Effect of Application of Biofertilizers and Water Treatments on Yield, Yield Components and Swelling Index of Isabgol (Plantago ovata Forssk.)

Isabgol belongs to the plantaginaceae family. It is known for its gentle laxative, cooling and diuretic properties. Some recent researches have shown that they may be effective in lowering cholesterol and controlling certain types of diabetes. Water is the limiting factor for biomass production in many countries around the world, particularly in arid and semi-arid areas. On the other hand, drought has been a serious problem in Iran in recent years. Drought stress reduces the biomass of many crops and medicinal plants as well as decrease of the concentration of nutrients in plants. Several scientists have shown that a plant under stress will produce secondary metabolites that may influence its medicinal properties. Water is one of the most important environmental factors that have a significant influence on the growth and active ingredient of medicinal plants. Water shortages cause serious damage in plant growth and development. During drought and salinity absorption will decrease due to the high concentration of salts in the root zone and increasing the osmotic potential of the soil nutrients. Therefore, a decrease in the soil moisture reduces rate and amount of nutrient absorption by plants. Organic fertilizers under drought stress mitigate impact of drought stress by increasing proline, soluble sugars and absorption of potassium and phosphorus and increase crop yield (Rahimzade, 2009). Bio-fertilizers are inputs containing microorganism which are capable of mobilizing nutritive elements from complex and non-usable form to simple and usable form through biological processes. Also, bio-fertilizers can be substituted and an ideal candidate for commercial fertilizers in sustainable agriculture. The present investigation aims to study the use of deficit irrigation and different bio-fertilizer treatments in an appropriate manner, to achieve the highest quantitative and qualitative yield of isabgol.

A field experiment was conducted based on split-plot in randomized complete blocks design with three replications at Darmian city, South Khorasan in 2014-2015 growth season. The main-plots were levels of drought stress including 40, 60, 80 of field capacity (FC) and sub-plots were different bio-fertilizers including nitroxin, phosphate barvar 2, combination (nitroxin + phosphate barvar 2) and control (spray with water). In this experiment traits measured including plant height, number of tiller per plant, number of spike per plant, number of seed per spike, thousand–seed weight, seed yield, turgid index, mucilage percentage and mucilage yield.

The results indicated that the number of tiller and spike per plant and thousand-seed weight were significant (p≤0.01) under drought stress and bio-fertilizer. The highest number of seeds per spike was obtained from 80% field capacity with nitroxin application and the lowest was obtained from 40% FC and non-application fertilizer. By increasing drought stress, the number of seeds per spike decreased. Interaction of drought stress and bio-fertilizer had significant effect on plant height, number of seed per spike, seed yield, swelling index and mucilage percentage. The highest 1000-seed weight was obtained from 80% FC, which did not have significant difference with 60% FC. The highest numbers of seed per spike and seed yield were obtained from 80% FC along with nitroxin application and the lowest of them were obtained from 40% FC and no fertilizer (control), which increased by 47.4 and 54.3 percent, respectively. The maximum mucilage percentage was achieved from 80% FC along with phosphate barvar 2 application, although not significant across other fertilizer treatments.

In general, for achievement of maximum isabgol yield, inoculate seed with bio-fertilizer and providing plants water requirements would be appropriate.