Dynamic monitoring of the spatial pattern of winter continuously flooded paddies (WFP) at regional scales is a challenging but highly necessary process in analyzing trace greenhouse gas emissions, water resource management, and food security. The present study was carried out to demonstrate the feasibility of extracting the spatial distribution of WFP through time series imagery of volumetric surface soil moisture content (θ_v) at the field scale (30 m). A trade-off approach based on the synergistic use of tasseled cap transformation wetness and temperature vegetation dryness index was utilized to obtain paddy θ_v. The results showed that the modeled θ_v was in good agreement with in situ measurements. The overall correlation coefficient (R) was 0.78, with root-mean-square ranging from 1.96% to 9.96% in terms of different vegetation cover and surface water status. The lowest error of θ_v estimates was found to be restricted at the flooded paddy surface with moderate or high fractional vegetation cover. The flooded paddy was then successfully identified using the θ_v image with saturated moisture content thresholding, with an overall accuracy of 83.33%. This indicated that the derived geospatial dataset of WFP could be reliably applied to fill gaps in census statistics.

Ammonia (NH₃) volatilized from cropland significantly impacts the ecological environment and human health. The identification and quantification of atmospheric sources of NH₃ from cropland are therefore important for NH₃ emission reduction and air pollution control. Choosing appropriate nitrogen (N) fertilizer types is one of the key ways to reduce NH₃ emissions from agricultural systems due to different N fertilizers with different emission factors. The natural abundance isotope of N (δ¹⁵N) values can well identify the source of NH₃ volatilization, although there is rare research on δ¹⁵N-NH₃ values volatilized when applying different types of N fertilizers. Here, we conducted an incubation experiment to study the characteristics of δ¹⁵N-NH₃ values during the whole volatilization process after different N fertilizers were applied to the soil. The results show that the cumulative NH₃ volatilization from urea (U), urease inhibitor fertilizer (UI), compound fertilizer (CF) and ammonium nitrate phosphate fertilizer (AP) treatment was 5.25 ± 0.00, 3.11 ± 0.00, 3.22 ± 0.19 and 1.38 ± 0.12 kg N ha⁻¹ at the end of the 15-day incubation period, respectively. The average δ¹⁵N value of NH₃ volatilized from the U, UI, CF and AP treatments was −36.02 ± 4.95, −29.08 ± 9.70, −35.18 ± 4.98 and −29.42 ± 4.33‰, respectively. Generally, the δ¹⁵N-NH₃ values ranged from −41.33 to −6.30‰ during the NH₃ volatilization process. The δ¹⁵N-NH₃ value was lower in the U treatment than in the UI and AP treatments (p < 0.05), which suggests that N forms and the slow-release additions of different fertilizers, such as NO₃⁻-N and urease inhibitors, can delay or slow down NH₃ volatilization, resulting in relative isotopic enrichment. Therefore, the basic properties of different N fertilizers, the changes in soil NH₄⁺-N and cumulative NH₃ during the volatilization process significantly impacted the δ¹⁵N-NH₃ values.

Investigating the sources of ammonia (NH₃) in the atmosphere and the contribution of each source is essential for environmental pollution control. The presented dataset aims to provide ¹⁵N natural abundance (δ¹⁵N) data collected from different controlled treatments to fill the knowledge gap between insufficient data of soil δ¹⁵N-NH₃ and accurately identifying atmospheric NH₃ source apportionments. Our results showed that the overall δ¹⁵N-NH₃ values emitted from soil ranged from −46.09 to 10.22‰, with an average of −26.81 ± 11.17‰. The mean δ¹⁵N-NH₃ values under different nitrogen (N) application rates, N fertilizer types, air temperatures, soil moisture, soil pH, soil types, and land use types were −29.41 ± 10.91, −32.43 ± 6.86, −29.10 ± 10.04, −30.31 ± 6.18, −24.84 ± 13.76, −23.53 ± 7.66, and −14.57 ± 12.54‰, respectively. Significant correlations were observed between δ¹⁵N-NH₃ values and soil pH, soil NO₃⁻-N concentration, and NH₃ volatilization. This unique database provides basic data and evidence for the qualification of atmospheric NH₃ source apportionments under different study area conditions.