Rice on saline soils in the Russian Federation

G.L. Zelensky

Kuban State Agricultural University, 350044, Krasnodar, Russian Federation

In southern regions of the Russian Federation there are large areas of saline land which have potential for rice cultivation. There are two ways of realizing this potential: through the adoption of agrotechnical methods of soil amelioration; or through breeding programmes to develop salt tolerance in rice plants at the germination and flowering stages. A new salt-tolerant variety, Kurchanka, has been produced using Russian and foreign varieties.

INTRODUCTION

Rice in the Russian Federation is cultivated to produce valuable dietary fibre. Rice crops play an important role in the reclamation of swamped and saline soils, which cannot be used for growing other crops. In southern regions of the Russian Federation there are huge territories that require large-scale improvement before they can be used for farming. In the Kuban river delta alone there are 110 000 ha of alkaline and saline soils within Krasnodar territory.

Rice growing started to expand very quickly in Kuban in the mid-1960s, and the total area covered by reclamation engineering systems has reached 250 000 ha. Reclamation of saline soils was preceded by wide-scale research, which showed the possibility and usefulness of rice cultivation in this zone. More than 30 years experience of land reclamation has shown that, after five to seven years of growing rice, soils lose excess salinity and, as a result, can be used for cultivating cereals, fodder crops and vegetables.

SALT RESISTANCE OF RICE

Rice's ability to grow on saline soils has been proved in many parts of the world. Many researchers consider rice to be a crop with medium salt resistance and, since water reduces salt concentration, plant growth is not inhibited. Investigations carried out by physiologists have shown that rice is most susceptible to saline soils at the germination, shooting and flowering stages.

It has been found that increased salt concentration has osmotic and toxic effects. The osmotic influence of salts causes the delay of water penetration into cells and the dehydration of protoplasm (Tur, 1978). Their toxic influence is especially strong in the case of excess accumulation of chlorine ions in shoots (Tuyakova, 1978). When rice is grown on saline soils, at emergence plant density is high but decreases at the two to three leaf stage as a result of the dying away of shoots. Salts influence seed germination and seedling growth in several ways: they inhibit enzymes, suppress breathing and the phosphorylation process and change the content of organic phosphate, nucleic acids, protein and nitrogen (Tur, 1978). This is why, at the germination stage, it is important not to have high salinity levels in the subsurface soil layer and irrigation water; and, to avoid this, water is normally replaced in the basins.

Two types of soil salinization are observed in rice growing areas of the Russian Federation - chloride and sulphate. As a rule, salinization involves a mix of both types at various ratios. Sodium chlorides are the most toxic. In both types, an increase of salt concentration causes a decrease in the dry weight of plants, nutrients uptake, nitrogen, phosphorus and potassium (NPK) content and grain yield (Table 1).

Both types of salinization suppress rice growth and yield. Plants perish at 0.7 percent chloride and < 1 percent sulphate soil salinization. However, it has also been found that low concentrations (up to 0.1 percent) of sulphate salts stimulate rice plants.

In rice cultivation in the Russian Federation, irrigation water is used more than once. The total volume of water discharged from Kuban rice fields for repeat use is about 1 billion m³. About 600 million m³ is used for rice irrigation of an additional 30 000 ha per year (Dzhulay et al., 1980).

Rice resistance to salinization varies depending on the growth stage, so it is very important that agronomists know when mineralized water can be used for irrigation and what salt concentrations can be accepted.

In special tests, which were started at the germination stage and continued at shooting and flowering, rice was irrigated with saline water at between 1.5 and 3.5 percent salt content (Table 2).

Depending on the growth stage reached, higher concentrations of salt solution had a negative influence on plants. Plant suppression resulted in reduced plant height, fewer productive shoots, lower grain weight per panicle and a dramatic increase of spikelet sterility. The greatest negative reaction on rice plants was observed when saline water was used for irrigation at the flowering stage: panicle sterility increased by six times. This means that irrigation water for rice should be reused only when its quality has been determined.

