Cultivation and Intercropping with Shrubby Ash (Fraxinus)

Wang Guangqin, Fan Wei, Zhao Yuhou, Guo Liang And Jin Lieyi

Henan Forestry Research Institute, Henan, P.R. China

ABSTRACT

The paper deals with morphological and ecological properties and growth patterns of shrubby ash trees. The cultivation techniques of trees with intercropping systems including species combination, disposition, etc. and economic benefits are presented in this paper.
Key Words Shrubby ash, intercropping, ecology, economics

Introduction

     Ash (Fraxinus sp.) are deciduous trees or shrubs of the family Oleaceae. They put out buds very easily and shoots are very flexible. Usually, ash is cultivated as shrubs to get shoots. So it is called "shrubby ash" which is very useful. It can be planted to block wind and sand. The stems can be woven into baskets which are elastic and tough. Leaves are good for fodder. Through a long-term practice of struggle against wind and sand, the farmers in the east of Henan Province intercrop shrubby ash with crops that made a distinctive model of agroforestry which has come to be called "shrubby ash-crop intercropping." In order to ascertain the biological and ecological properties, and to determine the suitable growing environment and develop the cultivation technology, especially in the intercropping system, a long-terin study on shrubby ash was carried out in Ningling County of Henan Province. The main research results are included in this paper.

The Growth Pattern of Shrubby Ash

     Twigs of shrubby ash are cut annually and branches are cut when they reach three years of age. The plant regenerates by resprouting for over 100 years if managed well. So it is important to study the growth pattern of shrubby ash for better understanding the resprouting ability at different growing stages, and guiding the production measures such as tending, regeneration, etc. According to the age, number, height and diameter of twigs, the life of the tree can be divided into three stages (Table 1). (1) Young growth stage (1-10 years old) -In the first three years (seedling stage), shrubby ash attains 50-60% of height growth of the adult stage, with main roots well developed. Twigs cannot be cut at this stage. From year 4 to year 10 (young plantation stage), the root system is well developed. Twigs can be cut, but not appropriate to produce ash rods at this stage. (2) Adult stage (11-60 years old) - Stems can be cultivated to obtain rods in this stage. It is the best stage for the shrubby ash tree to produce twigs and rods. (3) Aged regeneration stage (over 60 years old) - With the increase in age and cutting of twigs and rods every year, the growth slows down and the production of twigs and rods decreased. The root system degenerates.

Cultivation Technology of the Shrubby Ash Tree

Vegetative Propagation -

     Shrubby ash tree can be easily propagated by cuttings and the survival rate is very high. (a) Nursery preparation - In general, fertile and well drained sandy loam and loam are good soils for nurseries. Soil must be prepared carefully. After deep ploughing, base fertiliser (barn-yard manure or compost) should be added. After that, nursery beds size 1 x 10 in is made and ready for cutting. (b) Shoot selection - The cuttings can be from 1-2 years old saplings or twigs. The diameter of the shoots should range from 1-2 cm. The shoots can then be cut into 20-30 cm long pieces with at least three buds. The cut should be oblique and not tom. It is suggested that the cuttings are planted soon and if it is not possible, the cuttings can be temporarily placed in rice field for short duration (a couple of days). If the cuttings are collected in early winter to be planted next spring, the cuttings can be stored in sandy soil. (c) Season and methods - The best season for cuttings is early March. Cuttings should be inserted into soil obliquely, keeping a 60º angle. The inserting depth is about 25 cm with one bud in the air. Irrigation should be carried out after insertion.

Table 1. Growth of shrubby ash tree in different ages.

* Diameter at ground level.

Table 2. Relative wind velocity in ash-crop intercropping system with different structures.

Table3. Evaporation in ash-crop intercropping fields.

