Brett Petersen Kiwi Fertiliser and Golden Bay Dolomite

There are many phosphate products on the market and each one has different qualities. At Kiwi Fertiliser, we search the globe for quality products.

As far as phosphate is concerned, our choice is Sechura RPR. For a start it is a natural product and does not need to be manufactured with sulphuric acid to make it effective. It is an alkaline product that fits in nicely with our acid soils.

To get maximum effect, sulphur needs to be added, as our soils are sulphur deficient. When sulphur is added, the results are almost explosive. Here are several farmer reactions.

“Considering how poor the season has been we came through the winter drought reasonably well, the farm held its colour when other farms in the district did not.

“Also after the recent weather bomb there have been no metabolic issues which is wonderful. The ewes are milking up, must be the available calcium in Sechura as it has not been buggerised by acidification like superphosphate.”

Another said: “Very pleased, we put Sechura on the tiger country with big improvements seen in all areas”.

Plus: “Put it on, got a quick response just like using a soluble phosphate so the bio-availability is tops”.

And: “From a soil testing point of view it is certainly elevating phosphate which is awesome. So it is certainly coming into the system quickly, also another great benefit is you can put sulphur with it as the calcium in Sechura counters the acidity of the sulphur. It is great for elevating soil pH”.

“We are seeing better clovers and more soil biology such as worms and other beneficial critters.” And one said: “Blends incredibly well with Ag lime and is a farm better option than dicalcic superphosphate”.

Shane Hurley says he’s applied Sechura RPR with compost on a number of occasions on his hill country property Pohonui, between Hunterville and Taihape. “I’ve noticed increased clover growth on the hill, and stock health has improved. The requirements for dagging have been reduced and I put this down to the levels of useful calcium in Sechura. Acid in, runny stuff out. P levels have built using the Albrecht-Kinsey system of monitoring.”

Stock constitution

Another says: “We have been using Sechura RPR since the early 1990s, firstly on only one property. There was much improved clover growth on the hills, and stock constitution and health improved hugely. Two similar north-facing paddocks side by side, one had Sechura, the other super. At crutching the 1500 hoggets from the Sechura block were 10kg heavier, and 200 were dagged. Of the 1500 from the super block, only 200 didn’t need a dag and were noticeably inferior hoggets”.

Talking of dicalcic, one wag lauded reverted superphosphate’s inventor. “He was a bloody genius, he owned a lime works and was able to sell four parts phosphorus and 96 parts lime and that amount of NPK was all you needed for a sustainable farming system. He certainly built net wealth for his family and you have to admire him for that.”

The analysis of Sechura RPR varies as is normal with any mined product. A typical assay will be: phosphorus 12-13 per cent; potassium 0.45 per cent; sulphate two per cent; magnesium 0.65 per cent; calcium 25-27 per cent; sodium 1.8 per cent; boron ppm five-100; manganese ppm 70-1530; copper ppm 20-40; iron* ppm 4700-7550; zinc 80-220 ppm; liming value 70.

Cadmium is very low and citric solubility usually in the mid-40 per cent to mid-50 per cent range. *Most hill country we test is short of iron.

Constant concentration

Professor Ian Cornforth of Lincoln University commented: “The gradual dissolution of reactive phosphate rock fertilisers supplies plants with available phosphate at a rate roughly equal to the rate at which pasture plants absorb phosphate into their roots, so the concentration of phosphate in the soil solution remains reasonably constant.

“In contrast, phosphate fertilisers that dissolve rapidly produce a very high concentration of phosphate in the soil solution immediately after they have been applied. This encourages a reaction between the fertiliser phosphate and some soil constituents that decreases the availability of the phosphate to plants”.

Not all RPRs are equal. There is only one true Sechura RPR. For your own sake take a sample of any RPR you have bought and have it independently analysed. Some operators fine-grind their products before submitting that sample for analysis. That can inflate results.