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Precision Technology for Controlling Soil Moisture with Plug Seedlings
PRECISION TECHNOLOGY FOR CONTROLLING SOIL MOISTURE WITH PLUG SEEDLINGS Haruhiko Murase, Yoichi Matsushita, and Katsusuke Murakami
Graduate School ofAgriculture and Biological Science. Osaka Prefecture University
Abstract: This paper presents an example of microprecision technology implemented in a plug seedling production factory, as an example of variable rate application technology used in precision agriculture. A microprecision irrigation system was developed for a plug production system. The device was designed to fit a 300 x 600mm 72-cell tray made of moisture-permeable biodegradable paper pulp. This paper investigated tlle moisture permeability of the paper pulp, in order to seek a way of controlling tlle root zone moisture using microprecision technology. The experiment investigating the influence of humidity near the cells on evaporation from rite soil found that a higher humidity around the plug cells suppresses moisture loss significantly. This suggests a means of controlling the soil moisture of pulp plug cells. By controlling the humidity around the pulp plug cells, the movement of moisture through the pulp material can be regulated. Such control technology improves the prospects for microprecision agriculture. Key words : pulp plug tray, water potential, moisture permeability
1. INTRODUCTION
open-field system. The fully controlled environment of a plant factory is an ideal cultivation system in teons of alternative agriculture. Most of the environmental factors in a fully controlled plant factory are observable and controllable; a plant factory can be optimized more easily than an open field. This paper proposes a way to implement the concept of precision agriculture in a fully controlled plant factory. In this approach. PA becomes Microprecision Agriculture, which can then be implemented in plant factories to realize profitable alternative agriculture. This paper presents an example of microprecision
The development of precision technologies to reduce the use of off-farm inputs supported by the extensive application of information technology, including GPS and GIS, and mechatronic teclmoJogy, including sensor fusion and intelligent control, has become a major issue in precision agriculture. With significant support fro m both the agricultural and industrial sectors, PA now promises to be able to handle open-field agriculture, which is a very complex system. Although a plant factory is also a large-scale complex system, it is much less complex than an
49
technology implemented in a plug seedling production factory, as an example of variable rate technology used in precision agriculture. A microprecision irrigation system was developed for a plug production system. In this system, only seedlings that require water (nutrient solution) are irrigated, and the proper amount of solution needed for a particular plant is dispensed where the roots of each particular plant have developed. This minimizes wasted irrigation water, and there is no residual solution on leaf surfaces. No recycling of nutrient solution is considered, since there is no overflow of the nutrient solution. The nutrient solution must be supplied from the bottom of the cell by injecting it from a nozzle directly into the substrate (soil). The cells must have an appropriately sized hole at the bottom. The injection process should be completed as quickly as possible, since a very large number of seedlings must be irrigated. Leakage of solution from the cell should be minimized or avoided, both during and immediately after injection. With these factors in mind, a microprecision irrigation device was developed (Fig. 1).
The characteristics of the tray material enabled us to devise a technique for contro:iing the root-zone moisture of the plug seedlings. This is another microprecision teclmology for optimizing the root zone moisture of plug seedlings. This study investigated the moisture permeability of the paper pulp used for the plug tray to devise a way of controlling root zone moisture.
2. MATERIALS AND METHODS The first experiment investigated moisture loss or evaporation from the pulp tray. Soil was saturated with water and each plug cell was filled with moist soil and the tray was left for 2 days in a room at 25°C and 75% humidity. The moisture loss of cells at the locations specified in Fig. 2. was measured by the oven drying method. As a control, the same measurements were made using a traditional plastic tray. The total weight changes of the plastic and pulp trays were compared.
a
b
b
a
I)
a
c c
a
b
Fig.2 Cells tested The second experiment investigated the influence of humidity near the cell surface on the evaporation from the soil. A tray filled with saturated soil was prepared in !t.e same manner as in the first experiment; however, the bottom of the tray was covered Witll an impermeable material, as shown in Fig. 3. The space between the cover and the plug cell surface was filled with air at 80% relative humidity. The total moisture loss from the tray was measured by weighing the whole tray every 24 hours for 3 days.
Fig. l The microprecision irrigation device The device was designed to fit a 300 x 600 nun 72-ceIl tray. The solution is discharged from 72 nozzles fixed on an aluminum plate. Regulating the opening of solenoid valves, one connected to ::ach nozzle, controls the amount of solution discharged from the nozzle. All 72 solenoid valves are controlled individually, so that the amount of solution discharged from each nozzle can be varied as required. Another key technology introduced into this plug seedling factory is that the plug trays for this factory are made out of moisture-permeable biodegradable paper pulp and molded with the precision engineering accuracy required to locate the hole in each plug cell right over the injection nozzle.
