Control temperature of greenhouse for higher yield and higher quality grapes production by combining STB in situ service with on time sensor monitoring

Abstract

The use of plastic film to promote early cultivation is common by small farmers in Northern China for out of season facility fresh grape production, but the lack of effective technical indicators, sensors and temperature control techniques for facility temperature management has resulted in high cost and low yields. To explore effective ways of enhancing grape yield and quality through temperature monitoring and precise temperature control by sensors under the current plastic covering systems of small farmers. By providing a resident service in the Science and Technology Backyard (STB) and using intelligent sensors to monitor and manage the temperature in small farmers' facilities in real-time (on an hourly basis). We found that the phenological and effective accumulated temperature in plastic film-covered facilities was significantly different from those in open field cultivation, with a 15.9% advance in the phenological process and 19.5% reduction in effective accumulated temperature requirements, as well as a 51.4% increase in effective accumulated temperature requirements during the vegetative stage. In the case of the delay in temperature regulation of the plastic film cover system, it is necessary to control the minimum temperature and high temperature to match the effective accumulated temperature demand. By installing the Pycno temperature sensor, using units of minutes, accurately monitoring the temperature changes inside and outside the facility, and deploying smoke to prevent low temperature and open the air outlet to control the high temperature at the right time, plastic film can reduce the proportion of effective accumulated temperature distribution during the vegetative stage by 3.2% and reduce the vigorous growth of new shoots by 22.2%. The result had shown 40.2% increase in spike weight and 30.1% increase in yield. By combining real-time sensor monitoring with grape growth and development indicators, we have quantified the difference in effective temperature requirements between the vegetative and reproductive growth periods of grapes in current smallholder plastic cover systems and open field cultivation systems. By combining sensor monitoring and technical services in a precise manner, the production of grapes in facilities under smallholder plastic cover systems can also achieve smart agriculture and gain yield and quality improvements.

1. Introduction

China produces 46.3% of the world's fresh grapes [1,2], by using facility-based cultivation methods on 26.6% of the grape-producing area. By regulating the temperature of the facilities, it is possible to ripen the grapes at times when the outside temperature is not suitable. Recently it has become a common way of producing fresh grapes in grape's non-growing season in China as one of the coping techniques used to compensate for the unsuitability of the external climate [[3], [4], [5]]. With the development of greenhouse structures and equipment materials, the Netherlands and North-Western European Countries are mainly developing Venlo-type modern greenhouses and plant factories [6]. Modern greenhouses and precise temperature control can be used in the Northern hemisphere to advance the ripening of “Flame Seedless” grapes to the beginning of June [7]. However, the cost of building a glass greenhouse is high about 668.06 yuan/m² [8] which is not affordable for small farmers. In China, nearly 2,917,300 hm² of facilities are covered mainly with cheap plastic film, accounting for 63.42% of the total area of facilities and only 5.24% of the investment in glass greenhouses [9], and these facilities are able to achieve a 1 month earlier maturity than open-field cultivation, with a significant 1.2-fold increase in economic efficiency [10]. However, it was found that this plastic cover system leads to a decrease in yield and quality compared to open field cultivation [11], with high resource and environmental costs. The water use efficiency under flood irrigation was about 3–4 kg/m³, while the fertilizer use efficiency with flooding was about 31.0%, 5.26%, and 48.7% for N, P, and K [12], because the current facility cultivation mainly follows the management method of open field cultivation [13], the temperature decision-making indicators in facility production are not suitable, and the blind artificial control of temperature leads to a decrease in fruit set rate [14,15]. To improve yield and quality, farmers blindly overinvest in water and fertilizer to “feed” the grapes, which in turn leads to excessive branching and nutritional disorders, exacerbating the loss of yield and quality [16].

