Chapter 38
“Save the Soil with Math!”
(Kai and Rutia’s Summer Vacation Arc ⑦)
The next morning, Kai returned from the duke’s mansion to the farmland.
Rutia, his two older brothers, and the villagers were all waiting for him.
In the middle of the field stood a large board and some chalk—he was fully prepared in teacher mode.
“Alright then. Today’s lesson is Soil Studies.”
“Lesson…?”
“I’m a teacher, remember? So everyone here’s my students for today.”
The villagers looked at one another uncertainly, but soon their gazes turned serious.
Kai grabbed a handful of soil and took out a bottle the apothecary had prepared.
It contained a special herbal solution that changed color depending on whether the soil was acidic or alkaline.
“First, a pH check. If it’s acidic, it turns red. If it’s alkaline, it turns blue.”
When he put in the soil, the liquid turned reddish.
“See that? It’s leaning acidic. That’s one of the reasons your crops have been struggling.”
The villagers’ eyes widened.
“You can tell just from the color?!”
“Sir Kai, are you also an alchemist?”
“Nah, nah. Just a bit of scientific play, that’s all.”
Kai began writing an equation on the board:
Yield = aN + bP + cK + dH₂O
“N is nitrogen, P is phosphorus, and K is potassium—the three essential nutrients for plants.
And when they’re balanced with the right amount of water, that’s when you get a proper harvest.”
“Ooooh…”
The villagers murmured in awe.
“Right now, your soil’s got too much nitrogen and not enough phosphorus and potassium. That’s why the leaves grow like crazy, but no fruits form.”
The villagers exchanged glances.
“True… the leaves do grow well, but the fruit’s always small.”
“I see now…!”
Kai placed three fertilizer bags before them—
one rich in nitrogen, one containing bone meal (phosphorus), and one with ash (potassium).
“Mix these in a 1:1:1 ratio and spread it evenly. Then build a system to distribute water uniformly.”
“A ratio… it’s that simple?”
“Yep. Simplicity is strength. In both math and farming, balance is everything.”
They tested his advice on one corner of the field, spreading the fertilizer and drawing water from the well.
Kai even used a bit of magic to carve small irrigation channels to help the water soak in properly.
“Give it about a week, and you’ll start to see results.”
The villagers nodded—half in doubt, half in hope.
◆◇◆
A week later—
When everyone returned to the farm, what they saw took their breath away.
The crops were vibrant and green, bursting with life.
Where once only small fruits had grown, now hung large, ripe tomatoes and eggplants in clusters.
“Wh-what is this?!”
“The harvest has doubled—no, more than doubled!”
The villagers cheered and rushed toward Kai.
“Teacher! You’ve saved our fields!”
“With this, we can survive the winter!”
Rutia threw her arms around Kai, her eyes sparkling.
“My lord! I knew it—only you can save this land!”
“Stop calling me that! I’m just a math teacher!”
Brother Wilhelm nodded deeply, his expression earnest.
“Sir Cross, this deed is worth a hundred times more than wielding a sword in war.”
Julius smiled.
“To this land, you’re already a hero.”
“I’m no hero! Just a teacher!”
Then one of the farmers shouted,
“Banzai! Long live Master Cross, the son-in-law!”
“Don’t call me son-in-law!!!”
But the villagers only shouted louder—
“Son-in-law! Son-in-law!”—clapping and cheering.
Rutia clung to his arm, utterly delighted, refusing to let go.
