by
YOSHIHIRO MATIDA
Fresh-water Fisheries Research Laboratory
Hino-shi, Tokyo, Japan
Abstract
The paper reviews briefly some roles of soil in the mechanism of fish production in various kinds of fish culture in Asia and the Far East. Supply of nutrients from environs and bottom soil, relationship between mineralization of precipitated organic matter and properties of soil, and transformation of nutrient compounds with the change in physicochemical conditions in soil and with various practices such as drying, furrowing and liming are discussed. Attention is drawn to problems which need to be studied further.
LE ROLE DES SOLS DANS LA PRODUCTIVITE DES ETANGS DE PISCICULTURE EN ASIE ET EN EXTREME-ORIENT
Résumé
Cette communication passe succinctement en revue certains aspects du rôle des sols dans le mécanisme de la production de poisson dans divers types d'élevage en Asie et en Extrême-Orient. Diverses questions sont examinées : l'apport d'éléments nutritifs en provenance du sol des environs et du fond de l'étang, les rapports entre la minéralisation de la matiére organique précipitée et les caractéristiques du sol et enfin la transformation des composés nutritifs en fonction de la modification des conditions physico-chimiques du sol et de diverses pratiques telles que l'assec, le labourage et le chaulage. L'attention est attirée sur certains problémes qui demandent à être étudiés plus à fond.
LA FUNCION DEL SUELO EN LA PRODUCTIVIDAD DE LOS ESTANQUES PISCICOLAS EN ASIA Y EL LEJANO ORIENTE
Extracto
En este documento se examinan sumariamente algunas de las funciones de los suelos en el mecanismo de la producción piscícola en varias clases de piscicultura de Asia y el Lejano Oriente. Se estudia el suministro de elementos nutrientes de los alrededores y del suelo del fondo, la relación entre la mineralización de la materia orgánica precipitada y las propiedades del suelo, y la transformación de los compuestos nutrientes con el cambio de las condiciones físico-químicas del mismo, así como de varias prácticas tales como el desecado, trazado de zanjas y adición de cal. Se señalan, para su atención, los problemas que necesitan ser estudiados más a fondo.
Soils have several roles in the production of fish from ponds; in supplying nutrients to the inflowing water, in the mineralization of organic bottom deposits, and in the storage and release of nutrients to the water. They also provide shelter and food for bottomdwelling organisms (an aspect not included in this review).
The natural waters supplying fish ponds contain various dissolved substances which are essential for fish production. According to Schuster (1949), substances carried into the pond with the water are the main source of nutrients in Java, where ponds are not manured and the river water contains extraordinarily large quantities of nutrients as it is mostly drawn from volcanic mountains. Eruptions of the big volcanoes in East Java help to maintain the productivity of “tambaks” in Surabaya and Sidoardjo. Kobayashi (1958; 1960) analysed thousands of water samples of natural surface waters in Japan and South-East Asia and emphasized the close relationship between the mineral composition of the water and the geological properties of the basin.
Correlations have been found between concentration of minerals in river water and fish production (Moritsugu and Kobayashi, 1960), which is to be expected as the production of fish food depends on the minerals. Hickling (1962) noticed that the greater the supply of natural food in a pond, the greater the amount of supplementary food that can be given. It may mean that the greater the production of natural food, the greater would be the effect of supplementary food on the fish crop. So the use of water flowing over a fertile soil may also be beneficial in running-water fish ponds where intensive feeding is usually carried out. The value of such rich waters is generally recognized by running-water carp culturists in Japan.
The nutrients brought in with the inflowing water are usually insignificant compared with those supplied from the pond bottom in stagnant fish ponds (Hickling, 1962). However, intensive fish culture is most widely conducted in stagnant ponds in Asia and the Far East by heavy fertilization with organic manures and/or intensive feeding with artificial or supplementary foods. In Chinese fish culture, the techniques of which are summarized by Chou et al. (1961), almost no attention is paid to the supply of nutrients from the bottom soil.