There is a consensus that temperature is the most critical environmental factor driving the process of vegetative and reproductive growth in grapes [17,18]. The sensitivity of grapevine growth to temperature changes makes it possible and meaningful to regulate growth through temperature in facility production, and the phenological process and growth development of grapes are all affected by temperature changes. The study had shown that the average temperature in the European vineyard had increased by 1.2–1.4 °C over the last 40 years, leading to production area expansion suitable for grape cultivation to the higher latitudes of the North and South as well as advancement of the phenological period by 6–25 days for different varieties. The average times for bud break, flowering, veraison, and harvesting were 10, 15, 15, and 25 days earlier [19,20], and the average European temperature increase of 1 °C shortened the phenological period length by an average of 3–6 days [21,22]. This is also reflected in the significant advancement of the phenological stage in facility production by increasing the temperature through the cover film, but it is not clear whether the phenological process varies with temperature in facilities in the same way as in open field cultivation. Grapes also require a suitable temperature range for growth and development, and irreversible damage can occur when temperatures are above or below the critical level for grape tolerance. Studies have shown that dormant grape shoots can tolerate temperatures of −15 °C, but after bud break to flowering, young leaves experience temperatures below −1 °C, and shoots are susceptible to frost damage or even death if they experience temperatures of -3-4 °C [23,24]. Smallholder farmers generally sprout their grapes in February–March, when outside temperatures remain low and farmers often prevent frost damage through smoke fumigants, however, smallholder farmers are limited by untimely temperature monitoring inside and outside the facility, making it difficult to effectively use temperature regulation in production. It has been found that the optimum temperature for grapes is 25–35 °C [25]. High temperatures above 35 °C produce physiological stress, reduce photosynthetic rates, and when the temperature rises from 25 °C to 45 °C, the average photosynthetic rate is suppressed by 60% [26]. In addition, temperatures above 40 °C can cause irreversible damage to the core proteins of the photosynthetic system (PS II) of the leaf by inactivating them. In traditional facility production, grapes are often exposed to heat stress caused by temperatures over 40 °C due to the farmer's lack of knowledge of scientific temperature regulation.

The temperature affects grape growth and yield quality by influencing effective accumulated temperature, and the central issue in facility production is the coordination of vegetative and reproductive growth. Different studies had shown that warming in the context of climate change causes a reduced time between flowering and fruit ripening (reproductive stage). Increased competition for nutrients between vegetative and reproductive growth causes an imbalance in the sugar-acid ratio and a decrease in the number of aromatic substances in the fruit [20]. Higher temperatures also cause an acceleration of vegetation growth in the leaf and stem organs, with excessive branching bringing wasted nutrients and poor veraison due to insufficient nutrient accumulation in the fruit. In addition, higher temperatures were also reflected in a reduction in day/night temperature differences, with research showing that an average temperature increase of 1.7 °C during the growing season and minimum and maximum temperatures of 1.9 °C and 1.8 °C for day and night, respectively [21], causing a reduction in day/night temperature differences and decreased sugar accumulation in the berries at maturity. Compared to open field cultivation, facility cultivation has a 3% lower total sugar content, 7% lower soluble solids content, and lower quality than open field cultivation, mainly because the current smallholder production system which relies on farmers’ experience to control temperature cannot match the changes in weather conditions and crop demand. Compared to open-field cultivation, the leaf area of grapes in facilities increased by 10.8% [27], the length of new shoots by 5.67%, and the leaf area index by 20.6% [11], resulting in excessive nutritional growth-inhibiting reproductive growth and thus reducing yield and quality. Therefore, it is important to regulate the temperature of grapes to avoid physiological stresses caused by too high or too low temperatures and to ensure yield and quality by coordinating vegetative and reproductive growth through temperature control.

This study focuses on the lack of temperature monitoring and regulation in the production of typical smallholder grapes in northern facilities and uses intelligent sensors to monitor and regulate the low and high temperatures of grapes in traditional smallholder production systems through the Science and Technology Backyard to explore the effects of the phenological process and low and high-temperature control optimization on the accumulated temperature and growth, development and yield quality of grapes in facilities, aiming to make recommendations for temperature regulation and accumulated temperature management in current smallholder production systems.

2. Materials and methods

2.1. Trial sites and crop management

This study was carried out at Dezhong Vineyard, Quzhou County, Handan City, Hebei Province, China (36°48′22.7″ N, 114°59′35.3″ E), a northern facility for early cultivation, on clayey soil with 12.3 g kg⁻¹ organic matter, 1.43 g kg⁻¹ total N, 86.1 mg kg⁻¹ effective phosphorus, 614 mg kg⁻¹ fast-acting potassium and a pH of 8.2. In the present study, the vines of the “Flame Seedless” variety were planted in 2015 at a spacing of 2 × 0.7 m and were grown according to local practice in 5 m high arched greenhouses with a mixed bamboo and iron frame covered with 0.08 mm polyolefin (PO) film with a light transmission rate of 85%. The trial was divided into 3 plots (166 × 18 m each), with 2 located under greenhouse structures and set up as farmer traditional management (FM) treatments and optimized management (OPT) treatments and the other being open-air traditional management (OFM). Pruning was slightly different between the open-field and facility cultivation, with the facility cultivation being pruned in mid-November and the open-field cultivation being pruned in mid-December, keeping the same amount of pruning, with the exact amount of branches and buds left in place as shown in Table 1. The greenhouse has 2 side vents (East and West, 1 m wide) and 1 roof vent (Southnorth, 1.5 m wide), the opening and closing of which is controlled manually. According to the farmer's cultivation plan, the FM treatment and the OPT treatment use the medicament (cyanamide) to break grape dormancy on 20 January. This is a common way to break dormancy in facility cultivars and has been applied frequently on fruit trees such as grapes, kiwis and apples [[28], [29], [30]]. The methods were to close the air vents, add two layers of 0.01 mm polyethylene film to the shed for warmth and apply a 2% concentration of cyanamide. The grapes in open field cultivation were buried on November 20, 2018 to protect them from the cold and dug up on March 20, 2019 without artificial dormancy breaking. Irrigation and fertilization were identical for all 3 treatments, and water and fertilizer were adequately supplied. Only the FM and OFM treatments set different regulation standards for temperature regulation, as shown in the table below.

