Potassium fertilization of hemp (Cannabis sativa)

Potassium response trials were conducted on hemp on four sites with different levels of soil potassium in 2011 in which the main factor was variety and the second factor was potassium rate. Five rates of applied potassium were used (0, 60, 90, 120, and 150 kg K/ha). There was no significant relationship between hemp yield and either potassium rate or the level of soil potassium. Potassium uptake from the site with the lowest level of soil potassium was significantly lower (65 kg K/ha) compared to a site with a higher level of soil potassium (83 kg K/ha) suggesting that hemp will take up potassium when the element is not needed. Most of the absorbed potassium was concentrated in the stem (70–75%), harvest off-takes for most applications would consist of only stem and any potassium in root and leaves would remain in the field. The results of this limited investigation suggest that hemp has a lower requirement for potassium than other crops and that the optimal potassium fertilization strategy for soils with moderate to high levels of potassium (>70 mg/L; Morgan's test) is to replace off-takes after the hemp has been harvested. Further research is necessary to develop robust potassium fertilization guidelines for hemp.

► The potassium requirements of hemp crops are low.
► Hemp will take up more K than needed if excess quantities of K are available.
► Late maturing varieties will take up more K than earlier maturing varieties.
► Replacing K post harvest may be the optimal strategy on soils with higher levels of K.