What are the key technical points for protected cultivation of figs?

How are figs grown under protected cultivation? Fig protected cultivation techniques

Fund projects:Shandong Provincial Science and Technology Development Plan Project (2014GNC112007); Shandong Provincial Modern Agricultural Industry Technology System Fruit Tree Innovation Team Construction Project (SDAIT-06-19); Shandong Provincial Spark Science and Technology Demonstration Project (2015XH024).

1 Orchard establishment

Figs have strong adaptability to the environment, are tolerant of drought and poor soil, and are not demanding regarding soil. They can grow normally in ordinary sandy soil or sandy loam, but neutral sandy loam with deep soil layers and good water- and fertilizer-retention capacity is preferable. When establishing an orchard, choose a site sheltered from the wind and facing the sun; avoid waterlogged low-lying land and continuous cropping, and ensure drainage and irrigation are available.

For the protected structure, a solar greenhouse, plastic tunnel, or similar may be chosen to artificially create a special controllable microclimate that meets the needs of normal fig growth and fruiting, achieving the goal of producing high-quality fresh fruit. When forcing cultivation with less cold-hardy cultivars such as Masui Dauphine, choose a winter-warm solar greenhouse; when delayed cultivation is used with cold-hardy cultivars such as Qingpi and Bojihong, a plastic tunnel may be chosen.

The main limiting factor for open-field fig cultivation is low winter temperature. When the extreme minimum winter temperature falls below the cold-hardiness critical temperature of the cultivar, the aboveground parts of the plant suffer freeze damage. Therefore, if less cold-hardy cultivars such as Masui Dauphine are chosen for protected cultivation, the low temperature during dormancy should generally not be lower than -4°C; if more cold-hardy cultivars such as Qingpi and Bojihong are chosen, the low temperature during dormancy should generally not be lower than -7°C. Otherwise, after dormancy is completed in winter, the greenhouse should be covered early for cold protection.

2 Cultivation management techniques

2.1 Cultivar selection

For protected cultivation of figs, it is recommended to choose cultivars with attractive appearance, well-formed fruit shape, large fruit, good quality, and tolerance to pruning, such as Bojihong and Masui Dauphine. In trials, cultivars such as Jin'aofen, Meiliya, and Qingpi showed strong tree vigor and were prone to excessive vegetative growth, with poor overall performance.

2.2 Nursery stock preparation

Use high-quality 1- to 2-year-old vigorous hardwood cuttings. Requirements: seedling height >= 80 cm, trunk diameter >= 1.0 cm, root diameter >= 0.2 cm with no fewer than 6 coarse lateral roots, lateral root length >= 18 cm, no splitting of roots or trunk, and no shriveling of the bark.

2.3 Planting

Planting can be done from after leaf fall in autumn to the budbreak period in spring, that is, from mid-to-late November to mid-April of the following year. The specific planting time should be determined according to the construction progress of the cultivation facility. Generally, when the orchard is established first and the greenhouse is built later, spring planting is preferable, as it avoids freeze damage from autumn planting and ensures half a year of growth after planting, allowing delayed cultivation in the same autumn and ensuring that most autumn fruit ripens normally. If the cultivation facility is built in advance, then depending on the specific situation, spring or autumn planting can be carried out in the existing solar greenhouse or plastic tunnel, and after planting the plants can immediately enter protected forcing or delayed cultivation production.

Determine the suitable cultivation density and row orientation according to the facility type, cultivar, training system, soil fertility conditions, and orchard function (production orchard or pick-your-own orchard). Solar greenhouses run east-west; when using the single-arm horizontal tree form, an east-west row orientation may be used, with trellises built along the rows and a spacing of 1.5-2 m x 3 m. When using the open-center tree form, a north-south row orientation is mostly used, with a spacing of 1.5-2 m x 1.5-2 m (Figure 1). To facilitate management and harvesting, for the Bojihong cultivar, which has relatively good branch uprightness and whose fruiting branches during the growing season do not need trellis support and tying, north-south planting may be used, with a single-arm horizontal or open-center tree form. In the single-arm horizontal training, the two main fruiting mother branches can extend along the inter-row space, with a spacing of 1 m x 2.5-3 m. Plastic tunnels mostly run north-south, and seedlings are also planted in north-south rows.