Table 1.

Differences in temperature control measures between the 3 treatments.

Plant management	OFM	FM	OPT
Winter pruning	A total of 8–10 canes per vine, with each bearing 3 buds; each vine also bearing 2 spurs to form new canes as the replacement for the production of next year's yield.
Summer pruning	Only one leaf was left on the side shoot of all summer buds and then removed. Tendril was also removed, and the tip of the new shoot was removed before flowering.
Use a smoke agent to prevent freezing injury	no	traditional experience	In situ monitoring and ensuring that the minimum temperature in the breaking and budding stage is higher than 2 °C and that the minimum temperature in the leaf growing stage is higher than 3 °C.
High-temperature prevention	no	traditional experience	Timely monitoring and ensuring that the maximum daily temperature does not exceed 35 °C.

2.2. Monitoring and technical services

The Science and Technology Backyard (STB) is an integrated platform for technological innovation, knowledge transfer, personnel training and agricultural transformation towards sustainable intensification.STB professors, graduate students and extension staff live and work with smallholder farmers in rural areas. They identify problems that limit sustainable agriculture and provide smallholder farmers with systematic, integrated and holistic solutions without time lags, constraints, costs and distances [31]. The STB students began a permanent residency at the vineyard in April 2018 and carried out technical services based on theoretical knowledge of practical production problems. During this study, a TERRA sensor from the company Pycno (UK) was installed in the middle of the three test plots in November 2018 to achieve temperature regulation (Fig. 1). The sensor continuously monitors and records temperature data every 15 min on average, allowing accurate monitoring of the temperature in the facility. The STB student optimizes the temperature control in the OPT treatment greenhouse through real-time sensor feedback, including minimum temperature prevention through smoke fumigants and timely air venting to control maximum temperatures, while the FM and OFM treatments only install sensors to monitor temperatures without intervention, as detailed in section 2.1. In addition, the three treatments were monitored and recorded by STB students for the duration of the phenological period (Table 2), and fixed dates were chosen to determine the new shoot length, the 3rd internode thickness, and the SPAD value of the leaves at the spike position for the OFM and OPT treatments, and to determine the yield, the weight per spike, the soluble solids, the titratable acid content, and the vitamin C content after maturity.

Fig. 1.

System demonstration of intelligent sensors to regulate the temperature of smallholder greenhouses.

Table 2.

Timing of different treatment phenological periods.

Phenological	dormancy begin	dormancy break	bud break	Leaf growth	Flowering	Fruit set	Fruit development	veraison	harvest
FM	2-Nov-2018	20-Jan-2019	28-Feb-2019	8-Mar-2019	17-Apr-2019	25-Apr-2019	17-May-2019	9-Jun-2019	22-Jun-2019
OPT	2-Nov-2018	20-Jan-2019	28-Feb-2019	8-Mar-2019	17-Apr-2019	25-Apr-2019	17-May-2019	9-Jun-2019	22-Jun-2019
OFM	2-Nov-2018		3-Apr-2019	10-Apr-2019	12-May-2019	17-May-2019	26-May-2019	28-Jun-2019	5-Aug-2019

3. Results

3.1. Differences in accumulated temperatures and phenological periods between facilities and open fields

• 1)Differences in phenological periods

The smallholder facility production system uses the simplest insulation materials for early cultivation purposes, as shown by the results of the 2019 study on phenological monitoring through the small science and technology yard residency (Fig. 2). Compared to the OFM treatment in open field cultivation, the FM and OPT treatments under facility cultivation ripened 44 days earlier, mainly due to differences in the duration of the different phenological stages. Both the FM and OPT treatments, which were manually broken from dormancy on 20 January and covered with three layers of plastic film to raise the temperature, reduced the dormancy stage by 34 days compared to the OFM treatment in open field cultivation and reduced the phenological periods of fruit development and veraison by 10 and 25 days, respectively. However, the four periods of bud break, leaf growth, flowering, and fruit set times showed increases of 1 day, 8 days, 3 days, and 13 days, respectively.

