Yu ZHANG，Changjun BAl

Tropical Crops Genetic Resources Institute，CATAS/Ministry of Agriculture Key Laboratory for Utilization of Tropical Crops Germplasm Resources，Danzhou 571737，China

The Extension and Utilization of the Pasture in the Tropical Area of China

Yu ZHANG*，Changjun BAl

Tropical Crops Genetic Resources Institute，CATAS/Ministry of Agriculture Key Laboratory for Utilization of Tropical Crops Germplasm Resources，Danzhou 571737，China

This paper summarized the research and development of pasture in the tropical areas，and simply generalized the problems and methods for improvement and expected the advancement of the tropical pasture.

Tropical；Pasture；Utilization

B etween the tropic of carpricorn and tropic of cancer is the tropics，located close to the equator，in the northern and southern hemispheres at 23°26′，representing 39.8% of the total area of the world.In this tropical area，the year-round strongly sunlight and hot weather are known generally［1］.Tropical climate is characterized by year-round high temperature，and only the wet season and dry season shows little difference.Main climate types are tropical rainforest climate，tropical savanna climate，tropical monsoon climate and tropical desert climate.In China，the tropical areas including Hainan Island，Xishuang-ban-na and Red River in the south of Yunnan Province，Leizhou Peninsula in Guangdong，South China Sea Islands and the southern part of Taiwan Province.In these areas，tropical monsoon climate are typical，featured by sufficient light and heat and abundant rainfall，where crops can grow fast throughout the year.The current pasture in hotspots mainly includes Stylosanthes spp.，Pennisetum purpureum K.Scbumacb×P.typhoideum Rich，Panicum L.，Brachiaria Griseb.，Paspalum scrobiculatum L.，and so on［2］.Forage legumes such as Stylosanthes are widely planted in eucalyptus forest，young rubber plantations or orchards in Hainan，Guangdong，Guangxi and Fujian，but rarely found in Yunnan and Hubei.It is of great significance in terms of providing nutritious of green fodder，reducing soil erosion，improving soil fertility，preserving soil moisture，suppressing weed and so on.Therefore，it is an excellent green manure of cover crops［2-3］. Forage grasses such as the king of grass now had planting in Hainan，Guangdong，Guangxi，F(xiàn)ujian，Sichuan，with an application area of 50 000 m2［4］. Pasture in the hot zone of China has achieved some achievements，but in the application process also has many problems to be solved.

The Research and Development Status of Pasture in Tropical Area

Pasture germplasm resources are an important material foundation for animal husbandry development，for it provides basic materials for selecting and cultivating new varieties，promoting sustainable development of animal husbandry，accelerating adjustment of agricultural structure and advancing building of the ecological environment. In the countries which have developed animal husbandry，pasture collection，selection and utilization have been placed on an important position in agricultural production and stock breeding development［3-4］.In China，the tropical pasture research began in the 1960's，involving Stylosanthes spp. and others for the purpose of forest covering and green manure production，and a number of high quality pastures were introduced from foreign country.And then local pasture resources and the introduction of species were used for the base to cultivate new varieties for the tropical and subtropical regions，which served to China's feed production，livestock breeding and ecological construction. Tropical Pasture germplasm resources are the basis for the development of grassland animal husbandry in subtropical regions，which play a huge role in the south livestock production and people's lives.

lntroduced species

The choiceness legume and poaceae species were introduced from foreign country，which were planted in the tropical region to do adaptive test and select study to choose good performance varieties［3］.

To carry out a comprehensive survey and collection，identification of the tropical pasture germplasm resources

The research used GPS and other means of information acquisition and processing technology，combined with conventional ground surveys，to thoroughly investigate the type，quantity，distribution of pasture germplasm resources in China's tropical zone，clean up the collected germplasm materials， establish low-temperature preservation of seed conservation andgermplasm nursery for plant preservation and explore pasture germplasm different types in biological characteristics，agronomic traits，cytogenetics and molecular biology［4］.

The utilization of wild germplasm resources

The wild pastures have various features like strong resistance，as well as problems.Based on the original habitat，the research investigated wild pasture's characteristics，choosing a value in development and using germplasm materials for domesticated or related studies.

New varieties of artificial breeding

In the research，breeding varieties were chosen with consideration of high yield，adaptability，stress resistance，pest resistance，quality and others. Through the introduction and compared experiment，the research selected the high-yield，highly competitive variety which was suitable in the tropical environment with special climate，topography and soil to substitute for the local degraded pasture.