Fertile soil is the best for pond construction, because of its capacity to supply nutrients to the water, but in practice land unsuitable for agriculture is generally used, since such land can give a better income as fish ponds than in any other way (as advocated by Schäperclaus, 1933; Schuster, 1949; Chou et al., 1961; Hickling, 1962). The Tropical Fish Culture Research Institute at Malacca is carrying out pioneer experiments in the use of “gelam” soil, which is sterile and even toxic for agriculture because of the high sulphate content (Malacca, 1960; 1961; 1962; 1963). At Malacca the pond water remained neutral in the acid soil ponds because of the strongly absorptive ferric hydroxide on the surface of the pond bottom (Hickling, 1962). The liming of these ponds had no significant effect on the fish crop, but the application of about 2.2 kg P2O5/ha, without any limestone, had a remarkably significant effect (increasing the crop from 104 kg/ha to 232 kg/ha per six months), and harvests of about 900 kg/ha in six months were obtained with 90 kg P2O5 when proper combinations of species were stocked.
The retention of phosphorus in the pond soil and a residual effect on fish production were recognized at Malacca (Hickling, 1962; Malacca, 1963). The residual effect of phosphate fertilizer has been proved in Europe (Mortimer and Hickling, 1954; Hickling, 1962). The conversion of phosphate fertilizer into fish at Malacca was surprisingly more efficient (30 kg P2O5 with 10 kg fish) compared with conversion in European carp ponds and American bass ponds, which was probably because the fishes at Malacca feed directly on the plant growth stimulated by the fertilizer (Prowse, 1962; 1963; 1964).
Preliminary experiments have shown that precipitated phytoplankton was not well-decomposed in a pond with a concrete bottom, remaining as a green gelatinous layer several centimeters thick, whereas no such layer remained on sand- or paddy-soil bottoms (Matida, unpublished report). These trials have indicated how pond soil effectively decomposes precipitated organic matter, accelerating the turnover of nutrients, and retaining some nutrients in it. Even in running-water fish culture the benefits of using mud ponds or natural streams are commonly recognized by trout and sweetfish (Plecoglossus altivelis) culturists because they have a remarkable capacity for self purification, making frequent cleaning unnecessary. In addition, sweetfish utilize algae attached to the gravels and never suffer from malnutrition (Hidaka, pers. comm.).
Although there has been no thorough experimental work on the relation between the size of particles and decomposing activity in fish ponds, Chou et al. (1961) recognize that extremely fine particles such as clay are not suitable for Chinese fish ponds, where a great deal of organic manure and/or supplementary foods are used. Lin (1940) and Chou (1961) state that as the organic matter exceeds the decomposing capacity of the pond soil, ponds must be dried, and mud must be taken off once every one or two years. In the abovementioned experiment there was no significant difference between paddy-soil and sand as far as decomposing activity is concerned.
The preference for different types of soil varies with the type of fish culture, as exemplified by the brackish-water fish ponds of the Philippines and Java. Frey (1947) found that the greatest production of algae, on which the milkfish (Chanos chanos) feed, occurred in ponds having bottoms of peaty clay, either compact or matter in structure, or slimy clay, slightly organic and gelatinous in consistency, while the least production was associated with sandy bottoms. According to Schuster (1949), ponds are flooded with fertile estuarine water during the incoming tide and neither artificial fertilizers nor supplementary foods are used. The main roles of pond soil in fish culture seem to be the accumulation of nutrients brought in by the tides and the provision of a living place for benthic algae. Colloidal matter on the surface of bottom soil may have a very important role in this respect. The retaining of nutrients by soil colloids is well appreciated in European fish ponds, where fishes are raised with inorganic fertilizers and artificial foods, and considerable literature on this role of soil has been cited by Mortimer and Hickling (1954) and Maciolek (1954).