Figure 1 Low-trunk open-center form of figs in a winter-warm greenhouse

Before planting, deeply plow the whole orchard area and apply sufficient organic fertilizer. Dig planting holes 60 cm square and apply 20 kg of farmyard manure in each hole; or dig planting trenches and apply 2000 kg of decomposed organic fertilizer per 666.7 sq m. When digging, place topsoil and subsoil separately; mix the topsoil with organic fertilizer and backfill it into the trench, then fill in the subsoil, then water thoroughly so that the backfilled soil settles, then fill the planting trench full and wait to plant the seedlings. At planting, hold the seedling trunk upright, spread the root system, fill soil while gently lifting the seedling, and finally firm the soil by treading. Water thoroughly after planting. Determine the trunk-training height according to the target tree form. Generally, the trunk-training height for the natural open-center form is 30-40 cm, and for the single-arm horizontal form it is 20-40 cm. The trunk-training height should gradually increase from south to north according to the planting position of the plants.

2.4 Time of covering and removing the greenhouse covering

Determine according to facility conditions and outside temperature. Protected forcing cultivation usually begins covering the greenhouse and raising the temperature after figs have completed dormancy and before the outside low temperature drops to -5°C. In the Weihai area, solar greenhouses generally do this from mid-January to early February around the Spring Festival. After early May, as long as the nighttime temperature is not lower than 15°C, the straw curtains or greenhouse quilts can be removed. After early June, when the open-field temperature can meet normal growth and fruiting needs, the greenhouse film can be removed. For protected delayed cultivation, after entering September, cover the greenhouse film when the minimum temperature drops to 15°C; later, as the temperature falls, add straw curtains or greenhouse quilts to ensure that most autumn fruit ripens normally, extending the harvest period to around early December, then open the ventilation openings to let the plants in the greenhouse enter dormancy.

2.5 Temperature and humidity control in the greenhouse

Forcing cultivation. ① Temperature-raising and bud-forcing stage. Within 15 days from the start of heating, properly control the greenhouse temperature to avoid too rapid heating and overly urgent bud forcing, which can cause fast aboveground growth while soil temperature is low and root activity is slow, with insufficient absorption capacity, leading to uneven sprouting. At this time, keep the daytime temperature at 15-20°C and nighttime at about 10°C. After 15 days, gradually raise the greenhouse temperature, with daytime temperature at 25-30°C, and add straw curtains or greenhouse quilts at night to keep the temperature at about 15°C. During the bud-forcing stage, the greenhouse humidity should be relatively high, with relative air humidity kept at 80%-90%. ② New shoot growth stage. Daytime temperature 25-30°C, nighttime 13-15°C. Relative air humidity 60%-80%. If the temperature is too high and humidity too great during the new shoot growth stage, new shoots will grow excessively, and the node position of the first fruit will rise. In production, attention should be paid to properly controlling temperature and water to avoid excessive new shoot growth, which can lead to a dense canopy and deterioration of light conditions. ③ Fruit enlargement stage. The maximum daytime temperature should not exceed 32°C; later, the greenhouse film can be gradually removed to enter open-field production mode.

Delayed cultivation. In mid-to-late September, before the minimum temperature drops to 15°C, cover the greenhouse film in advance; when the nighttime temperature is below 15°C, add greenhouse quilts for insulation. Control the greenhouse temperature so that the maximum does not exceed 32°C and the minimum is not lower than 15°C, with an optimum temperature of 20-30°C, to promote the ripening of most of the later autumn fruit.

2.6 Training and pruning

For protected cultivation of figs, a low-trunk open-center form or a single-arm horizontal form may be used.

Low-trunk open-center form (Figure 1). After the seedlings are planted, train the trunk at 30-40 cm to promote sprouting and shoot growth. Select 3-4 branches with ideal orientation angle and growth vigor as main branches; when they grow to 40-60 cm, pinch them severely to promote lateral branches. In the second spring, cut back the lateral branches to plump outer buds to expand the canopy. After 3 years, each year cut back the extension shoots of the main branches to promote vigorous branches, and prune out useless branches such as overly dense branches, clustered branches, diseased and pest-infested branches, aged branches, and dried branches. When fruiting branches age, severely cut them back at the base for renewal. During the growing season, new shoots with strong growth vigor may be pinched after leaving 22-26 leaves, to promote secondary lateral shoots bearing fruit, and through protected delayed cultivation promote the ripening of fruit on the secondary shoots to increase yield.

