ABSTRACT
Due to the shallow groundwater level and high sodium content of irrigation water in Taibao Township, Chiayi County, Taiwan, the greenhouse soil drainage is poor and the soil sodium content is excessively accumulated, which is unfavorable for greenhouse cultivation. The shallow buried pipe can replace the action of washing salt which is flooded, and has fast drainage. It increases soil aeration, promotes root growth, reduces humidity accumulation in the greenhouse, and helps control and manage pests and diseases. The function of washing salt in the shallow underground pipe, affects the salt discharge and becomes more improved through time. After 5 months, the sodium concentration of the drain water from the hidden pipe reaches a maximum of 11 mmole/L, which is 5 times the sodium concentration of irrigation water. With the drip irrigation cultivation on the flat border, it can save manpower and fertilization becomes more precise, which can improve the yield and quality, and prolong the harvest season of cucumbers. Generally, the cucumber harvest season of the greenhouse is about 30 days, and the first season is as long as 57 days. Therefore, the average yield is greatly increased by 96.4 tons/ha/season, which is 74% higher than that of farmers in previous years (55-56 tons/ha/season), and 2.92 times that of the cucumber yield of 33 tons/ha in the 108 annual report of Taibao area. The second season of continuous cropping of cucumbers, the yield is as high as 107 tons/ha (harvest 74 days), increase of 11% compared with the first season, and the yield of the third continuous cropping season is as high as 173.2 tons/ha (harvest 132 days), increase of 80% compared with the first season and 62% compared with the second season. This shows that the improved effect of the hidden pipe is better with the use of time. Although buried pipes cost about 2.35 million per hectare, it is of great help to improve the cultivation environment, increase yield and quality. Such a high yield increases benefits which is indeed worthy of the government's investment of resources to help farmers break through the capital threshold set by the management.
Keywords: Shallow hidden pipes, Drainage, Drip irrigation, Soil salinity, Yield increase
INTRODUCTION
Many counties and cities in Taiwan rely on groundwater supply due to insufficient surface water. In order to monitor the changes in groundwater quality throughout Taiwan, the Soil and Groundwater Pollution Remediation Fund Management Committee and the Water Resources Administration have set up monitoring wells in various counties and cities throughout Taiwan to evaluate chloride, sulfate, alkalinity, calcium, magnesium, potassium and other items. It was found that chlorides and sulfates are concentrated in the southwest coast and some coastal areas of Lanyang Plain; nitrates are concentrated in the alluvial fan of Zhuoshuixi and the fan top area of Pingtung Plain; and iron, manganese and potassium are concentrated in the southwest coast and Lanyang Plain (Lin, 2014). According to the regulations of the U.S. Institute of Salinity, when the conductivity (EC) of irrigation water is 0.75 mS/cm, the sodium adsorption rate (SAR) is allowed to be a ratio of 6. If the conductivity exceeds 1.5 mS/cm and the SAR exceeds 5, it is not suitable for irrigation. The Council of Agriculture (COA), Taiwan also announced that the water quality standards for irrigation water on November 7, 1992, in which EC should be less than 750 μS/cm (25°C), and the sodium adsorption ratio should be less than 6 √meq/L (Farmland Water Conservancy Regulations, 2003). According to the database of the farmer's soil and plant nutrition diagnosis service system, the average EC of farmland irrigation water has increased every year. From 2010 to 2019, laboratory irrigation water received a total of 7,466 cases, and 4,631 cases (62%) with EC exceeding 0.75mS/cm showed the severity of irrigation water salinization.
Since irrigation water salinization has become a reality, although increasing the amount of irrigation water to crops can alleviate salt stress, it will increase soil salinity and cause more farming problems. Traditionally, hidden pipes are used to improve soil salinity and reduce the groundwater level. It is recommended to bury at least 2 meters above (Donnan and Schwab, 1974). However, Taiwanese greenhouses are mostly located in rice cultivation areas, with scattered locations and small areas. The soil drainage problem is mainly due to the characteristics of the plough bottom block and the high groundwater level, so the traditional hidden pipe technology cannot be used. A new underground pipe technology suitable for the local area is needed to quickly drain water and reduce salt damage. If it is matched with drip irrigation equipment to improve the utilization rate of water and fertilizer, which is a good compound improvement method. Therefore, this experiment mainly sets up a demonstration area to improve the cultivation of greenhouse crops through the establishment of shallow hidden pipes and the use of drip irrigation. In the process, the practical experience of farmers is established, and the results can also be used as a reference for the government's greenhouse equipment subsidy project. Through the introduction of new hidden pipe and drip irrigation technology, a high-yield and high-quality greenhouse vegetable and fruit cultivation model under healthy and reasonable fertilization conditions is established to benefit producers and consumers.
