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Learn · Soil & Agriculture

Soil is Alive

Discovering what temperature and moisture mean for the living world underfoot

Grades 6–8 30 min observation live IESH data

Students observe soil moisture and temperature readings, relate them to plant health and growth, and begin to understand soil as a living system rather than inert ground.

Learning objectives

  • Define soil moisture and soil temperature as measurable properties of the soil.
  • Explain why both measurements matter for plant growth.
  • Describe what healthy soil moisture levels look and feel like.
  • Connect Nepal's agricultural traditions to the science of soil health.

Background

Soil temperature controls the rate of nearly every biological and chemical process in the ground. Most crop seeds will not germinate below 10°C. Soil bacteria and fungi — which break down organic matter into nutrients that plants can absorb — are most active between 20°C and 35°C. In Nepal's hills, soil temperature at planting depth (about 5 cm) determines whether seeds planted in early spring will germinate or rot. A sudden cold snap after planting can be catastrophic.

Soil moisture is the percentage of the soil's pore spaces that are filled with water rather than air. Our capacitive sensor measures this as an electrical property — wet soil conducts electricity differently to dry soil. Plants need moisture in the root zone to draw water and dissolved nutrients upward. Too little water (drought stress) causes wilting and stunted growth. Too much (waterlogging) drives air out of the soil, suffocating roots and promoting root rot. The ideal range depends on the crop and soil type.

Soil is not just minerals and water — it is home to billions of organisms per gram: bacteria, fungi, earthworms, nematodes, insects. These creatures drive nutrient cycling, create the loose structure that lets roots penetrate, and produce the characteristic earthy smell (caused by a compound called geosmin produced by Streptomyces bacteria). When we measure soil temperature and moisture, we are measuring the conditions for this entire community of life.

Procedure

  1. Read the current soil temperature and soil moisture from the dashboard. Record them.
  2. Look at the soil moisture bar chart on the dashboard. What does the bar height tell you?
  3. Touch some soil if available. Does it feel consistent with the moisture reading? (Very dry = crumbly, falls apart; Moist = holds shape when squeezed; Wet = releases water when squeezed)
  4. If you have two soil samples at different moisture levels, predict which will show a higher sensor reading before testing.
  5. Draw a simple diagram of a plant in soil. Label: roots, soil moisture zone, soil temperature zone, sunlight.
  6. Discuss with a partner: what would happen to the plant if the soil moisture dropped to near 0% for a week?

Discussion

  1. Why might a gardener water their plants in the early morning rather than midday? (Hint: think about what happens to soil moisture on a hot, sunny day.)
  2. Farmers in Nepal traditionally plant rice only after the first monsoon rains. What soil conditions are they waiting for?
  3. What might cause the soil temperature reading to be higher in the afternoon than in the morning?

Worksheet

1. Record today's readings: Soil Temperature = ___ °C Soil Moisture = ___ % [2 marks]

Answer guide (for teachers)

Observational — verify students read correct sensor values.

2. Give TWO reasons why soil temperature matters for growing crops. [4 marks]

Answer guide (for teachers)

Seeds need warmth to germinate (typically >10°C for most crops); soil bacteria and fungi that supply nutrients to plants are most active at 20–35°C; cold soil can cause roots to grow slowly or seeds to rot.

3. A farmer's soil moisture sensor shows 8%. Is this good for growing vegetables? Explain what the farmer should do. [3 marks]

Answer guide (for teachers)

8% is very dry — below the wilting point for most vegetables. The farmer should irrigate. Most vegetables need 40–60% soil moisture. Students should also mention that watering should be gradual to avoid waterlogging.

Vocabulary

Soil Moisture
The amount of water held in the spaces between soil particles, expressed as a percentage.
Soil Temperature
The temperature of the soil at a given depth, measured in degrees Celsius.
Germination
The process by which a seed begins to sprout and grow, requiring sufficient moisture, warmth and sometimes light.
Nutrient Cycling
The process by which soil organisms break down organic matter and release mineral nutrients that plants can absorb.

Extension

Set up a simple experiment: plant identical seeds in two small pots with the same soil. Water one regularly and keep the other dry. Observe for two weeks and record the soil moisture using the sensor at each observation. Write a report on how moisture affected germination and growth.

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