TOWARD THE ESTABLISHMENT OF GRASSES AND CROPS ON THE LOESS PLATEAU IN CHINA

Saburo Tamura

The University of Tokyo, Bunkyo-ku, Tokyo, Japan

Introduction

The Loess Plateau in China is located in the middle reaches of the Yellow River. This plateau is covered by the largest and thickest loess deposit on earth. Before the dawn of history, abundant vegetation grew on the plateau. Traditionally, the plateau is said to be the cradle of Chinese culture and agriculture. However, due to human impact, especially irrational activities of agricultural production for long periods of time, the natural ecosystem has been completely destroyed. At present, the desolate landscape consists of innumerable denuded hills divided by deep gullies.

On the plateau, soil erosion is still continuing on a massive scale, and it threatens to result in the final desertification of this area in the near future. For the purpose of preventing soil erosion on the Loess Plateau, we, a Japanese research group, started a fundamental study in 1998 for the establishment of grasses and crops on the plateau. This study was conducted in Guyuan Prefecture of Ningxia Autonomous Region in cooperation with scientist from the Chinese Academy of Sciences. In this report, the results of our scientific activities on the Loess Plat eau over the past five years will be presented.

Ⅰ.General Features of the Loess Plateau

The location of the Loess Plateau is illustrated in Fig.1.It stretches over five provinces (Qinhai,Gansu,Shaanxi,Shanxi and Henan)and two autonomous regions (Ningxia and Inner Mongolia),and covers an area of 580,000km2,corresponding to one sixteenth of the whole area of China .The plateau has a population of more than 60,000,000,most of them living in extreme poverty. The elevation of the plateau 1,000-1,500 m above sea level, and the annual mean temperature 4-7℃(at Guyuan).

Fig.1.The Location of the Loess Plateau in China.

The site where we are working, in Guyuan Prefecture of Ningxia Autonomous Region, is located at the western part of the Loess Plateau. To get there we have to drive a car for 350 km along the Silk-road from Xi'an, the capital of Shaanxi Province, and then continue northward for an additional 40 km.

Loess is composed of yellow or greyish yellow fine particles and is more or less calcareous. The formation process of the Loess Plateau is not understood in detail, but the fine materials constituting the plateau are generally considered to have been transported from northwestern deserts by strong winds over along periods of time beginning 1,200,000 years ago. The thickness of the loess deposit on t he Loess Plateau is usually in the range of 50-100m.At some places, however, it attains a depth of 400m.

In general, the precipitation on the Loess Plateau is 300-450mm/year, 60%-70%of which falls from July to August in the form of torrential downpours. Since the structure of the loess deposit is extremely loose, the heavy rainfall causes severe soil erosion on every slope of the hills on the plateau.

As a result, the Yellow River, with total length of 5,464 km, is being made muddy by the enormous amount of loess streaming out from the Loess Plateau. The annual run off discharge of loess to the lower reaches of the river amounts to 1.6×109 tons ,and the average silt content of the Yellow River reaches 34kg/m3,wyich is 80 times that of the Yangtze River in China and 20 times that of the Nile River in Egypt.

For that reason, at the downstream end of the Yellow River, the level of river bed is rising 10 cm a year, owing to the sedimentation of loess, and serious disasters due to overflowing of water on the surrounding areas are expected. According to historical records, people living near the lower reaches of the Yellow River suffered from great floods 1,573 times during the period from 602BC to 1950. Thus, our research project aiming at the establishment of grasses and crops on the Loess Plateau is considered to be essential also for the prevention of flooding at the lower reaches of the Yellow River.

Ⅱ. Problems Concerning Agriculture on the Loess Plateau

It is said that the Loess Plateau was covered with green vegetation in the past. This fact has been proved recently by our radiocarbon dating experiments on the samples of black soil collected in Guyuan Prefecture, suggesting that the plateau was thickly covered with plants during the period from 5,000to 12,000 years ago.