MATERIALS AND METHODS
Shallow hidden pipe setup
Because the purpose of this experiment is to improve soil drainage efficiency and enhance the application potential of nutrient drip irrigation, the shallow buried pipe burying technology is different from the traditional hidden pipe. According to the current situation of greenhouse cultivation, the buried pipe burial location is planned, as shown in Figure 1. Take the double-span greenhouse as an example in this experiment. Half of the greenhouse is 7 meters wide and 88-83 meters long. It is cultivated in 3.5 plots. The depth of each plot is 50 cm below the soil surface. The width of the trench is about 30 cm. inch Polyvinyl Chloride (PVC) pipe (thickness 2 mm or more) is covered with 24-mesh gauze after opening, and the gauze is covered with at least 2 layers, and the gauze and PVC water pipe are fastened with ropes. The sand and gravel shall be buried at a depth of at least 5 cm, and an L-shaped pipe shall be installed at the front end of the hidden pipe to protrude from the soil surface to facilitate the subsequent maintenance of the hidden pipe. At least one set of sunk well water collecting pipe groups is buried at the end of the hidden pipe, so as to collect and discharge the drain water of the hidden pipe in a centralized manner.
Since there are 2 buildings in this test area, 16 hidden pipes are planned and divided into four tests for the test requirements. Therefore, 4 sets of shady well water collection pipe groups are required, and generally farmers only need 1-2 groups of shaded well water collection pipe groups. The details of the hidden pipe cost of this experiment are shown in Table 1. The experimental greenhouse area is about 0.25 hectare, and the hidden pipe cost is about NT$587,000, which is converted to NT$235,000/0.1 hectare.
Nutrient drip irrigation test
In this experiment, cucumber (CU-87) was used as the test material, and the drip irrigation system and programmable logic controller (PLC) controller were used to accurately provide the amount of fertilization required for each growth season of the test crops in each experimental area. The appropriate amount and frequency of nutrient solution, fertilizer and water supply was adjusted, and the amount of fertilizer, water, and cucumber yield and quality was recorded during the experiment. The nutrient solution formula refers to the concentration of the Dutch cucumber nutrient solution (De Kreij et al., 2003), and is adjusted according to the conditions of soil and irrigation water quality. The concentration of 50% - 100% is used during cultivation.
RESULTS AND DISCUSSION
The effect of hidden pipe system on soil fertility
According to the soil profile survey results of the test site, the temporary groundwater level of the first and third areas is 70-90 cm deep, and the purpose of the test is to improve soil drainage efficiency and enhance the application potential of nutrient drip irrigation, so the buried pipe has been set. On the other hand, the shallow underground pipe depth has been set to 50 cm, so as to avoid the loss of electric conductivity and the waste of water resources caused by the discharge of groundwater. The construction time of the hidden pipe is in late June. The soil analysis before and after the construction of the hidden pipe is shown in Table 2.
The topsoil was sampled at a depth of 0-15 cm, and the subsoil was sampled at a depth of 15-30 cm. Before the test, the content of phosphorus and potassium fertilizers in the topsoil of each area is higher than that of the subsoil, which is in line with the movement and distribution of fertilizers under drip irrigation. Although the EC (1:5) did not exceed the salt damage standard of 0.6 (dS/m), the M3-Na content in the soil was as high as 339-574 (mg/kg). This shows that the soil is at risk of high osmotic pressure and nutrient antagonism. And the soil sodium content in the topsoil of Sits 1-3 is lower than that of the subsoil. Because the small tomatoes are grown in the early stage of the greenhouse, the nutrient solution is supplied by drip irrigation, and the high frequency of drip irrigation is maintained to keep the soil moist and moisture content to facilitate root growth. Therefore, the sodium salt of the soil is leached, so that the lower the soil is the higher the sodium content. As for whether the sodium content of the soil below 30 cm is higher, although there is no direct sampling inspection, the construction of the burial pipe is buried, and the excavator mixes the upper and lower soils, and the sampling results of 2020/7/23 after the construction of the burrow pipe are shown in Table 2. It can be known that after 0-50 cm of soil was mixed, the M3-Ca, M3-Mg, and M3-Na contents of the four greenhouse soils were significantly increased than those before the construction of the hidden pipe, especially the sodium, indicating that the soil was caused by poor drainage and sodium salt. With the application of high-sodium irrigation water, the longer the cultivation time, the more serious the problem of high-sodium salt damage in the soil, which may be one of the reasons why the general greenhouse cannot be cultivated and utilized for a long time.
The mixing of the upper and lower soil layers after the construction of the hidden pipe is generally unfavorable for cultivation and growth, resulting in the deterioration of soil fertility of 0-30 cm. If the pH rises above 7.5, there may be problems with the utilization of overly alkaline fertilizers and root growth; the organic matter declines and has uneven distribution, there may be problems of soil agglomeration and uneven plant growth; excessive M3-Ca, M3-Mg, and M3-Na may cause nutritional imbalance and nutrient antagonism; EC increase may cause salt damage, etc. Although the construction of the hidden pipe seems to cause the deterioration of soil fertility, it solves the fundamental problem of poor soil drainage. As for the destruction of soil fertility and nutritional barriers, it can be overcome by providing uniform water and fertilizer through the nutrient drip irrigation technology. Through underground drainage and nutrient drip irrigation, the problem of high sodium salt damage in the soil can be improved while planting, without the need for traditional flooding and salt washing, which virtually increases the time farmers can cultivate, and can increase production yields.
