QUICK EXTRACTION AND DETERMINATION OF POTASSIUM IN FRESH LEAF SAP ANDITS USE AS A GUIDE TO POTASSIUM FERTILIZATION OF CANOLA, CHICKPEA, AND DWARF SUNFLOWER

Two simple methods to extract potassium (K) from fresh plant tissues f or use as possible quick K tests: i) freeze/squeeze in which the tissu e is frozen, thawed and extracted by placement in a syringe, and ii) p ress in which the sap is extracted by crushing fresh leaves in a garli c press, were evaluated. The K concentration in the leaf sap extracted using the two methods was determined using a hand-held ion selective electrode meter. Two separate growth chamber experiments were conducte d to evaluate method performance. In the first experiment, the relatio nships of fresh leaf sap K with total plant K and with K availability in the soil were determined using canola (Brassica campestris var, Pro fit) and wheat (Triticium aestivum var. Biggar). In the second experim ent, canola (Brassica campestris var, Profit), chickpea (Cicer arienti num), and dwarf sunflower (Helianthus) were grown on two soils low in available K with six rates of added K. The fresh leaf K extracted by t he two methods and measured using portable ion selective electrode wer e well correlated with total plant K concentration at harvest, and als o closely reflected the differences in K availability in the soil as i ndicated by soil extraction and rates of added K. Among the two method s, the press method using a hand-held squeezing device is the simplest one. However, the freeze/squeeze method may be a more suitable predic tor of the K availability in plant tissue that is less succulent.