Grassland agriculture can learn from the new development model of foreign countries.

As early as the Middle Ages, agricultural production in Europe generally implemented the "two-nursery system", that is, a simple farmland rotation system, which regulated soil production capacity through farming and leisure. However, with the increase of population and the gradual depletion of land fertility in Europe, the "two-nursery system" can no longer meet the needs of social development, and the "three-nursery system" came into being. The "three-nursery system", also known as "three-zone rotation system", divides cultivated land into three farming areas: leisure land, spring sowing land and autumn (winter) sowing land. Crop rotation in various areas, spring sowing cereals or legumes, autumn and winter sowing wheat or rye, rotation year by year, three-year cycle. Both the leisure land and the cultivated land after harvest are used as public pastures and are used together.

Compared with the two-nursery system, the three-nursery system can be harvested twice a year, and the area of leisure land can be reduced from 1 to 3, which is not only beneficial to reduce the risk of agricultural disasters or poor harvest, but also to improve the utilization rate of cultivated land and labor force. Therefore, the level of agricultural production is higher than that of the "two-nursery system".

After the 19th century, in the face of the population expansion and the decline of land productivity caused by the industrial revolution, Europeans found that the "three-nursery system" based on grain production could no longer meet the growing economic needs. From the beginning of the decline in grain production, they realized that without forage and animal husbandry, agriculture was incomplete, so they began to vigorously promote grain rotation.

The former Soviet pedologist William put forward that grass field rotation is a reasonable farming system. Based on the study of the process of natural fertility restoration and the effect of perennial mixed forage, he proposed to restore fertility through grass field rotation, thus opening up a way to shorten the process of soil fertility restoration under human intervention.

The United States has also experienced a similar process. In the period of rapid industrial development, the United States used to rely too much on chemical fertilizers and pesticides, and used its developed agricultural machinery to grow corn in the central region for many years, and the traditional rotation system was ignored. As a result, the soil was seriously eroded, the soil fertility decreased significantly, the diseases, insect pests and weeds were rampant, the maize yield decreased, and the economic benefit was seriously damaged. In order to ensure the sustainable development of agriculture, the United States requires a two-year rotation system, accounting for 27% of the 303 million hectares (4.545 billion mu) of arable land in the United States. After the rotation of spring wheat and leguminous forage in Montana, the wheat yield is 40% higher than that of continuous cropping.

In Australia in the 1830s, the "wheat-leisure" farming system was widely implemented in semi-arid areas, resulting in the destruction of soil structure, the decline of soil fertility, the decline of crop yield and the insufficient supply of forage grass. Later, Australia used legume grass and grain rotation, and the results showed that the grain yield of barley after "alfalfa-barley" rotation was 17.4% higher than that of continuous cropping, and the grain yield of wheat after "alfalfa-wheat" rotation was 18.2% higher than that of continuous cropping. The successful application of crop and legume rotation has enabled Australia to create the world-famous "wheat-sheep" farming system, which in turn has made the country a major wheat exporter.

At present, after years of development, "grain and forage rotation" has become a basic farming system in developed countries. In the "grass field rotation" in most developed countries, the proportion of forage in agricultural land has reached a high level, 40% in the United States, 30% in France, 58.8% in the Netherlands, 60% in Australia, and 70% in Denmark and Ireland. The grain rotation system not only ensures the yield of forage and crops, but also continuously recovers and improves the soil fertility, making these countries have relatively high grain yield and total yield.

During the period of primitive agriculture in China, the abandonment system similar to the "two-nursery system" was implemented, but after the implementation of iron plough and cattle ploughing into the traditional agricultural stage, the abandonment system was basically ended. Instead, it mainly focuses on the intensive cultivation of increasing the yield per unit area and making full use of land, and has embarked on the road of land continuous cropping system, so it is of great significance to sum up foreign experience and carry out "grain and forage rotation" in the adjustment of the current mode of agricultural production. it is of great significance to develop grassland agriculture.

(author Wang Chengzhang is a professor of Henan Agricultural University, Zhu Xiaoyan is a lecturer of Hebei Agricultural University, and Lu Xinshi is president of grass branch of China Animal Husbandry Association.)