Intercropping with Jujube in China
Scientific Name: Zizyphus jujuba
Family: Rhamnaceae
Jujube (Zizyphus jujuba
Mill.) is an excellent agroforestry intercropping tree species, which
has been cultivated in the form of intercropping for more than 2,000
years in China. It is currently widely planted by farmers. With small
leaves and sparse canopy, jujube adapts to many kinds of soils: plains,
highlands, sandy beaches, saline-alkaline soil, etc. The rainfall in
its growing area is from 200 mm to 1000 mm per year.
A suitable
planting model for jujube in an agroforestry intercropping system is
with 3-4 x 15m in spacing, 5-6m in height, and north-south row
orientation, and combining with crops in the form of 'high-low-high' or
'high-low-middle-low-high'.
Jujube agroforestry systems have
high ecological and economic benefits. Energy utilization rate is about
77% higher than that in monoculture. The systems can produce 9,000
kg/ha of grain plus 4,500kg/ha dried fruits annually. The output is 3
times higher in intercropping than that in monoculture.
Introduction
Jujube (Zizyphus jujuba
Mill.) originated in China. It probably evolved naturally and was
artificially selected from Z. spinosus Hu. With its main occurrence in
the middle-lower reaches of the Yellow river in Henan, Shaanxi, Shanxi,
and Shandong provinces, jujube falls in the temperate zone.
In
addition, it is widely grown in Hebei province, extending over east
longitude E.76-124°, north latitude N.23-42°. This species was
growing in west Asia more than 2,000 years ago, and was introduced to
India in 1930 and to Europe in 1837.
Its most notable value is
that its fruits are delicious, richly nutritious, and contain good
materials for medicines. The well-known ancient Chinese text, Book of
Medicinal Materials, recorded that dried jujube fruits are good for the
heart, liver, spleen, lungs and kidney, and for curing coughs,
prolonging life, etc. The sugar content of the dried fruit is
50.3-86.9%, the protein content is 1.2-3.3%. It contains 18 amino acids
of the 24 essential for human beings.
Jujube is a traditional
agroforestry species in China, rarely competing for water, nutrients
and applied fertilizers with intercropping crops. Its sparse canopy
allows a large amount of light to pass through, making this available
for use by the intercrops.
Jujube intercropping is a traditional
farming system in China. Intercrops are mainly wheat, corn, soybean,
cotton and vegetables, etc. Old records indicate that jujube was widely
planted around households and farmlands. It is long-lived, with a
record age of 1,800 years. Usually trees bear fruits for 80-100 years.
This agroforestry system has been rapidly developed during recent
years. In Hebei and Shandong Provinces alone, the intercropped area is
133,000 ha, and the output of dried fruits is about 65% of the national
production.
MODIFICATION OF MICROCLIMATE IN THE JUJUBE INTERCROPPING AGROFORESTRY MODEL
Modification of microclimate in the intercropping system is dependent on many factors.
Row Orientation
The
growing season of jujube is from April to October. Its sparse canopy
allows most light to go through. However, the rate of light penetration
is a function of row orientation.
In mature intercropped
orchards, east-west oriented rows with 1.2m between trunks, which allow
30% and 34% light penetration respectively on the north and south sides
of the canopy, are considered as better than north-south rows with 1.2m
between trunks, which allow 51% and 40% light penetration respectively
on the east and west sides of the canopy. There is a difference in
radiation between the two row orientations.
At a 3.5m distance
from a 5m high east-west oriented row, radiance duration is reduced to
6-8 hours. Differing crop yields are found between the two row
orientations, with wheat and corn yields of E-W oriented rows 15.7% and
30% lower than those of N-S oriented rows. The dried fruit yields of
E-W oriented rows are about 10-15% lower than those of N- S oriented
rows.
Spacing
At
different distances from the trees, the rates of light penetration are
different. The light index in N-S oriented rows is 0.8-0.87 at 2m from
the trunks, 0.96-0.98 at 4m, and 0.99-1.00 at 6-l0m. Minimum normal
distance between rows should be 8m.
Light duration is also
dependent on row separation. At 2m distance from N-S oriented rows,
18m, 15m, and l0m apart, light duration is 8.5h, 7.75h, and 5.78h
respectively, which is 57%, 52%, and 39% of the open-field values. The
15m row distance is accepted as optimum spacing. More crop shading
occurs at the l0m spacing, with only a small difference in microclimate
changes and crop yields between the 15m and 18m spacings.
Jujube
has a smallish canopy, 3.5-4.5m across. At 1.2m from the canopy, a
15,000 Lux light intensity reached the ground for 11 hours, while a
light intensity above 45,000 Lux lasted 7 hours. Daily total light
intensity is 19,884 x 101 Lux, which is about 66% of that in open field
is 3-4m x 15-18m.
