| DEFINITIONS soil - the outer weathered layer of the earth's crust. growing medium - the substrate in which plants grow. Usually applied to manufactured or synthetic soils, i.e. "potting soils", or highly amended soils, ex. landscape beds. FUNCTIONS OF WATER OR GROWING MEDIUM 1)Support and anchorage 2) Supplies mineral nutrients 3) Supplies water 4) Allows gas exchange - especially 02 and CO2, but also ethylene | |||||
| SOIL ORGANIZATION soil profile- morphology of horizons (layers) in a soil.
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| TYPES OF SOIL BASED ON COMPOSITION A)Organic soil - contain 20% or more organic matter 2 types 1) peat soil - contains greater than 65% organic matter 2) muck soil - contains 20-65% organic matter B) Mineral soil (field soil)- contains less than 20% organic matter. 4 Major Components (in a well watered, but well drained loam soil) 1) air- approximately 25% of volume; in larger pores 2)water - approximately 25% of volume; in smaller pores 3) mineral particles - 44-49% of volume | ||||||||
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| 4)organic matter - typically about 1% in nature litter - partially decayed organic matter on the soil surface. humus - highly decomposed, fine, amorphous organic matter in the soil. Functions of Organic Matter: 1) stabilizes soil structure 2) increases water retention and availability 3) increases drainage and aeration 4) increases cation exchange capacity 5) supplies nutrients upon decay (only if low C:N ratio) 6) stabilizes pH 7) food source for microorganisms |
| WHY PURE FIELD SOILS ARE NOT USED IN CONTAINER PRODUCTION 1)packs too much, which a) decreases total pore space, esp. large pores b) decreases aeration c) decreases drainage 2) must sterilize for disease and weed seeds 3)heavy - increases shipping costs and heavy to manually handle 4)hard to obtain good supply in many areas GROWING MEDIA Most container production uses specially prepared mixes called growing media, artificial media, soilless media orpotting soils, which are made from various organic and inorganic growing medium amendments. The highest quality peat moss is sphagnum peat moss. All the organic amendments, except peat moss, must be composted before use.
Typical Growing Medium Should Contain: 50-75% organic amendments - usually sphagnum peat moss, composted bark or coir 25-50% inorganic amendments- usually vermiculite, perlite, sand or styrofoam plus: lime, starter fertilizer and sometimes a wetting agent and gypsum |
| FORMS OF SOIL MOISTURE(1 bar = 0.987 atm) 1)chemically combined - occurs as a water shell around compounds and particles in soil; plants cannot utilize. 2)hygroscopic water - water adsorbed onto soil particles, held at less than -31 bars of tension; plants cannot utilize. 3)capillary water - water held by capillary attraction in the capillary pores in soils; held at -1/3 to -31 bars; plants can extract water in the larger capillary pores down to approximately -15 bars. 4) gravitational water- water in large pores immediately after watering or a rain, which drains from the soil (within 24 hr.) by the force of gravity; held at greater than -1/3 bars (0 to -1/3 bars); plants can utilize when present. SOIL WATER TERMINOLOGY field capacity - the amount of water a soil can hold against the force of gravity; - at field capacity, water is held -1/3 bars. wilting- the loss of plant turgidity due to excessive water loss. incipient wilting- when a plant wilts, but recovers when placed in a saturated atmosphere (100% R. H.), ex. overnight. incipient wilting point - the soil moisture content when a plant wilts, but recovers when placed in a saturated atmosphere (100% R. H.), ex. overnight. permanent wilting- when a plant wilts, but cannot recover when placed in a saturated atmosphere (100% R.H.). permanent wilting point - the soil moisture content when a plant wilts, but cannot recover when placed in a saturated atmosphere (100% R.H.). HOW TO DETERMINE WHEN TO WATER PLANTS 1) Based on soil a)experience - feel, looks, etc. b)measure soil water potential, usually use a tensiometer - an instrument that is inserted in the soil and measures the soil moisture tension. 2)Based on plant a)experience - wilting, looks, etc. b)measure plant water potential |
| mulch- any material applied to the surface of the soil or growing medium Mulches are almost always beneficial to use, and their use is highly recommended. In nature, the soil under plants is covered by a natural mulch of composting litter (leaves, twigs, etc.) TYPES OF MULCHES 1)organic - bark, leaves, sawdust, straw, hay, needles, paper 2)inorganic - plastic, gravel BENEFITS AND USES OF MULCHES 1)stabilizes soil temperature - cooler in summer; warmer in winter under a mulch 2) conserves water- decreases evaporation of water from soil surface 3)better water infiltration - more rain or irrigation water soaks-in due to slower runoff 4)controls erosion - due to slower runoff 5)mayadd nutrients - upon decomposition, if it is a) organic and b) has a low C:N ratio 6)decreases weed growth- decreases germination of weed seeds & growth of weed seedlings 7)appearance - used for decorative purposes |