organic matter

In midterm 2, I lost marks for not clarifying the effect of organic matter on nutrient retention and supply, and the water retention. I can't seem to find an answer to this question. How does organic matter affect these properties of the soil?

Aaron, lecture notes from Feb 13 list effects if SOM on physical, chemical and biological soil properties. Are you asking specifically about question 3a)? If yes, when you interpret data e.g. nutrient retention or water retention - base your rationale on all relevant characteristics.

Organic matter, due to its functional groups, have net negative charge in the pH range common in soils; consequently OM contributes to both CEC and water retention (via adhesion). Consequently when assessing the ability of a soil to hold water or nutrients, you should consider both texture and SOM as contributing factors.