Development of an In-line Nutrient Sensing System for Livestock Slurries

Abstract

An in-line nutrient sensing system was designed, built and fitted to a slurry tanker of 7 m3capacity. The system measured particular physical and chemical properties of the tanker contents to derive estimates of their ammoniacal nitrogen, total phosphorus and total potassium concentrations. The complete system was tested in the UK and Ireland using seven cattle slurries and 11 pig slurries. The nutrient estimates were based on calibration coefficients which related the nutrient concentrations to the measured physical and chemical properties. Results proved that most of these coefficients, which had been determined previously using a different sensing system, could be transferred directly to the tanker-mounted system.In the cases where the coefficients could be transferred, the overall standard errors per observation for estimation of ammoniacal nitrogen, phosphorus and potassium concentrations were ±0·29, ±0·29, and ±0·79 kg/m3, respectively. The respective ranges over which these values were determined were 0·63–5·29, 0·12–0·71 and 0·81–6·49 kg/m3. It was also demonstrated that re-calibration could improve the accuracy of estimation, particularly in instances where the system was used to determine the effects of aqueous dilution of slurries. In practice, the nutrient content of each tanker load of slurry was estimated within a period of 2 min, and thus could be completed whilst the tanker was moving from a slurry store to a spreading site, so that the target application rate could be adjusted to achieve a desired nutrient application. Therefore, it did not reduce the normal work rate of the tanker.