ChileanJAR

Seven Andisols and four Ultisols were studied. Under greenhouse conditions, K absorbed by plants (LoIium perenne), from exchangeable and non-exchangeable K forms of the soils, and the effect of K application on dry matter production and K absorption by plantswere studied. The values of the different K parameters of the soils were correlated with dry matter production and with K absorption by plants. The conclusions were:

1. Potassium absorption by ryegrass plants was, in average, three Ór four times higher from Ultisols than from Andisols, excepting Agua Fría and Chufquén soils, which characteristics were between both soil groups. Ryegrass plants extracted more K from exchangeable forms than from non-exchangeable forms. However, an mportant percentage of the K absorbed (9 to 44%, in Andisols, and 25 to 44%, in Ultisols) corresponded te the last forms.

2. Potassium absorption was significantly related te exchangeable K (r 0,97**) and te Step K (-r = 0.92**). At the same time, these parameters were related te the percentage of clay in the soil (r = 0.82** and 0.81**, respectively). Also, “maximum capacity of K desorption” presented a highly significative correlation with K absorption (r = Q,94**) and with exchangeable K (r = 0.97**).

3. ln Ultisois there was no response from plants te K application, excepting the Chufquénsoil. The higher response of plants was observed in the fIat Andisois, with the exception of the Agua Fría soil, and in the Santa Bárbara 1 Andisol. In the hilly Andisols, this response ‘bes lower, but also significative. The Agua Fría Andisol andthe Chufquén Ultisol showed a significative response, but intermediate between Andisols and Ultisols, and closer te this last group of soils.