【Knowledge Expansion】Mutual Promotion and Inhibition among Crops

I. Mutually Promoting Crops

In the long-term production process, it has often been found that when two crops are planted together, some get along closely and harmoniously, helping each other, while some are like enemies, competing with each other and causing damage to both (i.e., allelopathy).

1.Corn and soybeans are good friends. Corn likes to absorb nitrogen fertilizer, and soybeans can produce nitrogen fertilizer through root nodules. Besides using a small part for themselves, soybeans selflessly supply most of the nitrogen to corn. In return, corn can secrete high levels of carbohydrates, providing nutrients for the rhizobia needed by soybeans.

2.If vegetable farmers plant only one type of vegetable, pests often occur seriously. However, if some pungent vegetables such as garlic, onions, leeks and peppers are interplanted, pests will be reluctant to approach. When onions are planted next to wheat or peas, the secretions of onions can kill the smut spores of wheat or the black spot disease of peas within a few seconds. Onions are like green doctors, able to protect their neighbors safe and sound and help them achieve a good harvest.

3.Similarly, when garlic and cotton are planted together, garlic emits a bactericidal substance that can drive away aphids. Other pests will also flee when they smell this deadly gas.

4.Planting a few castor plants beside soybean fields can make scarab beetles run away. If sorghum is interplanted at intervals of 1.5 to 2 meters on both sides of cotton ridges, then sorghum aphids can attract various aphid natural enemies such as aphid wasps, spiders, ladybugs and hoverflies to control cotton aphids, feed on cotton bollworm eggs and young larvae. Meanwhile, interplanting 200 to 300 plants of sorghum or corn per 700 square meters will not affect cotton production and can also prevent cotton from lodging caused by wind and rain.

5.When potatoes are intercropped with barley, barley can achieve high yields. This is not only because they have different nutrient requirements and can make full use of soil fertility, but also because the leaves of potatoes secrete a substance that can promote the growth of barley like a growth hormone. Interplanting 300 to 400 lettuce or mint plants evenly per mu in the fields of cruciferous vegetables such as Chinese cabbage. Due to the alkaloids, volatile oils or other chemical substances contained in lettuce and mint, the cabbage white butterflies that harm cruciferous vegetables will stay away under the stimulation of the smell emitted by lettuce and mint.

6.Planting green manure, beans, peanuts, etc. in the orchard can not only fertilize the soil and control weeds, but also promote the growth and fruiting of fruit trees. Planting wheat under jujube trees, jujube trees hardly shade the wheat and can also reduce the threat of dry and hot winds before the wheat matures. Meanwhile, the fertilizer and water for wheat are also beneficial to the growth of jujube trees. If nematodes seriously damage the orchard, marigolds or asparagus can be planted in the orchard, so that the fruit tree nematodes in the ground will not be able to conceive and reproduce. Planting some nasturtiums beside pear trees and apple trees. Since the roots of these fruit trees can absorb the secretions of nasturtium roots, the occurrence of diseases and pests is also less.

7.Cherries and apples are mutually beneficial. If planted together, they can each release a volatile gas, absorb each other's gas, and thus promote their growth and development. The fruits they bear are especially sweet. Black locust and poplar are "good friends". Black locust is a shallow-rooted tree species, and poplar is a deep-rooted tree species. They do not compete for water and fertilizer with each other. Moreover, the rhizobia of black locust can fix nitrogen and supply it to poplar, promoting its growth. If cucumbers and cowpeas are planted together, they will both show exuberant vitality and increase in yield.

II. Mutually Inhibiting Crops

In the plant world, there are also some crops that are like enemies, which is called mutual inhibition.

1.The chemical substances secreted by hemp, mustard and flax have a significant inhibitory effect on wheat in the following crop rotation.

2.Sunflowers, tomatoes, apples and pumpkins can promote the occurrence of potato late blight.

3.If cypress trees are planted beside grapes, the grapes will hardly ripen.

4.When mustard and castor are planted together, although castor is taller and stronger than mustard and has an advantage in competing for sunlight, air and water, a large number of leaves at the bottom of castor always wither. The reason is that the secretions of mustard are harmful to the growth of castor.

5.There is also the weed Sonchus oleraceus in the field. The surrounding crops, even tall crops such as corn and sorghum, will turn yellow and wither. This is because the roots of Sonchus oleraceus will secrete a toxic anesthetic substance that can inhibit and kill these crops.

6.The influence of this kind of close or distant relationship among crops is not only manifested during the same growing period in the current year, but some also leave sequelae and continue to harm the next crop. This is the case with buckwheat and corn. When corn is planted in the field where buckwheat has been planted, although there is sufficient fertilizer and water and proper management, the corn always grows poorly and does not achieve high yields.

Why Do Such Relationships Exist?

It turns out that many crops can secrete some gases or juices, such as various volatile oils, organic acids, alkaloids, etc. These secretions are released from leaves, stems and flowers, or from roots. The secretions of one crop may play a role in promoting the growth of another crop, or indirectly affect other crops through the activities of various microorganisms and pests. These phenomena tell us that we must arrange planting scientifically according to the wonderful relationships among crops. Only in this way can we achieve higher yields.

III. Table of Mutual Promotion and Inhibition