Fig. 2.

Comparison of OFM, FM, and OPT treatment phenological processes.

• 2)
  Differences in accumulated temperature

The difference in phenological performance between the facility and open field cultivation is a factor of change in the growth process due to the difference in accumulated effective temperature. Through precise sensor monitoring of the temperature, every 15 min for both facility and open field conditions, the accumulated effective cumulative temperature at each phenological stage was obtained for the FM treatment under facility cultivation and the OFM treatment under open field cultivation in 2019 (Fig. 3). Management practices remained consistent between the 2 treatments, except for the time of rising temperature. Facility cultivation for farmer temperature management (FM treatment) achieved maturity by covering plastic film with 19.5% less accumulated effective cumulative temperature than open-field cultivation (OFM treatment). Compared to the OFM treatment, the FM treatment showed an effective cumulative temperature higher increase of 1.22 °C at the dormancy stage, 45.9 °C at the budbreak stage, 149.3 °C at the leaf growth stage, 26.3 °C at the flowering stage, and 115.0 °C at the fruit set stage. However, from the onset of fruit development, the facility cultivation showed a significantly shorter reproductive growth period, resulting in the FM treatment having 205.0 °C and 486.3 °C lower effective cumulative temperatures during fruit development and during veraison than the OFM treatment respectively. The FM treatment had resulted in an increase in effective cumulative temperature from 18.9% to 36.0% during the vegetative growth period and a decrease in effective cumulative temperature from 81.1% to 64% during the reproductive growth period in the original open field cultivation pattern by covering the film.

Fig. 3.

Comparison of effective cumulative temperature accumulation by phenological stage for the OFM, FM, and OPT treatments.

The OPT treatment was zoptimized based on the FM treatment for minimum and maximum temperatures, and a comparison of the effective cumulative temperatures at different phenological periods showed that the differences in effective cumulative temperatures were significant although the timing of the phenological periods was the same for the 2 treatments. Compared to the FM treatment, the effective cumulative temperature decreased by 92.03 °C (6%) throughout the phenological periods, including 4.91 °C (27.8%) during dormancy, 11.22 °C (17.5%) during dormancy break, 6.43 °C (8.7%) during bud break, 56.57 °C (14.6%) during leaf growth, 3.47 °C (3.7%) during flowering, 13.45 °C (5.3%) during fruit set, but increase 2.12 °C (0.6%) during fruit development, 1.90 °C (0.9%) during veraison revealing that OPT reduces the effective accumulated temperature of the vegetative growth period more.

3.2. Analysis of the difference in temperature control and cost between OPT and FM treatment

• 1)Differences in freezing injury prevention

Smoke fumigant insulation in facility cultivation is a common measure used to prevent frost stress in young shoots and newborn leaves by increasing smoke particles in the air, reducing radiation emanation from the ground to preserve temperature, and raising the minimum night time temperature. FM and OPT treatments were administered for low-temperature prevention 20 days after the dormancy break (starting on February 9, 2019 in the trial year). In this trial, the FM treatments relied overwhelmingly on experience and perception of body temperature, with a total of 10 applications of the smoke fumigant, divided into two applications during the dormancy break (10 February and 17 February), one application during the bud break (7 March) and seven applications during the leaf growth period (19 March, 21–23 March, and 29 March-31 March). The OPT optimization treatment in this trial set a daily minimum temperature threshold of 2 °C for dormancy break and bud break, depending on the low-temperature tolerance threshold (−3 °C to −4 °C for shoots and −1 °C for young leaves), which was monitored in real-time by sensors, and fumigant application started when the daily minimum temperature was below 3 °C. In practice, it was found through sensor monitoring data (Fig. 4a) that the cumulative external temperature during the dormancy break period (9 February to 27 February) was below 2 °C for 259.4 h, while the temperature below 2 °C in the facility cultivation in the FM treatment and OPT treatment was 6 h and 10.4 h (Fig. 4b). The accumulated number of hours during the bud-break period when the external temperature at below 2 °C was 36 h, while the temperature in both the FM and OPT treatments was above 2 °C (Fig. 4c). The cumulative number of hours that the external temperature at below 3 °C during the leaf growth period was 98.2 h, while the temperature at above 3 °C for both the FM and OPT treatments (Fig. 4d). The results show that only the dormancy period truly needs to be fumigated to prevent low temperatures in the facility, and neither the bud-break nor the leaf growth period needs to be fumigated. The OPT treatment raised the temperature with smoke fumigants only on 9 February and 16 February, which was sufficient to keep the facility temperature above the threshold and was very accurate. The FM treatment, on the other hand, used eight more ineffective insulation measures.

