FIRST performance comparisons of WA-produced Sulphate of Potash (SoP) fertiliser with imported Muriate of Potash (MoP) fertiliser have proved promising for the local product.
Preliminary results part way through a two-year study of local granular SoP versus imported MoP in glasshouse and broadacre cropping trials have suggested local SoP benefits of better plant uptake of potassium and sulphur, larger root biomass in some soils and superior crop germination safety in the field.
As previously reported in Farm Weekly, Australian Potash - identified as APC on Australia Security Exchange listings - supplied samples of its patent pending K-Brite SoP fertiliser product for the trials which began in March.
APC produced its SoP samples at a Cannington laboratory at the start of the year from potassium salts harvested from trial solar evaporation concentrator and crystalisation ponds that were filled with brine pumped from ancient palaeochannels (riverbeds) beneath Lake Wells, a remote salt lake 200 kilometres north east of Laverton.
The performance comparison trials involve collaboration between APC, The University of Western Australia (UWA) Institute of Agriculture and Western Australian No Tillage Farmers Association (WANTFA).
UWA researchers, led by Dr Zakaria Solaiman, collected 300 kilograms of soil from farms at Bolgart, Tammin, Southern Cross, Grass Patch and Kojonup to investigate the effects of SoP and MoP on yield, quality, value and soil biology, including soil pH before and after the trials.
They compared wheat and canola responses to rates of SoP, applications of SoP, MoP and MoP plus gypsum on yield and quality, potassium leaching of SoP, MoP and MoP plus gypsum, as well as germination and crop establishment.
Trial plots were benchmarked against fertiliser-free wheat and canola plots.
So far, the glasshouse trials have shown most soil types responded to potassium application with significant biomass and yield increases and more potassium and sulphur was taken up by plants in the SoP treatments compared to MoP.
This correlated to increased root biomass by up to 50 per cent with SoP, but not in all soil types and the application of gypsum with MoP helped overcome the biomass deficiency, researchers found.
Grain analysis from five cropping trial sites has shown significantly greater potassium uptake in canola than wheat, indicating a greater demand for the nutrient and, in turn, a greater loss from soil profiles where canola has been grown.
The field analysis also showed a significant increase in potassium and sulphur uptake when SoP was applied compared to MoP.
While this effect was inconsistent across all soil types and depended on the sulphur content of the soil investigated, researchers said the greater uptake offered overall grain health and protein benefits.
They pointed out sulphur was an essential nutrient for plant growth and improved grain protein and, although the amount added with SoP is relatively small compared to other sources, it may reduce the need for sulphur applications over time and lead to higher grain protein levels in marginal soils.
The five trials were sown to wheat in late May to early June, with SoP and MoP placed directly with the seed on WANTFA member farms at Tammin, Southern Cross and Kojonup.
Two trials showed crop emergence reductions of 10-30 per cent with a MoP application of about 30 units of potassium per hectare, while there was no reduction where SoP was applied directly with seed at rates up to 60u/ha of potassium.
In Southern Cross, where no reduction of germination between MoP and SoP was found when applied directly to the seed, the grower used a splitter boot seeding system and it was thought dilution of potassium between each split reduced the toxic effect of MoP on seed.
Biomass, yield and grain quality comparison results are yet to be determined in the field trials and a more detailed report is expected early next year.
WANTFA executive director Dr David Minkey, who oversaw the field trials, said initial trial results "are showing promise for SoP over MoP".
"The crop safety aspect alone will give the grower more flexibility with their K (potassium) application," Dr Minkey said.
"The reduction in root biomass with MoP, presumably due to the presence of chloride, needs to be explored further, along with soil health aspects in the longer term.
"The increased uptake in potassium and sulphur in plants when using SoP is also exciting for plant stress responses and possibly grain protein in situations of marginal potassium and sulphur," he said.
While SoP has the lowest salt index of any potassium fertiliser, which in theory should make it more suited for use on salt-affected areas of the Wheatbelt than widely-used MoP, it is currently also imported and sells at a significant price premium which tends to restrict its usage to high-return horticulture crops.
APC and several other Perth-based mining companies are developing relatively low cost local SoP fertiliser production projects using potassium-rich brine from beneath remote desert salt lakes to supply local and growing international demand for SoP.
The first of these projects is expected to begin commercial production towards the end of next year.
