The effect of phosphorus and potassium mineral nutrition on the growth and biofixation of nitrogen in soybean (Glycine max (L.) Merr) under waterlogging conditions in the vegetative stage (nodulation)

Dissertation for obtaining a master's degree in the field

Ecological Agricultural Engineering

Abstract

In order to investigate the effect of the flooding period and different amounts of phosphorus and potassium on the biological fixation of nitrogen in the vegetative stage (V4) of Soybean plant variety Dipiax (Ketol) in pots. In 2012, it was carried out in the Gorgan University of Agricultural Sciences and Natural Resources in the form of a completely random basic design with a factorial arrangement with three replications. The factors included: 1) inoculation with bacteria (Bradyrhizobium japonicum) and no inoculation with bacteria, 2) the combination of different amounts of phosphorus and potassium (first level: no fertilizer, second level: 200 mg of phosphorus and 150 mg of potassium in the pot, third level: 300 mg of phosphorus and 300 mg of potassium in the pot) and 3) the length of the flooding periods (0, 5, 10, 15 days). The results showed that the amount of peroxidase activity increased with the application of waterlogging stress for 5 and 10 days of waterlogging and decreased in the treatment of 15 days of waterlogging. Among the test treatments, the lowest peroxidase enzyme activity was observed in the conditions of no inoculation, no fertilizer use and zero days of waterlogging (78.5 nmol/min/g in wet tissue) and the highest activity (488 nmol/g in wet tissue) in the condition of inoculation with bacteria at the third level of fertilizer and 10 days of waterlogging. Catalase enzyme also decreased with increasing duration of waterlogging stress in all treatments. The most catalase enzyme (1600 nanomol/min/g in fresh tissue) was obtained by inoculation treatment with bacteria at the third fertilizer level and 15 days of waterlogging. As the duration of flooding increased, the concentration of phosphorus and potassium in the seeds, leaves, and non-leaf organs (pods and stems) of soybean showed a decreasing trend, but in the inoculation treatment at the third fertilizer level, it decreased with a lower slope than other treatments. The maximum seed yield (43.22 g/plant) was obtained in the inoculation treatment at the third fertilizer level and zero days of waterlogging, and the lowest (31.13 g/plant) was obtained in the non-inoculation treatment at the first fertilizer level and 15 days of waterlogging. The amount of biological nitrogen fixation (BNF) in the plant decreased with the increase in the period of flooding, but the amount of nitrogen fixed in the plant was less affected with the increase of nutritional levels. The highest nitrogen biofixation was observed in the third fertilizer level without flooding (280 mg/plant) and the lowest in the first fertilizer level and 15 days of flooding (94.5 mg/plant).

Key words: flooding period, phosphorus, potassium, antioxidant enzymes, yield, BNF

