JP2000197420A - Phyto-remediation technology using sea water irrigation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a phyto-remediation technology effective for suppressing the salt concentration below a specific level to enable the planting of salt- resistant plants and prevent the desertification by carrying out the irrigation with sea water under a specific condition. SOLUTION: Irrigation with sea water is carried out in flooded state. Salt- resistant plants can be planted on the land irrigated with sea water by the above method. The salt concentration in the soil is lowered to <=4% by the realistic quantity of water supply by the leaching effect (wash-out of salt by a large amount of irrigation water) caused by the irrigation with sea water to obtain soil having salt concentration comparable to that of the supplied water. The effective salt-resistant plants are e.g. Phoenix dacylifera and others distributed over ten orders such as order Liliiflorae.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to irrigating seawater and vegetating salt-tolerant plants to prevent desertification.

[0002]

2. Description of the Related Art Irrigated agriculture is carried out in arid and semi-arid lands due to lack of water. Due to unique natural conditions, irrigation causes salt accumulation in agricultural land, cultivation becomes impossible, and desertification is promoted. It has become. Water-saving irrigation such as drip irrigation is the mainstream irrigation method in the current desert greening. On the other hand, the concept of seawater irrigation, which uses abundant seawater for irrigation water, is old and was reported in the 1950s. However, there is a concern that salt accumulation may be promoted when seawater is introduced to land, and at present, only some trials have been conducted in Saudi Arabia and other countries.

[0003] The United States, which has a serious problem of salt damage, is conducting research on saltwater cultivation using a halophyte, mainly at the University of Arizona. For seawater irrigation using salty plants, Halophyte is used directly for seawater irrigation (G
lenn et al, 1993), and 120 reports of Halophytes evaluated under seawater irrigation conditions (Aronson, 1988).

[0004] For the availability of saline plants, see Tamali.
A number of salt-tolerant plants have been reported from trees such as x and Acasia to feed crops and oil crops (Biotechnology Association Report 1993, ISSN 0729-0012). For woody species, reference is made to (ISBN 1 86320 07809). However, none of them is beyond the category of empirically listing plants that are said to be salt-tolerant, and there are no cases of systematically studying plant classification based on seawater tolerance evaluation tests.

[0005] On the other hand, although there are many reports on physiological research and genetic research for elucidating the mechanism of salt tolerance, it has not been possible to target seawater-level concentrations. In recent years, reports on genetic analysis using biotechnology and research on recombinant plants have been increasing, but there is no report that salt tolerance actually functioned in the long term. Even a report of the introduction of a synthetic gene for an osmotic agent called betaine glycine into tobacco and rice is a result of only a few days, and at present the function has not been improved enough for practical use.

[0006]

It is an object of the present invention to perform seawater irrigation, suppress the salt concentration below a certain level, and vegetate a salt-tolerant plant to contribute to the prevention of desertification.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on the above problems, and have obtained effective results in controlling the amount of irrigation water and selecting salt-tolerant plants. That is, the present invention provides (1) an irrigation method characterized in that irrigation with seawater is performed in a flooded state, and (2) vegetation of salt-tolerant plants in an irrigated area with seawater. Regarding irrigation methods.

As a measure to prevent an increase in CO ₂ , it is effective to fix carbon dioxide using the ability of plants to fix carbon dioxide. The carbon dioxide fixation capacity of plants is estimated to be 6 t / ha (rice 1 t / ha) in forests, and an improvement in the CO ₂ reduction rate is expected in proportion to the area of greenery. On the other hand, global warming caused by an increase in CO ₂ accelerates desertification, and global desertification is about 6 million annually.
Progressing on a ha scale. Currently one-third of the planet is desert, with little vegetation. Greening this desert,
1 to 6 t / ha of carbon dioxide is fixed, and at the same time, it is also a technology for preventing desertification.

