I run a training class in Shu Han

Chapter 61 Bean and Wheat Rotation

The ancient traditional concept of soil conservation is not the same as the modern agricultural concept of soil maintenance. Rather, it refers to the practice of natural fallowing or extensive crop rotation to avoid excessive depletion of soil fertility.

Bashu has benefited from large-scale water conservancy projects such as Dujiangyan, which irrigate the land, improve soil moisture conditions, and enhance land productivity.

Later, when Cao Wei began to establish military agricultural settlements, it followed this method, digging deep ditches in the Huai River basin to irrigate farmland.

Fertilizer is also one of the effective means of maintaining soil fertility.

The fertilizer mainly comes from human and animal excrement.

Prior to this, Liu Shan had already instructed the Prime Minister's office to formulate a policy for improving the environment, which involved centrally piling up human and animal excrement.

In addition to reducing the occurrence of epidemics, human and animal excrement can be concentrated and fermented to become more efficient farmyard manure.

Another method is to burn straw and weeds to obtain potassium-rich wood ash, which can be buried in the soil to improve soil quality and provide trace elements.

These are valuable experiences that ordinary people have accumulated through long-term labor.

What Liu Shan is teaching today is another method of nourishing the land called "green manure".

Green manure is a method of fertilizing fields by turning over and compressing weeds, allowing them to decompose in the soil. Even without reading the textbooks compiled by Liu Shan, the students present were well aware of this method.

"There are so many kinds of grass in the world, but not all weeds can be used as fertilizer. The textbooks you all have have listed several plants that are suitable for fertilizer and the suitable soil types. If you have any questions, please feel free to ask."

Ancient people knew which grasses could be used as fertilizer, but when asked to explain why, they didn't know where to begin.

These are all summaries of long-term experience.

The textbook compiled by Liu Shan listed plants that could be used as green manure, such as sweet clover, red clover, vetch, radish, and sesbania, and explained in detail which types of soil they were suitable for planting.

Moreover, the book details the timing and depth of turning and compacting, as well as the timing of subsequent fertilization and water management, making it practically a guide for students.

This knowledge was the basic material Liu Shan needed when he was working on agricultural projects in his previous life, and he hadn't forgotten it even after transmigrating.

"Your Majesty, this old farmer is illiterate and cannot understand these words."

Most of the students in the agricultural science class were ordinary people who were illiterate, and some were even quite old, so they naturally couldn't understand the textbook content.

"It's alright. Then I'll just read it from the textbook." Liu Shan smiled and then read it from the textbook.

The information is so concise and clear that students can understand it immediately without any confusion.

"Besides learning farming techniques, you should also learn to read; this will be beneficial to you."

The students kept Liu Shan's earnest teachings in mind.

"Now there's another question: besides grass, what else can be used as green manure?"

The students looked up and exchanged bewildered glances.

Are there any other things in this world that can be used as green manure?

The officials sitting in the front row began flipping through the textbooks, searching for the answers.

But Liu Shan didn't write it at all.

"This is the key point of our lesson today. Remember this, everyone: it's soybeans!"

Soybeans?

The officials in the front row paused, wondering if they had misheard.

Soybeans are a grain, how can they be used as fertilizer?

"Your Majesty, beans are edible; why would you use them to fertilize the fields?"

An old farmer spoke the minds of everyone present.

Although beans are not a staple food, they can still fill your stomach. They are so precious, how can they be buried in the soil as fertilizer?

Liu Shan did not explain, but instead asked, "Then let me ask you, if you bury the beans you planted this year, and next year's wheat harvest will be 20% higher, will you bury them or not?"

Silence fell over the courtyard, for the students were filled with conflicting emotions.

To achieve a high harvest, one must forgo a season's worth of soybeans.

This season's soybeans may be their life-saving food.

This is gambling with the present for the future.

"But we need beans first..." someone muttered under their breath.

Liu Shan heard this and smiled slightly.

He knew that it wasn't that farmers were afraid to gamble, but rather that they didn't believe soybeans could fertilize the fields.

"Your Majesty, grass can fertilize fields, but that's because it rots in the ground. Beans are planted right here, they haven't even rotted yet, so how can they become fertilizer?"