The decomposition of organic matter withdraws large quantities of oxygen and may cause an oxygen deficiency. Deoxygenated or anaerobic conditions are avoided in all types of fish culture. Sano and Matsue (1957a, b) considered that dissolved oxygen was one of the most important factors controlling fish production in Japanese eel ponds. If deoxygenation becomes so intense that anaerobic or reducing conditions occur, various toxic substances are produced. Among them hydrogen sulphide has been studied extensively. In ponds where the water is rich in sulphate (for example in saline water) the reduction of sulphate ions to hydrogen sulphate easily occurs, and its presence in the bottom water or soil makes it impossible to raise fish in certain ponds.
Traditional measures to overcome deoxygenation include drying, liming and eliminating sludge. To improve the soil of prawn ponds in wet rice fields which cannot be drained, the bottom water is drained off through perforated pipes installed under the surface of the bottom sand (Yamamoto et al., 1960). In this case, the bottom water contaminated with excreta and food residue is merely discharged through the bottom sand, on which prawns creep and eat food, or in which they hide. But the water may be reused, since the decomposition or purification activity of sand can be utilized and the water can be mechanically oxygenated if necessary. In order to keep the bottom soil in oxidized condition, the drained water may have to contain more than 8 percent of oxygen. The observation of Pearsall and Mortimer (1939) is relevant in this respect. Such a technique is widely employed in aquaria. Saeki (1958) studied the relationship between the purification capacity of a sand filter, size of sand and amount of sand. Saeki and Aoe (1962) succeeded in raising 500 kg of carp by re-using 205 m3 of water. Chiba (private communication) found that nitrogen introduced as food in an aquarium was retained as nitrate and fish flesh; a recognizable loss of nitrogen was not observed. In this experiment water was kept neutral by occasional addition of sodium bicarbonate.
It is well known that bottom water contains many nutrients and vertical mixing by wind force or thermal convection is one of the most important mechanisms controlling the productivity of natural lakes and certain fish ponds. Maciolek (1954) has summarized the work on this subject with special reference to pond fertilization. The main reasons why fish ponds should not be too deep are related to this factor and the need for proper aeration.
Mortimer (1941; 1942; 1949; 1959), Inaba (1961) and Hickling (1962) have explained the reasons for diurnal or seasonal fluctations of dissolved oxygen of the bottom water and its role in production. Nutrient ions are produced by the decomposition of precipitated organic matter. Under oxidizing conditions the ions, except nitrite and nitrate ions, are adsorbed on soil colloids composed of clay minerals, ferric hydroxide, humus and so forth, and these ions are released into the water under reducing conditions. Stephenson (1951) also found that phosphate was given off rapidly from surface layers of estuarine mud when the supernatant water becomes de-oxygenated; he thought that the phenomenon might be partially due to catastrophic biological changes. If these released nutrients are then distributed in the pond water, they are taken up by plants, and thence by fish. Although ferrous ions may also be released and oxidized, the amount of ions adsorbed on colloidal ferric hydroxide will decrease when it is diluted in the upper layer, since Freundlich's adsorption isotherm suggests that the amount of ions adsorbed per unit weight of colloidal matter decreases in more dilute conditions. Furthermore, the nature of colloidal matter in supernatant water may be different from that on the pond bottom, though this problem has not been much studied. Freundlich's adsorption isotherm is recognized as the most widely applicable to adsorption in liquids, and the equation was also found to be applicable for pond water (Matida, 1956).
Ohle (1938) found that by raising pH, nutrients such as phosphate adsorbed on ferric hydroxide were easily washed out, and this may explain why nutrients are easily released in the more alkaline upper water. This amphoteric property of ferric hydroxide also explains how nutrients adsorbed by pond mud may be released even under oxidizing conditions if the ambient water is alkaline.