[0009] The present invention relates to the development of a technique for reducing carbon dioxide and preventing desertification by performing greening using abundant seawater (or salt water). By keeping the soil constantly moist with seawater (approximately paddy or keeping the soil moist by intermittent irrigation), the inventors have found that the salt concentration of seawater is 3%.
In the following cases, it has been found that the salt concentration in soil can be suppressed to 4% or less.

The salinity in soil is mainly determined by the amount of evapotranspiration, so that if the amount of supplied water is made infinite, it is expected that the salinity in soil will be the same as the concentration of supplied water. On the other hand, if the supply water is cut, the salt concentration in soil increases due to soil evaporation. By using the method of the present invention, a leaching effect (washing out salt with a large amount of irrigation water) works, and the salinity in soil becomes 4% or less at a realistic amount of supplied water.

That is, if seawater irrigation is performed in a flooded state,
The salinity of the feedwater and the salinity of the soil are almost the same. In the present invention, the “flooded state” includes both a case where water is constantly flooded and a case where flooding and drainage are repeated at a certain interval (semi-flooded). The long-term salinity formula without considering rainfall is based on Scofield's salinity formula.
It is expressed as follows by adding the items for preventing salt accumulation.

Viw · Ciw + Vgw · Cgw + Sm + Sf−Vdw · Cdw−
Sp-Sc-A = ΔSsw where ΔSsw: amount of increase in salt in field soil solution Viw, Vgw, Vdw: amount of irrigation water, groundwater, and drainage (Vgw is the amount of water that moves upward from the groundwater surface to the root area) Ciw, Cgw, Cdw: Salt concentration of irrigation water, groundwater, drainage Sm: Amount of salts entering soil solution from soil weathering, dissolution of salt sediments Sf: Soluble salts added from pesticides, fertilizers, improvers, compost, etc. Amount Sp: Amount of soluble salts in the irrigation deposited in soil after irrigation Sc: Amount of salts removed from soil solution by crop harvesting A: Amount of salts removed by salt accumulation prevention method Sustainable using seawater In order for irrigation to be possible, it is necessary that ΔSsw ≦ 0.

The water balance is expressed by the following equation. Viw + Vgw = Vdw + ET ET; Evapotranspiration

Using this Scofield salt balance equation, ΔSsw
That is, when the amount of increase in salt in the field soil solution was measured, the standard irrigation water amount (annual average about 30 mm / day) was 50 mm / d.
It was found that it was possible to suppress up to about 3.7% by increasing ay. In order to reduce the salinity during the irrigation period to 4% or less, it is necessary to increase the irrigation water volume by 30 mm / day.
This is about twice the normal amount, and increasing this amount of irrigation water about twice can be handled with a realistic amount of irrigation water.
(Fig. 1)

If irrigation water having a low salt concentration other than seawater can be used, it is advantageous to suppress an increase in salt concentration. I examined irrigation using seawater in brackish water near the estuary, where supply is relatively stable, unlike rainwater. Although the salt concentration of brackish water varies depending on the location, it is about 2.0% as a practical value. Unlike ordinary seawater, the amount of water is limited, so it can be used at one time of irrigation. The use of brackish water at the early stage of irrigation temporarily reduces the initial salinity, but eventually has no effect, as shown in FIG. Therefore, as shown in FIG.
If brackish water is used intermittently instead of pure seawater, the concentration of irrigation water can be reduced to a maximum of about 4%.

Although the specific method differs depending on the amount of brackish water and irrigation water, the use of brackish water as an auxiliary means for irrigation of seawater alone is an effective method even temporarily. Was. In addition, although seawater lacks nitrogen and phosphorus, it is necessary to fertilize plants vegetated in irrigated land by supplementing with nitrogen and phosphorus in domestic wastewater contained in brackish water. The effect of disappearing can also be achieved. In the present invention, "seawater" includes "brass water" and "brine water".

Next, to apply the irrigation method of the present invention, 4
A viable greening material (plant) is required at a concentration of less than 10%. As a result of an evaluation test of a plant having salt tolerance as a greening material, it was found that about 25 kinds of plants survived in seawater for 3 to 6 months, and some plants for 2 to 3 years.