Humidity 75%
~ Fig.3 Experiment two
50
iile third experiment investigated the influence of air currents on evaporation from a pulp pot. A pot filled with saturated soil was prepared as in the first experiment; however, there was airflow near the pot surface, as shown in Fig. 4. The total moisture loss from the pot was measured by the change of weight of the whole pot.
stagnant and humid. The soil inside the plug cells that have more sides facing the open air is more likely to lose more moisture. For instance, a plug cell at a corner has two sides exposed to the open air, while cells on the side of the tray have one side facing out.
o humidificasion
I!lli raw
500 400 '-' .~ 300 ~g. 200 100
i
a>
0
48
72
Fig.6 Difference in water content with cell location Fig.4 Experiment three
Figure 7 indicates that a higher humidity around plug cells can suppress the moisture loss significantly. .
3. RESULTS AND DISCUSSION
mplastic
o paper Figure 5 shows the results of the first experiment. There was an obvious difference in the moisture loss from the pulp and plastic trays. Since the area exposed to air was almost identical for each tray, the moisture loss must differ because moisture was removed from the soil through the sides of the moisture-permeable plug cells.
0.850 ~
~ 0.750 ~
(;j ~
0.650 0.550 A
o paper
B
mplastic
800
C position
Fig.7 Daily water loss in Experiment 2
;;., ----
~ 600
~
=
.9
Figure 8 shows the results of the third experiment. The average decrease in weight of 9 treated pots was greater than that of the control. Fig. 8 indicates that air currents around the paper pots accelerates the moisture loss.
400
~o 200
~
0 24
48 - - - air current
(g)
Fig.5 Daily evaporation in Experiment 1
250 200 150 100
Figure 6 also shows the influence of the moisturepermeable material on moisture loss. There was no difference in moisture loss between cells at different locations for the plastic tray. On the other hand. differences in location resulted in differences in moisture loss with the pulp tray, as shown in Fig. 6. At the center of the pulp tray, the air surrounding the pulp plug cells remains
....
::s: .... ~ '-.....
50
~
• - - - raw
-.... . -
o o
~ ho
Fig.S Change of weight with air current
51
4. CONCLUDING REMARKS
The results of this study suggest a basic means of controlling the soil moisture in pulp plug cells. Controlling the humidity around the pulp plug cells regulates the movement of moisture through the pulp material. Such a control technology improves the prospects for microprecision agriculture.
52
Graduate School ofAgriculture and Biological Science. Osaka Prefecture University
Abstract: This paper presents an example of microprecision technology implemented in a plug seedling production factory, as an example of variable rate application technology used in precision agriculture. A microprecision irrigation system was developed for a plug production system. The device was designed to fit a 300 x 600mm 72-cell tray made of moisture-permeable biodegradable paper pulp. This paper investigated tlle moisture permeability of the paper pulp, in order to seek a way of controlling tlle root zone moisture using microprecision technology. The experiment investigating the influence of humidity near the cells on evaporation from rite soil found that a higher humidity around the plug cells suppresses moisture loss significantly. This suggests a means of controlling the soil moisture of pulp plug cells. By controlling the humidity around the pulp plug cells, the movement of moisture through the pulp material can be regulated. Such control technology improves the prospects for microprecision agriculture. Key words : pulp plug tray, water potential, moisture permeability
1. INTRODUCTION
open-field system. The fully controlled environment of a plant factory is an ideal cultivation system in teons of alternative agriculture. Most of the environmental factors in a fully controlled plant factory are observable and controllable; a plant factory can be optimized more easily than an open field. This paper proposes a way to implement the concept of precision agriculture in a fully controlled plant factory. In this approach. PA becomes Microprecision Agriculture, which can then be implemented in plant factories to realize profitable alternative agriculture. This paper presents an example of microprecision
The development of precision technologies to reduce the use of off-farm inputs supported by the extensive application of information technology, including GPS and GIS, and mechatronic teclmoJogy, including sensor fusion and intelligent control, has become a major issue in precision agriculture. With significant support fro m both the agricultural and industrial sectors, PA now promises to be able to handle open-field agriculture, which is a very complex system. Although a plant factory is also a large-scale complex system, it is much less complex than an
49
technology implemented in a plug seedling production factory, as an example of variable rate technology used in precision agriculture. A microprecision irrigation system was developed for a plug production system. In this system, only seedlings that require water (nutrient solution) are irrigated, and the proper amount of solution needed for a particular plant is dispensed where the roots of each particular plant have developed. This minimizes wasted irrigation water, and there is no residual solution on leaf surfaces. No recycling of nutrient solution is considered, since there is no overflow of the nutrient solution. The nutrient solution must be supplied from the bottom of the cell by injecting it from a nozzle directly into the substrate (soil). The cells must have an appropriately sized hole at the bottom. The injection process should be completed as quickly as possible, since a very large number of seedlings must be irrigated. Leakage of solution from the cell should be minimized or avoided, both during and immediately after injection. With these factors in mind, a microprecision irrigation device was developed (Fig. 1).
