Sustainable Agrosilvicultural
Management Techniques in Northern China Dryland
Lu Qi1 Zhao Tishun2
(1 China National R & D Center for Combating
Desertification, Beijing 100091)
(2 Henan Academy of Forestry Survey and Design,
Zhengzhou 450003)
Abstract Five major types of agrosilivculture have
been practiced over the past 40 years in the North China Plain. In these
systems, trees, shrubs, and other woody perennials are interplanted with
agricultural crops or are planted for protecting farmland as shelterbelts, for
controlling gully erosion, “town-village” protection, or for establishing
fast-growing high-yield plantations. Tree species for interplanting are Paulownia spp., Ziziphus jujuba, Populus spp.,
Diospyros kaki, Fraxinus chinensis, Morus Cathayana, Metasequoia
glyptostroboides, Taxodium ascendens, Taxodium distichum, etc.
As compared with the control systems, wind
velocity was decreased by 20% to 40%, relative air humidity was increased by
10% to 20%, and evaporation decreased 9% to 25% in the agrosilvicultural
systems.
In the farmland shelterbelt, there were increases
of 5.9% in water content, 8.7% in water retaining capacity, 13.3% in effective
moisture of the surface soil (0-30 cm), 19.17% in organic matter, 8.3% in total
miarogen, 21.15% in hydrolyzable nitrogen, and 16.2% in rapidly available
phosphorus within the soil.
Biomass was increased 1.63 to
2.6 tons/ha/yr for Populous tomentosa
(10-18 years) in shelterbelt protected fields and 1.81 to 2.5 tons/ha/yr for Paulownia fortunei (10 years) in
inter-cropped field. The efficiency of light energy utilization was 1.0% to
2.98%, and the cycling ratio of nutrient elements was 9.53% to 20.0% higher in
the agrosilvicultural systems than in the open crop fields.
Crop yield was increased by 9.7% to 30% for wheat （Triticum
aestivum),
9.6% to 21.5% for maize (Zea mays),
20% for millet (Setaria italica),
10.3% for sorghum (Sorghum vulgare),
9.52% for soybean (Glycine max),
7.69% to 8.3% for cotton (Gossypium
spp.), 5.8% to 12.8% for peanut (Arachis hypogaea), and 9.5% for rapeseed (Brassica campestris).
Key
words: Agrosilviculture,
North China Plain, inter-planting, shelterbelt
1 Introduction
The
North China Plain is the largest plain in China, covering a wide region from
113°30¢
to 122°
41¢
E and from 31°18¢
N to 40°36¢
N. This region is about 509,000 km2 or 5.3% of the total land area
of China. It is a main region for grain, cotton, edible oil crops, and tobacco
in China. The major hydrographic network in the Plain includes the Yellow
River, the Huaihe River, the Haihe River, and the Luanhe River. The whole area
lies in a humid monsoon zone of temperate climate Zone with a mean annual
precipitation of 500 to 1,000 mm unevenly distributed in different seasons of
the year. The annual evaporation of 1,800 to 2,300 mm, three or four times of
the annual precipitation.
Since
1949, China has engaged in tree plantation in the plain to control the violent,
sand accumulation and wind disasters and improve agricultural potential. During
the 1950's, several large-scale afforestation programs were launched. The first
program was located along the lower reaches of the Yongding River to protect
farmland against sand invasion and wind disasters. The second was to establish
shelter belts in the sandy areas in the west of Hebei Province. The third was
the shelterbelt along the abandoned watercourse of the Yellow River in the east
of Henan Province.
In
the 1960's, afforestation on large scale was turned to plant tress on “four
sides”: house-side, village-side, road-side, and water canal. Inter-cropping
was widely used the farmlands that were often impacted severely by sands and
wind disasters. In the 1970's, with a view to further improve the ecological
environment for crop yields, plantation and crop farming were integrated into
agrosilvicultural system that was characterized by the full use of hills,
riverside, crop fields, roads, and small pieces of land. As a result,
shelterbelt networks have been planted around the squared crop fields and the
windbreaks and farmland protective shelterbelts were gradually established in
the wide plain area. By the 1980's, the green protective system has commonly
been practiced all over the North China Plain and remarkable advantages in
agroforestry management have been promoted through wide demonstration.
2 Types of
Agrosilviculture
2.1 Inter-cropping
Inter-cropping
is an agrosilviculture system in which trees and cereal crops were
inter-planted in various patterns. Seven different systems are practiced in the
North China Plain.
