Technical aspects concerning the detection of animal waste nutrient content via its electrical characteristics

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. se Surface Modelling gave the regression functions relating each investigated response only to the statistically-significant factors. 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). ototype probe gave reliable estimates (R2 ⩾ 0.744) 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 (R2 ⩾ 0.656) above 20 °C.