Progress on monitoring methods in nitrogen losses from orchard soils

Excessive nitrogen input, serious nitrogen losses, and low utilization rate are very common in orchard production system, which impede the sustainability of the fruit industry. Studies on monitoring nitrogen losses in orchards are relatively rare nationally and beyond, compared to those on grain and vegetable production, and there are no generally accepted monitoring methods. The situation makes it difficult to draw comparable and scientific conclusions, and greatly limits the understanding of nitrogen losses in orchards and the consequent environmental effects. Therefore, we summarized the monitoring methods of soil N₂O emission, NH₃ volatilization, nitrogen runoff, and leaching losses in orchard systems in China and internationally, and proposed the following suggestions: 1) the closed static chamber method for monitoring N₂O emission from soil has its shortcomings, but it is more applicable, operable, and is of low cost for orchards. 2) Intermittent aeration method is suggested to monitor the soil NH₃ volatilization at high nitrogen application rate in orchards; and the phosphoric acid glycerin double sponge ventilation method is better at low nitrogen application rate, and the thickness of sponge at about 2 cm is better. 3) In the monitoring of N₂O emission and NH₃ volatilization in orchard soil, the setting of sampling points should consider the fertilization area and non-fertilization area, and the most representative sampling time (segment), sampling frequency (total airtight time and sampling interval), sampling period and other key parameters should be defined. In addition to fertilization and irrigation, additional measurement should be considered in case of changes in soil environmental conditions and other special circumstances. 4) For the nitrogen leaching loss monitoring in orchards, the soil solution extraction method, field percolation disk method and model analysis method could be selected according to the type of fruit tree, field environment and specific test conditions. Moreover, runoff loss monitoring is recommended to use the runoff plot method. In the future, the researches on orchard soil nitrogen losses should be strengthened in the formulation of monitoring methods and standards, the development of monitoring equipment or systems, and the construction of nitrogen loss estimation model and so on.