1) Paulownia-crop inter-planting:
this type is practiced mainly in the sand-wind-impacted areas of the North
China Plain. Some counties, like Lankou, Minquan, Suixian, Fugou, and Yanling
in Henan Province have played a leading role in expanding this system. It is
extensive over large areas of land and has also been practiced in Heze,
Dongming, Yanzhou, and Bozhou Counties of Shandong and in some counties of
Anhui and Hebei Provinces. Three inter-cropping patterns are adapted.
Inter-planting
with crop domination is mainly practiced in areas where sands wind are less,
soil is relatively fertility, and the water table is below two meters. For
sustainable agricultural development, some crops and trees, such as wheat,
maize, and cotton, Paulownia trees are planted on the farmland in spacing of
four to five meters between individual trees and 30, 40, or 50 meters between
rows, depending on the specific conditions. The Paulownia trees were harvested
as timber source when its growth was eight to ten years.
Inter-planting
with Paulownia domination is mostly concentrated on the sand areas along rivers
course and in the sand-wind-impacted areas with less low density of population.
The main objective is to grow Paulownia timber with different crops. Trees are
usually planted in 5m×5m spacing. A thinning cut is
practiced five years after planting to praduce small and medium-sized logs. The
remainders then grow into large trees. In the first two years, the
inter-cropping patterns are Paulownia-wheat-cotton (or maize),
Paulownia-wheat-soybean (or peanut), Paulownia-wheat-garlic,
Paulownia-melons-garlic, Paulownia-peppermint, and Paulownia-vegetables.
Inter-planting
dominated by both crops and Paulownia is carried out mainly in the
semi-cultivated and abandoned cropland with sandy soils and frequent winds. The
inter-planting system is designed to protect crops from hot wind and sandstorms
and produce small and medium-sized logs. The spacing is about 5m×10m
to 6m×10m metres with an arrangement of 102 to 200
individual trees per hectare.
2) Jujube-crop inter-planting: Jujube,
an important fruit tree in the North China Plain, is widely planted in
cropfields with poor sandy soil in Xingzheng, Neihuang, Puyang, Yongcheng, and
Lingbao Counties of Henan Province and Liling, Shiping, Liaocheng, Zhouxian,
and Tengxian counties of Shandong Province. The jujube trees are planted in
spacing of 4m×8m to 6m×10
m with inter-cropped wheat and peanut.
3)
Wicker-crop inter-planting: Fraxinus chinensis,
Amorpha fructiosa, and Salix suchowensis are planted on farmland
for increasing grain and wicker. This system is practiced mainly in flooded
areas along the Yellow River, such as Ningling, Lankao, Minquan, and Kaifeng
Counties of Henan Province and Qingcheng County of Shandong Province.
Wicker-crop inter-planting plays an important role in wind control and sand
fixation. For example, ash tress (Fraxinus)
are planted in clusters, each cluster with three or four stems 0.6 to 1 meter
apart and two to four rows in a belt. The distance between belts varies from 4
to 22 meters. Wheat, peanut, and soybean are sewed inside the belts.
4)
Mulberry-crop interplanting:
Mulberry trees (Morus cathayana) with
inter-crops are mainly found in Maxian, Yuxian, Xiangxian, Wuzhi, Minquan, and
Qixian Counties of Henan Province, and even in some counties of Hebei,
Shandong, and Anhui provinces. There are two types are common. One is designed
to produce mulberry leaves for silkWorm breeding. Here, mulberry trees are
planted in 1m x 1m to 2m×2 m spacing and
managed by using the coppice method. The other type of inter-planting is
undertaken primarily to grow mulberry branches and stems for making forks of
treetrunk, a farm tool. Trees are planted in clusters. Usually one cluster has
three to five stems or, in some cases, even more than ten. Inter-crops are
wheat, sweet potato, and leguminous plants.
5)
Persimmon-crop inter-planting:
this type of inter-planting of persimmon (Diospyros
khaki) with crops is commonly practiced in Boai, Xingyang, Linxian, Lushan,
and Huixian Counties of Henan Province and in some parts of Shandong and Hebei
provinces as well as Beijing. Persimmon trees are planted in a distance of 15
to 20 meters apart from individual tree and in a distance of 20 to 25 meters in
row. There is no discrimination in crops for inter-planting due to the low
density of persimmon trees.
6)
Poplar-crop inter-planting:
this type of inter-planting is practiced in the basins of the Huaihe River and
the Yellow River in Henan Province and in some parts of Shanxi, Shandong, and
Hebei provinces. Three inter-cropping patterns are common. In inter-planting
with tree dominance, trees are planted three to four metres apart with four to
six metres between rows. In inter-planting with crop dominance, trees are
planted three to four metres apart with 30 to 50 metres between rows. And in
inter-planting with both tree and crop dominance, trees are planted in a 4m×8
m spacing. In all three patterns wheat and soybean are inter-cropped.