Chinese legend tells that, in the beginning, Chinese people learned how to cultivate crops from a public official, who was born as a son of heaven, on the bank of a river located on the southern part of the Loess Plateau. According to records from the Han Dynasty, which was prosperous around 2,000years ago, "The Loess Plateau was rich in water and vegetation, so that agriculture and stock-farming were flourishing there".

From the eleventh century on, however, the ecology of the plateau was gradually disrupted by successive military battles and drought injuries. Especially, after the seventeenth century, the rapid increase in population in this area accelerated the cuttings of forests and the cultivation of former grasslands on a large scale. The irrational use and poor management of the land markedly hastened the destruction of natural ecosystem on the plateau, resulting in vast stretches of fragmented and denuded hills.

Nevertheless, the Loess Plateau has maintained the potential for agricultural production up to the present. For example, although Xi'an and its vicinity are located on the Loess Plateau, this area is one of the most productive places for wheat in all of China .The loess is displaying its fertility due to the mild climate together with the abundant supply of water here.

Generally speaking, however, the agricultural productivity is being severely limited by the seasonal shortage of water supply on the Loess Plateau. There is hardly any rainfall on the plateau from March to June. Accordingly, from germination to ripening, the crops must utilize moistures stored in the soil from the summer of the preceding year .As a matter of fact, the growth of crops is extremely poor and the annual total yield is within the range of 500-1000kg/ha.

Therefore, the farmers in this region try expand the acreage under cultivation to compensate for the low yield .For this purpose, they, make terraced fields even on steep slopes and hill tops. Needless to say, their efforts in this direct ion expose the denuded land surface to heavy rainfalls, especially after harvesting.

As another factor to intensify soil erosion on the Loess Plateau, we should not overlook the pasturing of domestic animals, mainly sheep, on steep lopes where farming is hard to be carried out. Since the owner-ship of each grassland has not been established under law, farmers generally want to increase the numbers of animals, which provide the sole source of cash income, irrespective of carrying capacity, of the land. This results in overgrazing to an extreme, and the existing grasslands on the Loess Plateau seem to have almost lost their capability for re -generation already.

Ⅲ.Outline of our Research Program on the Loess Plateau

At the invitation of the Chinese Academy of Sciences, I visited Guyuan Prefecture for the first time in 1983 to make an on-site inspection on the Loess Plateau. During my stay at Guyuan. I was greatly impressed by the serious problems with which its inhabitants are being confront-gion freely on account of the high international tension between China and the Soviet Union.

In October 1989,as a result of changes in international relations, restrictions on travel by foreigners to Ningxia were liberalized by the Chinese Government / At time, I applied for a "Grant-in -Aid' to the Japanese Ministry of Education. Science and Culture to make a thorough investigation on the Loess Plateau. Being supported by this grant .I was able to visit Guyuan again during the summer of 1987.

Through this investigation I came to the conclusion that the following problems should be addessed in our research study on the Loess Plateau for the prevention of desertification.

a) To prevent soil erosion and destruction of land resources on the plateau, farming on steeply sloping terrain where farmers have constructed terraced fields should be suspended as soon as possible and grasslands should be established in stead.

To accomplish this object, it is important to introduce various kinds of herbage that are drought -resistant, cold -hardy, and palatable to domestic animals. At that time, however, Chinese agriculturists showed little interest in the introduction of new herbs other than two kinds of legumes, Astragalus adsurgens and Onobrychis uiciaefolia, both of which had been selected at other institute in China.

Needless to say, in order to increase the extent and diversity of grasslands on the Loess Plateau, a selection test should be conducted in a large scale to fin d a great variety of herbs other than those mentioned above.

b)To stop the farming on steep slopes ,it is essential to increase rapidly the productivity of crops on flatlands and gentle slopes to secure the supply of foodstuffs .For the accomplishment of this purpose ,various kinds and cultivars of crops should be introduced and examined their adaptability to the natural conditions of the Loess Plateau.

