Causes of the 1999 yield reduction of Jin jujube in Ning County and the solutions
Jin jujube cultivation in Ning County, Gansu Province is concentrated in Zaosheng Town. In 1999, the bearing area was 100 hectares, with a total yield of 212.5 tons, which was 22.3 tons less than the average over the years, a reduction of 12.5%, making it a year with relatively poor yield in history.
I. Causes of the Jin jujube yield reduction
1. Severe jujube witches' broom disease: According to a survey conducted in Xinzhuang Village, Zaosheng Town, Ning County, before 1997 the rate of diseased plants of jujube witches' broom accounted for 3.98% of the total number of trees, and all diseased trees were fruit-bearing trees. By 1999, the number of trees with jujube witches' broom had risen to 1387, accounting for 10.05% of the total number of trees, which was 2.2 times that of 1997. Each year, about 2600 fruit-bearing trees in the whole town were cut down because of jujube witches' broom.
2. Rain damage during the flowering period: From April to June 1999, right during the flowering period of jujube trees, there were 3 periods of continuous low-temperature overcast and rainy weather lasting 4 days each. Among them, the second period of low-temperature overcast and rainy weather occurred from May 20 to 25, with rainfall reaching 198.5 mm and an average temperature of 22.5°C. Because the humidity in the early stage was rather low, the second-period flowers were delayed by 10 days compared with the average date, and the full-bloom period appeared from May 18 to 24. In addition to affecting pollination, rainfall caused mechanical damage to some floral organs by raindrops. After the rain, because the temperature rose sharply and transpiration intensified, the stigma, stamens and young leaves wilted, and the flower and fruit drop rate reached 88.5%.
3. Extensive management: Jujube growers in the jujube area have traditionally never applied fertilizer to jujube trees, let alone pruned them or controlled pests and diseases. The ground was managed only when intercropping crops were grown, resulting in not only low yield but also serious alternate bearing.
4. Single variety: The varieties in the jujube area of Zaosheng Town are all Jin jujube. This variety has weak pollen vitality and a relatively low fruit-setting rate.
II. Ways to increase yield per unit area
1. Scientific fertilization: In view of the characteristics of poor soil and weak fertilizer retention capacity in jujube orchards, fertilizer application should be concentrated and carried out in batches, and the amount should be large and the nutrients comprehensive. This is even more important for high-yield densely planted jujube orchards. For 3-5 year old jujube orchards, apply 35-40 kg of farmyard manure, 0.5-1.0 kg of superphosphate, and 0.3-0.5 kg of potassium. At the same time, after the jujube trees leaf out and after flowering and pollination, apply urea in time as a top dressing. The first application is in mid-to-late May, with 0.1-0.2 kg of urea per tree; the second is in mid-to-late June, with 0.3-0.4 kg of urea per tree; the third is in mid-to-late July, with 0.3-0.4 kg of urea per tree, to promote fruit enlargement and coloring. In addition, during the growing season, foliar fertilizer should be sprayed once every 20-30 days, for a total of 4-6 times. After the intercropped crops between the rows are harvested, the stalks should be returned to the field to improve soil fertility.
2. Reasonable pruning: The tree shape of jujube adopts a natural semi-round shape with multiple main branches. The trunk height is 80-100 cm, with 3-4 main branches, and each main branch is equipped with 2-5 side branches. In view of the problem that local jujube orchards have been left to grow for many years, resulting in a closed canopy, densely growing branches, and poor ventilation and light penetration, winter pruning is mainly to renew and rejuvenate the jujube heads so as to prolong their fruiting years, and focus on cutting off crossing branches, densely growing branches, drooping branches, diseased and pest-infested branches, and dead branches, while retaining vigorous branches, gap-filling branches, peripheral branches and slanting branches. For upright-growing shoots inside the canopy that have space, short cutting can be carried out to train them into fruiting branch groups. Through winter pruning, the number of new jujube heads per tree should be adjusted to 20-30. After sprouting, all dried branches that do not sprout should be cut off and burned in a concentrated manner.
Summer pruning is carried out from late May to late June. Promptly cut off excessive sprouts inside the canopy, and promptly cut off new shoots growing from jujube spurs and water sprouts sprouting from the base of jujube heads before the branches become lignified, so as to reduce nutrient consumption, increase the fruit-setting rate, and improve light conditions. In June, the jujube heads should be pinched. Weak branches should be lightly pinched, and strong branches should be heavily pinched or pinched multiple times to control the growth of jujube heads. After pinching, the development of secondary branches and jujube bearing shoots is strengthened, which has obvious effects on increasing the fruit-setting rate and promoting fruit development.
3. Preserving flowers and fruits: Releasing bees in the jujube orchard during the flowering period can reduce flower drop caused by lack of pollination or poor pollination. Spraying 10-15 PPM gibberellin once during the full-bloom period can increase the fruit-setting rate. It is also possible to spray 5-10 PPM 2,4-D during the flowering period and 30-60 PPM 2,4-D after flowering, which can increase the fruit-setting rate and reduce fruit drop. It is also possible to spray 0.1%-0.3% boric acid or borax during the flowering period, which can increase the fruit-setting rate. Measures such as girdling and ringing can also increase the fruit-setting rate.
4. Drought prevention and drought resistance: In extremely dry years, after sprouting, during the rapid fruit growth period, and in late autumn and early winter, combined with fertilization, the whole orchard can be irrigated 3-4 times, or during drought periods, combined with pesticide application, spray 400-500 times "Handilong" drought-resistant agent, or spray pesticide after drought for rescue. For the pesticide, 1.8% Aiduoshou 6000 times plus Lufenwei No. 1 or No. 2 1000 times can be selected for canopy spraying.
5. Loosening soil and weeding: In order to reduce soil fertility consumption, after each heavy rain or watering, loosen the soil when the ground surface turns white. Persist in hoeing whenever there are weeds in the tree disk to prevent weed overgrowth.
6. Strengthen the prevention and control of jujube witches' broom: Use the period after fruit harvest to strengthen management. Heavily apply superphosphate, eliminate weeds in and near the jujube orchard and dig out root-sucker seedlings, whitewash tree trunks, saw off diseased branches, drill holes in the roots of infected trees, connect rubber tubes, and inject or pressure-infuse 500 ml of 1000 PPM tetracycline or oxytetracycline into the tree body. Generally, carrying out this 2 times can reduce the severity of the disease.