7) Other inter-planting types: in
recent years some, other inter-planting types have been developed in the Huaihe
River Basin. Tree species used for inter-planting are Taxodium distichum, Taxodium ascendens, and Metasequoia glyptostroboides. These trees are planted along the
ridges or inter-planted in the fields with inter-crops of wheat and rice.
2.2 Farmland
Shelterbelts
As
integrated parts of an agrosilvicultue system, the marginal lands along
cropfields, roads, and ditches can be fully used for tree planting to form
shelterbelts that play an important role in improving the ecological
environment and imcreasing crop yield. Such farmland protective shelterbelts
are extensively distributed not only in the areas where climate is arid and
sand and wind disasters are severe, but also in the regions with high yields of
crops in the North China Plain and in some parts of farming areas in the
mountainous areas.
Generally,
the distance between main shelterbelts is from 400 to 500 metres, forming a
"mesh size" of five to ten hectares. In the areas where sand and wind
disasters are severe, the distance between main shelterbelts is from 150 to 250
metres; whereas that between secondary shelterbelts is from 300 to 400 metres.
A main shelterbelt is formed by four to eight rows of trees and a secondary
shelterbelt by two to four rows of trees. The tree species used are Populus tomentosa, Populus euramericana cv.
Sacran-79, Populus fortunei, Ulmus
pumila, and Salix spp. In order
to increase the economic output, Amorpha
fructicosa and medicine herbs are planted under the shelterbelts, thereby
creating complex inter-plantations in the fields.
2.3 Social Forests
The
social forests are created by planting timber trees, fruit trees, and flowers
on the marginal lands in the front and back of houses, in courtyards, along
roadsides, and around villages. These can not only gardening the landscape and
improve the environment, but also produce integrated benefits in addition to
ornamentation such as supplies of fruit, timber, and fuelwood. Social forests
are the complex system. Especially in the east and the south of Henan Province,
farmers make full use of marginal lands in courtyards and around villages by
creating various types and components of these social agroforests.
Tree
species used for these purposes are mainly Paulownia spp., Papulus spp., Diospyros kaki,
Robinia pseudoacacia, and Ulmus pumila. Many cash crops, trees,
and garden flowers are also integrated into these social forests. According to
a forest inventory conducted in 1988, social forests in Henan Province occupy
an area of about 4.2×105
hectares with over 800 million trees, the total stocking volume of which
reaches 28.96×106 m3, which is
about 33% of the total stocking volume in Henan Province.
2.4 Fast-Growing
High-Yield plantations
In
recent years, many large tracts of fast-growing high-yield plantations have
been established in the vast flood plains of rivers, along the main canals, or
in the sand lands and sand-wind impacted areas in the North China Plain. The
size of these plantations varies from a few to dozens of hectares. The main
tree species planted are Paulownia spp., Populus
spp., Robinia pseudoacacia, and Ulmus pumila. Crops are planted before
the crown of the stands closed. Investment and input for the establishment was
provided by local governments. Short rotation operation is adopted for
plantation of social forests, which are usually harvested within 10 to 15
years. In a broad sense, these plantations are the main components of
agrosilviculture. Of the 3.0×105 ha of
fast-growing high-yield plantations and 2.33×105
ha of patch-forests in Henan Province, about 9665 hectares of Paulownia
plantations are inter-planted with crops. Those plantations inter-cropped in
Shandong and Hebei Provinces cover 1.26 x104 ha and 2.7×104
ha respectively.
3 Functions of
Agrosilviculture
3.1 Modification of
Microclimates
Farmland
shelterbelts and inter-cropping reduced wind velocity by an average of 20% to
40%. In summer, shelterbelts reduced the daily mean temperature by 0.5℃
to 2.6℃in
the cropfields. The Paulownia-crop inter-plantings reduced daily mean
temperature by 0.4℃.
The wicker-crop inter-plantings reduced maximum temperature by 0.8℃
to 1.0℃
and the daily mean temperature by 0.5℃. Within the farmland shelterbelts the mean
relative air humidity increased by an average of 10% to 20%. Evaporation was
decreased by 25% to 43% in the Paulownia-crop inter-cropping, 12.6% in the
jujube-crop inter-cropping, and 9.2% in the wicker-crop inter-cropping (Zhao
and Zhao, Tianbao 1986).
