Ravensdown manufactures Superphosphate at ISO 9002 certified factories in Dunedin (Ravensbourne), Christchurch (Hornby) and Napier (Awatoto). Superphosphate is manufactured by reacting finely ground rock phosphate with sulphuric acid to convert the insoluble mineral phosphate into a soluble, plant available form. The resultant product contains 9.3% total phosphorus, 10.8% sulphur (present in the sulphate form), and 20% calcium. As phosphate rock contains traces of other elements, there are also found in the final product. They include beneficial elements such as magnesium, iron, copper, zinc and manganese.
Potassium fertilisers are often referred to as ‘potash fertilisers’, a name originally given to an early form of potassium fertiliser which was produced by extracting a pot of wood ashes (pot ash). However, potassium is now mined from abundant mineral deposits. Potassium fertiliser has only been used extensively in New Zealand since the 1950’s. The most important potassium fertilisers in New Zealand are Potassium Chloride and Potassium Sulphate.
Ravensdown has developed the Cropmaster range of high-analysis fertilisers that provide quick release nutrients suitable for a wide range of arable, pastoral, horticultural and forestry uses.
Cropmaster products are blends of DAP with granular Ammonium Sulphate and/or chipped Potassium Chloride. These components all have similar particle size (2-4mm diameter) which minimises segregation during transport and spreading.
The colour of the individual components can vary depending on where they are sourced. DAP can vary from light brown to black, Ammonium Sulphate from reddish brown to white, and Potassium Chloride can be red-pink or white to grey. Please note that colour variations do not alter the chemical quality of the product.
Nitrogen is the most important nutrient for plant growth. Much of the N in pasture is supplied through N fixation by white clover. However, the inherent N deficiency of the grass/clover system will always limit annual pasture production. This N deficiency can be relieved by application of N fertilisers, which is best used as a strategic supplement to N fixed by clover plants.
Nitrogen fertiliser use should always be targeted so the extra grass grown satisfies a specific animal feed requirement. Used this way, N fertiliser has frequently been shown to be the cheapest and most profitable way of providing additional feed to stock.
Under cropping situations, when comparing nutrients it is the amount of N available to crops that has the largest influence on yields. Therefore the amount of N fertiliser that comes out of the bag for crops is critical. This will depend on a number of factors, such as the amount of mineral N remaining in the soil from the previous crop, as well as the potential for N to be released from the soil organic matter when the soil is cultivated.
Ammo Phos MAP-based Products
Ammo-Phos fertilisers contain monoammonium phosphate (MAP), which is manufactured by chemically reacting one molecule of ammonia with one molecule of phosphoric acid. Diammonium phosphate (DAP) is made the same way, except that two molecules of ammonia are reacted with each molecule of phosphoric acid. As MAP has only half as much ammonia in proportion to the phosphate, there is virtually no release of free ammonia, and therefore can be sown closer to seed compared to DAP.
Ravensdown have several MAP-based fertilisers, often blended with potassium chloride for soils with low to medium potash levels. Pea fertiliser also uses MAP as its base, due to the lower risk of seed burn with this fertilisers.
Magnesium is found in minerals such as dolomite, biotite and serpentine. Although magnesium is essential for both plants and animals, deficiency symptoms usually appear in grazing livestock before showing up in the herbage.
Soils generally contain between 0.1 and 1.0% magnesium, but not all of this is plant available. Magnesium is found in three forms in the soil: mineral Mg, exchangeable Mg and soil solution Mg. There is an equilibrium between soil exchangeable Mg and soil solution Mg. This exchangeable Mg represents about 5% of the total soil Mg and typically occupies between 4 and 17% of the soil’s cation exchange capacity.
Ravensdown have a number of Magnesium fertilisers available to their shareholders, ranging from the slow-release Magnesium Oxide, which relies on soil acidity for its dissolution, to readily available Magnesium Sulphate.