Soil Structure Clay, silt and sand particles are organized (glued together) into aggregates or soil structural units. How they are organized within aggregates and the aggregates organized within the soil influences water movement and retention, aeration, nutrients, and root growth.
Soil Structure Think of a sugar cube. Hundreds of individual grains of sugar glued together to form an aggregate in the form of a cube.
Soil Structure What happens if I step on the sugar cube ? Can I put the sugar cube back together ? What would be needed ? Glue !
Specific Surface Area a given volume of soil has differing specific surface areas depending on the proportion of clay, silt and sand in the soil. Particle Specific Surface Area Clay 100,000 x Silt 100 x Coarse Sand 1 x
Specific Surface Area A thimble full of clay particles has 100,000 times the surface area of the same thimble filled with sand particles.
Specific Surface Area Water holding capacity Internal drainage Runoff potential Nutrient retention Herbicide application
Porosity The size of pore spaces between soil particles determine the air and water characteristics of the soil. Aggregated soils have excellent porosity. Soils with excellent porosity have excellent permeability for air exchange, water movement, and root growth.
Aeration & Drainage Not because A comes before D
Photosynthesis & Respiration Photosynthesis Makes the food for the plant and stores it in plant tissues. Requires water from the soil. Respiration Breaks the food down into the basic building blocks for plant health and growth. Requires oxygen from the soil and gives off carbon dioxide into the soil.
Soil Aeration Soils must contain sufficient large pore space to allow oxygen to penetrate to the deepest of roots and carbon dioxide to exit from the soil.
Soil Aeration Get the good gas in and the bad gas out
Soil Aeration Respiration – Oxygen limited roots are only 25% efficient Nutrient Uptake – Decreased levels of oxygen in the root zone decrease the uptake of N, P, K, Zn, Cu, and B Microbial Activity – Oxygen deficient soils have decreased numbers of beneficial organisms and increased numbers of pathogenic organisms Root Growth – Oxygen deficiency or carbon dioxide toxicity kills root cells Seed Germination – Germination is reduced when oxygen levels are reduced
Aeration Management Promote soil particle aggregation Maintain large, open pore spaces Avoid destructive practices Don’t smash the sugar cubes ! If you must, then supply some glue to reform them.
Aeration Management Maintain high organic matter in the soil
Manage the soil to provide a healthy environment for growth
Manage the soil for water uptake and gas exchange
Why do we : Use an aerator ? Verti–cut or dethatch ? Topdress a lawn ?
What is the effect of a layer of mulch in a shrub bed ? Can too much be a bad thing ?
Amendments to Garden Soils Organic materials –Compost –Manure –Peat moss Sand Gypsum Other – Snake oils
“ Grow the roots and the top will take care of itself”
Fertility & Fertilizers Nitrogen – Highly soluble Leaches down out of root zone – Volatilizes Exits soil as a gas into atmosphere – One of three main fertilizer elements – Vegetative growth The addition of nitrogen stimulates plant growth in ever increasing amounts
Phosphorus Relatively insoluble Attaches strongly to soil particles Used by the plant One of three main fertilizer elements Primary function is energy transfer within plant process Is not responsible for stimulating flowering
Phosphorus Applying fertilizers containing high percentages of phosphorus does not increase flowering of plants in the landscape! High % P fertilizers only serve to cause extraordinary high levels of P to build up in the landscape over time. High % P fertilizers increase the pollution potential of our landscapes.
Nitrogen/Phosphorus Ratio Is Nonsense! Phosphorus has nothing to do with flowering! It is the level of nitrogen that controls vegetative growth vs. flowering The presence or absence of excess nitrogen influences flowering!
Phosphorus A plant only needs sufficient phosphorus to meet its needs. More than enough is a waste and goes unused by the plant. The unused phosphorus carries over in the soil. If more is added next year, the buildup only continues.
Fertilizer Apply only what the plant will use Fertilize to maintain plant health and controlled vigor Fertilize with knowledge of what you are doing and the effect on plant growth and pollution potential.
Enable your plants to eat, drink, and breathe the good life !