The Biosphere Blog

The other day I was chatting to a neighbour about, of all things, Casuarina sp. (’She-Oak’) and the mulch they create from all the ‘needles’ they shed. (Casuarinas seem to be a very much under-appreciated and much-maligned tree,… more »

Chromium (Cr) Chromium (Cr) occurs naturally in soils from weathered rocks, but mostly as the chromium(III), or Cr3+, ion. This ion clings tightly to the negatively-charged sites of clays and organic matter, or forms insoluble compounds unavailable to… more »

I’ll open this post by briefly referring back to nickel (Ni) in last week’s post: the element that walks a tight line between being beneficial and being toxic. Nickel (Ni) sits right next to cobalt (Co) on the Periodic Table, and closely… more »

The macronutrients and micronutrients covered earlier are the main twelve essential for plant survival and growth, and the ones routinely included in complete fertilisers. A few other nutrients not often mentioned also have beneficial roles, and these… more »

Deficiency Symptoms Which Appear on Oldest Leaves First The following deficiencies appear on older leaves first as the elements involved are very mobile within a plant. If a nutrient on this list isn’t available in sufficient quantities to satisfy… more »

Availability to Plants Boron in soil ranges from 20 to 200 ppm (parts per million), but most of that is unavailable to plants. The boron that is available ranges from 0.4 to 5 ppm, and mostly as the compound boric acid, B(OH)3. Boric acid readily… more »

Fun Fact: Lead gets its chemical symbol Pb from the Latin word for lead: plumbum. Molybdenum gets its chemical symbol Mo from the Ancient Greek word for lead: molybdos (μόλυβδος) as molybdenum ores were confused for lead ores! Availability to Plants… more »

Availability to Plants Copper is found in soil at extremely small concentrations of 5 – 50 ppm (parts per million), and mostly in rock minerals. Copper, as the Cu2+ ion,  binds tightly to organic matter, more so than other micronutrient cations such as… more »

Availability to Plants Zinc is found in very small amounts in soil, usually from 10 – 300 ppm (parts per million), and mostly in rock minerals. The Zn2+ ion can in fact replace Fe2+ and Mg2+ ions in minerals. Zinc can also be found on the exchange sites… more »

Last week’s discussion on iron became very ‘chemical’ very quickly with quite a crash-course on oxidation, reduction and oxidation numbers thrown in out of nowhere! I do appreciate that it would have been heavy going for people without… more »

Just as there are six macronutrients, so are there six micronutrients: iron (Fe), manganese (Mn), boron (B), zinc (Zn), copper (Cu), and moybdenum (Mo). Micronutrients are so named as they are needed in smaller amounts than the macronutrients. As they… more »

Magnesium (Mg) in soil ranges from about 0.05% in sandy soils up to 0.5% in clay soils. It is more prevalent in clay soils as these contain very weatherable magnesium-containing minerals. Some clay minerals themselves contain magnesium. Magnesium may… more »

Elemental calcium (Ca) makes up 3.64% of the Earth’s crust, making it the fifth most common element in the crust after oxygen (O), silicon (Si), aluminium (Al) and iron (Fe). This makes it the most abundant of all plant nutrients after oxygen and… more »

So far we’ve covered he big three macronutrients: nitrogen (N), phosphorus (P), and potassium (K) — the famous NPK. Today we’ll cover a lesser-known, but also important nutrient for plants: sulfur (S). It may surprise you that sulfur is an… more »

Of the six essential macronutrients a plant needs, the big three are nitrogen (N), potassium (K), and phosphorus (P), our subject for today. Availability to Plants Elemental phosphorus (P) makes up 0.02–0.15% of soil, and primarily exists as hydrogen… more »