INCREASE OF RICE PRODUCTIVITY ON SALINE SOILS

The results of research carried out by Russian scientists show that there are two ways of increasing rice productivity on saline soils. The first is to use agrotechnical methods of soil amelioration. This involves preliminary washing of saline fields, application of ameliorants (gypsum and gypsum phosphate), application of high rates of organic and mineral fertilizers, and replacement of the water layer in basins with fresh, non-mineralized water during rice vegetation.

The second method is to develop breeding programmes to increase the salt resistance of rice plants at the germination and flowering stages. Some success has been achieved in solving these problems. After rice irrigation systems have been constructed, saline soils are reclaimed by washing during winter. Ploughing is followed by filling basins with a 20 to 30 cm water layer. The first flooding is done during the period between 24 October and 18 November; the second from 24 November to 24 December. Discharge water is then removed from the irrigation system. As a result, the salt content of soil at the arable layer can be decreased to between one-seventh and one-eighth of its original level (Tur, 1978). During rice sowing a further decrease of salinization takes place in the fields. To avoid secondary salinization, it is recommended that the salt content of the arable layer be kept under constant surveillance and that non-irrigated crops be sown as soon as soil salinity has been reduced to normal levels.

The most efficient way of reclaiming alkaline soils is to apply chemical ameliorants. The most widely used products are gypsum, gypsum phosphate and other calcium products. Application of gypsum phosphate at rates of 8 to 10 tonnes/ha results in increases of grain weight, number of panicles per square meter and grain weight per panicle. Application of gypsum phosphate increases rice grain yields by 0.39 to 0.54 tonnes/ha (Kremzin et al., 1995). Experiments conducted by Vorobyov and Zhurba (1995) show that soil chloride salinization (0.35 percent NaCl) and water mineralization at the level of 0.35 g/litre inhibit rice plant photosynthetic activity, decrease foliar surface and net plant productivity, and considerably decrease above ground matter. The value of these alterations depends on the salt tolerance of the cultivar and the mineral nutrition level. The inhibition effect of salts on the salt-resistant cultivar Spalchick was less than that on the non-resistant cultivar Kulon. Plant nutrients, nitrogen in particular, positively influence the growth and development of salt-tolerant cultivars under saline, compared with standard, conditions. Thus, high fertilizer application rates result in higher grain yields from cultivar Spalchik under saline soil conditions (4.2 times) compared with standard conditions, where the increment was only 1.7 times.

Russian plant breeders have always paid a lot of attention to the production of salt-tolerant cultivars. Special breeding programmes have been carried out since 1975. A large number of rice samples that combine salt tolerance with other valuable characteristics have been chosen from rice collections. Early-maturing, dwarfish forms with salt tolerance below grade 7 are of particular interest (Table 3). They have been widely used in breeding programmes.

The hybridization process involved not only cultivars of Russian origin but also foreign ones as sources of particular valuable characteristics. Russian plant breeders are interested in Mediterranean rice cultivars. The new rice cultivar, Kurchanka, is a good example of such donor usage (Figure). It has been included in the State Cultivar Register since 1997. It has a medium ripening period, short stems, resistance to logging and falling off and high salt tolerance at the shooting and flowering stages. What makes this cultivar different from other similar cultivars, including Spalchik, is that it has been used as a standard for salt tolerance in plant breeding and physiological trials.

The new cultivar Kurchanka has now substituted Spalchik. This variety inherited the best characteristics of parent forms: plant phenotype, high lodging resistance, the ability to emerge through the water layer rapidly and an elongated kernel that produces good quality rice grits from cultivar Kulon (Table 4); and colour of glumes, high stability of year-to-year grain yield, resistance to rice leaf nematode and tolerance to soil salinization from cultivar Raduga. Raduga, in turn, had inherited high salt resistance from the Italian variety Hallila grand grosso, which appeared in the Russian Federation in the mid-1960s and was included in hybridization as a donor of low height and salt resistance.

It should be emphasized that in special trials, when soil solution salinity was 3.5 g/litre, the yield of cultivar Kurchanka did not decrease.

