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# Goal/Experiment:
To determine the appropriate methods for calculating and adding granular/dry fertilizers to soil in pot experiments before planting.
## Adding Solid Fertilisers to Soil in Pot Experiments V.2
**Matema L.E. Imakumbili**
Sokoine University of Agriculture
[dx.doi.org/10.17504/protocols.io.4engtde](http://dx.doi.org/10.17504/protocols.io.4engtde)
---
### Abstract
This protocol describes how rates of granular/dry fertilizer can be calculated and incorporated into soil for pot experiments before planting.
### Guidelines
It is important to clean all apparatus (shovels, pots, brushes, etc.) before use. This can be done by washing the equipment with tap water and soap. Thoroughly rinse off the soap with clean tap water. All equipment must be properly dried before use.
### Materials
- Soil
- Fertilizer (e.g., urea, TSP, muriate of potash)
- Large plastic sheet (2 m × 5 m)
- Weighing scale (5-20 kg capacity)
- Empty pots
- Analytical balance
- Small plastic bags (2 cm × 15 cm)
- Marker pen
- Mechanical kitchen/hanging scale (20 kg capacity)
- A brush or small broom to sweep soil with
- A dustpan
### 1. Determining the Amount of Fertilizer to Add to Soil in Pots
Field-based fertilizer rates (in kg/ha) are often used and converted to pot-based rates (in g/kg or mg/kg of soil) in pot experiments. This conversion requires some calculations.
#### Fertilizer Calculation Example:
In this example, we will add potassium to the soil at a rate of 80 kg/ha. The fertilizer used is muriate of potash (MOP), also known as potassium chloride (KCl), which contains 60% potassium oxide (K2O).
##### Calculation:
1. Amount of potassium to be added to each kilogram of soil:
\[
\text{mass of } K \text{ (kg)} = \frac{80 \text{ kg}}{2,000,000 \text{ kg of soil}} = 0.04 \text{ g K/kg of soil}
\]
2. Potassium to be added to 5 kg of oven-dry soil:
\[
\text{mass of } K \text{ to be added to 5 kg of soil} = 0.04 \text{ g K/kg } \times 5 \text{ kg} = 0.2 \text{ g K}
\]
3. Calculate the equivalent K2O needed:
\[
\text{Mass of one mole of } K_2O = 2 \times \text{K} + \text{O} = 78.1966 \text{ g K/kg}
\]
4. Using the mass ratio:
\[
\frac{0.2 \text{ g K}}{78.1966 \text{ g K}} = 0.241 \text{ g K}_2O
\]
5. Adjust for the 60% purity of MOP:
\[
\text{Amount of } MOP = \frac{0.241 \text{ g K}_2O \times 100 \text{ g MOP}}{60 \text{ g K}_2O} = 0.402 \text{ g MOP}
\]
### 2. Weighing the Fertilizer to Be Added to Pots
Using an analytical balance with an accuracy of ± 0.0001 g, weigh out the required amount of muriate of potash to be added to each pot. Ensure correct labeling and separate packing of the weighed packets of fertilizer for easy identification.
### 3. Mixing the Fertilizer into the Pot
#### Procedure:
1. Use a large plastic sheet for mixing the soil and fertilizer.
2. Divide the soil for each treatment into roughly equal portions.
3. Mix the fertilizer into a small amount of soil first and then into a larger amount.
4. Combine all parts thoroughly to ensure uniform mixing.
**Figures:**
- **Fig 1.** Fertilizer packed in small plastic bags for pot experiments.
- **Fig 2.** Bulked pile of soil on a plastic sheet.
### Notes:
1. **Accuracy:** Precision is crucial for each step of the process.
2. **Hygroscopic Nature:** Fertilizers tend to absorb moisture; pack tightly.
3. **Contamination:** Regularly clean equipment to avoid cross-contamination.
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