Historically, farmers in both study areas have generally practiced subsistence farming, which is typically rain-fed farming and is strictly subject to an erosive environment. To effectively control soil erosion and improve agricultural conditions, both districts have acted to conserve the soil since the 1980s using methods such as terracing on gentle slope lands and building check dams to form quality cropland in the valleys. As the pilot sites for the GGP, both districts have participated in the slope cropland retirement program and grazing prohibition to protect vegetation from excessive disturbance since 1997. Such soil conservation activities have greatly improved dryland farming condition. Just as the results of our analysis suggested, a total of 30,900 ha of the croplands on the steep slopes in the Ansai District were converted into woodlands and grasslands under the GGP during the period from 2000 to 2017. Accordingly, the average soil erosion rate decreased from 57.6 t ha 1 yr 1 in 2000 to 27.8 t ha 1 yr 1 in 2017, while agricultural output increased from 291 million CNY in 2000 to 1434 million CNY in 2017. Similarly, the amount of cropland on the steep slopes of the Anding District decreased by 7.7%, while the area covered by woodland and grasslands increased by 19.0%, and the average soil erosion rate decreased by 47.4%. Agricultural output rose by 225.9% over the same period. The increase in agricultural output shows a similar pattern to the decrease in soil erosion; that is, less soil erosion leads to more agricultural output, indicating a synergy between soil conservation and agricultural production in both study areas. Similar findings indicate that soil conservation in areas with rain-fed agriculture significantly improves soil moisture and retains soil nutrients in arable land. At the same time, increasing the amount of vegetation greatly improves the microclimate , reduces flood levels, nft growing system and enhances the capacity to preserve water resources , leading to an increase in production.

Our results support the argument for soil conservation-oriented dryland farming, which was introduced in the Loess Plateau by several scholars at the Institute of Soil and Water Conservation, Chinese Academy of Science in 1980s . There are several such paradigms of soil conservation-oriented dryland farming in both study areas. The small catchment of Xiannangou in Ansai, for example, has been involved in several environmental programs, including the GGP, which is the largest cropland retirement project in the world, since 1997. Following the concept of a coupled socialeecological system, the ecological engineering design in the small catchment of Xiannangou consists of revegetation belts on the upslopes, terraced apple orchards on the gentle slopes, and grain and cash crops on croplands that are fed via check dams in the valleys . Evidence shows that such a pattern of ecological engineering not only enhances the capability of an ecosystem to provide services but also improves the livelihoods and environmental awareness of stakeholders . Compared to Ansai, which has a landscape of narrow and deep valleys, Anding is covered by wide and shallow valleys with an average gully density of 2.4 km/km2 . To improve local dryland farming conditions, Anding has constructed terrace on the cropland with slopes >5 since 1960s . By the end of 2017, terracing represented approximately 88% of the cultivated cropland in this area. Anding has therefore invested heavily in potatoes and medicinal plants because its relatively flat landscape and climatic conditions are suitable for such crops. The output value of potatoes and medicinal plants has consequently risen from 14.3 and 10.2 million CNY in 2000 to 24.1 and 34.8 million CNY in 2017, respectively.In addition to soil conservation, factors such as population density, labor, agricultural machinery use, and irrigation also positively contribute to crop farming. In fact, the study areas experienced a sharp reduction in the available amount of arable land following the introduction of the GGP, and crop farming has consequently become concentrated within a few flat croplands and check dam-formed croplands in which sufficient water sources are available for irrigation and soil nutrition. Farmers have therefore tried to increase financial capital input into agriculture and irrigation per unit area to offset the significant decrease in the available area of slope cropland in order to maintain their income. Although a significant increase in livestock output has occurred, there appears to be a trade off between crop farming and livestock farming. The factors that facilitating crop farming exert adverse effects on livestock farming, as indicated by the Pearson correlation in both the study areas.

The output shares of crop production to agricultural production in the Ansai District increased from 80.89% in 2000 to 90.11% in 2017, while the output shares of livestock farming decreasing from 16.11% in 2000 to 9.89% in 2017, showing a clear trade-off between livestock farming and crop farming. Similarly, in the Anding District, the output shares of crop and livestock farming accounted for 84.38% and 15.62% in 2000, and 94.54% and 5.46% of the total agricultural production in 2017, respectively. These changes were as noteworthy as those observed in Ansai, livestock farming in this area has significantly diminished. The reasons for such a trade-off between crop and livestock farming likely included the following: First, both the study areas traditionally practiced livestock grazing, in particular sheep raising, before the implementation of the GGP. However, after the prohibition of grazing due to the GGP and other environmental programs, inaccessibility to grass resources forced livestock farming to shift to house feeding that, to a great extent, has been dominated by pig or cattle breeding and has largely relied on forage crop cultivation in both study areas. Thus, to provide animal feed, livestock farming competed with crop farming for land. Second, farmers in both areas traditionally preferred to invest most of their land, money, and labor resources in crop farming. As a result, the input of land, money, and labor into animal husbandry has been insufficient. Additionally, grazing prohibition has meant that much of the grassland that was previously converted from slope cropland under the GGP was currently not utilized. Grazing prohibition contributes to the restoration of degraded grasslands, conservation of the soil, and improvement of ecological quality . However, long-term grazing prohibition reportedly produces soil biocrusts , which affect hydrological processes even biodiversity . In contrast, moderate grazing improves the soil properties of grasslands, maintaining healthy grassland ecosystems . To mitigate the trade off between crop farming and livestock farming as well as to fully utilize grasslands while implementing the GGP, animal feeding should include a combination of house feeding and grazing, together with rotational grazing through zonation. Regarding the issues of implementing rotational and moderate grazing in the Loess Hills, the determination of the grazing intensity that is capable of simultaneously maintaining the service provision of grassland ecosystems is required in future.

