Soils and plant nutrients Soils and soil texture Soil texture triangle Plant nutrients Major nutrients Secondary nutrients Minor nutrients Exchange Capacity (CEC) Soil ph
Soils Consists of a series of layers called Topsoil (A horizon) upper most layer Soils consists of: Mineral particles determine soil texture Organic matter Air and Soil organisms
Soil texture - Introduction Soil texture coarseness or fineness of soil Why is soil texture important? It determines: size Pore space Amount of air (oxygen) flow through soil How easily the soil is worked = easily worked soil Three soil textures (sand, silt, clay)
Sand texture Largest particles Size from 0.2mm (finest sand) to 2 mm (coarsest sand) Warms up and dries early in the spring Does not hold water or Feels gritty if rubbed between fingers
Silt texture Intermediate particle size 0.002 to 0.05 mm Often referred to as rock Can be transported long distances in water or air Feels silky or floury to the touch
Clay texture Smallest particle size < 0.002 mm in size Does not drain well Slow to warm up Difficult to work (not ) growth poor due to small spaces between particles Retains nutrients Feels sticky to touch and forms a ribbon
Soil type Most soils are a mixture of different soil textures Often a soil type will be dominated by a particular soil texture Example: sand Important to know the soil type because it will determine the practices you need to use What is the drainage? Do soil amendments need to be added?
Soil texture triangle Allows you to know the soil type of your garden s soil Three axis - % clay, %, % sand Example: 20% clay, 40% silt, and 40% sand is a loam soil
Nutrients needed by plants
Nutrients needed by plants Can divide the nutrients needed by plants into 3 categories Major plant nutrients Nutrients needed in largest amounts plant nutrients Nutrients needed in moderate amounts Minor nutrients Nutrients needed in very small amounts
Major plant nutrients Consist of: Nitrogen (N) (P) Potassium (K) also called Potash Major plant nutrients are listed on fertilizer bags %N, %P, %K Form of nutrients will be listed in smaller print
Nitrogen Nitrogen under goes a cycle in environment N is essential building block of plants. Used in: Proteins Plant pigments Secondary metabolites Plant hormones (i.e. ) Needed in largest amounts Most N is in atmosphere In soil most N is in organic matter Unavailable to plants
Nitrogen Plants absorb the nitrate form of N The nutrient most likely to be deficient Ways nitrogen becomes unavailable to plants Downwards movement of N and other nutrients in the soil solution Runoff when bound to clay or organic matter Harvest of crops Denitrification In soils, N can be converted by microbes into atmospheric N
Nitrogen Nitrogen deficiency Symptoms: of the leaves, especially the older leaves Treatment: apply a material high in N Excess nitrogen Easy to over apply nitrogen Will cause: maturity Uneven ripening Overly succulent
Phosphorous (P) Plants use phosphates Phosphates can be pollutants Most soils contain large amounts of P but not in forms available to the plant Functions It is important for use and storage of energy Stimulates root, fruit, and seed development
Phosphorous Phosphorous deficiency Symptoms: Slight stunting of the plant, older leaves will be, and undeveloped root system Treatment: Apply meal Apply a synthetic fertilizer containing a high level of P Phosphorous does not move much in the soil
Potassium (K) also known as Potash Where did the name potash originate? Considered to be in the form of K 2 O Not readily Is essential for synthesis of proteins and carbohydrates Is needed in higher amounts by root crops Organic fertilizers are often low in K
Potassium Potassium deficiency Symptoms: Small inferior flowers and fruits and plants. Yellowing along the edges of older leaves Leaves become Treatment is to apply a fertilizer high in K
Secondary Nutrients Calcium Plays an important role in wall development Calcium deficiency problems: Calcium deficiency is rare but plants sometimes cannot adequately distribute calcium
Calcium Symptoms in lettuce and cabbage Blossom-end rot in tomatoes Treatment There is no immediate cure for calcium deficiency problems Adding materials high in calcium will not solve the problem Maintain even watering the plants Maintains more even soil moisture
Secondary Nutrients Magnesium Magnesium deficiency Symptoms: yellowing starting between the of the older leaves Sulfur Generally not a problem Used for making soils more and is found in compost and manures
Micronutrients Introduction Are needed in very small quantities Generally all micronutrients are available in materials you apply to the garden Best treatment is to prevent the problem from occurring in the first place Availability is determined by soil
Micronutrients Examples of important micronutrients Iron: needed in synthesis of Boron: deficiencies are more likely on soils Molybdenum: deficiency generally due to acid soil conditions
Cation Exchange Capacity (CEC) It is the ability of clay, organic matter, and to attract positive ions Clay, organic matter, and humus all have charges on their surfaces Most nutrients (P, K, Ca, etc) are or have positive charges Opposites attract
Soil ph: Acidity and Alkalinity What is ph? ph is log[h + ] ph is a scale from 1 to Why is ph important? Because nutrients are more or less available depending on the soil s ph The ideal range is 6.2 to
Soil ph Influences disease problems Acid soils promote root disease of cabbage Adjusting the ph is used to raise the ph Sulfur is used to the ph