Fig. 4.

Comparison of daily minimum temperatures and cumulative hours below the threshold during the hypothermia prevention phase.

• 2)
  Difference in high temperature prevention

(Note: (a) shows the comparison of the daily minimum temperatures of the three treatments during the low-temperature prevention stage; (b), (c), and (d) show the cumulative number of hours below the threshold temperature for the three treatments during the dormancy breaking, budding and leaf growth stages.).

The accumulation of temperature in facilities has a direct impact on the growth of new shoots, but excessive temperatures can also cause stress to grapes. To avoid heat stress, the 35 °C upper limits for the optimum temperature for grape growth was chosen as the heat threshold indicator. Starting at the bud break period (28 February), the top air vents of the OPT treatment facility shed were artificially opened and closed by the STB students through an accompanying service. The maximum daily temperature of the OPT treatment was controlled according to the sensor temperature data which is below 35 °C. The FM treatment operated according to the farmer's experience in temperature control. A comparison of the daily maximum temperatures from bud break to flowering showed that the average temperature outside the facility during the bud period (28 February - 7 March) was 18.4 °C, with the maximum temperature reaching only 20.62 °C. The maximum temperature in the FM and OPT treatments in the facility was already over 35 °C (Fig. 5a). The FM treatment exceeded 35 °C for a total of 5 days on 1 March, 3–4 March and 6–7 March for a duration of 14.5 h, whereas the OPT treatment with temperature control was above 35 °C for a duration of 2 h only on 1 day, 3 March (Fig. 5b). The average external temperature during the new growth period (8 March-16 April) rose to 23.8 °C, and the maximum temperature reached 33.3 °C. The maximum temperature in the facility was above 35 °C for 17 days and 47.6 h for the FM treatment and 7 days and 11.9 h for the OPT treatment (Fig. 5c). Although the OPT treatment did its best to control the temperature at all times, there was a lagging effect in the temperature change of this plastic-covered facility; e.g., from 24 March to 26 March, the maximum outside temperature rose from 25.5 °C to 33.3 °C. The OPT treatment did not effectively reduce the temperature inside the shed by opening the air vents at the scheduled time of 8 a.m., resulting in a maximum temperature of over 35 °C at 2 p.m. Therefore, from 27 March, the air vents were opened at 7 a.m., and the maximum temperature for the OPT treatment on that day was 34.7 °C, while the FM treatment exceeded the threshold of 37.6 °C. During the flowering period (17 April - 24 April), the average temperature reached 25.6 °C, and the maximum temperature was 31.9 °C due to a steady rise in external temperatures. The maximum daily temperature in the FM and OPT treatments in the facility was above 35 °C for 2.3 h and 2.7 h (Fig. 5d), even though the artificial opening and closing of the top plastic air vent at 7 a.m. was no longer able to regulate the temperature in the facility to within safe values.

Fig. 5.

Comparison of daily maximum temperatures and cumulative hours above the threshold from the bud break to the flowering stage.

• 3)
  Cost-effectiveness analysis

(Note: (a) shows the comparison of daily maximum temperatures for the three treatments at the heat prevention stage; (b), (c), and (d) show the cumulative number of hours above the threshold temperature for the three treatments at the bud break, leaf growth, and flowering stages.).

The cost inputs for the FM and OPT treatments in temperature management are shown in Table 3. Based on a facility size of 166 m × 18 m, each freezing injury prevention requires 4 bags of smoke agent at a cost of 60 yuan. The sensor equipment has a life of 8 years, which translates into a hardware cost of 77.4yuan per year for the OPT treatment in combination with the total planted area of 33 ha. Each treatment has the same labour cost for the high temperature prevention phase. This is due to the fact that the wind vents are opened in the morning for all treatments, but at different times. The results showed that compared with the FM treatment, the OPT treatment reduced costs by 1522.6 yuan ha⁻¹.

Table 3.

Different treatment cost analysis.

