 Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil Fertile soil is not necessarily a productive soil Why? Poor Drainage, Insects, Drought, and other factors can limit production

 Existing plant-soil relationships affect soil productivity  External factors control plant growth Air Temperature Light Mechanical support Nutrients Water  Plants rely on soil to provide all these except light

 Water and air fill pore spaces in soil  Factors that affect water relationships also affect soil air  Nutrient availability is influenced by soil and water balance and temperature  Root growth is influenced by soil temperature as well as soil, water, and air

Soil Productivity

 What is organic matter?  Plant, animal, and microbial residues Varying stages of decay  Adequate levels of O.M. benefit soil by:  Improving physical condition and tilth  Increases water infiltration  Decreases erosion loss  Supplies plant nutrients

 Organic matter contains about 5% N  N is not immediately available  Decomposition must occur first  Fertilizer (inorganic) N is needed for non- legume plants  Organic matter also provides soil with a variety of other mineral elements that plants need to be healthy  Some include: phosphorus, magnesium, calcium, sulfur, and others

 Soil Depth  Depth of soil material favorable for plant root penetration  Plants need soil to be:  Deep  Well-drained  Correct texture  Correct structure  Deeper soils provide for more nutrient storage

 Roots can extend 3-6 feet or more when soil depth permits  Rooting depth is affected by Physical barriers Chemical barriers High water tables  Hardpans, Shale beds, Gravely Layers and accumulations of salts are very hard to correct

 Surface slope is part of what?  Topography  Determines the amount of runoff and erosion  Also determines:  Irrigation method  Drainage  Conservation practices  The steeper the land the more management is needed  More labor and equipment costs

 At certain slopes, soil is no longer suitable for row crops.  What are some row crops?  Potential productivity is largely determined by ease of erosion along with percent of slope

 Many different organisms live in the soil  Usually in the first foot of top soil  Depend on organic matter for food  Factors that affect the amount soil organisms:  Moisture  Temperature  Aeration  Nutrient supply  Soil pH  Crop that is being grown

 Some of the microscopic organisms cause many favorable soil reactions  decay of plant and animal residues  speed nutrient cycling.  Other reactions can be injurious  development of organisms that cause plant and animal diseases

 Nutrient balance is a vital concept in soil fertility and crop production  Nitrogen is the first limiting nutrient in non- legumes  Without adequate amounts of the other nutrients, N cannot do its best  As Nitrogen fertilization raises yields, the crop demands more of the other nutrients

Soil pH

 The measure of acidity or alkalinity of the soil  pH is determined by the concentration of hydrogen ions(H+) and hydroxyl ions(OH-) in the soil solution  Pure water has an equal number of H+ and OH-

 Another term for alkaline is basic  Acid = high in H+  Basic = high in OH-  A soil with a pH of 6.0 has 10 times as much active H+ than neutral

 Plants will not thrive in soil that is too acid or too alkaline  The soil pH directly affects the availability of mineral nutrients  Example  Low pH: phosphates may be bound chemically in the soil so plants are unable to access them Also means that nitrate production in the soil is reduced

 Several factors influence Soil pH  Organic matter  Parent material  Rainfall leaching  Forest vs. grassland  Harvesting crops  Legumes  Soil depth  Fertilizer application  Flooding

 How to measure soil pH  Indicator dyes  pH meter  Which do you think is more accurate?  The meter  If our soil’s pH was too acidic what would we add to amend it?  Lime

 Soil pH is not the determining factor on how much lime to add  What else do we need to consider? Texture of soil Amount of organic matter  The amount of clay and organic matter in a soil will determine the ability of a soil to resist pH change  More clay/organic matter = more pH buffering  The process is very complex  Example: Al and water

 Lime requirement  Amount of Ag limestone needed to establish the desired pH range for the cropping system being used  Lime reduces soil acidity  Look at Al and water example  Uses Ca ion  Soil will become more and more acidic if a liming program is not followed  We do not apply lime to soils here in Northern Utah very often… Why?

 In the case of high pH  Lowering pH is not usually economical  These are generally high in salts  Find plants that tolerate high salt levels

 As soils form  Some particles are broken down into extremely small particles  Chemical weathering breaks them down until they cannot be seen with the naked eye  The smallest are called colloids  Colloids are responsible for chemical reactivity in soil  Each colloid has a negative(-) charge

 The neg. charge will attract positively(+) charged particles  What does that mean if they run into another negative?  Cations: Positive Charge  Anions: Negative Charge  Colloids act like a magnet and holds cations  Other cations can take their place  They are exchangeable

 Can a soil hold more cations than it has colloids?  no  We need to know our soil’s CEC  Higher CEC = more cations can be held  Depends on clay and organic matter  Lots of clay = higher CEC  More organic matter = higher CEC

 Leaching is reduced by higher CEC  Knowing our CEC will help determine how much fertilizer to apply and how often