Under field conditions on saline soils, yields of cultivar Kurchanka are 0.5 to 0.6 tonnes/ha higher that those from other cultivated cultivars; it has not been observed under non-saline soil conditions.

Genealogy of salt-tolerant rice variety Kurchanka

This is the basis for recommending cultivar Kurchanka for cultivation on saline soils in southern areas of the Russian Federation, according to ecologically safe technology without pesticide application. Such practices help, not only to increase the efficiency of rice growing in the given area, but also to decrease the chemical pollution of arable lands and to improve the ecological situation.

REFERENCES

Dzhulay, A.P. et al. 1980. Rice in Kuban. Krasnodar, the Russian Federation.

Kremzin, N.M. et al., (1995). Fertilizer application to rice on alkaline soils of North Caucasus. Krasnodar, the Russian Federation.

Smetanin, A.P. & Dolgikh, L.V. 1966. Rice salt resistance at different stages. Doklady VASKHNIL, 11: 28-31.

Tur, N.S. 1978. The peculiarities of rice growing on saline soils. Krasnodar, the Russian Federation.

Tuyakova, Z.F. 1978. Rice on saline soils. Moscow.

Vorobyov, N.V. & Zhurba, T.P. 1995. Salt resistance increase of rice varieties at high level of mineral nutrition. Agrokhimiya, 7: 25-32.

Culture du riz sur les sols salins en Russie

En Russie, le riz est cultivé pour produire des semoules alimentaires très prisées. La culture du riz joue aussi un rôle important pour la mise en valeur des sols marécageux et salins, qui ne peuvent pas être affectés à d'autres cultures. Dans le seul delta du Kuban, situé dans le territoire de Krasnodar, on compte 110 000 ha de sols alcalins et salins. La culture du riz a commencé à se développer très rapidement dans le Kuban au milieu des années 60, et a atteint 250 000 ha. Il est également possible et utile de cultiver du riz dans les régions méridionales de la Russie. On signale deux méthodes pour l'utilisation de ces sols: la première consiste à utiliser les techniques agricoles d'amélioration des sols; la deuxième repose sur un programme de sélection qui permette d'obtenir des plants de riz tolérants au sel au moment de la germination et de la floraison. Au cours de la mise en valeur des sols alcalins, les meilleurs résultats sont obtenus lorsque des engrais chimiques sont appliqués. Les produits couramment utilisés sont la chaux, le phosphate de chaux, ainsi que d'autres produits calciques. Une nouvelle variété résistante au sel, le riz Kurchanka, a été mise au point en utilisant des variétés russes et étrangères, et l'on conseille son utilisation sur les sols salins de Russie méridionale, en adoptant des technologies ne portant pas atteinte à l'environnement, et sans utiliser de pesticides.

Cultivo del arroz en suelos salinos de la Federación de Rusia

En la Federación de Rusia, el arroz se cultiva para producir sémolas alimentarias muy preciadas. La ricicultura ejerce una función importante en la bonificación de suelos salinos y de manglares que no pueden servir para otros cultivos. Sólo en el delta del río Kuban hay 110 000 ha de suelos alcalinos y salinos dentro del territorio de Krasnodar. El cultivo del arroz se desarrolló en Kuban a partir de mediados de los años sesenta. La superficie total de los sistemas de cultivo en tierras rehabilitadas alcanzó las 250 000 ha. Existe la posibilidad de cultivar arroz en regiones meridionales de la Federación de Rusia. Son dos los métodos para aprovechar esos suelos: el primero consiste en emplear métodos agrotécnicos de mejora del suelo; el segundo, en establecer un programa de mejoramiento del arroz que determina en la planta una tolerancia a la sal en las fases de germinación y floración. En el rescate de los suelos alcalinos se alcanza la máxima eficacia cuando se aplican productos químicos de mejoramiento como el yeso, el fosfato de yeso y otras sustancias cálcicas. La nueva variedad Kurchanka, tolerante a la sal, que se ha desarrollado empleando variedades rusas y extranjeras, es la recomendada para el cultivo en los suelos salinos del sur, con arreglo a una tecnología ecológicamente inocua sin necesidad de aplicar plaguicidas.