Treatment	Cost(yuan/ha−1)				Total
	Smoke Agent cost	Times of use	Sensor cost	labour cost
FM	200	10	/	/	2000
OPT	200	2	77.4	/	477.4

3.3. Analysis of differences between the OPT and FM treatments for the soil moisture consumption

Through continuous monitoring of soil water consumption of 20 cm and 40 cm (Fig. 6a and b).The analysis showed that the FM and OPT treatments had different water consumption at different depths (20 cm and 40 cm), although the amount and timing of irrigation was the same. Analysis of the vegetative and reproductive growth stages revealed that the trends in soil water consumption during the dormancy break and budbreak periods were similar between the FM and OPT treatments. The FM treatment had higher water consumption than the OPT treatment on 17 March and 30 March during the leaf growth period, which means that the high temperature in the FM treatment caused stronger water consumption at 20 cm in the soil. One reason is that high temperatures lead to excessive nutritional growth and the transpiration pull of the stems and leaves promote the uptake of large amounts of water by the roots for nutritional growth, while another reason may be that high temperatures lead to increased soil evapotranspiration and enhanced water dissipation from the soil surface. The FM treatment showed stronger changes in water consumption than the OPT treatment on 24 April at flowering, 14 May at fruit set and 24 May at version, with excessive nutrient growth leading to rapid soil water consumption, exacerbating the supply conflict between water availability and grape growth.

Fig. 6.

Changes in soil moisture stress in FM and OPT treatments (20 cm and 40 cm).

(Note: (a) shows the soil water consumption of 20 cm at each prevention stage; (b) shows the soil water consumption of 40 cm at each prevention stage.).

3.4. Effective accumulated temperature distribution and the deployment of vegetative and reproductive growth

The response of grape shoot growth to temperature is very sensitive. Temperatures that are too high during the vegetative growth stage in the facility can easily cause elongation of the new shoots and affect the source and reservoir relationship between branches and leaves and fruit, thus reducing fruit yield and quality. Therefore, in traditional cultivation, strong heart removal is carried out at flowering to promote the transfer of nutrient supply from branches and leaves to fruit, but excessive nutrient growth in the early stages leads to an increase in the amount of branches and leaves removed, which affects the accumulation of nutrients in the fruit. By intervening in the minimum and maximum temperatures of the OPT treatments with the STB in-residence service, especially the control of the maximum temperature, the effective accumulated temperature by the FM and OPT treatments at different stages of vegetative and reproductive growth was altered. In this experiment, the dormancy, budbreak, and leaf growth stages were used as vegetative growth stages, and the flowering, fruit set, fruit development, and veraison stages were used as reproductive growth stages for visual analysis. Using the daily average temperature to calculate the effective accumulated temperature, the cumulative percentage of effective accumulated temperature in the FM treatment during the vegetative stage and the reproductive stage was 36.0% and 64.0% while the cumulative percentage of effective accumulated temperature in the OPT treatment during the vegetative stage and reproductive stage decreased to 32.8% and then increased to 67.2% through temperature control respectively (Fig. 7a). By analyzing the effective temperature accumulation time at temperatures above 10 °C, we found that the effective temperature accumulated 713.2 h during the vegetative growth stage outside, while through facility cultivation the FM treatment accumulated 1421.6 h, the temperature-controlled OPT treatment accumulated 1328.1 h (Fig. 7b), and the outside effective temperature accumulated 1489.9 °C during the reproductive growth stage. The facility FM treatment accumulated 1592.6 °C, while the OPT treatment accumulated 1595.9 h (Fig. 7c). It is clear that by controlling the maximum temperature, the STB Companion Service effectively avoids excessive nutrient growth due to excessive accumulation of temperature during the vegetative growth period without affecting the accumulation of temperature during the reproductive growth period.

Fig. 7.

Effective accumulated temperature by phenological stage in FM and OPT treatments and the number of hours of effective temperature accumulation in the three treatments.

(Note: (a) shows the accumulation of effective accumulated temperature by phenological stage for FM and OPT treatments; (b) and (c) show the cumulative hours of effective temperature above 10 °C for the external, FM, and OPT treatments at the vegetative and reproductive growth stages.).

3.5. Analysis of the difference in physiological processes between OPT and FM treatment

As a typical representative of the vine, the length and thickness of new shoots are key indicators of the vegetative growth stages of the grape. Leaf chlorophyll content represents the ability of a plant to receive solar light for exchange of material energy and is monitored in this study by leaf SPAD values. Changes in fruit equatorial diameter during the reproductive growth stage represent the rate of fruit expansion and reflect the process of fruit growth and development.