Nutrients are precipitated not only as dead organisms but also in other forms. Einsele (1938) considered that phosphate ions are precipitated as ferric phosphate, but Mortimer and Hickling (1954) prefer to regard the precipitation process as one of adsorption of phosphate ions on colloidal ferric hydroxide, because the concentration of phosphate decreases well below the concentration calculated from the solubility of ferric phosphate. Hepher (1958) indicated that in the very calcareous pond muds of Israel, most of the added phosphate is fixed in the pond mud as insoluble calcium phosphate. Suspended matter of 0.5 to 1.2 μ was analyzed from a fertilized pond, where the amount of phosphate applied was well below the solubility of calcium phosphate (Matida, 1956), and the content of inorganic phosphorus in the suspended matter was found to be higher in deeper layers than in the surface layer. Enough iron could not be detected in the particles to satisfy the stoichiometric relation of ferric phosphate. There may be other processes of precipitation by the adsorption of phosphate ions on detritus and silt.
The analogy between rice fields and fish ponds is not complete, as aquatic organisms depend mostly on the nutrients released into the water by the decomposition of precipitated matter, mainly organic matter as mentioned above, but rice plants depend on the nutrients in the mud itself. Knowledge of the chemistry of waterlogged soil, especially chemical processes in it, depends largely on the researches on rice field soil. Various aspects of these researches on rice field soil of significance in fish culture have been summarized by Hickling (1962).
As in certain fish ponds, the upper soil of rice fields is furrowed when it is dried. After flooding the furrow slice is in a reduced condition, except for the surface layer in contact with the supernatant water. According to Shiori and Aomine (1940) and Aoki (1941), mixing in organic manures, drying well before flooding, or making neutral or slightly alkaline by liming, decreases the redox potential of the subsurface soil, and the formation of ammonia, ferrous ions and sulphide ions after flooding are thereby accelerated, and the availability of phosphate is also increased. The effects of these practices are believed to make organic compounds more easily decomposable. In the three to ten mm thick top layer, nitrate, sulphate and ferric ions are stable, and the redox potential is always higher than 0.3 volts at pH 5. In the lower layer, ammonia, sulphide and ferrous ions are stable, according to Shioiri and Tanada (1954). These results agree with observations in lakes by Pearsall and Mortimer (1939) and Mortimer (1941; 1942).
The chemical changes mentioned above are accompanied by an increase in pH and the sorption capacity of soil to ammonia and phosphate (Kawaguchi, 1950). These physicochemical properties of paddy soil after flooding not only minimize the losses of nutrients by seepage and water exchange, but also increase the availability of nutrients. They may explain the role of pond soil as a reservoir of phosphorus in fish ponds and the residual effect of phosphorus. Osugi et al. (1932 - cited in Kawaguchi, 1950) and Lu and Chung (1964) have studied the solubilities of various phosphate minerals under different pH values. Solubilities of most phosphates increase under alkaline conditions. These results also explain the mechanism of phosphorus cycle in fish ponds. According to Watts (1965a,b), most phosphates in the pond mud of Malacca are organic - and occluded - forms, and the remainder chiefly in association with iron, aluminium or calcium in the layer. He also found that the retention capacity of fresh mud was higher than that of air-dried mud, and the depth of penetration of phosphorus was about 2 cm.
It is generally recognized that nitrate is less effective than ammonia in rice fields. This is partly due to the escape of nitrate ions with water exchange because nitrate is not well adsorbed by soil compared with ammonia (Kawaguchi, 1950). In addition nitrate is reduced to nitrogen by chemical and biological processes at the boundary of reducing and oxidizing layers. Shioiri and Tanada (1954) confirmed the occurrence of nitrogen loss by this process by determining the increase in nitrogen gas and the decrease in nitrate. Furthermore, it is well known that some blue-green algae can fix very considerable quantities of atmospheric nitrogen. Although the exact form in which it is fixed is not known, an excess is excreted into the water, and the present author (Matida, 1956) confirmed that the amount was enough to make the application of nitrogen fertilizers unnecessary. It is well known that some soil bacteria also fix atmospheric nitrogen (Kawaguchi, 1950) but its practical significance is unknown. This may explain why the effect of nitrogen fertilizers is not well evaluated in fish ponds.
