01717naa a2200229 a 450000100080000000500110000800800410001910000170006024500370007726000090011452011200012365000210124365000240126465000140128865300240130270000230132670000190134970000140136870000160138270000150139877300740141310287652010-03-08       2004    bl ---       0--  u    #d1 aLEMOS, S. G.  aIn-soil potassium sensor system.  c2004  aA potentiometric sensor system based on potassium ion-selective electrodes was developed for agricultural purposes. Sensors were built using PVC ion-selective membranes over an inner solid contact prepared with graphite-epoxy composites. A copper plate was used as a reference electrode. A Iwo-stage electronic circuit composed of current and voltage amplifiers was designed to interface lhe sensors to a distributed data acquisition system. Three ion-selective sensors and three off-the- shelf temperature sensors and their associated circuils were mounted in a PVC tube to seI up a soil probe. The electronic contrais were placed in an airtight box fixed at lhe upper part of lhe probe. The system was evaluated in lhe field, where lhe sensors presented sensibility within lhe range of 69- 71 mV dec-1. Extracts of soil samples were analyzed by a current lIame photometry approach, and the results, compared with the probe measurements, showed a linear relationship (r2 = 0.992 and 0.995, respectively, to 5 and 20 cm depths), which implies viability and instrumentation reliability for agricultural applications.  aAnálise do Solo  aFertilidade do Solo  aPotássio  aForça dos sensores1 aNOGUEIRA, A. R. A.1 aTORRE-NETO, A.1 aPARRA, A.1 aARTIGAS, J.1 aALONSO, J.  tJournal of agricultural and food chemistrygv.52, 2004. p. 5810-5815.