An organic-based amendments with biochar and rabbit urine improve maize (Zea mays L.) growth, physiology, and soil microbial activity in acidic soils of Cameroon

Imagine the soil beneath our feet not just as dirt, but as a bustling, underground city. In this city, tiny microbes are the workers, breaking down food and recycling nutrients so plants can eat. But sometimes, this city gets into trouble. In many parts of the world, especially in tropical regions, the soil has become "acidic," which is like turning the city's water supply sour and washing away the essential building blocks plants need to grow. When the soil is tired and sour, crops like maize (corn) struggle to survive, leaving farmers with empty fields and hungry communities.

To fix this, scientists have been looking for ways to give the soil a "reset button." Two popular tools in this quest are biochar and rabbit urine. Think of biochar as a sponge made from burnt plant material; it's full of tiny holes that can hold onto water and nutrients, preventing them from washing away in the rain. Rabbit urine, on the other hand, is like a liquid energy drink for plants, packed with nitrogen and other nutrients that help them grow tall and strong. The big question researchers wanted to answer was: What happens if you mix these two together? Does the sponge (biochar) help the energy drink (rabbit urine) work better, or do they get in each other's way? This study dives into that mix to see if it can turn a sour, struggling soil into a thriving garden.

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The Experiment: A Cornfield Cocktail Party

In the school farm of the University of Dschang in Cameroon, a team of scientists set up a massive experiment to test these ideas on maize plants. They treated the soil like a laboratory, creating eight different "recipes" to see which one made the corn grow the best.

Some plots got nothing (the sad, unamended control). Others got just the standard mineral fertilizer (NPK), which is like a pre-packaged vitamin pill for plants. Then came the fun stuff: some plots got just biochar, some got just rabbit urine, and the real magic happened in the combinations. They mixed biochar with urine, biochar with pills, urine with pills, and even tried a "triple threat" of all three ingredients together.

The scientists were looking for three things:

1. Growth: How tall did the corn get? How thick was the stem? How many leaves did it have?
2. Health: How much "food" (sugars and proteins) and "sun-catchers" (chlorophyll) were inside the leaves?
3. The Underground City: How active were the soil microbes? (They measured this by seeing how fast the soil could break down a special dye, which acts like a heartbeat monitor for the soil's tiny workers).

The Results: Who Won the Race?

The results were a mix of "everything is better than nothing" and "different mixes do different jobs."

The Growth Champions
First, the bad news: The corn that got no help at all was tiny. It only grew to about 93.20 cm tall with a skinny stem. But almost every other treatment made the corn grow significantly taller and stronger.
The clear winner for sheer size was the Rabbit Urine + NPK combo (T4). These plants were the giants of the field, reaching 176.59 cm tall with the thickest stems (27.46 mm). It seems the liquid energy drink combined with the mineral vitamins gave the corn a massive boost in height.
However, if you wanted the most leaves, the Biochar + Rabbit Urine mix (T5) took the crown with 12.81 leaves per plant. And if you wanted the biggest leaf surface area to catch the sun, the triple mix (Biochar + Urine + NPK) produced the largest leaves at 609.91 cm².

The Underground City (Soil Microbes)
This is where things got interesting. The soil microbes love the Rabbit Urine + NPK combo (T4). This treatment made the soil microbes the most active, with a reading of 3.45 µg mL⁻¹. It's like the microbes threw a massive party because they had both the easy-to-digest food from the urine and the minerals they needed.
But here's a twist: The triple mix (T7), which you might think would be the ultimate super-fertilizer, actually resulted in the lowest microbial activity of all, even lower than the empty control plot. The scientists suggest that maybe there was just too much of a good thing, or the mix created an environment that was too chaotic for the tiny workers to function properly.

The Plant's Internal Health
Inside the leaves, different mixes did different things:

• Protein Power: The Biochar + Rabbit Urine mix (T5) produced the most soluble proteins (48.58 µg BSA-eq g⁻¹ FW). This suggests the plants were building strong muscle tissue.
• Sun Catchers: The Biochar + NPK mix (T6) had the highest chlorophyll (7.02 µg mL⁻¹), meaning these plants were the best at photosynthesis, turning sunlight into energy.
• Stress Signals: Plants that got only rabbit urine or only NPK had high levels of phenolic compounds. In plant language, high phenolics often mean the plant is a little stressed or fighting off trouble. The Biochar + NPK mix had the lowest levels (9.17 µg eq g⁻¹ FW), suggesting these plants were the most relaxed and least stressed.

What Does It All Mean?

The study shows that you don't have to choose between organic and mineral fertilizers; mixing them can be a game-changer. The Rabbit Urine + NPK combination was the superstar for making plants grow tall and waking up the soil microbes. Meanwhile, adding Biochar to the mix helped the plants build more protein and stay less stressed, likely because the biochar acted like a sponge, holding onto the nutrients and keeping the soil environment stable.

However, the experiment also taught a valuable lesson about balance. Just because three things are good doesn't mean putting them all together is better. The "triple threat" mix didn't win every category and actually seemed to confuse the soil microbes.

In the acidic soils of Cameroon, where farming is tough, this research suggests a promising path forward. By using locally available resources like rabbit urine and biochar alongside standard fertilizers, farmers might be able to grow taller, healthier corn and revive their tired soil without breaking the bank or hurting the environment. It's a reminder that sometimes, the best recipe isn't just one ingredient, but the right combination of the right ones.