The behaviour of phosphates and nitrates in shallow sea soil is similar to that in rice field soil, and has been studied by Okuda (1953a,b; 1955a,b; 1957a,b).
The existence of areas of podzolic or degraded rice field soil is well recognized by soil scientists. In such soils the content of free iron, active manganese and phosphorus in the furrow slice is far less than in normal rice field soil, and sulphuretted hydrogen is easily liberated under the reduced conditions. This condition is remedied by mixing surface and deep soil, or by enriching iron and manganese. The electrokinetic potential difference (zeta potential) of negatively charged soil colloids is decreased by ferrous ions under neutral or slightly acid conditions. Shioiri and Nishigaki (1938) observed that the zeta potential of soil colloids is decreased under reducing conditions by the ferrous ions liberated, and they concluded that the elluviations of iron, manganese, phosphorus and organic matter in rice field soil are ascribable to the decrease in zeta potential. Shioiri and Yokoi (1950) also found that the leaching was accelerated by peptization of ferrous sulphide with excessive sulphuretted hydrogen.
It may not be unreasonable to expect that similar degradation of pond soils occur. In addition, precipitated organic matter and sulphate ions in saline water supply much sulphur in excess of the active iron in pond soil. Koyama and Sugawara (1951) found that sulphate ions in water were taken into soil by co-precipitation. The degradation of fish pond soil by the processes mentioned above is thought to have made Japanese eel culturists employ the technique of rice farmers; namely, the application of lowgrade iron ore (Satomi, private communication).
Nitrogen and phosphorus in pond soils have been studied by many workers but enough attention has not been paid to trace elements. Henderson (1949) found that the application of manganese promoted the growth of phytoplankton in a pond. Mortimer (1939) also found that the lack of some unknown nutrients, which were normally brought in from the surrounding land, limited the production of algae in a lake. These examples, the general productiveness of soil drainage and the successful use of soil extracts in algal cultures, all seem to suggest that studies on the cycles of trace minerals and other unknown growth-promoting substances will become important. Such a study has already been initiated by Donaldson, Olson and Donaldson (1959) in a cold-water lake.
In addition, most chemical studies of bottom soil have been mainly focused on the tracing of chemical transformations which connect both processes of supply and consumption in the cycle of nutrient elements. More studies on the nature of soil colloids seem to be necessary in order to fully understand the mechanisms of various chemical changes in pond soil.
Aoki, M., 1941 Studies on the behavior of soil phosphoric acid under paddy field condition (1). J.Sci.Soil, Tokyo, (15):182–202
Chou, U. et al., 1961 Fresh-water fish culture in China. Peking, Science Publishing House. 612 p.
Donaldson, L.R., P.R. Olson and J.R. Donaldson, 1959 The Fern Lake trace mineral metabolism program. Trans.Amer.Fish.Soc., 88:1–6
Einsele, W., 1938 Uber chemische und kolloidchemische Vorgänge in Eisen-Phosphat-Systemen unter limmochemischen und Limnogeologischen Gesichtspunkten. Arch.Hydrobiol. (Plankt.), 33:361–87
Frey, D.G., 1947 The pond fisheries of the Philippines. J.Mar.Res., 6:247–58
Henderson, C., 1949 Manganese for increased production of water-bloom algae in ponds. Progr. Fish.Cult., 11(3):157–9
Hepher, B., 1958 On the dynamics of phosphorus added to fish ponds in Israel. Bamidgeh, 10(1):3–18
Hickling, C.F., 1962 Fish culture. London, Faber and Faber, 295 p.
Inaba, D., 1961 Fresh-water fish culture. Tokyo, Koseisha Koseikaku. 318 p.
