Fund.

Editor | Wang Tingting

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