Tuesday, 1 July 2014

Superphosphate and Kiwi soils


As New Zealand’s most widely used fertiliser, superphosphate is a key driver of pasture growth. The use of superphosphate and legumes has transformed many infertile soils into productive agricultural areas. The resulting economic prosperity over the decades can be measured in hundreds of billions of dollars.

Superphosphate provides calcium, phosphorus and sulphur to promote legume growth and increase nitrogen fixation symbiotically from the atmosphere. Other elements are added where required, for example potassium - a highly efficient system to promote pasture production.

After more than 130 years being made right here in New Zealand, superphosphate remains the country’s most widely and effectively used fertiliser for pastoral, cropping and horticultural uses.

Because it has been around for so long, “Super” is one of the most researched products in New Zealand rural environments. Two sheep-grazed trials established and run by AgResearch at Ballantrae (Manawatu) and Winchmore (Canterbury) have been run for 30+ and 60+ years respectively. Both compare applying no fertiliser with annual superphosphate applications of up to 375 kg/ha. Large increases in pasture production, quality and stocking rates have been sustainably achieved over these timeframes.

Long-term studies also show that it does not lower soil pH. Its use on grazed pastures promotes organic matter returned to soils through excreta, uneaten herbage and root turnover which stimulates the vigour and population of soil microbes and worms, thus improving soil health and fertility.

Super combines well with almost all other fertilisers. Sulphur-enriched superphosphates are widely used in New Zealand. The amount of sulphur required will dictate which product is used. Sulphur super has a maintenance role particularly where topdressing is infrequent, on sedimentary, pumice and peat soils under high rainfall and on soils where the sulphur requirement is significantly higher than phosphate.

Significant increases in dry matter production and quality are possible with the correct balance of phosphorus and sulphur.

Sulphur super contains both quick acting sulphate sulphur and slow release elemental sulphur.