Influence of hidden pipe system on drain water
The quality analysis of irrigation water and drain water at the test site is shown in Figures 2 and 3. The biggest problem of groundwater used for irrigation in this test is that the sodium content is too high, which may also be the common problem of groundwater in Taibao area. Although sodium is not one of the necessary elements for plant growth, general plants can still absorb some sodium without causing growth obstacles. For example, in the case of cucumbers and tomatoes which are often cultivated in Taibao area, when the sodium content <0.8 (mmole/L) of the cucumbers grows normally, the sodium content >6 (mmole/L) will cause the phenomenon of sodium poisoning; while the sodium content in the nutrient solution <1 (mmole/L) the tomato grows normally, but sodium toxicity occurs when the sodium content is >8 (mmole/L). (De Kreij et al., 2003; Van Eysinga. & Smilde. 1981) The sodium content of the groundwater used for irrigation in this experiment was as high as 2.7 (mmole/L). Although it would not cause sodium poisoning to cucumbers, it would affect the normal growth of cucumbers. Moreover, when the soil was poorly drained and excessive sodium could not be eliminated, the more water is used, the higher the sodium accumulation in the soil, which eventually causes sodium toxicity and makes it impossible to plant.
Through the burial of hidden pipes, the soil in the experimental area can be planted while removing sodium salts. The sodium content of the drain water in the 8/13 hidden pipe is 6.55 (mmole/L), which has already caused the sodium poisoning of cucumbers, and is higher than the original irrigation water of 2.7 (mmole/L). It is shown that the hidden pipe can already exert the effect of washing salt, and exert 3.44 times the sodium excretion concentration. The sodium content of the drain water in the 11/5 hidden pipe is 10.0-12.0 (mmole/L), which exerts 5.3-6.3 times the sodium excretion concentration.
The time it takes for soil improvement to drain salt through shallow burrows is currently uncertain. However, it reached a peak at the 5th month, and then continued to decline until 21 months later, the average sodium content of the drain water was still as high as 4.68 (mmole/L), which was 73% higher than that of the original irrigation water. If it is judged according to the sodium toxicity standard of cucumber > 6 (mmole/L), the drain water can be lower than the standard of about 11 months after the burial of the hidden pipe, and there is no need to perform other water treatment during the cultivation season. The efficiency of salt discharge using shallow hidden pipes must be much higher than that of traditional whole-area water treatment. Because the salt discharge range of the shallow underground pipe is mainly in the excavation range of 30 cm wide and 50 cm deep, and the whole area of Zhanshui has to deal with the soil range of 175 cm wide and 70-90 cm deep. And in the case of the original poor drainage, the effect is questionable. Due to diffusion, a wide range of high-sodium areas can also be gradually improved to facilitate the growth of plant roots under the shallow hidden pipe salt discharge.
The highest concentrations of anions and cations in the test cucumber nutrient solution were NO3-N=13.9 (mmole/L), K=7.3 (mmole/L), and the concentrations in all exudates were very low (Figures 2 and 3). It was shown that during the 21 months of nutrient drip irrigation, no loss of soil nutrients was caused by under-pipe drainage. On the contrary, it can effectively remove excess calcium, magnesium, sodium, sulfate, carbonate, etc. in the soil, and reduce the problem of soil salinity and element imbalance.
The effect of hidden pipe system on the yield of cucumber
When the garden owner did not operate the hidden pipe system, the average yield of CU-87 cucumbers in previous years was about 55-56 tons/ha/season. According to the annual report of 2018, the output of cucumber in Taibao area is 33 tons/ha/season. The production technology of the owner is 1.68 times that of the local farmers. In the early stage of the establishment of the hidden pipe, although the soil fertility was deteriorated due to disturbance, the average total yield of cucumbers in the first phase was 96.4 tons/ha/season, which was still 2.92 times the annual yield, and the harvest season of cucumbers in the experimental area was as long as 57 days, which is much higher than the 30 days in the harvesting season of general greenhouse cucumbers. The cumulative yield of each treatment is shown in Figure 3. The highest in the Sit-3 (pipe drainage + biochar) is 99.8 tons/ha/season, while the Sit-1 (pipe undrained) is as low as 92.0 tons/ha/season. The rest are 96.9 tons/ha/season for the Sit-2 (pipe drainage) and 96.8 tons/ha/season for the Sit-4 (pipe drainage + high fertilizer). Although the test in Sit-1 (pipe undrained) was not actively drained, the plough bottom was broken when the underdrain was buried in Sit-1 and the sand layer around the underdrain also helped to drain the water. Although the underdrain at Sit-1 was closed during the test, it was still apparent that the well was drained and the aisles on site were dry with no standing water. Therefore, the four treatments in this experiment can be regarded as all having the benefit of underground pipe drainage.
