Investigating Some Physical Characteristics of Soil and Growth Traits of Fenugreek Plant under Application of Biofertilizer and Water Stress

The stability of soil structure has a great effect on plant growth. In fact, soil structure is considered as key factor for determination of soil quality. Soil structure can influence the growth and development of plants through maintaining soil water, soil elements and air, etc. Water stress is one of the most important factors limiting the physiological and nutritional growth of plants, which will lead to a decrease in biomass and yield. Fenugreek L. (Fuenum graceum) is a plant belonging to the legume family, which is widely grown in temperate and tropical Mediterranean regions of Europe, Asia and Africa. In sustainable agricultural systems, any improvement should lead to an increase in production and a reduction in the destructive effect on the environment, which will ultimately lead to an increase in the sustainability of the agricultural system. One of these methods is the application of biofertilizers. Biofertilizers are a set of preservatives with a large number of beneficial microorganisms or their metabolic products. Mycorrhiza fungi and seaweed are two widely used biofertilizers.

This research was carried out as a factorial experiment based on completely randomized design with three replications, at research greenhouse of the Faculty of Agriculture, Lorestan University during the year 2021. Experimental factors included five levels of irrigation I60, I70, I80, I90, I100 (60, 70, 80, 90 and 100 % based on soil moisture depletion) and four levels of biofertilizer (control, vecozium algae 5 L ha-1, algae 5 L ha-1, mycorrhiza 50 g pot-1). At the end of the plant growth season (70 d after planting), the plants were harvested and characteristics such as soil moisture curve, mean weight diameter of soil aggregates, organic carbon, aerial part fresh weight, total chlorophyll, electrolyte leakage and proline were measured.

The results showed that under control condition (I100), the highest total chlorophyll content, mean weight diameter of soil aggregates and organic carbon were 19.72 mg g-1 FW, 0.77 mm and 1.72 % which were recorded in mycorrhiza treated plants. Using biofertilizers under stress conditions increased fresh weight of aerial part, total chlorophyll content, mean weight diameter of soil aggregates, organic carbon and soil moisture, and decreased proline and electrolyte leakage in comparison to control condition.The increase in soil moisture content due to the application of biofertilizers could be attributed to the hydrophilic properties of biofertilizers that lead to changes in soil properties. The increase in mean weight diameter of aggregate in this research could be related to the effect of fungal hyphae that develop inside the soil to form a skeletal structure and physically hold the primary soil particles together and improve soil aggregation. According to the results of this research, the amount of organic carbon decreased due to drought stress, while the application of biofertilizer alleviated this effect. The application of biofertilizers increased the growth characteristics of fenugreek plants under drought stress conditions, which could probably be attributed to their role in increasing root growth, photosynthesis rate and nutrients absorption rate. In stress conditions, excessive accumulation of reactive oxygen species in plant cells causes membrane damage and lipid peroxidation resulting in loss of semi-permeable characteristic of the membrane, reduction of membrane stability and increasing electrolyte leakage. Therefore, biofertilizers enhance plant resistance against stress condition by increasing membrane stability. The results of the present research showed that drought stress increases proline content in fenugreek leaves. Osmoregulation is one of the efficient mechanisms of plants to maintain cell turgescence under drought stress conditions which increases drought tolerance threshold through the accumulation of sugars and amino acids such as proline. The increase in the concentration of compatible osmolytes such as proline has been proven under the influence of environmental stresses such as drought.

The research results generally showed that drought stress causes a decrease in mean weight diameter of aggregate, organic carbon, fresh weight of aerial parts and total chlorophyll, and an increase in electrolyte leakage and proline content. Also, the use of biofertilizers under stress conditions can significantly improve plant and soil characteristics and alleviate stress negative effects.