Soil Nutrients C, H, O, from the air, water The rest from the soil

Soil Nutrients Many nutrients are in adequate supply in the soil, and do not need to be added Some are readily lost from the soil, or are present but not available. These need to be added as fertilizer. N, P, sometimes K, Fe, rarely S.

Soil Nutrients The only way to tell if your soil has special needs, or even routine needs, is by a soil test kit.

Soil pH Soil pH is a measure of relativite acidity and alkalinity Soil pH affects root function and nutrient availability, Most soils have pH’s between 5 and 9, with somewhere around 6.5 being ideal for most plants. Many of our soils are quite acid. Why?

Optimal range for most plants Neil Barry

Nutrient availability in soils Neil Barry

Neil Barry

Soil pH Many of our soils are highly weathered. This means that most of the basic cations (K, and especially Ca and Mg) have been washed out of the soil. They are replaced by protons (H), which are the basic unit of acidity. This contrasts to younger soils, which are less weathered and more neutral.

Controlling Soil pH How do we control soil pH? If the soil is acid, we need to raise the pH towards neutral. The most common way is to lime the soil. Lime is calcium carbonate, or calcium plus magnesium carbonate. The amount required will depend on the soil, and should be determined by a soil analysis. Lime granule size is important also.

Soil Cation Exchange Capacity CEC is important because it represents a reservoir of nutrients for the plant. Cations stick fairly tightly to the soil particles, but on occasion come off and go into solution in the soil water. These cations can then be absorbed by the plant roots.

Soil Cation Exchange Capacity CEC is a measure of how negatively charged a soil is, and is related to clay content. Sands have very low CEC’s, silts somewhat higher, but clays usually have very high CEC’s. Cation exchange sites occur at the surface of a soil particle, and are negatively charged. They attract cations, such as NH4, K, Ca, Mg, etc.

4 minute clip on Iron exchange http://www.youtube.com/watch?v=6aC-WTAWgOg

Cation Exchange Clay particle K+ Ca++ NH4+ _ _ K+ _ _ _ _ K+ Mg++ _ _

Oes cwestinau gyda chi? Neil Barry