The yield of each sit in the second season is shown in Figure 5. The harvest season is as long as 74 days, and the average total yield is 107.2 tons/ha/season, which is 3.25 times that of the local farmers and 11% higher than that of the first crop. The yield of third season is shown in Figure 6. The harvest season is as long as 132 days, and the average total yield is 173.2 tons/ha/season, which is 5.25 times that of local farmers, 80% higher than that of the first crop, and 62% higher than that of the second crop. The yield comparison of each season is shown in Table 3, which shows that the total yield of cucumbers in the hidden pipe test area has increased gradually. Because the soil environment is still improving, it may not have reached the maximum yield threshold. The reasons for such high yield are as follows: 1. Soil Drainage improvement: In previous years, the accumulated water in the field could not be removed smoothly, which caused the soil to be too wet and even the foot of the aisle would sink in between the borders. Poor drainage also led to the absorption of nutrients by the root system. However, the problem of high EC and high sodium in the soil cannot improve the utilization efficiency of fertilizers, so the growth of plants is limited. 2. Improvement of environmental humidity: In addition to promoting the environment for root growth, the hidden pipe treatment has a significant improvement in the reduction of environmental humidity in the greenhouse. In previous years, due to poor drainage, the leaves were a little secreted in the morning due to too much water, and the high humidity caused the occurrence of diseases and insect pests. 3. Prolonged harvesting season: Due to the improvement of soil and environmental conditions, the harvesting season of cucumbers in the experimental area has been greatly extended, from 57 days to 132 days, which is much higher than the 30-day harvesting season of general greenhouse cucumbers.
In the case of 3 consecutive crops of cucumbers without land preparation, the yield of each crop has been greatly increased. It is shown that in the farmland with salt damage and poor drainage, the shallow hidden pipe technology is the key technology to break through the bottleneck of high yield. In less than 2 years of improvement, the production can be increased by 5.25 times of the local average production without wasting the time and water volume of Cham water treatment. Such a high yield increase benefit is indeed worthy of the government unit's investment of resources to help farmers break through the capital threshold set by the initial management.
CONCLUSION
Due to the shallow groundwater level and high sodium content of groundwater in the Taibao area, the greenhouse soil has poor drainage and excessive accumulation of soil sodium, which is unfavorable for cultivation operations. The shallow buried pipe can achieve rapid drainage, increase soil aeration, promote root growth, shorten the waiting time for planting, reduce the accumulation of humidity in the greenhouse, and help control and manage pests and diseases. With the rapid salt washing function of the shallow hidden pipe, and with the increase of used time, the effect of salt discharge is more and more improved. After 3 months, the sodium concentration of the drain water from the hidden pipe reaches a maximum of 11.1 mmole/L, which is 5 times the sodium concentration of irrigation water. Cooperating with flat border drip irrigation cultivation can save manpower and achieve precise fertilization, which can improve yield and quality, and prolong the harvest season of cucumbers. Generally, the harvest season in greenhouse is about 30 days, and the dark tube technology can be as long as 57 days to 132 days, so the yield is greatly increased. In the case of continuous cropping of cucumbers for 3 seasons without land preparation, the yield of each crop was greatly increased. The yield of the third season of continuous cropping was as high as 173.2 tons/ha (production season of 132 days), which was 5.25 times of the local average yield, which was higher than that of the first season. The production increased by 80% and the second phase increased by 62%. This shows that the dark tube improves over time with better results. Although the cost of burying the buried pipes is expensive, about 2.35 million / hectare is required, but it significantly improves the cultivation environment and improves the yield and quality. Such a high yield increase benefit is indeed worthy of the government unit's investment of resources to help farmers break through the capital threshold set by the initial management.
REFERENCES
Zhang Ai Hua. 1981. Current soil measurement methods in the province. p. 9-26. Crop fertilizer requirement diagnostic technology. Taiwan Provincial Agricultural Experiment Institute Special Issue No. 13.
Zhang Shu Xian. 1981. Current plant analysis methods in the province. p. 53-59. Crop fertilizer requirement diagnostic technology. Taiwan Provincial Agricultural Experiment Institute Special Issue No. 13.
Yi Jie Xiang, Lu Liangxue, Liu Guodao. 2006. Soil acidification and acid soil improvement studies. Journal of South China Tropical Agricultural University 12(1): 23-28.
Wu Zhen Gzong. 2001. Diagnosis and improvement of salt-damaged soils. Xingda Agriculture, Issue 36, Page(s) 19-23.
Wang Shu Zi, Peng Zongren, Wang Zhonghe. 2001. Salinization status of water quality in major rivers in central Taiwan and evaluation of its suitability for irrigation. Journal of Agriculture and Forestry 50(3):39-53.
Farmland water conservancy regulations. 2003. Announce the water quality standards for irrigation water. Nonglin Zi No. 0920031524.
Lin Jing Wei. 2014. The understanding and application management of agricultural irrigation water. Tainan District Agricultural News Issue 88.
Xie Ming Xian, Liu Yichang, Xu Hanjun, Jiang Wenjin, Zhong Ruiyong, 2010, Research on drip irrigation management of small fruit tomato. Tainan District Agricultural Improvement Field Research Report 59: 45-53.
Jiang Wen Jin. 2018. Introduction to facility hydroponics (1). Tainan District Agricultural News Issue 105.
Jiang Wen Jin. 2016. Improve facility nutrient and water use efficiency. Harvest Society, Volume 66, Issue 08.
De Kreij, C., Voogt, W., & Baas, R. 2003. Nutrient solutions and water quality for soilless cultures (No. 191). Applied Plant Research, Division Glasshouse.