Presently, however, kinds of crops being cultivated at Guyuan are few. These include wheat, millet, buckwheat, common millet, Avena nuda, pea, lentil, flax (as oil crop) and potato. Moreover, the number of cultivars corresponding to each crop is also limited, and their productivities are fairly low in general. The expansion of this crop list may prove difficult, since it seems that Chinese agriculturists are not necessarily eager to introduce new crops.

Based on these observations, we applied for another grant in 1998 to the Ministry of Education, Science and Culture under the subject, "Fundamental Study on the Establishment of Grasses and Crops on the Loess Plateau in China". To achieve the goal of this study, we made a scheme to carry out our experiments on the following topics in cooperation with Chinese scientist, most of them being members of the Northwest Institute of Soil and Water Chinese Academy of Sciences.

1) To introduce herbs including pasture grasses and examine their adaptability to the natural ecosystem at the Loess Plateau.

2) To establish models of natural and artificial grasslands.

3) To increase the agricultural productivity by means of the introduction of various kinds and cultivars of crops.

4) To establish a system of cultivation techniques suited to local conditions of the plateau.

To carry out this study, I organized a research group consisting of a dozen of or so Japanese scientists. Except for myself as a bio-organic chemist, the specialties of the members were crop breeding, agronomy, weed science, grassland science, soil science, agricultural meteorology, and geography, From the spring of 1988, we started research activities at Guyuan.

IV. Some of the Results Obtained through Our Research Activities on the Loess Plateau during 1998-1992

During the period from 1988 to 1992,every member of our research group played an active part on the Loess Plateau according to his own schedule, and we obtained excellent results beyond our expectations. Here, the results concerning mainly the introduction of herbs and crops to the plateau will be reported.

a) The selection test for herbage was begun in the spring of1988. From Japan and abroad, we collected seeds of 267 species of herbage, which were sown on a slope of a hill and grown without irrigation and manuring.

Most of the seeds did germinate, died shortly after germination or showed only poor growth. To our surprise, Echium vulgare, Tragopogon pratensis and several gramineous grasses belonging to the genera Agropyron, Elynus and Festuca grew vigorously under the severe conditions on the Loess Plateau, Moreover, these herbs withstood the intense cold on the plateau during the winter of 1988 and exhibited remarkable growth followed by flowering and seed setting in 1989.It is noteworthy that Bronus inermis belonging to Gramineae grew poorly in 1988, but showed marked propagation and root elongation in 1989.

On the basis of the results obtained in 1988,we collected seeds of 256 species of herbage and sowed them in 1989.The results were quite similar to those obtained in the preceding year. In succession, similar experiments have been carried out up the present.

Table 1 is indicated the list of the herbage which showed good growth on the Loess Plateau during 1998-1991.It is deserving special intention that, through our experiments, several kinds of herbage including gramineous grasses have been found to possess adaptability to the natural ecosystem on the plateau, in addition to the leguminous herbs already known.

At present, we are conducting the tests on the mix-seeding of the herbs which have been confirmed to be promising, as well as on the large-scale cultivation of each herb.

In 1992 people on the Loess Plateau suffered from a long drought which was the most serious since the founding of the New China in 1949,and there was hardly any harvest at Guyuan. Under such climatic conditions, however, Echium vulgare, Onobrychis viciaefolia, Medicago sativa, Agropyron intermedium, Agropyron mongolicum, Bromus inermis, Elymus dahuricus, Elymus juncea, Festuca elatior and Festuca ovina, which had been sown before 1991,were still continuing to grow vigorously. Of the gramineous herbs, Bromus inermis showed the strongest resistivity to the drought.

b) As for the introduction test on crops, we mainly examined the adaptability of wheat, which is the principal food of residents on the Loess Plateau, as well as of barley and Triticale. For this purpose, we collected seeds of 717 wheat lines, 387 barley lines and 25 Triticale lines from Japan and abroad. As is commonly know, Triticale is a kind of crop resulting from crossing between wheat and rye.

