THE INVESTIGATION BEGINS! Each team will create 4 water and soil mixtures. The water in the mixtures will dissolve the chemicals responsible for the pH of the soil.

A farmer needs good land to successfully raise crops A farmer needs good land to successfully raise crops. What is the probability of finding fertile soil on our watery planet?

71% of the Earth is water and 29% is land. 29% of land

Of that 29%, only 11% of the land is capable of growing crops. 11 % of land

Of that 11%, 30 to 40% of the land is too acidic for most crops. Remaining fertile land

The world’s population is projected to increase from 7 billion to 9 billion people by 2050. Can global food production be increased to feed so many more people? Can technology improve crop production on land that is less than ideal—land that is too acidic or too basic?

What is soil? Soil is one of the three major natural resources (along with air and water). It is the upper layer of earth in which plants grow. It is made up of a mixture of organic remains (like decayed leaves, wood, and dead organisms), clay, and rock particles. It also contains water, air, countless living organisms, and minerals from the breakdown of rock particles.

“To be a successful farmer, one must first know the nature of the soil “To be a successful farmer, one must first know the nature of the soil.” Xenophon

Why is soil important? Soil is the “skin of the earth” and is essential for life on Earth. It provides a place to grow for all kinds of plants. It takes in and gives off gases like carbon dioxide, methane, and water vapor. It provides homes for animals, microorganisms, and fungi. It absorbs, holds, releases, and purifies the water that runs through it.

Plants get important nutrients from soil, just as you get nutrients from food and vitamins. Calcium Iron Phosphorus Magnesium Sulfur Zinc Nitrogen Potassium

Soils found around the world are very different from each other. Their characteristics are dependent on the type of rock from which they are formed and the climate in which they are located. Different soils have unique physical and chemical properties.

Physical properties of soil include layering, color, and texture.

The focus of this activity is the identification of a soil’s pH level. Chemical properties of soil include cation exchange capacity and soil pH. The focus of this activity is the identification of a soil’s pH level.

The pH level in soil is a measure of how basic or acidic it is. pH is determined by the concentration of the hydrogen ion, the term pH meaning “power of hydrogen”. Acids have a pH of 0 - 6 because they have excess hydrogen (H+) molecules, and bases have a pH of 8 -14 because they have excess hydroxide (OH-) molecules. Pure water is considered neutral with a pH of 7 because the concentrations of H+ and OH- ions are equal.

A pH scale provides a visual way of measuring acids and bases.

Indicators are used to measure pH because they change color in the presence of acids and bases. Some plant pigments are natural pH indicators. Red grapes, hibiscus flowers, and red cabbage contain such pigments.

Red cabbage juice is the indicator in this activity. Anthocyanin found in red cabbage reacts with both acids and bases. Strong acidic solutions turn the anthocyanin red and strong bases turn it greenish-yellow. Weaker acids create a pinkish-purple color, and weaker bases create a deep blue color.

Standard pH scale Red cabbage pH scale

Plants are unable to grow successfully outside of a preferred pH range. Acidic soils (low pH), dissolve aluminum and manganese in the soil. The dissolved metals bind with critical plant nutrients such as calcium and phosphate making them unavailable to plants’ root systems. Basic soils (high pH) prevent vital nutrients from dissolving enough for plants’ roots to fully absorb them.

In the U.S., very acid soils can be found in the Blue Ridge Mountains in the Appalachians. pH levels there can be as low as 3.5. That is equivalent to orange juice.

Extremely alkaline soils can be found in the western United States. Soils in Utah can reach an alkalinity level of 8.0, nearly that of baking soda.

Acid soils are an increasingly serious global threat to successful crop production. Acid soils with a pH of less than 5.5 limit crop production on 30 to 40% of the world’s potentially farmable land. Aluminum toxicity is the single most important factor and leads to stunted root growth.

The application of agricultural lime can help raise soil pH The addition of lime increases root cell growth and lowers the absorption of aluminum.  However, this is not a practical solution for all parts of the world due to the expense of application and erosion on hilly terrain.

Scientists are investigating ways to increase crop production in areas where lime applications are impractical. Through selection and breeding strategies, aluminum-tolerant varieties of major crops are being developed. The resulting higher crop yields will help to feed the world’s rapidly growing population.

INVESTIGATION WRAP-UP A very small percentage of Earth’s land is fertile enough to raise crops. Appropriate soil pH levels are critical for successful crop growth. Aluminum toxicity due to acidic soils is an increasing problem. Farmers routinely test their soil for pH levels. Knowing the pH levels helps farmers make intelligent decisions for achieving the best crop production. Due to the world’s growing population, maximizing crop production is critical.

“We can grow more food, but we can’t grow more soil.” Many companies are committed to maximizing farmers’ corn yields. One program integrates 20 different data sets (including water and soil pH) to identify which seeds best fit a field’s soil condition. Farmers receive prescriptions unique for each of their fields.