Donnan, W. W.; Schwab, G. O. Current drainage methods in the USA. Drainage for agriculture, 1974, 17: 91-114.
Johnston, A. E., K. W. T. Goulding, and P. R. Poulton. 1986. Soil acidification during more than 100 years under permanent grassland and woodland at Rothamsted. Soil use and management2(1): 3-10.
R.S. Ayers and D.W. Westcot. 1985. Water quality for agriculture. Food and Agriculture Organization of the United Nations Rome, 1985. ISBN 92-5-102263-1.
Trent Biggs and Bin Bin J. Pearce. 2009. Soil Salinity and Exchangeable Cations in a Wastewater Irrigated Area. Journal of Environmental Quality 38(3):887-96.
Lucia Bortolini, Carmelo Maucieri , and Maurizio Borin. 2018. A Tool for the Evaluation of Irrigation Water Quality in the Arid and Semi-Arid Regions. Agronomy 2018, 8, 23.
Locascio, S.J., Smajstrala, A.G., 1995. Fertilizer timing and pan evaporation scheduling for drip irrigation method. In Proceeding of the Fifth International Micro Irrigation Congress on Micro Irrigation for a Changing World. Conserving Resources/ Preserving the Environment held at Hyatt Regency Orlando, Orlando, Florida, April 2-6, pp. 175-180.
Miller, R.J., Rolston, D.E., Rauschkolb, R.S., and Wolf, D.W., 1976. Drip irrigation of nitrogen is efficient. California Agriculture. 30:16-18.
Papadopoulos, I., 1992. Fertigation of vegetables in plastichouse: present situation and future aspects. Acta Horticulturae 323:151–174.
Nutritional Disorders in Glasshouse Tomatoes, Cucumbers, and Lettuce by J. P. N. L. Roorda van Eysinga (1981-12-04).
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Effects of Shallow Hidden Pipes on Soil Salinity of Greenhouse Cucumber
ABSTRACT
Due to the shallow groundwater level and high sodium content of irrigation water in Taibao Township, Chiayi County, Taiwan, the greenhouse soil drainage is poor and the soil sodium content is excessively accumulated, which is unfavorable for greenhouse cultivation. The shallow buried pipe can replace the action of washing salt which is flooded, and has fast drainage. It increases soil aeration, promotes root growth, reduces humidity accumulation in the greenhouse, and helps control and manage pests and diseases. The function of washing salt in the shallow underground pipe, affects the salt discharge and becomes more improved through time. After 5 months, the sodium concentration of the drain water from the hidden pipe reaches a maximum of 11 mmole/L, which is 5 times the sodium concentration of irrigation water. With the drip irrigation cultivation on the flat border, it can save manpower and fertilization becomes more precise, which can improve the yield and quality, and prolong the harvest season of cucumbers. Generally, the cucumber harvest season of the greenhouse is about 30 days, and the first season is as long as 57 days. Therefore, the average yield is greatly increased by 96.4 tons/ha/season, which is 74% higher than that of farmers in previous years (55-56 tons/ha/season), and 2.92 times that of the cucumber yield of 33 tons/ha in the 108 annual report of Taibao area. The second season of continuous cropping of cucumbers, the yield is as high as 107 tons/ha (harvest 74 days), increase of 11% compared with the first season, and the yield of the third continuous cropping season is as high as 173.2 tons/ha (harvest 132 days), increase of 80% compared with the first season and 62% compared with the second season. This shows that the improved effect of the hidden pipe is better with the use of time. Although buried pipes cost about 2.35 million per hectare, it is of great help to improve the cultivation environment, increase yield and quality. Such a high yield increases benefits which is indeed worthy of the government's investment of resources to help farmers break through the capital threshold set by the management.
Keywords: Shallow hidden pipes, Drainage, Drip irrigation, Soil salinity, Yield increase
INTRODUCTION
Many counties and cities in Taiwan rely on groundwater supply due to insufficient surface water. In order to monitor the changes in groundwater quality throughout Taiwan, the Soil and Groundwater Pollution Remediation Fund Management Committee and the Water Resources Administration have set up monitoring wells in various counties and cities throughout Taiwan to evaluate chloride, sulfate, alkalinity, calcium, magnesium, potassium and other items. It was found that chlorides and sulfates are concentrated in the southwest coast and some coastal areas of Lanyang Plain; nitrates are concentrated in the alluvial fan of Zhuoshuixi and the fan top area of Pingtung Plain; and iron, manganese and potassium are concentrated in the southwest coast and Lanyang Plain (Lin, 2014). According to the regulations of the U.S. Institute of Salinity, when the conductivity (EC) of irrigation water is 0.75 mS/cm, the sodium adsorption rate (SAR) is allowed to be a ratio of 6. If the conductivity exceeds 1.5 mS/cm and the SAR exceeds 5, it is not suitable for irrigation. The Council of Agriculture (COA), Taiwan also announced that the water quality standards for irrigation water on November 7, 1992, in which EC should be less than 750 μS/cm (25°C), and the sodium adsorption ratio should be less than 6 √meq/L (Farmland Water Conservancy Regulations, 2003). According to the database of the farmer's soil and plant nutrition diagnosis service system, the average EC of farmland irrigation water has increased every year. From 2010 to 2019, laboratory irrigation water received a total of 7,466 cases, and 4,631 cases (62%) with EC exceeding 0.75mS/cm showed the severity of irrigation water salinization.
