Estimation of the nutrient value of agricultural slurries by measurement of physical and chemical properties

A prototype nutrient sensing system was used to investigate relationships between the nutrient status of agricultural slurries and a range of physical and chemical properties. These properties were all measured using devices suitable for possible installation in full-scale slurry handling systems. The prototype system was tested on a total of 160 slurries, comprising approximately 20 cattle and 20 pig slurries from each of four European countries. Linear relationships were identified between ammoniacal nitrogen concentration and the electrical conductivity of the slurries and between total phosphorus and the density of the slurries. Generally, regressions for total potassium were weaker than those identified for either ammoniacal nitrogen or total phosphorus. The results show that a practical nutrient sensing system is feasible for farm use. For example, such a system could be used on a slurry tanker to estimate the nutrient status of the whole tanker contents, thus eliminating the sampling errors associated with sub-sampling from a large store.