There’s certainly plenty of interest in liquid potassium (K) fertilisers – at least in some parts of the state.
In response to this interest, we set up a trial near Quairading this year to (1) test three liquid K products on wheat, and (2) compare them to the conventional approaches of using granular NPK fertilisers at seeding and topdressing MoP before seeding.
The liquid K fertilisers being trialled are potassium nitrate, potassium acetate and potassium thiosulfate. They were applied following label recommendations.
Early responses to K supplied by MacroPro Extra and K-Till Max confirmed that we had a very responsive site (see photo).
Agstar Extra (0K) v K-Till Max (18K) - 14 June (7 WAS)
The first of the liquid treatments (potassium nitrate) was applied at the three to four leaf stage. Plant testing 20 days later showed little impact from the foliar application, but highlighted greater efficiency gains from banding NPK fertilisers compared to topdressing MoP.
Three weeks later, potassium nitrate, potassium acetate and potassium thiosulfate were applied to plots that had no K fertiliser beforehand. Another treatment had a second application of potassium nitrate.
The trial was tissue tested again on July 17 - 33 days after these treatments were applied. As expected, K uptake increased with increasing K inputs but none of the liquid K treatments had a significant effect on K uptake (see table).
Without K applied, the crop had recovered 26kg K/ha (treatment 1). It is no surprise that the application of just 2 kg K/ha supplied by 5-10 L/ha of a liquid product has little if any impact on crop nutrition.
Potassium is a major nutrient – it is required in large amounts by plants.