Since irrigation water salinization has become a reality, although increasing the amount of irrigation water to crops can alleviate salt stress, it will increase soil salinity and cause more farming problems. Traditionally, hidden pipes are used to improve soil salinity and reduce the groundwater level. It is recommended to bury at least 2 meters above (Donnan and Schwab, 1974). However, Taiwanese greenhouses are mostly located in rice cultivation areas, with scattered locations and small areas. The soil drainage problem is mainly due to the characteristics of the plough bottom block and the high groundwater level, so the traditional hidden pipe technology cannot be used. A new underground pipe technology suitable for the local area is needed to quickly drain water and reduce salt damage. If it is matched with drip irrigation equipment to improve the utilization rate of water and fertilizer, which is a good compound improvement method. Therefore, this experiment mainly sets up a demonstration area to improve the cultivation of greenhouse crops through the establishment of shallow hidden pipes and the use of drip irrigation. In the process, the practical experience of farmers is established, and the results can also be used as a reference for the government's greenhouse equipment subsidy project. Through the introduction of new hidden pipe and drip irrigation technology, a high-yield and high-quality greenhouse vegetable and fruit cultivation model under healthy and reasonable fertilization conditions is established to benefit producers and consumers.
MATERIALS AND METHODS
Shallow hidden pipe setup
Because the purpose of this experiment is to improve soil drainage efficiency and enhance the application potential of nutrient drip irrigation, the shallow buried pipe burying technology is different from the traditional hidden pipe. According to the current situation of greenhouse cultivation, the buried pipe burial location is planned, as shown in Figure 1. Take the double-span greenhouse as an example in this experiment. Half of the greenhouse is 7 meters wide and 88-83 meters long. It is cultivated in 3.5 plots. The depth of each plot is 50 cm below the soil surface. The width of the trench is about 30 cm. inch Polyvinyl Chloride (PVC) pipe (thickness 2 mm or more) is covered with 24-mesh gauze after opening, and the gauze is covered with at least 2 layers, and the gauze and PVC water pipe are fastened with ropes. The sand and gravel shall be buried at a depth of at least 5 cm, and an L-shaped pipe shall be installed at the front end of the hidden pipe to protrude from the soil surface to facilitate the subsequent maintenance of the hidden pipe. At least one set of sunk well water collecting pipe groups is buried at the end of the hidden pipe, so as to collect and discharge the drain water of the hidden pipe in a centralized manner.
Since there are 2 buildings in this test area, 16 hidden pipes are planned and divided into four tests for the test requirements. Therefore, 4 sets of shady well water collection pipe groups are required, and generally farmers only need 1-2 groups of shaded well water collection pipe groups. The details of the hidden pipe cost of this experiment are shown in Table 1. The experimental greenhouse area is about 0.25 hectare, and the hidden pipe cost is about NT$587,000, which is converted to NT$235,000/0.1 hectare.
Nutrient drip irrigation test
In this experiment, cucumber (CU-87) was used as the test material, and the drip irrigation system and programmable logic controller (PLC) controller were used to accurately provide the amount of fertilization required for each growth season of the test crops in each experimental area. The appropriate amount and frequency of nutrient solution, fertilizer and water supply was adjusted, and the amount of fertilizer, water, and cucumber yield and quality was recorded during the experiment. The nutrient solution formula refers to the concentration of the Dutch cucumber nutrient solution (De Kreij et al., 2003), and is adjusted according to the conditions of soil and irrigation water quality. The concentration of 50% - 100% is used during cultivation.
RESULTS AND DISCUSSION
The effect of hidden pipe system on soil fertility
According to the soil profile survey results of the test site, the temporary groundwater level of the first and third areas is 70-90 cm deep, and the purpose of the test is to improve soil drainage efficiency and enhance the application potential of nutrient drip irrigation, so the buried pipe has been set. On the other hand, the shallow underground pipe depth has been set to 50 cm, so as to avoid the loss of electric conductivity and the waste of water resources caused by the discharge of groundwater. The construction time of the hidden pipe is in late June. The soil analysis before and after the construction of the hidden pipe is shown in Table 2.
