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

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

3. Soil Properties Chemical Properties pH –Measure of acidity (hydrogen ions - H + ) –Range = 0 -- 14 –Based on acidity of pure water 0.0000001 g H + / liter water 10 -7 g H + / liter water pH = 7

4. Soil Properties Chemical Properties

5. Soil Properties pH vs Plant Nutrients 7.08.09.010.06.05.04.0 Cu, Zn Manganese Phosphorus Boron Iron Relative Nutrient Availability vs pH

6. 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 - ))

7. 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

8. Soil Properties OM Distribution

9. 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

10. Soil Properties Chemical Properties Organic Matter Additions: –A biologically active soil can sustain OM additions of 15-30 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

11. 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

12. Soil Properties Water Holding Capacity

13. 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

14. 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