A high temperature tends to lead to a rapid increase in the length of new shoots and an increase in nodal spacing. By reducing the effective accumulated temperature distribution during the vegetative growth stage, there was a significant change in new shoots length between the OPT and FM treatments during the leaf growth period (Fig. 8a). In particular, from 8 March to 31 March, the cumulative number of hours with temperatures above 35 °C was 39.8 h lower in the OPT treatment than in the FM treatment by controlling the maximum temperature (Fig. 8c). The cumulative hours of effective cumulative temperatures greater than 10 °C were reduced by 50.8 h (Fig. 8b). As a result, new shoot stem length growth was lower in the OPT treatment than in the FM treatment from 23 March onwards, reducing the phenomenon of new shoot growth and showing a significant difference after 27 March, with a significant reduction of 22.2% in new shoot growth (p＜0.05). New shoots thickness was significantly higher in the OPT treatment than in the FM treatment on 20 May (p＜0.05), but not significantly different at other times (Fig. 8d). The comparison of leaf SPAD values (Fig. 8e) shows that there was no significant change in leaf SPAD values although the OPT treatment regulated the maximum temperatureindicating that the control by high temperature did not cause a reduction in new leaf growth and photosynthesis but rather regulated the stem length of new growth through the regulation of the maximum temperature and promoted the timely transfer of nutrients to reproductive growth. Fruit equatorial diameter was significantly higher in the OPT treatment than in the FM treatment (Fig. 8f) on 20 May, 3 June and 25 June (p＜0.05). No significant differences were found only on 18 June. The temperature optimization reduced the length of the new shoots and thus promoted rapid fruit development.

Fig. 8.

Comparison of changes in new shoot length, new shoot thickness, leaf SPAD and fruit equatorial diameter between FM and OPT treatments.

(Note: (a) shows the new shoots length for FM and OPT treatments; (b) shows the cumulative hours of effective cumulative temperatures above 10 °C from 8 March to 31 March; (c) show the cumulative number of hours with temperatures above 35 °C from 8 March to 31 March; (d) show the new shoots thickness for FM and OPT treatments; (e) show the leaf SPAD value for FM and OPT treatments; (f) show the fruit equatorial diameter for FM and OPT treatments).

3.6. Yield and quality comparison between the OPT and FM treatments

Through the temperature regulation of vegetative and reproductive growth, the OPT treatment was significantly better than the FM treatment in terms of yield and quality. In terms of yield, the OPT treatment showed a significant 32.4% higher than the FM treatment on single fruit weight (Fig. 9c) and further contributed to a significant difference between panicle weight and yield, with the OPT treatment showing a significant 40.2% higher panicle weight than the FM treatment at 286 g (Fig. 9a). The OPT treatment showed a significant 30.1% higher yield than the FM treatment (Fig. 9d). However, there was no significant difference in mature spike number (Fig. 9b). In terms of fruit quality, the OPT treatment showed a significant 15.1% reduction in titratable acid content compared to the FM treatment (Fig. 9f), while soluble solids (Fig. 9e), solid to acid ratio(Fig. 9g), and vitamin C content (Fig. 9h) did not show significant differences.

Fig. 9.

FM and OPT treatment yield and quality comparison.

(Note: (a) shows the panicle weight for FM and OPT treatments; (b) shows the mature spike number for FM and OPT treatments; (c) show the single fruit weight for FM and OPT treatments; (d) show the yield for FM and OPT treatments; (e) show the soluble solids for FM and OPT treatments; (f) show the titratable acid content for FM and OPT treatments; (g) show the solid to acid ratio for FM and OPT treatments; (h) show the vitamin C content for FM and OPT treatments.).

4. Discussion

4.1. Effectively accumulated temperature requirements and characteristics of grapes in facilities

The effective accumulated temperature requirement for grapes in plastic film-covered facilities is lower than that in open-field conditions. Alonso [7] estimated the accumulated temperature for the “Flame Seedless” variety under facility production and open field cultivation conditions to be 1542 °C and 1633 °C, respectively, and the effective accumulated temperature for the FM treatment in facilities and the OFM treatment in open field cultivation in this trial year was 1481.7 °C and 1835.3 °C. The slight difference in the calculations is because Alonso used a lower threshold of 5 °C to calculate the effective accumulated temperature from sprouting, whereas this experiment used a lower threshold of 10 °C to calculate the effective accumulated temperature from dormancy, but both showed a lower effective accumulated temperature requirement and earlier maturity in the plastic film covered facility compared to open field. Fraga [19] found that the increase in average temperature in Europe over the last 40 years led to an acceleration of the phenological process, mainly due to a reduction in the duration of the reproductive growth period, and that the change in the phenological process of grapes was more pronounced under facility cultivation by raising the temperature artificially [32]. This experiment found that the budbreak period, the fruit development period and the veraison period were 34 days, 13 days, and 12 days earlier, respectively, in facility cultivation, but the budbreak to veraison period showed different degrees of prolongation effects, probably due to the rapid heat dissipation by traditional plastic films and the intermittent occurrence of temperatures above 10 °C suitable for grape growth in the facility during the vegetative growth stage due to lower external temperatures, thus causing the prolongation of the duration of the phenological period, which is also a key feature of the current effective accumulated temperature requirements in the production system of smallholders in facilities. Longer vegetative growth and shorter reproductive growth indicate that a higher risk of excessive nutritional growth and a more urgent need for nutrients and water during reproductive growth. Adequate knowledge of this characteristic will help to improve the management of temperature, irrigation, and zfertilization in the production of grapes in facilities.