The topsoil was sampled at a depth of 0-15 cm, and the subsoil was sampled at a depth of 15-30 cm. Before the test, the content of phosphorus and potassium fertilizers in the topsoil of each area is higher than that of the subsoil, which is in line with the movement and distribution of fertilizers under drip irrigation. Although the EC (1:5) did not exceed the salt damage standard of 0.6 (dS/m), the M3-Na content in the soil was as high as 339-574 (mg/kg). This shows that the soil is at risk of high osmotic pressure and nutrient antagonism. And the soil sodium content in the topsoil of Sits 1-3 is lower than that of the subsoil. Because the small tomatoes are grown in the early stage of the greenhouse, the nutrient solution is supplied by drip irrigation, and the high frequency of drip irrigation is maintained to keep the soil moist and moisture content to facilitate root growth. Therefore, the sodium salt of the soil is leached, so that the lower the soil is the higher the sodium content. As for whether the sodium content of the soil below 30 cm is higher, although there is no direct sampling inspection, the construction of the burial pipe is buried, and the excavator mixes the upper and lower soils, and the sampling results of 2020/7/23 after the construction of the burrow pipe are shown in Table 2. It can be known that after 0-50 cm of soil was mixed, the M3-Ca, M3-Mg, and M3-Na contents of the four greenhouse soils were significantly increased than those before the construction of the hidden pipe, especially the sodium, indicating that the soil was caused by poor drainage and sodium salt. With the application of high-sodium irrigation water, the longer the cultivation time, the more serious the problem of high-sodium salt damage in the soil, which may be one of the reasons why the general greenhouse cannot be cultivated and utilized for a long time.
The mixing of the upper and lower soil layers after the construction of the hidden pipe is generally unfavorable for cultivation and growth, resulting in the deterioration of soil fertility of 0-30 cm. If the pH rises above 7.5, there may be problems with the utilization of overly alkaline fertilizers and root growth; the organic matter declines and has uneven distribution, there may be problems of soil agglomeration and uneven plant growth; excessive M3-Ca, M3-Mg, and M3-Na may cause nutritional imbalance and nutrient antagonism; EC increase may cause salt damage, etc. Although the construction of the hidden pipe seems to cause the deterioration of soil fertility, it solves the fundamental problem of poor soil drainage. As for the destruction of soil fertility and nutritional barriers, it can be overcome by providing uniform water and fertilizer through the nutrient drip irrigation technology. Through underground drainage and nutrient drip irrigation, the problem of high sodium salt damage in the soil can be improved while planting, without the need for traditional flooding and salt washing, which virtually increases the time farmers can cultivate, and can increase production yields.
Influence of hidden pipe system on drain water
The quality analysis of irrigation water and drain water at the test site is shown in Figures 2 and 3. The biggest problem of groundwater used for irrigation in this test is that the sodium content is too high, which may also be the common problem of groundwater in Taibao area. Although sodium is not one of the necessary elements for plant growth, general plants can still absorb some sodium without causing growth obstacles. For example, in the case of cucumbers and tomatoes which are often cultivated in Taibao area, when the sodium content <0.8 (mmole/L) of the cucumbers grows normally, the sodium content >6 (mmole/L) will cause the phenomenon of sodium poisoning; while the sodium content in the nutrient solution <1 (mmole/L) the tomato grows normally, but sodium toxicity occurs when the sodium content is >8 (mmole/L). (De Kreij et al., 2003; Van Eysinga. & Smilde. 1981) The sodium content of the groundwater used for irrigation in this experiment was as high as 2.7 (mmole/L). Although it would not cause sodium poisoning to cucumbers, it would affect the normal growth of cucumbers. Moreover, when the soil was poorly drained and excessive sodium could not be eliminated, the more water is used, the higher the sodium accumulation in the soil, which eventually causes sodium toxicity and makes it impossible to plant.
Through the burial of hidden pipes, the soil in the experimental area can be planted while removing sodium salts. The sodium content of the drain water in the 8/13 hidden pipe is 6.55 (mmole/L), which has already caused the sodium poisoning of cucumbers, and is higher than the original irrigation water of 2.7 (mmole/L). It is shown that the hidden pipe can already exert the effect of washing salt, and exert 3.44 times the sodium excretion concentration. The sodium content of the drain water in the 11/5 hidden pipe is 10.0-12.0 (mmole/L), which exerts 5.3-6.3 times the sodium excretion concentration.
The time it takes for soil improvement to drain salt through shallow burrows is currently uncertain. However, it reached a peak at the 5th month, and then continued to decline until 21 months later, the average sodium content of the drain water was still as high as 4.68 (mmole/L), which was 73% higher than that of the original irrigation water. If it is judged according to the sodium toxicity standard of cucumber > 6 (mmole/L), the drain water can be lower than the standard of about 11 months after the burial of the hidden pipe, and there is no need to perform other water treatment during the cultivation season. The efficiency of salt discharge using shallow hidden pipes must be much higher than that of traditional whole-area water treatment. Because the salt discharge range of the shallow underground pipe is mainly in the excavation range of 30 cm wide and 50 cm deep, and the whole area of Zhanshui has to deal with the soil range of 175 cm wide and 70-90 cm deep. And in the case of the original poor drainage, the effect is questionable. Due to diffusion, a wide range of high-sodium areas can also be gradually improved to facilitate the growth of plant roots under the shallow hidden pipe salt discharge.
The highest concentrations of anions and cations in the test cucumber nutrient solution were NO3-N=13.9 (mmole/L), K=7.3 (mmole/L), and the concentrations in all exudates were very low (Figures 2 and 3). It was shown that during the 21 months of nutrient drip irrigation, no loss of soil nutrients was caused by under-pipe drainage. On the contrary, it can effectively remove excess calcium, magnesium, sodium, sulfate, carbonate, etc. in the soil, and reduce the problem of soil salinity and element imbalance.
