Ammonia emissions are an important issue in livestock production. Many mitigation measures have been proposed in order to reduce the environmental impact of livestock farms, and reliable field measurements are required to evaluate the amount of released or reduced ammonia while applying these measures. Following the guideline of the Verification of Environmental Technologies for Agricultural Production test protocol, five commercially available gas analysers, i.e., INNOVA 1314, Picarro G2103, Rosemount CT5100, Gasmet CX4000, and Axetris LGD F200-A, were validated as alternative methods to the wet-chemistry method (reference method) for measuring ammonia in livestock houses. High correlations ( $r>0.99$ ) were found between the analysers and the reference method. The measurement errors of the tested analysers were below 2 ppm_v or 10%. Equivalence to the wet-chemistry method was demonstrated for the INNOVA and Rosemount analysers without a recalibration and for the Picarro and Axetris analysers with a recalibration. The Gasmet analyser was seemingly subjected to an interference from carbon-dioxide and, after compensating for the cross-sensitivity, the equivalence to the wet-chemistry method could also be demonstrated. Calibration curves that were based on a certified gas cylinder were inconsistent with that based on wet-chemistry measurements, which suggested that field calibration might be necessary for optimal measurement accuracy.

The application of entomopathogenic nematodes (EPN) is generally done using standard spray application techniques. However, in contrast to chemical pesticides, these biological antagonists must remain viable during and after the application process. For the application of EPN, a good agitation system is indispensable as the nematodes tend to sediment fast in a spray tank without agitation. Three agitation systems, viz. mechanical, pneumatic and hydraulic agitation were tested for their ability to keep Steinernema carpocapsae (Rhabditida: Steinernematidae) suspended in an undamaged way. Hydraulic agitation was tested using a centrifugal and a diaphragm pump. Nematode damage was quantified based on viability and infectivity of the EPN. The ability of the agitation system to keep the nematodes in suspension was examined by comparing the nematode concentration observed in the samples taken at different agitation times. Only the hydraulic agitation using the centrifugal pump damaged the nematodes. After 120 min of recirculation, only 19.3% of the nematodes survived. Infectivity was even reduced to 0%. An additional experiment revealed that the temperature rise, from 21.7 to 45.4°C, was responsible for the observed nematode damage. The concentration measurements showed that the pneumatic agitation was unstable. Agitation during 120 min using the other agitation systems resulted in a significant loss of nematodes at 15 cm above the spray tank bottom. In conclusion, mechanical and hydraulic agitation using a diaphragm pump can be recommended when S. carpocapsae is applied, although attention should be paid to possible nematode loss during application.

Damage caused to entomopathogenic nematodes by spray application is generally assessed by observing the viability of the infective juveniles under the microscope. To improve the quality and speed of this observation we developed an image processing technique and tested the efficacy of acetic acid and sodium chloride as chemical stimulants. Because of the lower standard error on the results obtained (0.7 vs 1.7), sodium chloride was eventually selected for all subsequent observations. The viability as observed with the image processing technique rose significantly with the time after the nematodes were suspended in water; however, viability as observed under the microscope was not influenced by the time. These differences can be attributed to the difference in type of stimulant (mechanical vs chemical) used. After nematodes had been in suspension for 3.5 h, the viability as measured using the image processing system was still significantly lower than the viability as measured under the microscope. This difference did not disappear after 24 h at 4, 15 or 24°C. Maintaining nematodes for 24 h at 35°C significantly decreased the viability to 5.9% (microscope) or 11.0% (image processing technique). The decrease in viability as observed with the image processing system corresponded better with the decrease in infectivity (i.e., 13.8%). Our results support further use of the image processing technique, not only to observe the viability of entomopathogenic nematodes but also to count the mobile or total number of nematodes of any species.