- 1- History and importance of soybean

Soybean is a native plant of East Asia, one of the oldest cultivated plants in this region and is considered a vital grain and oil crop (Asadi and Faraji, 2008). Soybean cultivation as an oilseed began around 1342 by importing its seeds to Iran in areas such as Mazandaran, and subsequently, soybean cultivation by the oilseeds joint-stock company became common in some other parts of the country. Since 1970, the production of small batch soybeans has been twice the production of other oil crops such as peanuts, sunflowers, rapeseed. Soybean's share of world oilseed production has increased from 32% in 1965 to more than 50% in the 1980s. Dry soybeans contain 18-25% oil and 30-50% protein. Soybean is one of the major agricultural products in the world, which plays a special role in the preparation of vegetable oil and providing protein for humans and livestock (Hatami et al., 2008). Soybean has an important place among the industrial plants of our country, especially in Golestan province, so that according to the report of the FAO statistics office, the total area under soybean cultivation in the country in 2012-13 was equal to 80,000 hectares, from which 200,000 tons of soybeans were produced. Golestan province, by allocating 76% of the country's total soybean cultivation area and 75% of the total seed production of this product, was placed in the first position of soybean production in the country. Golestan province, with an area of ??20,380.7 square kilometers in the north of Iran, is one of the main centers of agricultural production, and almost every year, along with Fars and Khuzestan provinces, it is at the top of agricultural and industrial producers. In Golestan province, about 90% of soybean cultivation is done as a second crop (summer) after harvesting wheat, canola and barley, which produces a lower yield than spring cultivation (Nakhei and Hazar Jaribi, 2013). In the crop year of 2010, Golestan provinces accounted for 65%, Mazandaran for 16%, and other provinces for about 19% of the cultivated area.. In the crop year of 2010, Golestan provinces occupied 65%, Mazandaran 16% and other provinces about 19% of the cultivated area of ??this crop. Golestan province has been prone to cultivating oilseeds due to its suitable climatic conditions and fertile soil and with the cultivated area of ??60 thousand hectares, it is considered the most important soybean area in the country and with the production of 45% of the country's oilseeds in recent years, it ranks first in the production of this crop. provinces of the country (Khadem Pir et al., 2013). This issue shows the important role of this plant in the life and economy of the farmers of the province, which makes the need for more studies about this plant essential. Considering the importance of the subject and the location of soybean cultivation in Golestan province, it seems necessary to investigate the factors reducing the nitrogen fixation of soybean cultivars and finally to introduce new methods to increase its yield qualitatively and quantitatively. Legumes are a subfamily of butterflies and a family of three leaves. The first two leaves of this plant are simple and opposite, and the rest of the leaves are three leaflets with alternating arrangement. The stem can be seen standing in different soybean cultivars. In terms of the state of flower formation on the stem, soybean cultivars are divided into two groups: limited growth and unlimited growth. Of course, the intermediate group called semi-limited growth can also be added to this group. In limited growth cultivars, reproductive growth begins with the transformation of the terminal meristem of the main stem into a reproductive meristem. In this way, with the start of reproductive growth, vegetative growth almost stops, but in unlimited growth cultivars, vegetative growth continues even after the start of reproductive growth and the terminal meristem of the stem is not transformed into reproductive meristem. Soybean inflorescence, which is the result of the growth and development of the lateral bud located in the angle between the leaf and the stem, is a cluster type and consists of 3 to 15 flowers. The flowers are white or purple. The formation and flowering of flowers starts from the lower part of the inflorescence and continues upwards. The structure of the flower in Soybean, like other plants under the butterfly family, consists of five petals (2 petals, 2 wings and a sepal), 10 diadelphus stamens (9 continuous stamens and one stamen separate from the others) and a pistil and a bract. Soybean fruit is a type of niam. Niamh after processing is light brown or close to it, depending on the cultivar, and covered by short hairs. 1 to 5 seeds, usually 2 to 3 seeds are seen in each niam. The weight of 1000 seeds in soy is usually between 60 and 200 grams, with an average of about 150 grams. The color of the seed in oil soybean cultivars is usually yellow, but especially in non-oil cultivars, it may be seen in other colors such as green, brown, black, and a combination of them. Soybean is a short-day and heat-loving plant and needs a lot of light and heat. Currently, soybeans are planted from latitude 40 degrees south to more than 50 degrees north and from zero to more than 2100 meters above sea level. This plant is sensitive to salinity, and a neutral to slightly acidic pH is suitable for its growth. It is sensitive to shading and competition with weeds. Soybean is resistant to wilt, but due to epigyal germination, it is very sensitive to sorghum and compaction. The minimum temperature for its growth is 10 degrees Celsius and the lethal temperature is -2 degrees Celsius (Khajepour, 2016).

1- 3- Definition of the problem

Many evidences indicate the appropriate response of soybeans to soil fertility and optimal fertilizer consumption (Hatami et al., 2018). On the other hand, the creation of water stress in the plant growth environment due to the reduction of root conductivity and the closure of the stomata reduces the availability of fertilizer nutrients such as nitrogen, phosphorus and potassium, because with the closure of the stomata, the main driving force of water and its passive absorption is stopped, and the non-absorption of water-soluble elements becomes passive (Paser Kelly, 1999). In these conditions, the discharge of dissolved oxygen depends on the temperature, the respiratory activity of plants and microorganisms, as well as the abundance and continuity of soil saturation, leading to a decrease or absence of oxygen within a few days to a few hours (Galshi et al., 2008). Long-term waterlogging favors the conditions for the increase of anaerobic microorganisms and they use other electron receptors instead of oxygen.