As salt-tolerant plants, Phoenix dacylifer
a, Crinum asiaticum, Ophiopogonjaponicus, Juncus s
p.Iran, Festuca arundinacea, Zoysia marcrostachya,
Zoysia tenuifolia, Zoysia matrella, Cynodon dactyl
on, Spartina alterniflora, Spartina patens, Sporob
olus virginus, Paspalum sp.Hawai, Fimbristyliss
p., Chenopodium album, Chenopodium stenophyllum, C
henopodium acuminatum, Atriplex patula, Atriplex g
melinii, Atriplex subcordata, Suaeda maritima, Sal
icornia bigelovii, Lampranthus sp. Sesuvium sp. Se
suvium portulacastrum, Portulaca pilosa, Limonium
wrightii, Tamalix sp. Sedum sp. Acacia amplicepus, A
cacia bivenosa, Rhizophora sp. Conocarpus sp. Cocc
olba unifera, Avicennia germinans, Aviceria marin
a, Cnidium japonicum, Hedyotis biflora, Eucalyptus
camal, Bruguiera nucronata, Kandelia candel, Mala
lenca leucadendra, Salvadra persica, Casuarina cun
ning hamiana, Casuarina gluaca, Casuarina equiseti
Either folia, Casuarina obesa or Ixeris stolonifera has been found to be effective.

These include Lilies, Cyperaceae, Poaceae, Nadesicoceae, Isopine, Violets, Mansaceae,
It is distributed in the tenth order of Acer, Rubiaceae and Chrysanthemum.
In addition, in agriculture in arid land, drainage control for controlling soil moisture and groundwater level is indispensable at the same time as irrigation. It is necessary to improve drainage channels and culverts and to devise ways to lower the groundwater level below the critical depth. The depth of the groundwater level varies depending on the stratification state of the soil, etc., but one guideline is a depth of 1.2 to 1.5 m for sandy soil and 1.5 to 2.0 m for clayey soil. . That is, irrespective of a special method, the controllable items for suppressing the salt concentration include evapotranspiration, water reduction depth, irrigation water, and salt removal by crop absorption.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION

[0021]

Example 1 Seawater irrigation experiment using lysimeter 1) Simulated desert field As shown in FIG. 4, a lysimeter (earth tank capable of measuring water balance) was constructed. Plane shape 1.7m × 1.7m, depth 50cm
The size of the tank is waterproof with vinyl so that water can be stored, and a drain port is provided in the lower corner and a valve is installed. 2) Soil In order to simulate desert soil, mountain sand from Ichihara City, Chiba Prefecture was filled. Table 1 shows the physical properties.

[0022]

[Table 1]

3) Method (1) Flooding Using seawater from Tokyo Bay as irrigation water, the amount of drainage was set so as to be constantly flooded, and the change in salinity in the field was measured. The drainage was set to 20 mm per day, including the net drainage and the reduction depth.

(2) Semi-flooding Water was immersed in the seawater of Tokyo Bay until it was flooded, the drain was opened, and the water was drained. The water level was set to be 10 cm below the soil surface. After that, natural drainage was performed for 3 to 4 days. This one
It was repeated as a cycle. As a result of the above experiment,
FIG. 5 shows changes in temperature and humidity in the vinyl greenhouse. The measurement time was 10 am every day. Although the values fluctuated due to changes in the weather, the average temperature was around 40 ° C., close to the daytime temperature in the desert. FIG. 6 shows a change in the salt concentration in the field when flooding irrigation is performed.

As the irrigation is performed, the salinity gradually increases from 3% of the seawater salinity and reaches about 4% after 4 months, but tends to almost converge to 4%. FIG.
Shows the change of salinity in the field in the case of irrigation under semi-flooded condition. Since cultivated plants were planted, fresh water was used initially and the salt concentration was 0%, but gradually increased after using seawater, and exceeded 4% four months later. FIG. 8 shows the results obtained when the evapotranspiration in Saudi Arabia was calculated based on the above assumptions. As can be seen, the overall salinity of the field also rises due to the overall increase in evapotranspiration, which may exceed 7%, but the irrigation water volume is 30 mm higher than in Japan.
If it increases by about / day or more, it will almost return to the domestic level at the end of the irrigation period, suggesting that irrigation can be sustained.

