Accelerated drying of cut lucerne (Medicago sativa L.) by chemical treatments based on inorganic potassium salts or alkali metal carbonates

Abstract

AbstractLiquid treatments to accelerate drying were applied to lucerne under laboratory conditions by brief immersion (∼3s) of cut shoots. Aqueous solutions of the alkali metal carbonates Li2CO3, Na2CO3 and K2CO3 were found to reduce drying times to 33% moisture content (MC) on a dry weight basis (dwb) by 45%, 55% and 65% respectively. Effectiveness was related to the ionic radius of the cation.From a range of potassium salts (KCl, K2CO3, KHSO4, KOH, K2SO4) in aqueous solution, the only useful reductions in drying time to 33% MC (dwb) came from the alkaline KOH (68%) and K2CO3 (65–76%).It is considered that K+ has a specific function in increasing water loss through the plant cuticle and that association with CO32‐ provides the high pH necessary for this activity.An aqueous solution of K2CO3 (0·16 M) gave greater acceleration of drying than the organic solvent petroleum ether and no benefit was gained by combining these treatments. Addition of a surfactant did not improve the effectiveness of K2CO3 as a desiccant but mixing with a rape‐seed oil emulsion reduced the drying time to 33% MC (dwb) by 11% relative to K2CO3 alone.Under field conditions K2CO3 as an aqueous solution gave only small reductions in the drying time to 33% MC and effectiveness was reduced by the addition of the rapeseed oil emulsion.Better results with K2CO3 (aq) might have been achieved with a more ventilated swath structure but the results strongly suggest that the oilseed rape emulsion is unlikely to improve the effectiveness of K2CO3 under field conditions.