The Soil Moisture Active Passive (SMAP) satellite makes coincident global measurements of soil moisture using an L-band radar instrument and an L-band radiometer. It is crucial to evaluate the errors in the newest L-band SMAP satellite-derived soil moisture products, before they are routinely used in scientific research and applications. This study represents the first evaluation of the SMAP radiometer soil moisture product over China. In this paper, a preliminary evaluation was performed using sparse in situ measurements from 655 China Meteorological Administration (CMA) monitoring stations between 1 April 2015 and 31 August 2016. The SMAP radiometer-derived soil moisture product was evaluated against two schemes of original soil moisture and the soil moisture anomaly in different geographical zones and land cover types. Four performance metrics, i.e., bias, root mean square error (RMSE), unbiased root mean square error (ubRMSE), and the correlation coefficient (R), were used in the accuracy evaluation. The results indicated that the SMAP radiometer-derived soil moisture product agreed relatively well with the in situ measurements, with ubRMSE values of 0.058 cm³·cm⁻³ and 0.039 cm³·cm⁻³ based on original data and anomaly data, respectively. The values of the SMAP radiometer-based soil moisture product were overestimated in wet areas, especially in the Southwest China, South China, Southeast China, East China, and Central China zones. The accuracies over croplands and in Northeast China were the worst. Soil moisture, surface roughness, and vegetation are crucial factors contributing to the error in the soil moisture product. Moreover, radio frequency interference contributes to the overestimation over the northern portion of the East China zone. This study provides guidelines for the application of the SMAP-derived soil moisture product in China and acts as a reference for improving the retrieval algorithm.

The value of agro-ecosystem services is closely related to crop yield. As a production input component in an agro-ecosystem, agro-ecosystem services have practical value. It is generally believed that agroecosystem services are substitutes for purchase investment and can decrease agricultural production costs. Crop yield increases may negatively affect agro-ecosystem protection, and conversely, agroecosystem protection may result in crop yield reductions. Based on the established production model of agro-ecosystems, we determined the reasonable substitutive conditions and production outputs, and we quantitatively studied the ratio of the land area for agricultural production to that for ecosystem services. With the upper Yongding River Basin in China as the study area, we calculated agricultural yield elasticity and concluded that the corresponding crop yield would be reduced by 2.7% when the land area for ecosystem services in the basin increased by 1.0%. At present, the ecological service value of the Yongding River Basin showed an increasing trend.