Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Chapter 7 Soil Fertility and Management

Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Sixteen Essential Plant Nutrients Non-mineral: carbon, hydrogen, oxygen, nitrogen Mineral: –macro: nitrogen, phosphorus, potassium –secondary: calcium, sulfur, magnesium –micro: boron, copper, zinc, iron, manganese, molybdenum, chlorine

Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. The Importance of Nitrogen One of Earth’s most abundant and mobile nutrients Part of every plant cell, including chlorophyll, which gives plants their green color Subject to many physical, chemical, and biological processes that can result in significant losses of the nutrient

Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Main Pathways for Nitrogen Loss Leaching—nitrates are the type of nitrogen most subject to this kind of loss through movement of soil H 2 O Erosion—nitrates move primarily in runoff H 2 O, while ammonium and organic forms of nitrate move with sediment, which can be reduced by using soil conservation

Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Main Pathways for Nitrogen Loss (continued) Denitrification—soil is saturated with H 2 O, bacteria convert nitrates to gaseous form of N 2, which is lost back to atmosphere Volatilization—urea is converted to ammonium carbonate, which in turn breaks down into ammonia gas, which is lost back to the atmosphere

Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Nitrogen Cycle and Nitrogen Fixation Nitrogen cycle—N 2 is converted to usable nitrogen and then back to N 2 (elemental or atmospheric nitrogen) Nitrogen fixation—N 2 is removed from the atmosphere by rhizobia (soil bacteria) living in root nodules of legumes and converted to usable form

Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Carbon:Nitrogen Ratios of Some Organic Materials

Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Soil pH and Phosphorus Availability

Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Potassium Second only to nitrogen in amounts used by plants Much of potassium found in soils is tied up by soil minerals Muriate of potash (potassium chloride) is primary source of fertilizer potassium; another source is potassium sulfate

Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Nutrient Availability Nutrients in soil can be unavailable for plants to use because they are in –insoluble chemical compounds –Un-weathered or un-decomposed soil minerals or rock fragments –organic matter or plant residues –soil particles

Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Function of Lime as Soil Additive “Sweetens” the soil (increases pH or alkalinity)—most plants do not grow well in acid (“sour”) soil Improves availability of plant nutrients Increases effectiveness of applied nitrogen, phosphorus, and potassium Increases activity of microorganisms Improves plant growth and crop yields

Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Choosing a Fertilizer Complete/mixed—contain three primary nutrients Should be selected based on economics, market availability, other factors, not solid versus liquid Placement is critical—GIS/GPS systems can help

Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Choosing a Fertilizer (continued) Alternatives to commercially made fertilizers include –manure: quality is affected by age/kind of animal, what it ate, amount/kind of litter/bedding used, way manure handled –compost: especially good for improving soils low in organic matter

Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Soil Management Concerns Erosion—removes topsoil and causes environmental problems; can be prevented by soil conservation Compaction—usually caused by increased use of heavy farm equipment Drainage—well-drained soils can grow a wide variety of plants