Overview of Soil Properties for Crop Production By J.G. Mexal Department of Agronomy & Horticulture New Mexico State University

Soil Properties Important Soil Properties Physical –Texture –Structure Chemical –pH –C.E.C. –W.H.C. –Organic Matter

Soil Properties Chemical Properties pH –Measure of acidity (hydrogen ions - H + ) –Range = –Based on acidity of pure water g H + / liter water g H + / liter water pH = 7

Soil Properties Chemical Properties

Soil Properties pH vs Plant Nutrients Cu, Zn Manganese Phosphorus Boron Iron Relative Nutrient Availability vs pH

Soil Properties Chemical Properties Cation Exchange Capacity (CEC) –ability of soil to hold positively charged ions e.g. ammonium (NH 4 + ), calcium Ca ++, sodium (Na + ) –Function of Texture and Organic Matter finer texture and O.M. increase CEC –Soils have little ability to hold negatively charged ions (e.g. nitrate (NO 3 - ))

Soil Properties Chemical Properties Organic Matter –Living and dead plant and animal matter present in and on soil –Can be added (e.g. manure & waste) –Other terms: litter humus

Soil Properties OM Distribution

Soil Properties Chemical Properties Benefits of Organic Matter –Increases CEC (fertility) of soil –Increases infiltration of water –Increases water holding capacity –Provides nutrients for plants –Reduces root diseases

Soil Properties Chemical Properties Organic Matter Additions: –A biologically active soil can sustain OM additions of t/ha/yr. –A ‘strong’ wastewater (TOC = 300 mg/L) could supply about 6 t OM/ha/yr. –Total nitrogen would limit loading rate before OM loading becomes problematic

Soil Properties Water Holding Capacity Water Holding Capacity (WHC): amount a water held by a soil; a function of texture. Field Capacity (FC): amount of water held against the force of gravity after irrigation. Permanent Wilting Point (PWP): amount a water at which the plant wilts permanently. (Does not hold well for desert plants) Available Water (AW): FC - PWP = AW

Soil Properties Water Holding Capacity

Soil Properties Porosity & WHC of Soils and Soil Mixes/ Craul ‘99 Pore Space (%) Key: c=coarse, f=fine, S=sand, Sl=silt, C=clay, P =Peatmoss

Soil Properties Porosity & WHC of Soils and Soil Mixes/ Craul ‘99 Pore Space (%) Key: c=coarse, f=fine, S=sand, Sl=silt, C=clay, P =Peatmoss