4.2. Effective accumulated temperature distribution and potential for regulation in the facility grapes

In the present study, we found significant differences in the distribution of the effective accumulated temperature between the two stages of vegetative and reproductive growth between facility cultivation using plastic film cover and open field cultivation, with the percentage of effective accumulated temperature in the vegetative and reproductive growth stage being 18.9% and 81.1%, respectively, in the open field model, while this ratio was adjusted to 36.0%:64% for FM and 32.8%:67.2% for OPT in facility production. Facility production is more susceptible to vigorous growth than open-field production due to the increase in the amount of heat distribution during the vegetative stage. To reduce excessive nutritional growth, the OPT treatment reduced the proportion of effective accumulated temperature distribution during the vegetative stage to 32.8%, reducing vigorous new growth by 22.2%, optimizing the supply of nutrients to reproductive growth and increasing crop weight by 40.2% and yield by 30.1%. By changing the time of manual release the OPT treatment reduced the duration of high-temperature stress by 12.5 h and 35.7 h during the budbreak and leaf growth periods respectively. Although the OPT treatment showed a cumulative reduction in the effective accumulated temperature of 74.2 °C compared to the FM treatment, the time to maturity was the same, probably due to the stressful effect of the high temperature of the FM treatment, which inhibited the growth and development process of the grapes [5]. However, it is worth noting that the current smallholder production system had challenges for controlling temperature by simply covering with plastic film, and high-temperature control during the budbreak to leaf growth period has been achieved only with the services of the STB students accompanying them throughout. By increasing the control of maximum temperatures and appropriately increasing minimum temperatures, it is predicted that the ratio of effective accumulated temperature between the vegetative and reproductive growth stages of grapes will be further optimized and that yields and quality will be further improved.

5. Conclusion

Under current smallholder production systems, the rational regulation of the effective accumulated temperature requirements of grapes in facilities to achieve a harmonious ratio between vegetative and reproductive growth relies on timely temperature monitoring equipment and temperature decision indicators. Based on the rapid development of computer technology, sensing technology, and internet technology, the advanced Venlo greenhouse with IoT technology abroad can achieve the monitoring of temperature in the greenhouse and other monitoring and automatic control of facilities and equipment [33]. Although it is not possible to automate the temperature control of traditional smallholder grapevine production in China, using temperature sensors to monitor and adjust the temperature in conjunction with human intervention can optimise the distribution of effective accumulated temperature in facilities. In this trial, the OPT treatment provided timely feedback from the sensor data to prevent frost damage on 9 February and 16 February during the dormancy period, whereas the farmers' traditional FM treatment chose to prevent frost damage on the following day, missing the best time for control and increasing the cost of eight ineffective fumigant applications by relying only on experience. The OPT treatment achieves a reduction in the duration of high-temperature stress through sensor-based temperature monitoring and high-temperature threshold criteria and optimizes the harmonious relationship between nutritional and reproductive growth, improving yield and quality through STB accompaniment. Therefore, the use of sensors to monitor temperature is a very cost-effective way of enhancing the potential of effective accumulated temperature regulation in the current system of smallholder grape production facilities, which is a necessary step in the development of intelligent and automated smart agriculture in facility cultivation.

Author contribution statement

Weifeng Zhang and Zengyuan Li: Conceived and designed the experiments.

Zengyuan Li and Hao Huang: Performed the experiments.

Weifeng Zhang and Zhiping Duan: Contributed reagents, materials, analysis tools or data.

Zengyuan Li and Zhiping Duan: Wrote the paper.

Funding statement

Weifeng Zhang was supported by the Academy of Green Intelligent Compound Fertilizer, CNSIG Anhui Hongsifang Fertilizer Co., Ltd. [FYGS-JS-202111], the Shanghai Municipal Agricultural Commission [2020,2-2], the Quzhou Municipal Bureau of Agricultural and Rural Affairs, Zhejiang Province [2021,27].

Data availability statement

Data will be made available on request.

Declaration of interest’s statement

The authors declare no competing interests