Kawaguchi, K., 1950 Chemistry of the soil, No.6. Chemistry of paddy soil. Tokyo, Yokendo. 89 p.
Kobayashi, J., 1958 Chemical studies of the rivers in South East Asia. Nogaku Kenkyu, 46(2):63–112
Kobayashi, J., 1960 Studies on the average water quality and characteristics of Japanese rivers. Nogaku Kenkyu, 48(2):63–106
Koyama, T. and K. Sugawara, 1951 Sulphate co-precipitation in lake and sea and its concentration in the bottom deposits. J.oceanogr.Soc.Japan, 6(4):190–1
Leitritz, E., 1959 Trout and salmon culture. Fish.Bull., Sacramento, (107):169 p.
Lin, S.Y., 1940 Fish culture in ponds in the new territories of Hong Kong. J.Hongkong Fish. Res.Sta., 1(2):161–93
Lu, R.K. and P.F. Chung, 1964 On the availability and transformation of crystalline iron phosphate (strengite) in acidic paddy soils. Sci.sin., 13(1):93–6
Maciolek, J.A., 1954 Artificial fertilization of lakes and ponds. A review of literature. Spec.sci.Rep.U.S.Fish Wildl.Serv.-Fish., (113):49 p.
Malacca, 1960 Tropical Fish Culture Research Institute, Rep.trop.Fish.Cult.Res.Inst., 1957–9
Malacca, 1961 Rep.trop.Fish.Cult.Res.Inst., 1959–60
Malacca, 1962 Rep.trop.Fish.Cult.Res.Inst., 1960–61
Malacca, 1963 Rep.trop.Fish.Cult.Res.Inst., 1961–62
Malacca, 1964 Rep.trop.Fish.Cult.Res.Inst., 1963
Matida, Y., 1956 Study of farm pond fish culture. No.3. Fates of fertilized elements and the relationship between the efficiency of fertilizer and bio-chemical environment in the pond. Bull.Freshw.Fish.Res.Lab., Tokyo, 6(1):27–39
Moritsugu, M. and T. Kobayashi, 1960 Study of trace metals in bio-materials (1). Geographical difference of metals contained. Nogaku Kenkyu, 47(3):149–88
Mortimer, C.H., 1939 Physical and chemical aspects of organic production in lakes. Ann.appl. Biol., 26:167–72
Mortimer, C.H., 1941 The exchange of dissolved substances between mud and water in lakes. J.Ecol., 29:280–329
Mortimer, C.H., 1942 The exchange of dissolved substances between mud and water in lakes. J.Ecol., 30:147–201
Mortimer, C.H., 1949 Seasonal changes in chemical conditions near the mud surface in two lakes of English Lake District. Verh.int.Ver.Limnol., 10:353–6
Mortimer, C.H., 1959 The physical and chemical work of the Freshwater Biological Association, 1935–57. Advanc.Sci., 61:524–30
Mortimer, C.H. and C.H. Hickling, 1954 Fertilizers in fish ponds. Fish.Publ.Lond., (5):155 p.