The Loess Plateau is underdeveloped relative to the rest of China and suffers low investment in agriculture. These issues have, to some extent, hampered agricultural development in this area. According to the Annual Yearbook of Chinese Agriculture, the average investment level per unit of cropland was 18,269 CNY/ha nationwide; in contrast, it was only approximately 7637 CNY/ha for the Loess Plateau in 2017. Additionally, the Loess Plateau is the main area from which rurale urban migration occurs in China. A report on Chinese migrant workers in 2017 by the State Statistics Bureau indicated that the number of rural laborers migrating to cities rose to 287 million, representing over 49.7% of China’s rural population, and more than half of those migrants were between the ages of 18 and 35. The Loess Plateau has suffered particularly severe loss of young labor over the past two decades and the combination of insufficient investment and rural-urban labor migration places heavy restrictions on farming and rural development , as the relations between agriculture and the variables of labor force and population density indicated in this study. Therefore, more attention should be paid to improving agricultural infrastructure and technical investment in this region. Resolving the loss of rural labor in the underdeveloped areas of China is therefore a particularly important challenge for policymakers to address. In addition, the education and skills of rural laborers are key factors for agricultural development . Given that labor is an important determinant for agricultural development, as indicated by the regression results in this study, more resources should be dedicated to rural education and skill training for rural laborers.Grasslands cover approximately 26% of the total global land area and are the most widely distributed terrestrial ecosystems on Earth . In China, grassland areas cover over 2.6  108 ha, accounting for about 27% of the country’s land area. Therefore, conservation and rational use of such grassland resources in China have been the focus of scientists in various disciplines. Grazing is the most important utilization practice of grasslands, and grazing livestock is considered one of the critical biological components of grassland ecosystems. From a historical perspective, the primary purpose of grazing has been producing meat and milk products for humans, which occurred at the expense of many other potential functions of grasslands . In recent decades this perspective has changed due to several studies, nft hydroponic system which found that grazing by large herbivores maintains the stability of grassland ecosystems and increases the multi-functionality of grasslands . Therefore, livestock grazing was determined to be an essential pathway to producing livestock products and maintaining and promoting grassland ecological service functions. Consequently, pasture-based ruminant farming systems with full- or part-time grazing have increasingly emerged as a strong option for achieving “wine win” outcomes between grassland ecological functions and livestock production functions , which have significance in promoting the sustainable development of livestock farming.

The following passages discuss grassland-based ruminant farming systems’ ability to meet current human needs for highquality livestock products and grassland ecosystem services. We provide insights into the main challenges and future scientific research directions associated with the development of grassland based ruminant farming systems.Grazing is the most economically conservative way to raise livestock because the cost of the herbage consumed by grazing ruminants is lower than that of mixed rations . Additionally, in a grazing system, ruminants feed autonomously, with minimal mechanized equipment and labor. Hence, grassland-based livestock farming systems can be highly profitable, as shown by Mwebe et al. , who found that farmers who allow grazing in small herds made higher profits than those who tried other feeding strategies. Apart from the low-cost production of livestock products, grassland grazing allows farmers to produce high-quality, niche foods with a higher market value than similar products derived from intensive, indoor livestock management. For example, higher antioxidant activity was observed in goat cheese from grazing goats due to greater quantities of polyphenols, hydroxycinnamic acids, and flavonoids consumed during grazingd resulting in goat cheese with higher bioactivity. Previous studies have also demonstrated that grazing ruminants showed improved milk quality, with enhanced sensory properties , increased mineral content , and greater odd- and branched-chain fatty acid concentrations . Furthermore, grazing also improved the meat quality of ruminants by enhancing the fat color and increasing the n-3 polyunsaturated fatty acid and vitamin E content in the muscle.Higher-quality products may result from the fact that livestock welfare is improved within grassland-based systems.Therefore, grazing systems can reduce feeding costs and produce high-quality livestock products.Livestock grazing plays a vital role in regulating grassland ecosystems functions , allowing suitable grazing systems have the potential to provide valuable ecosystem services for humans. For example, Sollenberger et al. reported that the excreta of grazing livestock was a source of nutrients for grasslands. Their study determined that managing livestock grazing to increase the uniformity of excreta deposition increased the efficiency of nutrient cycling and changed the composition of soil microorganisms and above ground plants. Several studies have shown that moderate grazing improved grassland ecological functions: boosting plant productivity and biodiversity, improving soil structure, fertility, and microbial biomass, enhancing carbon and nitrogen storage, and limiting erosion. Gong et al. found that moderate grazing resulted in higher species diversity and below ground root biomass, driving greater productivity in grass species.