Search

Field studies on soil ammonia (NH3) volatilization are restricted in many countries owing to the high costs commonly demanded for accurate quantification. We assessed the accuracy of a simple, open chamber design to capture NH3under field conditions, as affected by different chamber placement schemes. Urea-15N was surface applied to lysimeters installed in the spaces between maize rows. Open chambers made from plastic bottles were installed on each lysimeter with variations in i) N rates (3, 8, 13, and 18 g m–2), ii) the height of the chamber above the soil surface (0, 5, and 10 mm), and iii) chamber relocation (static vs. dynamic). Reference lysimeters without chambers were used to measure NH3losses by 15N-balance. Losses of NH3-N accounted for more than 50% of the applied N. Relocation of the chambers had no impact on their NH3-trapping efficiencies, proving to be an unnecessary procedure. Variation in the height of the chambers above the soil surface affected the capture of NH3, but the results still maintained high linearity with the NH3losses quantified by the reference method (R2> 0.98). When the same placement scheme used in the introductory study describing the chamber was utilized (static and touching the soil surface), we found a trapping efficiency of 60%, which was very similar to that (57%) obtained in the previous study. Our results show that this simple, open chamber design can be used with satisfactory accuracy under field conditions, provided that simple, standardized procedures are warranted.

Measuring ammonia (NH3) volatilization from urea-fertilized soils is crucial for evaluation of practices that reduce gaseous nitrogen (N) losses in agriculture. The small area of chambers used for NH3volatilization measurements compared with the size of field plots may cause significant errors if inadequate sampling strategies are adopted. Our aims were: i) to investigate the effect of using multiple open chambers on the variability in the measurement of NH3volatilization in urea-amended field plots and ii) to define the critical period of NH3-N losses during which the concentration of sampling effort is capable of reducing uncertainty. The use of only one chamber covering 0.015% of the plot (51.84 m2) generates a value of NH3-N loss within an expected margin of error of 30% around the true mean. To reduce the error margin by half (15%), 3–7 chambers were required with a mean of 5 chambers per plot. Concentrating the sampling efforts in the first two weeks after urea application, which is usually the most critical period of N losses and associated errors, represents an efficient strategy to lessen uncertainty in the measurements of NH3volatilization. This strategy enhances the power of detection of NH3-N loss abatement in field experiments using chambers.