Propagation by Seeds -

     Seeds of ash are ripe in October and the bunches fruits do not fall down from the mother tree. The ripen fruits can be collected by sickle, and air dried. Before storage, seeds can be disseminated by wind or water. Sowing season is in mid-March and the seeds should be vernalised before sowing. Ash seeds are sown in rows. The normal rate of seeding is 3 kg per mu (1115 ha). Seed purity is 95% and germination rate of 75%, 30,000 seedlings can be raised from one mu of nursery, and height of seedlings can reach 30-40 cm in one year. Seeding, watering, loosening of soil and weeding should be carried out in time.

Establishment Techniques of Shrubby Ash Plantation -

The shrubby ash plantation can be established by four methods: burying cuttings, cuttings, seedlings and root division. The cuttings should be from 2-3 years old robust saplings and the season for planting cuttings is early spring or winter, unless the earth is frostbound. The cuttings can be buried 6-9 cm deep into the soil when ploughing. Both winter and spring periods are suitable for inserting ash cuttings. First, select robust 1 - year old twigs and cut them into 26-30 cm long cuttings, then insert three to five ash cuttings into soil that have been prepared with the shape "\" or "::", with planting space of 60 - 100 cm. The best season for outplanting of seedlings is spring. Seedlings should be carefully lifted from the nursery and transported to the planting site. Root systems and top buds of seedlings should be protected during the lifting and transporting. In winter, some stumps with roots can be divided from the plantation in which the density is too high. The divided stumps can be stored in winter and replanted next spring.

Table 4. Comparison of soil wind erosion between intercropped and open fields.

Table 5. Biomass of ash-crop intercropping systems (tons/ha).

Table 6. Productivity of ash-crop intercropping system (ton/ha/yr).

Management of Shrubby Ash Plantation -

     In the early period of growth, for protecting the root system, soil cultivation should be carried out in the winter season. The root system will develop well during first three years. The season for cutting twigs in the 4th year is autumn when the leaves have fallen. The height of stumps is 3-5 cm and it should be covered by soil after twig harvest. Fertiliser application is also needed for high yield in ash plantations. Both chemical fertiliser and farm manure can be used. In addition, superfluous branches should be removed in the summer, and special attention should be paid to control harmful pests. The adult growth stage is an important period for rod and twig production (Table 1).

     The root system of ash trees in the adult growth period is very robust. Because the ash tree is usually planted in farmland, the root system will over develop if there is no appropriate control. This will harm agricultural crops and negatively affect the production of twigs and rods. Therefore, the root system must be controlled by deep ploughing of the soil between shrubby ash tree rows (1-2 m apart from the planting rows) in the spring. In order to obtain high quality rods without nodes, superfluous branches should be pruned in the summer season.

     The main kinds of pests are longicorn and shell-insect. Poisonous bamboo arrow and cotton dipped in 80% DDVP or 40% Rogor emulsion can be inserted in the holes to control longicorn. In addition, cutting wounds of ash must be sterilised with 0.5-1 degree lime-sulphur mixture to prevent harmful pathogenic bacteria from entering after twigs or rods are cut. After the robust growth stage, the ash tree enters slow growth period. The ability of sprouting, production of twigs and rods decline. The major management activities include irrigation, fertilisation, etc. to keep the plants healthy.

Table7. Comparison of circulation rate (CR) of nutrient intercropping and monoculture systems (kg/ha/yr).

Cultivation of Rods (Long Stems) -

     Rods obtained can be used to make small furniture, handles and sporting goods. Rods protect the tree in intercropping system and rod cultivation is an important way to manage shrubby ash. Farmers collect rods when the ash tree is 10 years old, by then the root system will have developed completely. But in good site conditions, rods can be cultivated ahead of this schedule.

     In the stage of 10-20 years, the growth of ash tree twigs decreased by 30% and the number decreased by 60% if one rod is kept per stump. But if two rods are kept, there was a 50% reduction in height growth and 60% in twig number. Keeping three rods, there was a 63% reduction of height growth and 75% in twig number. Concerning the length of time for cultivation of rods, four to five years will be needed for one rotation of rod cultivation if three rods are kept per stump. Only three years needed if one or two rods per stump are kept. The old plants are unsuitable to cultivate rods. When cultivating rods, robust and straight twigs must be selected and kept well-distributed on the stump. To increase the quality of rods, superfluous buds should be removed. The top bud should also be removed when the rods reach 3 m in length, thus promoting a greater diameter. The standard period for rod harvest is in autumn after leaf fall.

