ESTIMATION OF THE NUTRIENT VALUE OF AGRICULTURAL SLURRIES BY MEASUREMENT OF PHYSICAL AND CHEMICAL-PROPERTIES

A prototype nutrient sensing system was used to investigate relationsh ips between the nutrient status of agricultural slurries and a range o f 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 s lurries, comprising approximately 20 cattle and 20 pig slurries from e ach of four European countries. Linear relationships were identified b etween ammoniacal nitrogen concentration and the electrical conductivi ty 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 tan ker to estimate the nutrient status of the whole tanker contents, thus eliminating the sampling errors associated with sub-sampling from a l arge store. (C) 1998 Silsoe Research Institute.