Hengzhi HUO, Jinyu CHEN, Qingfeng ZHU, Chunyan WAN, Bingyi CHEN, Jinfeng LI, Lin MI

1. Zhenjiang Institute of Agricultural Science, Jurong 212400, China;

2. Huayang Street Agricultural Service Center, Jurong 212400, China;

3. Jurong Agriculture Committee, Jurong 212400, China

Shelf cultivation of strawberry with substrates mitigates farmers’ work load and improves work efficiency[1-2].The cultivation with substrates, for example, dramatically enhances fruit yield and quality besides activates roots[3-4]. Furthermore, the cultivated fruits are hanging, so that the fruits are clean,and free from pollution, attracting more customers to come to pick fruits.Therefore, it is a good project for green agriculture to advance cities in terms of sightseeing tour and picking fruits[5-7].

Nevertheless, the cultivated fruits hanging in the air are prone to being affected by temperatures. In winter,temperatures in the south of the Yangtze River in Jiangsu Province generally keep below -5 ℃, and it is hard for preventing flowers and fruits from freezing only relying on mediumsized or large greenhouses and some plants would even enter a dormant phase, affecting strawberry yield and quality. It is obvious that it is key for success of shelf cultivation with substrates to resolve the issue of heat preserving in winter. However, it is low carbon economy that matters in future, instead of heat preserving depending on consuming energies[8-9].Since 2011, experiments have been conducted on heat preserving based on shelf cultivation with mulch and natural energy.

Materials and Methods

Cultivation facility

The test was carried out in a strawberry orchard in Zhenjiang Institute of Agricultural Science. Specifically, a steel-framed greenhouse (70 m of length and 6 m of width) was divided into two halves. The treatment with substrate cultivation was conducted in a half of the greenhouse and the treatment with soil cultivation proceeded in the other as a control.The facilities of medium-sized and large greenhouses were available for both treatments. For the treatment with substrates, three shelves were constructed,and net height to the ground was 1 m.A u-shaped cultivation beds were paved with color steel tiles on the shelves, 40 cm wide, 25 cm high, andshelf distance of 80 cm.The cultivation substrates included fermented rice chaff, reed residue, highly-efficient organic fertilizer, and sandy loams, representing 60%, 30%, 5% and 5%, respectively. For ground cultivation, 6 ridges were constructed, with width of 90 cm and height of 30 cm.

Heat preserving methods

The temperature preserving in the treatment with substrates on shelves was carried out with transparent mulch covering on medium-sized and large greenhouses and thin films covering shelves. Specifically, when temperature dropped below 10 ℃, thin films were fixed with pipe clamps on cultivation beds, hanging in a u-shape under the cultivation beds, and the top of mulches was fixed with pipe clamps on fruit poles, and the other end was pressed with bricks. When temperatures reached the lowest in winter, hot water of solar hot water heater was transported to cultivation beds through drop irrigation for heat preservation.The heat preservation for the treatment cultivated on ground involved mulches in small, medium-sized and large greenhouses.The seedling cultivations on ground and shelves proceeded in the same greenhouse and ventilation and heat preservation were the same in medium-sized and large greenhouses.

Test design

Heat preserving with mulches/thin films On November 8, 2011, shelf temperature was preserved with thin films;5 treatments on shelves were arranged randomly and a ground treatment was set as a control. The treatments included treatment 1 where white mulches and black thin films were prepared, treatment 2 where black mulches and white thin films were prepared, treatment 3 where black mulches were used, treatment 4 where white mulches were used,treatment 5 where none mulches were used, and treatment on ground with ridges. Then, the temperatures of substrates in different depths, covering 5,10, 15 and 20 cm, and ground soils were measured on the locations in middle of cultivation beds of shelves and ridges on ground (similarly hereinafter). Meanwhile, the temperatures in mulches/thin films and in the greenhouses were measured accordingly.After three days of heat preserving with mulches/thin films on shelves,the temperatures were measured every 4 h from 6:00 am,for 72 h successively.

