Ag Science

1. Ag Science Soil and Plant Growth

2. The Plant Environment • In order to grow properly, plants require a certain environment. • Divided into two parts: • The underground - roots grow and live. • The aboveground – visible plant

3. The Underground Environment • Rhizoshere: The 24 inches of soil just below earth’s surface. • Soil is made up of sand, silt, clay, organic matter, and pore spaces Air & Liquid = 50% Water = 25% Air = 25% Solid portion = 50% Mineral Matter = 45% Organic Matter = 5%

4. Soil • Soils are classified according to the percentage of sand, silt, and clay they contain. • Soil particles vary in size. Sand > Silt > Clay • Clay particles hold water and food elements much more effectively

5. Soil continued • Soils composition • Some soils are formed from rock breaking down, others are formed as certain materials are deposited by water/wind • Soil profile consists of three layers: • Topsoil-the depth normally plowed or tilled • Subsoil-a well defined layer under topsoil • Soil bedrock or lower subsoil

6. The Ideal Soil • The ideal soil is about 50% solid & 50% pore space • The solid matter is mainly minerals and a small portion of organic matter. • The pores are small holes between solid matter and are filled with water and air • Ideal water/air ratio is half and half • The amount of water and air depends on the soil structure and type • Sandy soils have large pores (well-drained soils) • If soils contain too much clay, they do not drain well

7. Types of Water in Soil • Gravitational: Unable to be held against the force of gravity. Becomes part of ground water • Capillary water: Held in pore space against the force of gravity • There are 3 types: • Free moving: Moves in all directions • Available (field capacity): Water left after capillary movement stops - Roots move toward it. • Unavailable: Held tightly and can only be moved as vapor

8. Sandy Soil: Sandy or light soils include soils where clay or silt make up less than 20% by weight. Drain well but hold little moisture or nutrients • Clayey Soil: Must contain at least 30% clay. Poor drainage and aeration • Loamy soils: Most desirable for general use. Mixture of equal parts of sand, silt and clay.

9. Soil Triangle

10. Soil Improvement • Large Scale • Soils may be improved by adding increased drainage, irrigation methods and plant food • Small Scale • Organic matter and plant food

11. Drainage • Drain tile • Add organic matter • Raising plant beds • Place ditches between planting beds

12. Moisture Retention • Irrigate • Leaving land fallow • Adding organic matter • Mulch • Fertilize to add plant food

13. Disease control • Use resistant varieties of crops • Use chemicals sparingly • Pasteurize soil • Soil or sand should be heated thoroughly for 30 minutes at 180 degrees F

14. Nutritional Deficiencies • Nutritional or plant food deficiencies often show up on leaves • Nitrogen = yellow/pale • Phosphorus = purple on underside • By the time these symptoms appear, damage already done • Soil Testing

15. Major Elements Required in large amounts nitrogen phosphorus potassium Minor Elements Required in smaller amounts calcium magnesium sulfur iron manganese boron copper zinc Plant Food Elements

16. Plant Food and Fertilizers • Water = most important plant food. Makes up 90% of the weight of plants. • Most limiting factor of plant growth. • All food elements are dissolved in water and move in a soluble form. • Only 1% of the water absorbed is used by the plant. • 99% is lost through the process of transpiration.

17. Transpiration • Transpiration of water is high when soils are wet (stoma fully opens) • An estimated 250,000 stomata in 1 square inch of the underside of an apple leaf. • For each 18 degree increase F, the loss of water is doubled. • A single corn plant can use 2 quarts of water per day. • Stomata open in response to light. • Transpiration is of little use. The cooling is minimal.

18. Nitrogen • Encourages above ground vegetation growth and gives a dark green color to leaves. • Produces soft, tender growth • Regulates the use of other major elements. • Too much nitrogen may lower disease resistance, weaken the stem, lower the quality of fruit, and delay maturity

19. Phosphorus • Flowers and seeds will not form without it • Quickens maturity • Encourages root growth • Makes potassium more available

20. TOO MUCH: Increases soluble salt which can dry out roots by pulling water from the roots TOO LITTLE: Purple coloring on underside of leaves Reduced flower, seed and fruit production Susceptible to cold injury Susceptible to disease Poor quality fruit and seeds Phosphorus

21. Potassium • Rarely available in sufficient amounts • Encourages resistance to disease • Encourages strong roots • Essential for starch formation • Necessary for chlorophyll development • Encourages efficient use of carbon dioxide

22. Lime • Acts as plant food • Affects soil acidity • Furnishes calcium which is important in formation of plant cell walls.

23. Soil Acidity (pH) • To lower acidity, use materials such as sulfur, iron sulfate or aluminum sulfate • To increase acidity, apply lime

25. The Environment Above the Ground • Temperature • Light • Humidity • Plant diseases • Insects

26. Temperature • The temperature has one of the strongest effects on plant growth • Lettuce, cabbage and kale grow best in cool temperatures • Corn, beans and tomatoes prefer hot weather • Plant growth increases up to about 90 degrees

27. Light • Light must be present for plant to manufacture food. • Some plants prefer full sunlight, others shade

28. Photoperiodism • Definition: The response of plants to different periods of light and darkness in terms of flowering and reproductive cycles. • Short Day: Flower only when days are short and nights are long. (chrysanthemum and Christmas Cactus) • Long Day: Flower when days are long and nights are short. (lettuce and radishes) • Indifferent: Plants that do not depend on periods of light to flower.

29. Other Reactions to Light • Plants grow toward their source of light because the plant stem produces more growth hormones on the shady side.

30. Humidity • The moisture level in the air • When humidity is very high (80-100%), problems of fungal disease may occur.

31. Plant Diseases and Insects • Any time a plants is suffering for disease or insect damage, production will suffer. • Leaf damage reduces ability to produce food • Stem damage may girdle (circle) or clog up a stem and kill the entire plant.

32. Student Activities • Bring in one jar 1/2 full of soil. Add water to 2 inches from top. Replace lid and shake well. Next class, examine layers. Classify soil according to texture triangle.