Single-arm horizontal form ("T" shape) (Figure 2). After the seedlings are planted, when the new shoots grow to 15 cm, keep 2 vigorous new shoots along the row and train them as main branches extending 180° in a single horizontal line toward the inter-row spaces on both sides, and remove all the rest. The extension direction and opening angle of the two main branches can be fixed with bamboo poles or iron wire, and the growth vigor of the two main branches should be kept as balanced as possible. At winter pruning in the same year, cut back by retaining about 2/3 of the branch length, leaving a plump lateral bud at the cut. In the following spring before sap flow (mid-April), set up No. 8-10 iron wire at about 20 cm above ground to tie the main branches. After the buds on the main branches sprout, select and keep sprouts alternately at 20 cm intervals as fruiting branches, and remove the remaining buds as early as possible. When the selected fruiting branches reach 1-1.2 m, set up a second layer of iron wire to guide and fix them. In summer, according to growth conditions, promptly remove root suckers and secondary shoots, and control growth vigor by pinching to promote fruit ripening. At winter pruning, the extension shoots of the main branches should be cut back at plump buds according to plant spacing to control them (based on adjacent main branches being close but not overlapping), and the fruiting branches on the main branches should be severely cut back at the base, retaining 1-2 buds, with the cut bud facing outward. Thereafter, at winter pruning each year, retain 1-2 buds on the fruiting mother branches and severely cut back to an outer bud. Alternatively, in the year of planting, allow the new shoots to grow naturally upward; before covering the greenhouse and raising the temperature, select branches with ideal orientation and growth vigor and train them flat in a single horizontal line. The later selection and retention of fruiting branches, growth management, and winter pruning are the same as above.

Figure 2 Single-arm horizontal tree form

2.7 Fertilizer and water management

Base fertilizer is generally applied from mid-to-late October to mid-November, mainly decomposed manure, with the application standard being 2 kg of fertilizer for every 1 kg of figs produced, plus a small amount of compound fertilizer. Topdressing is divided into early-stage topdressing and late-stage topdressing. From mid-April to early June is the peak fertilizer demand period; during this period, apply topdressing 1-2 times, mainly nitrogen-phosphorus-potassium compound fertilizer. From early July to early September is the fruit ripening and harvest period; topdressing may be applied 1-2 times, mainly phosphorus and potassium fertilizers, combined with trace elements or low-nitrogen high-potassium water-soluble flush fertilizer.

Figs are drought-tolerant and afraid of waterlogging, so excessive watering is not suitable. Generally, water once each during the new shoot growth period in mid-to-late March and after autumn base fertilizer application in mid-to-late October. After topdressing during the growing season, water moderately to maintain field relative water-holding capacity at 60%-80%. During the fruit ripening period, water as little as possible to avoid fruit cracking and fruit rotting. Where conditions permit, orchards may be equipped with drip irrigation and integrated water-fertilizer technology to reduce waste of fertilizer and water, alleviate soil compaction, and save labor. In rainy seasons, drain waterlogged areas promptly.

2.8 Pest and disease control

In the Weihai production area, pests and diseases occur little in fig cultivation, and spraying is basically unnecessary. In recent years, it has been found that two-spotted spider mites damage leaves and fruit in some protected cultivation orchards. For control, 25% azocyclotin wettable powder at 1500 times, or 34% pyridaben emulsifiable concentrate at 2000 times, or 1.8% abamectin emulsifiable concentrate at 2000-4000 times may be used.

2.9 Ripening period regulation

According to market demand, at the end of the fruit enlargement stage, when the fruit eye opens, the fruit top bulges, and the fruit skin color enters the initial color-turning stage (Figure 3), use edible vegetable oil such as peanut oil or rapeseed oil, dip a cotton swab with a little, and drip it into the fruit eye from the fruit eye, so that the fruit can be marketed 2-3 days earlier.

Figure 3 Dripping oil into fig fruit to promote ripening

2.10 Harvesting and packaging

For near-market sales, harvest when the fruit has fully changed color, is enlarged and soft, and shows the cultivar's inherent flavor; for external sales, fruit at the eight-tenths ripe stage, when the fruit is fully colored and fully enlarged but the skin is not yet soft, is preferable; early morning is the best harvest time. Figs do not store well, so promptly dissipate field heat and enter cold storage for pre-cooling, and market in small packages (about 2 kg).