36.0 Introduction

1. Plants too Require Nutrients
1. Lack of Certain Nutrients Effects Growth, Resistance to Disease
2. Plants Acquire Nutrients from Soil through Roots fig 36.1

1. The Soil
1. Produced from Weathered Rocks
1. Composition related to structure of parent rocks
2. Includes 92 naturally occurring elements tbl 2.1
3. Elements combined into inorganic compounds called minerals

2. Composition of Soil
1. Most soils show signs of biological processes
2. Organic materials result from biological activities fig 36.2
1. Effects are obvious in the topsoil as well as deeper layers
2. Soil fertility related to decomposition, recycling organic debris
3. Topsoil = mineral particles + living organisms + humus fig 36.3
1. Topsoil may be lost by erosion or poor landscaping
2. Soil nutrient and water-holding capacity affected

3. Varying size of soil particles fig 36.4
1. Coarse sand has largest particle size
2. Clay has smallest particle size

4. Half of soil volume is occupied by empty space
1. Filled with air or water
2. Not all water in soil is available to plants

3. Water in Soil
1. Nature of water affects interaction with soil
1. Water forms hydrogen bonds with itself and other materials
2. Water stays tightly bound to negatively charged clay particles
3. Water adheres to small particles with greater surface area, like clay
4. Water drains rapidly through sandy soil

2. Best soil for plant growth
1. Contains balanced mixture of fine and coarse particles
2. Called loam

3. Water drains through soil by force of gravity
1. Water held in soil pores and available to plants is called capillary water
2. Amount of water remaining after gravity drainage is called field capacity
3. Water unavailable to plants associated with permanent wilting point

2. Cultivation
1. Natural Processes Add Nutrients to Soils
1. Include decomposition and nitrogen fixation
2. Plants can remove nutrients faster than they are replaced
1. Nutrients taken up by plant become part of plant
2. If nutrients not replaced soil looses its fertility
3. Fertility: Soil's ability to supply plants with nutrients

3. Nutrients returned when plant dies and decays
1. Few nutrients returned when crop is harvested
2. Next crop planted may not grow if nutrients are lacking

2. Farming Methods Attempt to Maintain Soil Fertility
1. Grow different crops in subsequent years
1. Example: Corn then soybeans
2. Crops remove different nutrients from soil
3. Soil doesn't remove same nutrients two years in a row
4. Soybeans are valuable to soil
1. Add nitrogen back to soil
2. Have nitrogen-fixing bacteria in nodules on roots

2. Alternating crops called crop rotation
3. Fields may be allowed to lie fallow
1. No crop grown for year or two
2. Natural processes rebuild soil nutrients

4. Plow leftover plant materials into soils fig 36.5
1. Maintain soil fertility
2. Analogous to leaving grass clippings, leaves on lawn
3. Crop residues include stems, roots, husks, leaves

5. May grow crop specifically to plow it back under
1. Adds organic material to soil
2. Decomposers turn plant material into humus

3. Fertilizers
1. Natural Communities Recycle and Reuse Nutrients
1. Cultivated crops require input of additional nutrients
1. Exposed soils lose nutrients to erosion
2. Crops carry nutrients away from source
3. Tropical soils particularly devoid of nutrients, fertilizers increase yield

2. Additional minerals include nitrogen, phosphorus, potassium tbl 36.1
1. Required in large quantities
2. Most likely to become deficient in soils
3. May be source of pollution in certain circumstances

3. Grading of commercial fertilizers fig 36.6
1. Three numbers reflect percentage of N, P and K
2. Proportions needed depend on natural fertility and type of crop
3. Nitrogen often supplied to soil, has dramatic effect on crop yield

2. Organic Fertilizers
1. Include manure and dead animal remains
2. Are not nutritionally superior to inorganic fertilizers
1. Provide additional source of humus
2. Enhance capacity to hold water and nutrients
3. Nutrient availability may be improved

1. Plant Nutrients
1. Two Kinds of Inorganic Nutrients Are Required by Plants tbl 36.1
1. Macronutrients are required in relatively large amounts
1. Include carbon, hydrogen, oxygen, nitrogen, potassium, calcium, phosphorus, magnesium and sulfur
2. Each nutrient approaches or exceeds 1% of plant's dry weight
3. Importance has been known for the last century

2. Micronutrients are required in trace amounts
1. Include iron, chlorine, copper, manganese, zinc, molybdenum, boron
2. Constitute several hundred to less than one part per million
3. Importance only recently recognized

3. Important nutrients determined by hydroponic culture
1. Known or suspected nutrients left out of culture medium
2. Plants grown and studied for abnormal symptoms fig 36.7
3. Micronutrients in growing vessel may supply sufficient amount to plant

2. The Roles of Plant Nutrients fig 36.7

1. Carnivorous Plants
1. Some Plants Obtain Nutrients Directly from Other Organisms
1. Carnivorous plants usually grow in acidic soils
1. Include bogs
2. Not favorable habitat for nitrogen-fixing bacteria

2. Plants obtain nitrogen by capturing and digesting small animals
3. Grow in otherwise unfavorable conditions

2. Adaptations of Carnivorous Plants fig 36.8
1. Plants lure and trap insects, small animals
2. Digest prey with enzymes secreted from various glands
3. Venus flytrap
1. Grows in bogs of North and South Carolina
2. Each side of leaf has three sensitive hairs
3. Trigger halves of leaf to snap together when touched
4. Enzymes secreted, digest prey caught within leaf

4. Pitcher plants
1. Attract insects with bright flowerlike colors within pitcher-shaped leaves
2. May also have sugar-rich solutions for attraction
3. Insects slide into cavity of leaf, filled with water and digestive enzymes

5. Bladderworts
1. Small aquatic plants
2. Sweep animals into bladderlike leaves by rotating trapdoor

6. Sundews
1. Glandular trichomes secrete sticky mucilage and digestive enzymes
2. Small animals entrapped and digested