Drowning weeds

  Barnyard grass used to be the ancestor of rice. For thousands of years, under the continuous intervention of humans, it eventually evolved into rice. After rice has become a food crop, it grows together with barnyardgrass and sedge, which are indistinguishable from each other. People often refer to barnyardgrass and sedge as weeds.
  Weeds and rice grow together, and they rob soil nutrients with rice, which is extremely detrimental to the growth of rice. Scientific research has found that if there are ten weeds in a square meter of rice field, rice yield will be greatly affected. If weed seeds are mixed into rice, the quality and taste of rice will also be greatly reduced. Therefore, farmers always try to get rid of weeds.
  Rice and weeds are close relatives. They are very similar when they just grow out of the ground. They are flat and slender. However, experienced farmers can still distinguish them from each other. The unique ears and tongues on the leaves can distinguish the two. In addition, some people distinguish them by the color and hairiness of the leaves. The principles of the two methods are basically the same, mainly relying on human eyesight. However, the efficiency of manual separation and removal of weeds is too low to meet the demand for large-scale rice planting.
  In order to get rid of weeds, humans have tried various methods, but the effect is very little. After thousands of experiments, humans found that rice can survive in water, but weeds have difficulty adapting to life in water. So smart humans flood the rice fields to drown the weeds.
  Under normal circumstances, it is difficult for plant roots to breathe underwater, but rice can tolerate a certain amount of water. After the first irrigation, the rice plant was almost dying, the leaves drooped to one side, and the body became soft. But don’t worry, rice can endure one day and one night in the water.
  Some people worry that the rice will rot if it is soaked in water. In fact, in the process of phylogeny and evolution, rice has formed tissues with efficient ventilation, air permeability, and air storage functions in the body-air cavity and marrow cavity. As long as a few leaf tips can be exposed above the water, they will not suffocate. Dead and able to perform aerobic breathing. If the rice is completely immersed in water, it will be forced to undergo anaerobic respiration and will die in four to five days.
  Rice needs to be irrigated after transplanting, tillering, panicle formation, and after heading and blooming. The first irrigation can remove most of the weeds. After the water is drained, the rice can quickly resurrect. After several irrigations, the weeds can also be removed to varying degrees.
  Although humans have already mastered the technology of drowning weeds with water, no one really understands the mystery. In the 1940s, the Dutch botanist Van Raert first uncovered the water tolerance of rice.
  Van Raert found that soaking rice in water will cause the cell death of some of the rice roots, but the dead cells quickly become aerated tissue coleoptiles that communicate with the leaves to ensure that the roots can breathe freely.
  Because weeds are close relatives, weeds are also adaptable to irrigation, but their water tolerance can’t compete with rice, so they will drown early. On the other hand, the method of flooding to remove weeds and reduce the use of herbicides is a very environmentally friendly approach.
  So, the deeper the irrigation, the more likely the weeds will be drowned? The answer is no. The water depth of five to twenty centimeters is the limit that rice can tolerate. Rice will be drowned if it exceeds this height. Therefore, controlling the water depth and draining the water in time can ensure the rapid resurrection of rice.
  Drowning weeds is the survival wisdom of rice.

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