Heat preserving with natural energies On December 30, 2011, the minimal temperature outside reached below -5 ℃and water of solar heater was transported to cultivation beds.Besides, two treatments on shelves and a ground treatment were designed randomly, as follows: treatment 1 involving white mulch and black thin films, treatment 2 involving white mulch and black thin films, and water from solar heater, and treatment 3 involving ground ridging. Temperatures of substrates in the depths of 5,10,15 and 20 cm and ground soils were measured accordingly. Besides, temperatures in mulches/thin films of treatments 1 and 2 and of shelves were measured every 4 h from 6:00 am,for 72 h successively.

Results and Analysis

The effects of heat preserving with mulch/thin films on substrate temperatures in different depths

As shown in Fig.1-Fig.4, the temperatures in the treatment with white mulches and black thin films kept higher compared with rest treatments in different times or depths, which averaged 18.4 ℃in the depths of 0-20 cm, 1.5 ℃higher compared with both of the treatment with black mulches and white thin films, and the treatment with black mulches, 1.8 ℃ higher compared with white mulches, 2.6 ℃higher compared with the treatment without mulches or thin films, and 2.2℃higher compared with the treatment cultivated on ground. The results indicated that the treatment with white mulches and black thin films performed the best in heat preserving.

The effects of heat preserving with mulch/thin films on the temperature in mulches

As shown in Fig.5, temperatures in the treatment with white mulches and black thin films kept significantly higher after 14:00 compared with rest treatments. The temperatures of the treatment with white mulches and black thin films averaged 17.6 ℃,which was 1.5 ℃ higher compared with inner mean temperature of black mulch and white thin films and inner mean temperature of black thin films,2.0 ℃ higher compared with inner mean temperature of white thin films,and 2.8 ℃higher compared with exterior temperature. The results suggested that the growth of temperatures in mulches or thin films is conductive toincreasing of substrate temperatures,showing positive correlation.

Effects of natural energy-based heat preservation on temperature of substrates with different depths

As shown in Fig.6-Fig.8,after irrigation at 17:00 with transported hot water from solar energy, substrate temperatures were significantly higher from 18:00-6:00 in the treatment with white mulches and black thin films in the depths of 5,10,15,and 20 cm,respectively, compared with rest treatments.

Substrate temperatures in the treatment with white mulches and black thin films depending on hot water transported by solar energy averaged 12.3 ℃in the depths of 0 -20 cm,which was 1.5 ℃ higher compared with the treatment with black mulches and white thin films, and 0.7 ℃higher compared with ground cultivation. The results indicated that the treatment with white mulch and black thin performed the best.

Effects of natural energy-based heat preservation on temperatures in mulches/thin films on shelves

As shown in Fig.10, the temperature in the treatment with white mulches and black thin films kept higher compared with rest treatments after 17:00; the mean temperature of the treatment reached 10.9 ℃, which was 1.6 ℃higher compared with the treatment with that of black mulch and white thin films, and 2.6℃ higher compared with exterior temperature.The results indicated that when substrate temperature in the treatment with white mulch and black thin films irrigated with water from solar energy grew, the temperature in mulches/thin films grew, showing positive correlation.

Conclusions and Discussions

The test incorporated that the treatment with white mulches and black thin films performed the best in heat preservation, because the lack ground mulches play the role of heat absorbing and white thin films play the role of heat preservation. If temperatures keep lower outside in winter, hot water can be transported by solar energy to increase and maintain inner temperatures.It is obvious that both of increasing inner temperatures in mulches/thin films and substrate temperature would preserve heats, showing positive correlation.

Based on heat preservation methods above, it is feasible to overcome the difficulty of heat preservation in winter, which lays foundation for strawberry growth in terms of yield and quality in winter, and provides supports for large scale cultivation of strawberry on basis of substrates on shelves.

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