Needless to say, wheat, barley and Triticale are usually more productive following autumn seeding than following spring seeding. At Guyuan, however, the average temperature in January is -℃and snow does not cover the fields during inter. As a result, the drop of the soil temperature is so severe during the period from winter to early spring, that cultivation of crops with winter habit is almost impossible. Accordingly, we tested the growth of wheat, barley and Triticale based on the general practice of the actual place, and sowed their seeds on a field located on a fluvial terrace in the mid-March of 1989 with organic fertilizer as basal dressing.

In this test, we sowed a cultivar of wheat called "Hongmangmai" in Chinese as a control. This cultivar was discovered before the foundation of the New China, and has been cultivated until quite recently as the sole cultivar at Guyuan due to its excellent resistivity to drought and coldness.

Most of the seeds tested went into ears in June of the same year, though some seeds did not germinate. As a general tendency, the cultivars of each crop cultured exhibited late ripening. short culmination and short earing.

In 1989 the climate at Guyuan was moderate, and 31 lines of wheat, 41 lines of barley and 7 lines of Triticale ultimately showed good growth. From that time on, selection tests have been conducted annually on these lines, of which several have been confirmed to be promising as parent materials for breeding.

In 1990 we made experiments to examine the effect of the three major nutrients on the yield of spring wheat ("Hongmangmai") using urea, superphosphate and potassium sulfate. Unexpectedly, both of the nitrogenous and potash fertilizers hardly showed and effect, while superphosphate markedly caused an increase in the yield, irrespective of the coexistence of other nutrients. The fact that, of the three kinds of fertilizers used here, only superphosphate distinctly exhibited positive effect might be due to some unknown factor(s)in the loess deposit, and the mechanism inducing this pecaliar phenomenon is under examination.

c) Additionally, we conducted introduction tests with plant species to be used for vegetable crops .In 1989we introduced 30lines of rappelled to be cultivated ins tad of flax as an cilia crop. Several lines exhibited adaptability to the natural conditions on the Loess Plateau in the same year. Since this plant is self-income pitiable, we intend to conduct mass selection by means of variety crossing at the test site. With such a pro-gram, we should be able to develop promising new lines after several years.

Some cross lines of sunflower introduced in 1998 from the United States showed excellent results in the same year, and the Chinese scientists as well as the Gap anise research group had high hopes for the continuation of the sunflower expire meanest in the succeeding year, However, the introduction of sunflower seeds was refused in 1989by the Quarantine Station of the Government of Ningxia Autonomous Erg ion without any explanation. This might be due to the fact that a unified system for quarantine regulations has not yet been established throughout China.

d) The rearing of shrubs on the plateau is also being studied by Chinese forestry experts, but our research group has not been involved with this project at present.

V. Conclusion

Our experimental research, which we conducted at Guyana from 1988 to 1992,is con sided to be the first systematic study on soil and water conservation on the Loess Plateau through biological means. Although we were able to obtain several good results in this study beyond our expectations, the scope of our activities is much too small when compared with the vastness of the plateau, It might take more than one hundred years to recover the whole plateau with rich green even if it is possible theoretically.

However that may be, if we allow the soil erosion to continue at its current rate, the Loess Plateau will certainly become a desert in the comparatively near future, In my opinion, we should do our best on the plateau without delay to protect this part of our unique planet against destruction. It is the goal of our research group to lay down a tangible scheme, at least, for the establishment of grasses and crops on the Loess Plateau at an early date, on the basis of the results of our ideas and our activities.

Acknowledgments

I wish to express my best thanes to every member of the Japanese research group for his great contribution toward the success of pour undertaking. Thanks are also due to the Chinese colleagues for their sincere collaboration with us in conducting the Japan-China joint research on the Loess Plateau, In addition. I wish to thank the Chinese Academy of Sciences for their continued encouragement to the joint project, I am most grateful to the Japanese Ministry of Education, Science an d Culture for their financial support.