Ecological and Economic Benefits of Shrubby Ash-Crop Intercropping

     Ash-crop intercropping farming systems, as in other agro-forestry systems, such as Paulownia-crop intercropping and shelter belt systems in farmland, can improve the microclimate of the farmland and crop growth. A wind break is formed by ash rods (upper layer) and twigs (lower layer). The rate of wind break is 0.3-0.7 and protection effect against wind is very obvious. In the range from the ash tree to 15H (H is the height of tree), wind velocity is reduced by 20-30% (Table 2).

     Temperature - As the wind velocity changes, the air exchanges in both horizontal and vertical directions weaken. So, the air temperature in the field also changes, but the pattern is complicated. The air temperature in the intercropping system, compared with the open field, increased by 0.5-0.8ºC in winter and early spring, and decreased by 0.5ºC in summer.

     Evaporation - Average evaporation reduction of 10% was found in the range from the ash tree belt to 15H (leeward) (Table 3).

     Soil moisture - Ash barriers conserve soil water and increase soil moisture by the reduction of wind velocity and evaporation. Under inter-cropping system, there was a 6.7% increase of water content, 11.3% increase of available water content, and a 5% increase of soil moisture in the upper layer of soil (0-60 cm) during the growing season of wheat. Ash barriers can also conserve snow drifting and increase soil water in winter.

Table 8. Comparison of soil microbe numbers in intercropping systems and open field.

     Air humidity - In the range of 15H from the ash tree rows, there is a 20% increase of relative humidity (absolute humidity increases of 5 mb) in daytime compared with the open field. In the prevailing season of hot winds, the increase of relative humidity can reach up to 20%.

     Radiation - Gross radiation is reduced in ashcrop intercropping fields depending on the spatial direction of shrubby ash barriers. Ash barriers in the south-north direction with spacings of 30 m could reduce gross radiation by 5%. However, a 6.1 % reduction was found in an intercropping field with ash barriers in the east-west direction. But scattered radiation increased in intercropping fields because of the reflection of ash barriers. Scattered radiation increased by 3.7% and net radiation by 4.2%

     Reduction of wind erosion - In spring of 1986 soil erosion decreased by 9.5% in shrubby ash-crop intercropping fields compared with the open fields (see Table 4).

Increase of Productivity and Circulation Rates of Energy and Materials -

     Shrubby ash-crop intercropping ecosystems can make full use of sunshine and other natural resources. It can increase the biomass production of the land. The biomass increase (Tables 5 and 6) showed that the biomass accumulation of ash-crop intercropping systems reached 30.9851-65.4078 tons/ha with an annual productivity of 20.6529-30.7511 tons/ha/yr. Calculated according to a commonly used photosynthetic formula (4176 Kcal energy needed for synthesis of 1 kg biomass) and the total annual radiation of 119 Kcal/cm², the energy use efficiency of the ecosystem is up to 0.7-1.1%. The circulation rate of nutrients in ashcrop intercropping system is higher than that in monoculture systems (Table 7).

Biological Functions -

     The ecosystem provides a good habitat for small animals, insects and microbes. According to observations, over ten frogs were found in the 20 m long ash barrier and there were 20% more arthropods present in surface soil than in open fields. The natural insect enemies of plant pests increased by 17% in total population in the intercropping systems compared to open fields (Table 8).

Crop Yield in Ash-Crop Intercropping System -

     After many years of observation of intercropping systems, it has been shown that intercropped wheat yields increase by 7-10%, soybeans by 5% and peanuts by 4.7% compared with the monoculture of the same crops.