Watchdog 2900et

A randomized complete block design was used in the study in which the main plots consisted of three replicates (Fig 1). The main plots were divided into four subplots corresponding to the four treatments: a high amount of treated swine slurry with a low amount of ¹⁵N-labeled ammonium sulfate (HTSS+LAS), a low amount of treated swine slurry with a high amount of ¹⁵N-labeled ammonium sulfate (LTSS+HAS), ¹⁵N-labeled ammonium sulfate with phosphorus and potassium (AS), and a control (C, no soil amendments). Each treatment was evenly distributed on the soil surface in the lysimeter (0.073 m²) using different colored stickers to distinguish each subplot. The temperature and humidity data were collected at a weather station (WatchDog 2900ET, Spectrum Technologies, Inc.) at the experimental site (Fig 2). The source water for the simulation was tap water, which was stored in a 1.0 m³ tank for at least two weeks before rainfall to remove hypochlorite. Three rainfall events (June 03, August 10 and September 21) with moderate intensity (9.0 mm hr^-1) were applied during the experimental period. The surface water level of each plot was maintained at 2 cm above the soil surface through rainfall and irrigation until September 30 to exemplify a waterlogged paddy plot.

The meteorological variables (air temperature, Ta: relative air humidity, HR: wind speed, u: precipitation, rain: and solar radiation, Rs) were measured within the area of the “lluteño” maize crop. In addition, reference evapotranspiration (ETo) was calculated using the FAO56 Penman–Monteith method [45 ] using meteorological variables recorded at 30-min intervals from an automatic weather station (WatchDog 2900ET, Spectrum Technologies, IL, USA).

The outdoor soil burial test was performed in a natural environment. Field trials were conducted between March 2017 and March 2018 at Tangquan Experimental Station of The Institute of Soil Science (32°04′ N latitude, 118°28′ E longitude, and 7 m elevation) in Jiangsu province, China. The soil had been previously used to grow wheat. The basic physicochemical properties of the soil were: pH (H₂O) 6.7, soil organic matter 24.65 g kg⁻¹, total nitrogen 1.51 g kg⁻¹, total phosphorus 0.87 g kg⁻¹, and total potassium 14.2 g kg⁻¹ [21 ]. The weather information was measured by a WatchDog 2900ET weather station (Spectrum Technologies, Springfield, Illinois, USA). The average temperature was 16.2 °C and the total rainfall was 1118.3 mm in 12 months. The average solar radiation was 161.2 wat m⁻² and the average wind speed was 2.61 km h⁻¹.
Sixteen films were placed at the burial depth, 10 cm from the soil surface. The samples were separated by 10 cm horizontally. Every 4 films (about 800 mg) were removed after every three months, brushed softly, washed with distilled water several times and dried until they did not lose weight for one month. Drying and weighting were carried out in a constant temperature incubator, set to 25 °C. The air humidity was 22%RH. Finally, the films were submitted for further analysis.