The characteristics of the tray material enabled us to devise a technique for contro:iing the root-zone moisture of the plug seedlings. This is another microprecision teclmology for optimizing the root zone moisture of plug seedlings. This study investigated the moisture permeability of the paper pulp used for the plug tray to devise a way of controlling root zone moisture.
2. MATERIALS AND METHODS The first experiment investigated moisture loss or evaporation from the pulp tray. Soil was saturated with water and each plug cell was filled with moist soil and the tray was left for 2 days in a room at 25°C and 75% humidity. The moisture loss of cells at the locations specified in Fig. 2. was measured by the oven drying method. As a control, the same measurements were made using a traditional plastic tray. The total weight changes of the plastic and pulp trays were compared.
a
b
b
a
I)
a
c c
a
b
Fig.2 Cells tested The second experiment investigated the influence of humidity near the cell surface on the evaporation from the soil. A tray filled with saturated soil was prepared in !t.e same manner as in the first experiment; however, the bottom of the tray was covered Witll an impermeable material, as shown in Fig. 3. The space between the cover and the plug cell surface was filled with air at 80% relative humidity. The total moisture loss from the tray was measured by weighing the whole tray every 24 hours for 3 days.
Fig. l The microprecision irrigation device The device was designed to fit a 300 x 600 nun 72-ceIl tray. The solution is discharged from 72 nozzles fixed on an aluminum plate. Regulating the opening of solenoid valves, one connected to ::ach nozzle, controls the amount of solution discharged from the nozzle. All 72 solenoid valves are controlled individually, so that the amount of solution discharged from each nozzle can be varied as required. Another key technology introduced into this plug seedling factory is that the plug trays for this factory are made out of moisture-permeable biodegradable paper pulp and molded with the precision engineering accuracy required to locate the hole in each plug cell right over the injection nozzle.
Humidity 75%
~ Fig.3 Experiment two
50
iile third experiment investigated the influence of air currents on evaporation from a pulp pot. A pot filled with saturated soil was prepared as in the first experiment; however, there was airflow near the pot surface, as shown in Fig. 4. The total moisture loss from the pot was measured by the change of weight of the whole pot.
stagnant and humid. The soil inside the plug cells that have more sides facing the open air is more likely to lose more moisture. For instance, a plug cell at a corner has two sides exposed to the open air, while cells on the side of the tray have one side facing out.
o humidificasion
I!lli raw
500 400 '-' .~ 300 ~g. 200 100
i
a>
0
48
72
Fig.6 Difference in water content with cell location Fig.4 Experiment three
Figure 7 indicates that a higher humidity around plug cells can suppress the moisture loss significantly. .
3. RESULTS AND DISCUSSION
mplastic
o paper Figure 5 shows the results of the first experiment. There was an obvious difference in the moisture loss from the pulp and plastic trays. Since the area exposed to air was almost identical for each tray, the moisture loss must differ because moisture was removed from the soil through the sides of the moisture-permeable plug cells.
0.850 ~
~ 0.750 ~
(;j ~
0.650 0.550 A
o paper
B
mplastic
800
C position
Fig.7 Daily water loss in Experiment 2
;;., ----
~ 600
~
=
.9
Figure 8 shows the results of the third experiment. The average decrease in weight of 9 treated pots was greater than that of the control. Fig. 8 indicates that air currents around the paper pots accelerates the moisture loss.
400
~o 200
~
0 24
48 - - - air current
(g)
Fig.5 Daily evaporation in Experiment 1
250 200 150 100
Figure 6 also shows the influence of the moisturepermeable material on moisture loss. There was no difference in moisture loss between cells at different locations for the plastic tray. On the other hand. differences in location resulted in differences in moisture loss with the pulp tray, as shown in Fig. 6. At the center of the pulp tray, the air surrounding the pulp plug cells remains
....
::s: .... ~ '-.....
50
~
• - - - raw
-.... . -
o o
~ ho
Fig.S Change of weight with air current
51
4. CONCLUDING REMARKS
The results of this study suggest a basic means of controlling the soil moisture in pulp plug cells. Controlling the humidity around the pulp plug cells regulates the movement of moisture through the pulp material. Such a control technology improves the prospects for microprecision agriculture.
52