[0026]

Example 2 In order to set a target management level of field salinity over a period of several months over a medium to long term, seawater irrigation experiments were conducted on the relationship between salinity and plant salinity using salt-tolerant plants. The selected salt-tolerant cultivated plants are as shown in FIG.

The cultivation field used a lysimeter (FIG. 4) in a vinyl greenhouse to grow plants on sandy soil.
The cultivated plants were grown for about one month without flooding with tap water to survive. After the rooting, 1. water was immersed in seawater with a salt concentration of 3% until the state of flooding, and 2. drainage was opened and drained, and the water level was set to be 10 cm below the soil surface. 3. After 3 to 4 days, the water was drained naturally.
This was repeated as one cycle.

FIG. 10 shows the test results. Trees have a salinity of 2
%, It tends to wither, and it is difficult to withstand a salt concentration of 3% in seawater except for TAMALIX. Monocotyledons are 4% even if damaged
It was found that it survived about half a year tolerating moderate salt concentration. In dicotyledons, shiroza was found to be strong and tolerated 4% concentration, but other species tended to wither at 2% or more like trees. The succulent tight turtle was found to survive even at 4%. Therefore, in consideration of the salt concentration from the plant side, even if it is set to 4% as the target management salt concentration value in the field, it is a realistic value in view of the current state of the existing salt-tolerant plants.

[0029]

Example 3 The effect of removing weeds (plants other than those for cultivation purposes) by seawater irrigation was tested under the same conditions as in Example 1, and the results as shown in FIG. 11 were obtained. That is, it was found that many weeds die within 3 months without using herbicides by seawater irrigation.

[0030]

By combining seawater irrigation technology with plants that can survive in seawater, areas with little fresh water (deserts)
Can be planted, carbon dioxide can be reduced by carbonation fixation of planting plants, and it can contribute to the mitigation of local warming phenomenon. It also has the effect of removing weeds without using a herbicide.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between irrigation water volume and field salinity.

FIG. 2 is a diagram showing a change in field salinity when brackish water is used at the beginning.

FIG. 3 is a diagram showing irrigation using intermittent brackish water.

FIG. 4 is a diagram showing a lysimeter cross section and flooded irrigation.

FIG. 5 is a diagram showing changes in temperature and humidity in a greenhouse.

FIG. 6 is a diagram showing a change in field salinity during flooding.

FIG. 7 is a diagram showing a change in field salinity in semi-flooded water.

FIG. 8 is a diagram showing a change in field salinity in Kafuji.

FIG. 9 is a diagram showing a list of selected salt-tolerant cultivated plants.

FIG. 10 is a view showing the results of a middle / long-term seawater resistance test.

FIG. 11 is a view showing a seawater weeding effect.

FIG. 12 is a view showing a seawater weeding effect. Continuation of FIG.

FIG. 13 is a view showing a seawater weeding effect. Continuation of FIG.

FIG. 14 is a view showing a seawater weeding effect. Continuation of FIG.

Continuing from the front page (72) Inventor Mitsuki Yoshida 1-25-1, Nishishinjuku, Shinjuku-ku, Tokyo Taisei Construction Co., Ltd. (72) Inventor Miho Akiyoshi 1-25-1, Nishishinjuku, Shinjuku-ku, Tokyo Taisei Construction F term in the company (reference) 2B022 AA01 AB02 AB20 DA19

Claims (2)

[Claims] 1. An irrigation method characterized by performing irrigation with seawater in a flooded state. 2. The irrigation method according to claim 1, wherein a salt-tolerant plant is vegetated in a seawater irrigated area.