Abstract
The variables influencing corrosion of three metals (galvanised steel, stainless steel, brass) usable for a manure nutrient probe were examined, identifying the best material for field applications. The nutrients in 18 liquid manures were then estimated through the voltage drop between the terminals of a prototype probe.Response Surface Modelling gave the regression functions relating each investigated response only to the statistically-significant factors.After 168. h in the manure, it was determined that: stainless steel was the most suitable material for very close electrodes (mass: -1.8% at 15. mm), brass can be used with any inter-electrode distance (mass: -13.0% maximum at 35. mm).The prototype probe gave reliable estimates (R20.744) of Ntot, Namm, Ptot, Ktot when dry matter and temperature were also accounted for in the regression analysis. Not considering dry matter but just electronically-detectable quantities (temperature, voltage drop), the estimates were only reliable (R20.656) above 20°C. © 2013 Elsevier Ltd.