The Loess Plateau is divided into 6 agro-ecological and economic systems in this paper. The authors analysed the productivity in each system from many aspects including land use structures

bio-community

productive value structure

energy flow and conversion efficiency in food chains

N-cycle in farmlands

crop water use efficiency as well as water and soil conservation benefits. Also

they proved their viewpoints with the typical examples

and pointed out the directions for the future development. It can be seen from the analysis of the existing conditions that the system of fruit

forests

agriculture and animal husbandry developed in Liang and hill area represented by Miaogou village in Yanan Municipality has the high economic returns owing to a large scale development of apple production

In 1990

per capita net income reached 166.7 Yuan

being 1.9 times higher than that in the surrounding villages. At present

one hectare orchard can support 6.7 persons

being 8.3 times higher than one hectare grassland supports. Up till to 1995

one hectare orchard can support 32.6 persons. In the system of fruit food crops

sideline production and animal husbandry formed in mound and hill area represented by Qianjiagou village in Mizhi county

the modulus of soil erosion has been reduced from 16

000 t/(km2·a). in the 1960s to 3

000 t/(km2·a ). at present owing to a large scale basic farmland construction and conversion of sloping lands into planting trees and grasses. In 1990

per capita net income was 656.4 yuan

being more than double that in the surrounding villages. At present one hectare orchard can support 14.3 persons

being 1.4 persons higher than that supported by one hectare cultivated with food crops. Up till to 1995

one hecgare orchard can support 28.5 persons.