A comparison of extraction methods to assess potassium availability for Thai upland soils

摘要

The effectiveness of several extraction procedures for K in predicting K uptake by Guinea grass in the glasshouse was determined for 18 upland soils from Thailand. NH_4OAc solution extracted exchangeable K that is closely related (R~2=0.97) to plant Kuptake at 168 days, by which time most plants had died from K deficiency. This linear relationship has near unit slope so that plant uptake of K is quantitatively determined as exchangeable K. HNO3-K and NaTPB-K determine different forms of non-exchangeable K in these soils that were relatively weakly related to the plant K uptake (R~2=0.62 for HNO_3-K and R~2=0.45 for NaTPB-K). These relationships indicate that exchangeable K is the K available to plants and non-exchangeable K was not readily available for plant growth over the time scale of the experiment. The XRD patterns of clay from the soils after cropping mostly show no change from that of the initial soil confirming that plant growth did not affect mineral forms of K. XRD patterns for samplesextracted with NaTPB show a decrease in illite (001) peak-intensity with a concomitant increase in vermiculite (001) peak-intensity due to K removal from interlayer site in illite by NaTPB.