The Effect of Integrated Chemical and Biological Fertilizers on Growth Indices and Mucilage Yield of Isabgol (plantagoovata Forssk) across Different Plant Densities

Introduction Isabgol (plantagoovata Forssk) is an important annual medicinal plant which is under cultivation in Iran. Isabgol has been used in medicine since ancient times, however, it has only been cultivated as a medicinal plant in recent decades. It is a diuretic, alleviates kidney and bladder complaints, gonorrhea, arthritis and hemorrhoids. In general, plants known as medicinal are rich in secondary metabolites and have potential as drugs. The biosynthesis of the secondary metabolites is controlled genetically and affected strongly by environmental factors especially chemical fertilizers. The environmental and economic impacts of chemical fertilizer application such as water pollution, low quality of agricultural production and decreasing soil productivity have encouraged farmers to use alternative nutrient sources. Sustainable farming on the basis of natural fertilizer application with the aim of omitting or decreasing chemical elements is a desirable approach to prevent these problems. Biofertilizers are some non-symbiotic and symbiotic microbes in the soil that stimulate plant growth and contribute the improvement of ecosystem. Many genera of plant growth promoting rhizobacteria such as Azospirillum, Azotobacter, Bacillus and Pseudomonas are used as biofertilizers for economically important crops. Several studies have shown that beneficial microbes, such as Azotobacter and Azospirillum, not only affect nitrogen fixation but also exhibit other favorable properties such as production of growth hormones. Nitrogen and phosphate chemical fertilizers could be replaced by biofertilizers containing Azotobacter, Azospirilium, Bacillus and Pseudomonas. In this study, we evaluated the effects of integrated application of chemical fertilizers and bio-fertilizers under different plant densities on growth indices, grain and mucilage yield of Isabgol. Materials and Methods A field experiment was conducted based on randomized complete block design with three replications at the Agricultural Research Station of Bu-Ali Sina University in2011. The mean annual precipitation was 330 mm. The Soil of experimental field was loamy clay with pH 7.7, containing 8.2 mg kg-1P, 0.1 mg kg-1N , 220 mg kg-1K, and EC 0.409 dS m-1. Three levels of plant densities (70, 100, and 130 plant per m2) and three combinations of fertilizers including 100% chemical fertilizer (control), 50% chemical fertilizer+Nitroxin (Azotobacter sp., Azospirilium sp.) and Biophosphorus (Bacillus sp., Pseudomonas sp.), 25% chemical fertilizer+Nitroxin and Biophosphorus were applied. Two biofertilizers including Nitroxin (2 liters per hectare) and Biophosphor (100 gram per hectare) were used. The population of bacteria in Nitroxin was 108 cell ml-1 and in Biophosphorus was 107 cell gr-1.The plant height, number of branches in plant, maximum leaf arearindex (LAImax), maximum crop growth rate (CGRmax), total dry matter (TDM), and grain and mucilage yield was measured. All variables were submitted to analysis of variance using the statistical analysis system (SAS, 9.1) and significant differences among means were identified by Duncan test at the 0.05 level of significance. Results and Discussion The interaction between density and fertilizer treatments was significant forplant height, number of branches in plant, LAImax, CGRmaxTDM, grain and mucilage yield, whereas it was not significant for length of spike. Acrossall fertilizer treatments, increasing plant density decreased the number of branches per plant. The grain yield obtained from 130 plants per m2 was on average 15.49% and 41.44% higher than 100 and 70 plants per m2, respectively. Grain yield was mostly affected by the application of 50 % of chemical fertilizer + biofertilizersfor allthree plant densities. The highest mucilage yield and TDM (314.69 unit and 497.65 gr m-2, respectively) were obtained from 130 plants per m2 by using 50% of chemical fertilizer + biofertilizers. In density of 130 plant per m2, there was no significant differencebetween using 100% chemical fertilizer and 50 % of chemical fertilizer + biofertilizers. The lowest mucilage yield was obtained from 70 plants per m2 by using 25 % of chemical fertilizer + biofertilizers. Conclutions The integrated application of chemical fertilizer and biofertilizer showed maximum effect on growth indices and the quality and quantity characteristics of Isabgol, therefore application of 50% chemical fertilizers+biofertilizers and 130 plants per m2 is recommended in similar conditions.