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.
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.
DATE: May 1991
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