Real-time on-farm N loss measurement

Abstract

Empirical measurements of nutrient-leaching losses on farms are required in order to allow validation of models used to assess nutrient losses from New Zealand farmland. However such on-farm measurements have, to date, been generally impractical. A new in-field leaching loss measurement system has been developed, based on well-established research methodologies. This system combines large strip lysimeters (10–20 m long) with largely automated, real-time leachate monitoring, which allows measurements to be taken over much larger areas for greatly reduced costs compared with other systems currently on the market. A spatial computer modelling simulation showed that one such lysimeter can generate results of equivalent accuracy to an array of 12 fluxmeters, three lysimeters are equivalent to an array of 64 suction cups, and a larger number of lysimeters can be used to obtain more accurate results. Nutrient loss is measured using off-site chemical analysis of flow-proportional subsamples of drainage water. In addition, electrical conductivity (EC) of the drainage water is measured continuously and correlated with past chemical analyses to provide real-time estimates of nutrient loss. Real-time EC measurements were strongly correlated with Total N concentration determined off site (R2 = 0.89), which suggests that EC can be used as a proxy for Total N. However, a site-specific regression of EC and N should be used for any actual estimation of N from EC.