Trunk Height
In
pure orchards, jujubes with short trunks are easier to manage and their
output is nearly equal to other fruit trees. However, high trunks are
needed in intercropping systems so as not to affect the intercropped
crops.
It is reckoned that a trunk height of 1.4m is suitable
for growing crops under the trees With a 1.4m trunk height, light
intensity under the canopy during the growing season was 15,000-48,000
Lux, while with 1.2m trunks it was less than 20,000 Lux.
Intercropped Crops
The
effect of shading on intercrop growth varies with the distance from the
hedgerows. With a spacing of 4 x 15m, crown width of 5m, and trunk
height of 1.4m under the canopy, light penetration in summer is only
15,000-48,000 Lux, which represents 27-59% of that in open fields. Thus
suitable intercropping crops in summer are short, shallow-rooted,
shade-tolerant crops like soy bean, mung bean, daylily, etc.
Within
2m of the trees, where the direct light duration is 1.5 hours shorter
than that in open fields, short crops with high compensation like
cotton, millet, etc. should be intercropped. Beyond this range, where
the microclimatic system is similar to that in open fields, tall crops
such as corn and sorghum can be intercropped. In addition to the above,
winter wheat is considered as an appropriate intercrop. In winter, when
trees become leafless and dormant, the microclimate anywhere near the
trees is nearly the same as that in open fields.
During the
early growing season of the wheat, when tree leaves have not yet
emerged, light intensity under the canopy is about 6,500-9,500 Lux,
which is 96% of that in open fields. Jujuba leaves start to emerge when
the wheat reaches the jointing stage (at the end of April in western
China). However, the newly emerged leaves still allow almost 96% of
light to penetrate the canopy. When the wheat proceeds to the flower
and fill stages, and the tree is in faster growth, the light intensity
is 20,000-70,000 Lux, which is more than what the wheat requires (at
this stage the wheat light demand is 20,000-30,000 Lux). The jujube may
also protect the wheat from harm by the hot and dry strong winds.
Recommended
models of crops arrangement at different distances from hedgerows are
described as 'high-low-high' or 'high-low-middle-low-high' forms. 'Low'
crops (cotton, bean, wheat) grow between two 'high' hedgerows of trees,
and 'low-middle-low' crops (corn, sorghum, etc) also grow between the
'high' rows of trees.
ECOLOGICAL AND ECONOMIC BENEFITS OF JUJUBE INTERCROPPING AGROFORESTRY
The
modification of microclimates in jujube agroforestry and its effect on
the inter-crop yields have been widely studied. Acting as shelterbelt,
the jujube interplanted in the system can reduce wind velocity and
minimize its mechanical and physiological damage to the crops. The
temperature and the wind velocity are decreased 0.5-1.0°C and 64%
respectively, the relative humidity is increased by 6.0%-8.2%. This
kind of agroforestry system has many advantages over monoculture
systems.
A significant role of the agroforestry system is to
protect the jujubes from production losses caused by the hot and dry
winds. The multiple layers of trees and crops can also utilize natural
resources more efficiently, especially heat integral radiation. The
heat utilization efficiency in a jujube-wheat-corn intercropping system
is 177% of annual integral temperature, which is 77% higher than that
of corn and wheat together in a monoculture system and 159% higher than
that of corn in a corn monoculture. The microclimate modification and
the high thermal energy utilization efficiency favour the growth of
intercropped crops and consequently increase crop output. Thus, an
intercrop system yields on average 2,235-5,925 kg/ha of fresh fruit and
about 1,352 kg/ha of grain.
Drawing of Jujube twig and fruit.
The
net incomes from intercropped trees at spacings of 4 x 7, 4 x 15 and 4
x 21m are 7.0, 3.7 and 2.7 times higher than those in monoculture
fields. Now benefits have been demonstrated, farmers are more active in
pursuing jujube intercrop agroforestry. For instance, the Zhuji commune
in Lelin county, Hebei province, has intercropped 1,666 ha,
representing 73.5% of the total farmland. The grain output has
increased 25%.
Lishangzhuang village in Xian county intercropped
59.3ha, representing 83.4% of its total farmland in 1965. The total
grain output in 1982 was 179,000 kg ,which is 50% more than that in
1965. The jujube fruit provided a very significant extra income for the
farmers. For example, in the Gaozhuang commune in Zhang county, Hebei
province, the area of intercropped crops was only 13.6% of the total
area, but 64.8% of its total income was provided by the jujube fruit.
In
conclusion, jujube intercrop agroforestry is playing a significant role
in modifying microclimate and increasing productivity and income. It
looks to have a bright future with increasing interest being shown by
both researchers and farmers.
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