Ohle, W., 1938 Die Bedeutung der Austauschvorgänge Schlamm und Wasser für den Stoffkreislauf der Gewässer. Vom Wasser, 13:87–97
Okuda, T., 1953a On the soluble nutrients in bay deposits. 1. An examination on the soluble nutrients in bay deposits. Bull.Tohoku Fish.Res.Lab., 2:109–17
Okuda, T., 1953b On the soluble nutrients in bay deposits. 2. On the possibility of supply of the nutrients of muddy deposits into the sea water by bottom harrowing. Bull.Tohoku Fish.Res.Lab., 2:118–25
Okuda, T., 1955a On the soluble nutrients in bay deposits. 3. Examinations on the diffusion of soluble nutrients to sea water from mud. Bull.Tohoku Fish.Res.Lab., 4:215–42
Okuda, T., 1955b On the soluble nutrients in bay deposits. 4. An experiment on the behaviour of phosphate-phosphorus between mud and sea water. Bull.Tohoku Fish.Res.Lab., 5:79–91
Okuda, T., 1957a On the soluble nutrients in bay deposits. 5. Influence of the temperature on the formation of ammonia-N and phosphate-P during the storage of bottom muds. Bull.Tohoku Fish.Res.Lab., 9:143–50
Okuda, T., 1957 On the soluble nutrients in bay deposits. 6. Seasonal changes of the inorganic nitrogen and phosphorus in the pore water of bottom muds. Bull.Tohoku Fish.Res.Lab., 9:151–64
Pearsall, W.H. and C.H. Mortimer, 1939 Oxidation-reduction potentials in waterlogged soils, natural waters and muds. J.Ecol., 22:483–501
Prowse, G.A., 1962 The use of fertilizers in fish culture. Proc.Indo-Pacif.Fish.Coun., 9(2):73–5
Prowse, G.A., 1963 Neglected aspects of fish culture. Curr.Aff.Bull.Indo-Pacif.Fish.Coun., (36):10 p.
Prowse, G.A., 1964 Some limnological problems in tropical fish ponds. Verh.int.Ver.Limnol., 15:480–4
Saeki, A., 1958 Studies on fish culture in the aquarium of closed-circulating system. Its fundamental theory and standard plan. Bull.Jap.Soc.sci.Fish., 23(11):684–95
Saeki, A. and M. Aoe, 1962 An example of raising one ton of carp in a closed-circulating pond. Aquiculture, Tokyo, Extra Ed. (1):13–27
Sano, K. and Y. Matsue, 1958a Oxygen metabolism in eel culture ponds. 1. Theoretical fish culture methods based on oxygen metabolism. Aquiculture, Tokyo, 6(1):43–9
Sano, K., 1958b Oxygen metabolism in eel culture ponds. 2. The application of theoretical fish culture method for eel cultures. Aquiculture, Tokyo, 6(1):50–5
Schäperclaus, W. and F. Hund, 1933 Textbook of pond culture. Rearing and keeping of carp, trout and allied fishes. Fish.Leafl.Wash., (311):260 p.
Schuster, W.H., 1949 Fish culture in brackish-water ponds of Java. Spec.Publ.Indo-Pacif.Fish. Coun., (1):143 p.
Schuster, W.H., G.L. Kesteven and G.E.P. Collins, 1954 Fish farming and inland fishery management in rural economy. FAO Fish.Stud., (3):64 p.
Shiori, M. and S. Aomine, 1940 The effect of drying the paddy soil before flooding. Spec.Rep. agric.Exp.Sta., 30 p.
Shiori, M. and S. Nishigaki, 1938 Colloidal behaviour of waterlogged paddy soil. J.Sci.Soil, Tokyo, (17):287
Shiori, M. and T. Tanada, 1954 The chemistry of paddy soil in Japan. Tokyo, Ministry of Agriculture and Forestry, 46 p.
Shiori, M. and H. Yokoi, 1950 The leaching mechanism of iron sulphides in degraded rice soils. J.Sci.Soil, Tokyo, 20:157–61
Stephenson, W., 1951 Preliminary observations upon the release of phosphate from estuarine mud. Proc.Indo-Pacif.Fish.Coun., Sect. 3:184–9
Watts, J.C.D., 1965a Liming of the local acid sulphate soils. Invest.Rep.trop.Fish.Cult.Res. Inst., (1):4 p.
Watts, J.C.D., 1965b The chemical analysis of muds from the pond system of the Tropical Fish Culture Research Institute. Invest.Rep.trop.Fish.Cult.Res.Inst., (3):9 p.
Yamamoto, T. et al., 1960 The under-drain for the shrimp culture pond. Its purpose, method of construction, and effect. Aquiculture, Tokyo, 8(2):133–7