3.2 Resistance to
Natural Calamities
In
Boai County, Henan Province, 21, 000 hectares of farmland protective
shelterbelts have been planted since 1972. Analysis of meteorological data
obtained from 1965 to 1983 reveals clear changes in the region's climate that
may be divided into three periods that correspond to the non-shelterbelt period
(1965 to 1971), the initial stage of shelterbelt plantation (1972 to 1977), and
the functional stage of shelterbelt (1978 to 1983) (Wang and Zhao, 1986).
The
absolute maximum temperature was reduced by 0.6℃,
the absolute minimum temperature was increased by 1.9℃,
and the absolute difference in temperature was reduced by 2.5℃.
The growth of trees has promoted relative air humidity (RH). The annual change (A) in relative air humidity from 1965 to
1983 can be expressed by the following formula:
RH=138.67+5.2144A-0.0328A2 (r=-0.85)
The
mean wind velocity was sharply reduced by 29.6%.
The
days of strong winds totaled 17 during the non-shelterbelt period was decreased
to 13 days in the initial shelterbelt period and 8 days in the functioning
shelterbelt period.
The
values for mean annual evaporation over the three periods were 1,917.8 mm,
1,746.6 mm, and 1,612.7 mm respectively. Compared with that during the
non-shelterbelt period, mean annual evaporation was reduced in the initial and
functioning shelterbelt periods by 8.9% and 15.9% respectively.
The
days of hot winds per year averaged 9.7 days (the highest being 17 days in
1965) during the non-shelterbelt period, and was reduced to 5.2 days (the
highest being 8 days in 1972) in the initial shelterbelt stage and 3.5 days
(the highest being 7 days) in the functioning shelterbelt stage.
Deserving
of special mention is the fact that large-scale farmland shelterbelts are
capable of increasing rainfall. After the land was brought under farmland
shelterbelts, Boai County had an increase in mean annual precipitation of
16.7%, an addition of 85.8 mm of rainfall to the system when compared to that
prior to shelterbelt establishment. Qinyang County, which borders Boai to the
west and had not established farmland shelterbelts, shows a gradual decrease in
precipitation; whereas, annual precipitation was 99.5 mm greater in Boai County
than that in Qinyang. Wuzhi County, which lies to the east of Boai County,
received 61.5 mm of precipitation yearly than Boai County. These increases in
annual precipitation are probably due to the fact that the trees within
farmland shelterbelts greatly increase total evapotranspiration within the
region, which in turn increases regional water vapor and accelerates the
micro-circulation of water resources.
Lankao
County of Henan Province experienced 25 sand and dust storms in 1962. After
Paulownia-crop plantations were established extensively across the county, sand
and dust storms occurred only twice in 1982 and by 1988, when forest coverage
reached 20.4%, there were no such storms. Moreover, grain yields in the entire
county increased from 30 million kg in 1962 to 190 million kg in 1982, 193
million in 1989, and 207 million in 1990 (Jiang, 1990).
3.3 Improvement of
soil conditions
The
approaches for protecting farmland by shelterbelts in the eastern portion of
Henan Province show that moisture contents within the top 20 cm was increased
by 261 m3, about 2.3 times greater than that of farmland without
trees. In Zhangruji Township in Boai County, the moisture content of farmland
protected by shelterbelts was increased by an average of 23%.
In
addition, in the farmland shelterbelts, moisture content, water-holding
capacity, and effective moisture of the surface soil (0-30 cm) were increased
by an average of 5.9%, 8.7%, and 13.3% respectively, during the entire growing
season as compared with the control areas. Under the protection of
shelterbelts, 144.9 tons/ha of water were saved after 14 days of irrigation.
Trees
also play some roles in lowering the water table, thus preventing the soil's
re-salinization and controlling saline-alkali soil. The farmland in Zhangruji
Township had all been brought under the shelterbelt system in 1972. After ten
years, the previously existing heavy saline-alkali land (12.8% of the total)
and the light saline-alkali land (50% of the total) were eliminated as the
water table was lowered two meters. The previously waterlogged fields were
transformed into fertile land and the agricultural yield was doubled.
3.4 Enhanced Biomass
and Light Energy Utilization
A
new agrosilvicultural ecosystem was formed by trees that planted into existing
farmland and thereby diversifying the biological composition and structure
within the ecosystem. These changes increased the efficiency of solar energy
utilization and raised the biomass.
Based
on the results of researches, in a 10-year-old stand where Populus tomentosa was the dominant tree species along with Salix spp. and Amorpha fructicosa, the biomass of trees reached 13.7936 tons/ha or
37.3% of the total biomass of the farmland ecosystem. The productivity of the
trees amounted to 1.63 tons/ha/yr and the total productivity of the farmland
shelterbelt ecosystem was improved. The solar energy conversion rate of Populus tomentosa was 2.9%, which was as
same as the net increase in efficiency of solar energy utilization as compared
with monocultures of crops.