The effect of hidden pipe system on the yield of cucumber
When the garden owner did not operate the hidden pipe system, the average yield of CU-87 cucumbers in previous years was about 55-56 tons/ha/season. According to the annual report of 2018, the output of cucumber in Taibao area is 33 tons/ha/season. The production technology of the owner is 1.68 times that of the local farmers. In the early stage of the establishment of the hidden pipe, although the soil fertility was deteriorated due to disturbance, the average total yield of cucumbers in the first phase was 96.4 tons/ha/season, which was still 2.92 times the annual yield, and the harvest season of cucumbers in the experimental area was as long as 57 days, which is much higher than the 30 days in the harvesting season of general greenhouse cucumbers. The cumulative yield of each treatment is shown in Figure 3. The highest in the Sit-3 (pipe drainage + biochar) is 99.8 tons/ha/season, while the Sit-1 (pipe undrained) is as low as 92.0 tons/ha/season. The rest are 96.9 tons/ha/season for the Sit-2 (pipe drainage) and 96.8 tons/ha/season for the Sit-4 (pipe drainage + high fertilizer). Although the test in Sit-1 (pipe undrained) was not actively drained, the plough bottom was broken when the underdrain was buried in Sit-1 and the sand layer around the underdrain also helped to drain the water. Although the underdrain at Sit-1 was closed during the test, it was still apparent that the well was drained and the aisles on site were dry with no standing water. Therefore, the four treatments in this experiment can be regarded as all having the benefit of underground pipe drainage.
The yield of each sit in the second season is shown in Figure 5. The harvest season is as long as 74 days, and the average total yield is 107.2 tons/ha/season, which is 3.25 times that of the local farmers and 11% higher than that of the first crop. The yield of third season is shown in Figure 6. The harvest season is as long as 132 days, and the average total yield is 173.2 tons/ha/season, which is 5.25 times that of local farmers, 80% higher than that of the first crop, and 62% higher than that of the second crop. The yield comparison of each season is shown in Table 3, which shows that the total yield of cucumbers in the hidden pipe test area has increased gradually. Because the soil environment is still improving, it may not have reached the maximum yield threshold. The reasons for such high yield are as follows: 1. Soil Drainage improvement: In previous years, the accumulated water in the field could not be removed smoothly, which caused the soil to be too wet and even the foot of the aisle would sink in between the borders. Poor drainage also led to the absorption of nutrients by the root system. However, the problem of high EC and high sodium in the soil cannot improve the utilization efficiency of fertilizers, so the growth of plants is limited. 2. Improvement of environmental humidity: In addition to promoting the environment for root growth, the hidden pipe treatment has a significant improvement in the reduction of environmental humidity in the greenhouse. In previous years, due to poor drainage, the leaves were a little secreted in the morning due to too much water, and the high humidity caused the occurrence of diseases and insect pests. 3. Prolonged harvesting season: Due to the improvement of soil and environmental conditions, the harvesting season of cucumbers in the experimental area has been greatly extended, from 57 days to 132 days, which is much higher than the 30-day harvesting season of general greenhouse cucumbers.
In the case of 3 consecutive crops of cucumbers without land preparation, the yield of each crop has been greatly increased. It is shown that in the farmland with salt damage and poor drainage, the shallow hidden pipe technology is the key technology to break through the bottleneck of high yield. In less than 2 years of improvement, the production can be increased by 5.25 times of the local average production without wasting the time and water volume of Cham water treatment. Such a high yield increase benefit is indeed worthy of the government unit's investment of resources to help farmers break through the capital threshold set by the initial management.
CONCLUSION
Due to the shallow groundwater level and high sodium content of groundwater in the Taibao area, the greenhouse soil has poor drainage and excessive accumulation of soil sodium, which is unfavorable for cultivation operations. The shallow buried pipe can achieve rapid drainage, increase soil aeration, promote root growth, shorten the waiting time for planting, reduce the accumulation of humidity in the greenhouse, and help control and manage pests and diseases. With the rapid salt washing function of the shallow hidden pipe, and with the increase of used time, the effect of salt discharge is more and more improved. After 3 months, the sodium concentration of the drain water from the hidden pipe reaches a maximum of 11.1 mmole/L, which is 5 times the sodium concentration of irrigation water. Cooperating with flat border drip irrigation cultivation can save manpower and achieve precise fertilization, which can improve yield and quality, and prolong the harvest season of cucumbers. Generally, the harvest season in greenhouse is about 30 days, and the dark tube technology can be as long as 57 days to 132 days, so the yield is greatly increased. In the case of continuous cropping of cucumbers for 3 seasons without land preparation, the yield of each crop was greatly increased. The yield of the third season of continuous cropping was as high as 173.2 tons/ha (production season of 132 days), which was 5.25 times of the local average yield, which was higher than that of the first season. The production increased by 80% and the second phase increased by 62%. This shows that the dark tube improves over time with better results. Although the cost of burying the buried pipes is expensive, about 2.35 million / hectare is required, but it significantly improves the cultivation environment and improves the yield and quality. Such a high yield increase benefit is indeed worthy of the government unit's investment of resources to help farmers break through the capital threshold set by the initial management.
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