Although nitrogen application and cutting frequency (CF) are two important factors affecting forage productivity and quality, their effects on alfalfa (Medicago sativa L.), particularly in humid areas, remain less understood. Here, we investigated the fertilization and cutting regimes for seasonal alfalfa cultivation in humid areas in southern China. Treatments performed over a 2-year period were of a split-plot design with four N application rates (60, 120, 180, and 240 kg N ha⁻¹) and three CFs (five, four, and three times.). After cutting, forage components, yield, and quality were measured. In both 2-year cutting cycles, the effects of N application × CF interactions on forage yield and quality were non-significant. N application and CFs influenced plant height, mass shoot⁻¹, leaf area shoot⁻¹, and shoots plant⁻¹. CF had remarkable effects on forage quality under different N applications, with forage cut five times having the best nutritive value and quality. However, neutral and acid detergent fiber contents were lower than when cutting three times, and produced the lowest yields. Forage cut four times had the highest in vitro digestible dry matter. In conclusion, to obtain high yields and desirable quality, the application of 180 kg N ha⁻¹ and cutting three to four times in spring could be a suitable strategy for alfalfa forage production during seasonal cultivation in humid areas of southern China.

As the most extensive terrestrial ecosystem, grassland exhibits substantial ecological functions and scientific research significance. Conducting a scientific assessment of the soil fertility of grasslands is of paramount importance for attaining sustainable grassland management, especially for the Tibetan Plateau, which has the most vulnerable ecosystem. This study endeavors to evaluate the soil fertility and spatial differentiation patterns of the natural grasslands in the Tibetan Plateau. Initially, we developed a Soil Fertility Evaluation Index (SFEI) for natural grasslands by integrating three representative soil indicators (total nitrogen, soil organic matter, and bulk density) and a vegetation indicator (fractional vegetation cover). The selection of these indicators followed the Minimum Data Set (MDS) principle, ensuring both ecological relevance and consistent data availability across all sampling plots in the Tibetan Plateau. Subsequently, validation based on field sampling data showed an overall accuracy of 69.89%. Moreover, the evaluation result revealed a clear eastward-increasing gradient in soil fertility, with low fertility in the western regions (e.g., Ngari and Nagqu) and medium-to-high fertility in the central and eastern regions (e.g., Lhasa, Yushu, and Golog), consistent with regional hydrothermal patterns. The proposed method offers a novel and practical framework for assessing soil fertility of natural grassland in the Tibetan Plateau, with significant implications for differentiated grassland management and ecological restoration.