Yang
(1986) studied the biomass, net productivity, and efficiency of solar energy utilization
of 10-year-old inter-cropped Paulownia
elongata with spacing of 4.3 m in eastern Henan Province. According to this
work, Paulownia was a major contributor to both biomass and net productivity in
this system of agrosilviculture (Table 1).
Table
1. Biomass, Net Productivity, and Efficiency of Solar Energy Utilization
In
Paulownia-crop Inter-cropping in Eastern Henan Province
|
|
Lime-earths & Clay soils |
Black sandy soils |
Silts |
|
Total biomass (tons/ha) |
33.7 |
26.7 |
27.7 |
|
% from Paulownia |
51.6 |
48.6 |
38.1 |
|
Net productivity (tons/ha/yr) |
18.8 |
15.7 |
18.9 |
|
% from Paulownia |
13.3 |
12.2 |
9.6 |
|
Efficiency of solar energy utilization (%) |
1.32 |
1.10 |
1.30 |
Data from Yang (1986)
Wang
and Guan (1984) studied the biomass of wicker-crop inter-planted fields that
featured Fraxinuds chinensis at a
variety of spacing as well as differing agricultural inter-crops. In their
work, biomass varied considerably due to both the different tree spacing and
the combinations of inter-crops. Here it was clear that biomass increased as
distance between wicker rows decreased (Table 2). The efficiency of solar
energy utilization fluctuated between 0.7% and 1.1%. The average cycling rate
of nutrient elements in the wicker-crop ecosystem was 20% greater than in the
monoculture cropfield control, with the cycling rate of nitrogen being 12.5%
higher, phosphorus 32.75% higher, potassium 34.36% higher, calcium 23.4%
higher, magnesium 26.8% higher, and manganese 8.66% higher.
Fan
(1991) found similar improvements in soil fertility in farmland protected by a
shelterbelt of Populus tomentosa. The
average cycling rate of nutrient elements was 15.28%, a rate 9.53% higher than
that of monoculture crop field. Nitrogen cycling was increased by 4.79%,
phosphorus by 7.03%, potassium by 13.92%, magnesium by 56.98%, and manganese by
27.43%.
Research
conducted in several provinces of eastern China (Wang and Zhao, 1986; Zhao and
Zhao, 1986) has shown that many types of agroforestry, including
agrosiliviculture, play an active role in increasing the yields of a broad
variety of crops (Table 3).
Measurements
carried out in a 13-hectare protected area in Xiaowinan village in Xiuwu
County, Henan Provine, showed that the shelterbelts' "edge effect"
area where crop yield decreased considerably took up only 2.2% of the total
area, while the area where yields increased due to the protection of trees
accounted for 88.4% of the total. These edge effects could have been minimized
if proper measures such as digging trenches, trimming root systems, and
improving irrigation and fertilization had been employed.
Table
2. Biomass of Wicker-Crop Inter-cropped fields in Ningling County, Henan
Province (Unit: Tons per Hectare)
|
|
Crops |
Total |
||||
|
Distance Between Rows(m) |
Fraxinus Chinensis |
Wheat |
Maize |
Peanut |
Fraxinus +wheat +maize |
Fraxinus +wheat +peanut |
|
22 |
8.644 |
15.779 |
12.880 |
6.563 |
37.30 |
30.99 |
|
10 |
19.017 |
9.772 |
12.144 |
6.188 |
40.93 |
34.98 |
|
8 |
23.772 |
10.533 |
11.806 |
6.016 |
46.11 |
40.32 |
|
4 |
47.543 |
7.740 |
10.120 |
5.156 |
65.40 |
60.44 |
Table 3. Agroforestry¢s
Function in Increasing Yields
|
Types |
|
Crop |
Increase in yield (%) |
|
Farmland Shelterbelt (Henan Province) |
|
Wheat Wheat Maize |
20.0 to 30.0 30.0 21.5 |
|
Tree-Crop inter-cropping (Henan Province) |
Wicker-Crop |
Wheat |
11.3 |
|
Paulownia-Crop |
Wheat Millet Sorghum Mungbean Wheat Wheat Maize |
10.1 to 28.0 20.0 10.3 6.3 16.0 4.0 to 5.0 9.6 |
|
|
|
Persimmon-Crop Jujube-Crop Mulberry-Crop |
Wheat Wheat Wheat |
6.9 9.7 to 22.4 10.0 to 30.0 |
|
|
|||
|
Agrosilivicultural System (Hebei, Shandong, and Anhui Provinces) |
|
Cotton Peanut Rape |