MICROWAVE METHOD FOR THE DETERMINATION OF NITRIC ACID EXTRACTABLE POTASSIUM IN SUGARCANE SOILS

摘要

Potassium (K) is an essential nutrient for plant growth. It helps the plant use other nutrients and water more efficiently. Most soils contain large amounts of K, however, only a small percentage is available to the plant.Two analytical methods are conducted by SRA to assess soil potassium status. They are the exchangeable potassium test (K exchangeable), which is a measure of the available K that is readily accessible by the crop, and the nitric acid potassium test (K nitric), which is a measure of the reserve K that is slowly available to the crop.Both these analytical methods, either independently or in combination, can be used for the assessment of K levels in soils in order to provide fertiliser recommendation and feedback to growers.This study evaluates and compares the two procedures for the determination of nitric acid extractable potassium in sugarcane soils. The standard method for the nitric acid potassium utilises a hotplate extraction procedure that is time consuming, requires constant monitoring and has high acid consumption.The newly developed microwave-assisted procedure is unique and has not been used previously for the nitric acid extraction of soil K. It provides an efficient, cost effective and robust approach.Approximately one hundred soil samples were analysed by both methods. The dried and ground soil samples were heated in 1M nitric acid using a MarsXpress microwave system, cooled and then analysed for K by inductively coupled plasma optical emission spectroscopy (ICP-OES).Results showed that the K values obtained by the microwave extraction technique correlated highly with those obtained by the standard chemical method (R~2=0.99).Thus this new microwave method can be adopted for future potassium analysis of soil as not only it is rapid and cost effective, but also it improves sample throughput and reduces safety risks.