The Problems and Improved Methods in Pasture Utilization

Blind plant

Even if a sort of pasture with different species have varied requirements including the geographic location，soil，water，climate and others，blind introduction without experiments will cause poor growth and low utilization rate.Hence，it is necessary to take regional and seasonal factors into consideration for a better choice of the strong adaptability pasture.

The laggard planting manner

The poor soil quality，weed，low fertility and backward planting technology willdirectly resultin slow growth and low coverage of pasture，and full covering and poor management will lead to plentiful pasture in abandoned，which is a waste of manpower，material and financial resources.

Therefore，it is necessary to fully use the edge of the field，channel，pool，the land returning farmland to forests，the slack to plant pasture and through change the planting way to increase soil fertility，namely the first year plant legume like Stylosanthes spp.，Arachis L.，etc.，when the pastures were cradled twice while directly cut down into the soil，or inoculated with rhizobia and used with phosphorous fertilizer［5］.At the same time，it is important to control the high-yield cultivation and management technologies to exert high yield potential of variety.

The lag of developmental concept

Pasture germplasm research and utilization cannot meet the need of forage industry development and environment construction.Formerly the farmers thought that provided pastures are distributed in the barren hills，slopes，and field border，why do we also plant pastures？And because they did not previously explore the breeding area，size and layout，which conduce the single species，the low yield and the poor quality，it is far away from the requirements of different types of pasture for the livestock industry［6］.

The development of artificial planting pasture should be according to the local conditions，so that the development of stock breeding could be implemented in a scientific way.According to the pasture nutrition and accumulated material required by the natural ecosystem conditions in the tropical region，the sub-agricultural production should consider some factors，including stock breeding，pisciculture，mushroom cultivation and others to choose specific variety.Grassland stock breeding covers broadly，which can expand to the county，the village and the household，and its long industrial chain can benefit more people.

The rupture of industry chain

Most farmers believed that the pasture was only used for livestock breeding which simplified the real function，and did not effectively recycle the organic material including pastures straw，manure and others products by breeding herbivorous animals.In contrary，it reduced the rate of energy utilization in the tropical areas that made agricultural economy develops slowly.

To process the pasture products including food products，industrial raw materials，special processing，garden landscaping，forage handling，the drugs handling and so on，which could enhance the pasture's value and the rate of utilization，to increase the effective value of animal husbandry，finally to achieve a balanced supply to the needs of pasture in breeding animals［7］.

Outlook

To develop the tropical grassland resources and grassland animal husbandry is of important strategic significance，which not only meets the increasing demands on animal products，but also ensures food safety in China.

The research objective is to increase the extent of tropical pasture，increase the basic application on study，select new variety which could eliminate the soil and groundwater contaminations due to excessive application of nitrogen in the past，new variety which could be raw materials to produce pulp and paper，and new pasture variety which can be a source of biomass energy or forage［8］.

To deeply study the construction of artificial lawn，grass products processing，livestock supporting technologies，fruit-grass inter cropping and others studies，the research explored energy and ecology of the pasture utilization to increase the choice of local pasture resources，with pigeon pea（Cajanus cajan Millisp.）as an example. There are over 20 pigeon pea varieties all over the world，and 10 varieties grow in China's tropical regions.It is notable that pigeon pea has many characteristics，such as drought resistance，barren resistance，fast-growing，soil amending，easy propagation and cultivation.It is an excellent pioneer seed for forestation in dry-hot valley，and an ideal nutritional supplement food for the people whose staple food are grain and cereal.Pigeon pea has high protein forage for livestock including chickens，pigs and others，and also a sort of ideal forage for ruminant animals like flocks and herds，even it can breed lac bug to product lac.Thus，planting pigeon pea has comprehensive benefits in ecological，economic and social aspects［9］.Attention should be paid to cultivation，generalization，exploiture and utilization of the ecological resources which were appropriate for environmental conditions，geography and climate in the local re-gion that has important effect and strategic significance for ecological construction，stock breeding development and sustainable development of grass industry.

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Responsible editor：Xiaoxue WANG

Responsible proofreader：Xiaoyan WU

Supported by Ministry of Agriculture Species Resource Protection"Tropical Forage Germplasm Resource Conservation"Projects；Ministry of Agriculture Tropical Crop Germplasm Resources Protection Project（No.12RZZY-09）.

*Corresponding author.E-mail:ztxs0219@126.com

Received:September 3，2015 Accepted:October 13，2015