Since no one dared to ask, Yang Min, as the supervisor of agriculture, naturally stepped forward.

"I ask you, why does the excrement people produce fertilize the fields after they eat?"

"Because there's something in the manure that makes the crops grow well."

"Yes. Where does the stuff in the excrement come from?"

Yang Min was stumped by the question.

Not only him, but no one present could answer the question.

Liu Shan continued, "Soybeans have a unique ability that no other crop possesses: they can transform things that are inedible in the sky into edible things in the ground."

The trainees stared wide-eyed.

Have you ever seen those little bumps that grow on the roots of soybeans?

Yang Min thought for a moment, then whispered, "Is it something round, like a tumor?"

"Yes. There are invisible 'little bugs' living in that lump."

Liu Shan paused for a moment, realizing that the term "rhizobium" was too advanced for his time, so he changed his mind and said, "I will call it 'hibernating insect.' This insect can turn the air from the sky into fertilizer for the earth."

Can the air in the sky turn into fertilizer?

This is yet another piece of knowledge that is beyond our comprehension.

Seeing that everyone still looked blank, Liu Shan continued, "Among the twenty-four solar terms, there is one called Jingzhe (Awakening of Insects)."

"The so-called 'awakening of hibernation' in the first month of the lunar calendar means the awakening of hibernating creatures. All things emerge from the 'Zhen' trigram, which represents thunder, hence the name 'Awakening of Insects'."

Suddenly, a student said, "Is the hibernating insect His Majesty mentioned related to the solar term 'Awakening of Insects'?"

Liu Shan's eyes lit up; finally, someone was keeping up with the pace.

Upon closer inspection, it turned out to be Lü Yi, the agricultural supervisor.

"As you all know, the 'Awakening of Insects' (惊蛰) means that spring thunder awakens insects from their winter slumber, marking the beginning of spring plowing. The louder the spring thunder, the better the crops will grow. What do you all think?"

The students nodded in agreement; these were words passed down from the older generation.

"Why is it that the louder the spring thunder, the bountiful the harvest?"

"Because when spring thunder comes, it will bring the air from the sky into the soil. Hibernating insects will eat this air and then turn it into fertilizer to nourish the land."

Liu Shan compiled teaching materials, and the knowledge was not difficult.

The principle behind nitrogen fixation by these rhizobia is that the root nodules convert inorganic nitrogen in the air into ammonia nitrogen that plants can absorb, thus providing nitrogen nutrients for the plants.

During thunderstorms, lightning can combine nitrogen and oxygen in the air to form nitrogen oxides, which enter the soil with rainwater and become nitrogen fertilizer that plants can absorb.

Lightning can also increase the germination rate of rice.

The difficulty lies in how to package modern scientific knowledge into language that ancient people could understand.

Liu Shan used familiar old sayings and wrapped them in a mythological veneer, making them more acceptable to the ancients.

Do you all still think that planting soybeans to fertilize the fields is a waste?

Yang Min stood up awkwardly and bowed deeply: "It is because of my limited knowledge."

At this moment, an old farmer slapped his thigh and said, "No wonder, we planted beans in our field, and the wheat harvest the following year was better than elsewhere."

Liu Shan was overjoyed again; someone else had come to provide assistance.

"Old man, you've hit the nail on the head. This is another key point I want to make next—soybean and wheat rotation."

"Soybeans not only don't deplete the land, they also nourish it. Planting one crop of soybeans leaves hundreds of kilograms of fertilizer per acre from the 'hibernating insects' on the roots. Burying the soybean stalks in the soil adds another hundreds of kilograms. The wheat planted next year will benefit from this fertilizer, growing taller and stronger, with a yield more than 20% higher!"

"In the future, we will plant one season of soybeans to fertilize the land, and then plant one season of wheat. We can harvest two crops of grain a year."

"The more the land is cultivated, the more fertile it becomes, and the more grain is harvested."

The old man's unintentional remark turned out to be a brilliant strategy from the emperor. He had shown off his skill in front of everyone, feeling both proud and embarrassed, and kept his head down with a smile.