AGRICULTURE Session 04: Soil Chemistry
Learning Objectives
- Students will investigate soil nutrients and the chemical compounds that comprise plant nutrient requirements.
Background:
- Utilize the knowledge gained from the previous lesson (Session 03) regarding soil composition, texture, and particle size. The correct amount of plant nutrients is essential for growing healthy crops. It is important to know if a crop should be fertilized and what type of fertilizer to use by conducting a soil test. Review the procedure for taking a soil sample and Background Information from Extension Agent, Cory Tanner.
- Review procedure
- Background Information for Soils Lesson
- The continued development of farming technology and precise management of fertilizer inputs is necessary for farmers to grow more food on less land to feed our growing population. In 1910, the discovery of the Haber-Bosch process for fixing atmospheric nitrogen gas into commercial fertilizer dramatically increased the amount of food that farmers could grow. It is estimated that nearly half the world’s population is dependent upon commercially produced fertilizers. Not all fertilizers contain the same amounts of primary nutrients (NPK). Fertilizers are prepared in different compositions so the consumer, farmer, or home gardener can apply precisely what is needed.
- Primary Nutrients: Nitrogen (N), Potassium (P), and Phosphorus(K)
These are the three most commonly deficient nutrients in the soil. After carbon, hydrogen, and oxygen, plants take up more potassium and nitrogen through their roots than any other nutrient. - NITROGEN ’N’ – Nitrogen forms new cells and is essential to total plant development. A shortage of nitrogen halts plant growth and cell production. Symptoms of nitrogen deficiency are a yellowish brown color along the veins and tips of leaves, stunted growth of the plant or paleness in color on older leaves. Too much nitrogen can cause tall, spindly plants that easily topple over and nitrate poisoning (look for a strong red tint to the leaves). Nitrogen is also essential to the compost pile, as it aids in the breaking down of old plant residues. Good sources of nitrogen include: blood meal, cottonseed meal, fish meal, soybean meal, rabbit manure and tea grinds. You can also grow a cover crop of legumes in the fall to raise the nitrogen level for the next spring’s crop.
- PHOSPHORUS ‘P’ – Phosphorus produces vigorous seed and root development. A shortage of phosphorus slows cell division and results in stunting of growth and late maturity of the plant. A symptom of phosphorus deficiency is spindly plants with purple streaks in the stems. Since phosphorus moves very slowly in the soil, it is essential to have it available during early plant development. Good sources for phosphorus include: bone meal, rock phosphate and colloidal phosphate. Incorporating organic matter (compost) into the soil makes the phosphorus present more readily available to the plants.
- POTASSIUM ‘K’ – Also called Potash, this nutrient helps produce strong and sturdy stems. It advances root growth and helps plants resist disease and cold weather. Shortages of this nutrient cause stunting and stem weakness. Symptoms include a yellowing of leaf edges and yellowing of the leaves veins. This nutrient must be available during early plant development. Good sources of potash are: cow manure, compost, granite meal and wood ashes.
- pH (6.5/slightly acidic) – pH is a measure of acidity or alkalinity on a scale of 0 to 14, with 7 being neutral. The pH of the soil affects many elements, including nutrient availability, plant nutrient uptake, and microorganism activity. Because soil pH affects many factors, it is important to maintain proper pH throughout the growing season. Considering the complexity of factors involved, the recommended soil pH for each individual variety of plant is very important. Regular pH testing will allow you to make informed decisions if soil pH adjustment is necessary. In general, your pH should not need to be altered as the majority of plants manage well on a pH around 6.5.
Materials and Resources
1. Soil sample bags
2. Bucket, trowel, or shovel
3. Timer (clock, watch, cell phone)
4. Teaspoon (tsp)
5. Pan or newspaper for ‘cleaning’ & spreading soil out
6. Measuring cup/beaker
7. Pipette
8. Extraction tube (30ml)
9. Test Tube
10. Testing tablets- Lamotte testing kit and strips
Ag Services Lab
Opening Activity: ~15 minutes
1. Collect soil samples for analysis and comparison utilizing the soil sample bag and procedure. The samples will be sent to the Clemson lab for testing on main nutrients and recommendations for the condition of the soil (you can be specific on what you are utilizing the soil for so they may test on that. Label your soil bag with the correct crop code listed below).
2. Crop codes 090 Home vegetable garden
3. Example: Soil Report
4. How to read a soil report
Content Lesson and Activities: ~60 minutes
1. The soil chemistry lab; performing a similar test to what Clemson University is doing. We will be classifying soil texture, testing for the presence of nitrogen, phosphorus, potassium, and pH
2. Review procedure for collecting soil sample
3. What happens at the soils lab videos: Ag Services Lab
Procedure:
Soil sample collection
1. Each group will choose a location at your site/yard and collect a soil sample for chemical testing of the levels of the primary nutrients (N, P, K). Make sure to follow procedures and record all data.
2. Collect a soil sample following protocols on the back of your soil bag. Write a description of the location you sampled.
3. Mix your soil sample thoroughly in the bucket.
4. Spread soil out on the newspaper. Pick out any large leaves, stones or sticks and crush any large lumps. Record your observations of what you find in your soil sample in the data section below.
Soil chemistry activity:
1. Follow the instructions on your soil kit handout for the Extraction process.
2. Follow the instructions on your soil kit handout for testing your assigned nutrient. [each group will be assigned one nutrient to test (N,P,K)]
3. Record all data in the appropriate sections on the data sheet
4. Soils_ChemLab_datasheet
Virtual adaptation:
- Virtual soil lab tour link
Leaders have an in-depth discussion of the soil and nutrients available for plants. Preparation can be conducted ahead of time for the learner to do a simple pH test of their soil at home. The leaders could interpret the results of the Clemson soil sample with the group.
Materials:
pH strips
Soil sample results
Closing Activity: ~15 minutes
Discussion questions and conclusions (these results will later be compared to soil analysis by Clemson University- it takes approx. 2 weeks).
Journal prompt: Describe something you learned today that will help you grow healthy crops.
Career connection: Elmo St.Brady Chemist
Emmett Chappelle Biochemistry
Source:
South Carolina 4-H Youth Development
Home and Garden Information Center, Clemson University
Cory Tanner, Horticulture Program Team Director, Clemson Cooperative Extension Service