Walnut (Juglans regia)
Walnut is believed to be originated from Northern West Himalayan region from Iran to karnali zone of Nepal at an altitude of 1200 to 2500m above sea level. In hilly region of Karnali region of Nepal, thin hard shell to thick hard shell wild walnut trees are found abundantly. Improved varieties of walnut are believed to be brought as English & Persian cultivar having thin hard covering Dante walnut 4 decades before and distributed all over Nepal. The far-western region of Nepal is more popular for walnut cultivation.
The major cultivated cultivars of walnut all over world & Nepal are:
- Local harde walnut
- Thin shell
For successful cultivation of walnut, plain area with 20-degree slopy land is suitable. It can also be cultivated in bunds of field, grassland, public land & community forest.
Walnut can resist slight frost & light snowfall however, heavy snowfall cause damage to trunk. High temperature during summer season is also not suitable for walnut tree. So, it can be cultivated successfully from 1000m to 2500m altitude from sea level. It requires annual 700 to 1500 hours chilling injury. Annual rainfall required is 760mm & above for successful cultivation.
Walnut requires well drainage facility, adequate moisture retaining deep soil upto 3 meters, rich in organic compounds, silty to clayey loamy soil. Optimum pH level for walnut is 6-7 for better production.
Walnut tree is large in size so, layout must be done with better consideration. Plant to plant distance is maintained 10 meter which assure 100 trees in a hector of land. Contour system is followed during layout of walnut tree. A frame can be used for drawing contour lines.
Pit digging & filling:
Pit size of 1m diameter and 1m height is digged two month before planting. 25 kg FYM (1 doko), 5kg ash, 500 grams bone ash, 200 grams nitrogen, 100 grams phosphorus, 200 grams mop, & 25 grams furadan is applied inter-mixing each other to fill the pit. At the center of pit, after 2 months plants are planted.
Propagation of walnut tree is quite difficult in respect to other fruit trees. Propagation through seed & vegetative propagation both is possible in walnut.
- Propagation through seed: It requires 7-8 years for flowering & fruiting.
- Vegetative propagation: Dormant bud is taken from previously fruiting tree in the mother rootstock plant (Hardey Okhar) to prepare sapling which are grafted. Rootstock of Hardey Okhar is taken & dormant bud of Dante Okhar is taken.
Walnut saplings are transplanted during Poush-Magh with the help of planting board to maintain sapling in the center of pit. Staking is necessary to ensure root stabilization.
Mulching with grass straw or hay or paddy straw around 1-meter perimeter of plant with enough thickness is necessary. Do not cover the stem of sapling which can propagate insect & disease attack. Mulch helps is moisture maintenance & weed control.
Clean the orchard repeatedly to make healthy growth of saplings. Apply 5-8 ml of glyphosate in 1 liter of water & spray in between the saplings to control the weed.
Irrigate the orchard immediately after planting saplings. Thick mulch helps in conserving moisture for longer duration, so during the early days of transplantation, moisture in the field must be carefully observed. After the fertilizer application, during flowering period, irrigation is mandatory.
Apply fertilizer after pruning during the winter season. 1 doko FYM for non-fruiting tree while 2 dokos FYM for fruiting trees. Chemical fertilizer is applied as below:
|Age of tree||Nitrogen (gram)||Phosphorus (gram)||Potassium (gram)||Distance from base of trunk|
Training & pruning:
Modified leader system & center leader system are followed in walnut tree for its training. Heavy pruning is not necessary in walnut however, during pruning special attention is required as its new flushes & flowering bud are present in tip of branches. Heavy pruning at the tip of branch can cause zero production.
Flowering & fruiting:
Male & female flower occur at different branches in same walnut plant. Male flower occur in one year old branch in bunch hanging whereas female flower occur in new flushes in the tip of branches. Due to polyandry or different period of flower maturity in walnut tree. Cross pollination occurs that suggest to plant different cultivars in same orchard. Wind helps in pollination in walnut which ensure adequate fruiting.
Harvesting of walnut is done in Bhadra – Asoj month according to climate of Nepal. Fruit matures in different stages where outer covering is dehisced & fruit turn brown which indicates maturity stage. For synchronizing maturation of fruit, ethephon can be applied 15-20 days before fruit maturity. It is applied 200-500 ppm (0.2-0.5 ml/liter water) solution is applied all over tree.
After harvesting moisture is maintained to 8% for long term storage & shipping.
Mature tree age is of 10-12 years in case of grafted tree while in seedling developed tree it is 15-20 years. At this stage, 150-200 kg/plant is obtained. However, average production is 40-50 kg/plant.
- Trunk/Shoot Borer:
- Walnut weevil
- Codling moth
- Husk fly
- Foot & root rot
- Crown gall
- Walnut blight
Trainers manual, Temperate fruits, By M. Ranjit & L.Pun, DOA, Agri & MPDP-1990
Walnut production technology, M.K.Verma, IARI, New Delhi-110012