Rice (Oryza sativa L.) nutrient management using mycorrhizal fungi and endophytic Herbaspirillum seropedicae

Integrated nutrient management with biological and chemical fertilizers can improve rice (Oryza sativa L.) productivity, bio-fortification, soil health and fertility. Accordingly, this study was planned to evaluate the combined effects of biological fertilizers including arbuscular mycorrhizal (AM) fungi (Glomus mosseae) and free-living nitrogen-fixing bacteria (Herbaspirillum seropedicae), as well as chemical fertilizers on the yield and nutrient contents of wetland rice under field conditions. Seedlings were inoculated with AM fungi and the bacteria in the nursery and were then transplanted to the field. The experiment was carried out as a split factorial design with three replicates. Treatments included three rates of nitrogen (N1, N2 and N3) and phosphorous (P1, P2 and P3) fertilizers (100, 75 and 50% of the optimum level) in the main plots and mycorrhizal and bacterial treatments in the sub plots. The total of urea (g) used per plot was equal to N1=200, N2=150 and N3=100 at three different growth stages (seeding, tillering and heading) and the total of P (g) per plot used once at seeding using triple super phosphate including P1=16, P2=13 and P3=10. Plant growth and yield as well as the concentration of nitrogen (N), phpsphorous (P), potassium (K), iron (Fe), and zinc (Zn) were measured in the soil, straw and grains. N-fertilizer and biological fertilizers had significant effects on root, shoot and grain yield of rice, however, P-fertilizer just significantly affected root and shoot dry weights. Interestingly, analyses of variance indicated that biological fertilization significantly affected all the experimental treatments except straw N. AM fungi, N1 and P1 resulted in the highest rate of rice growth and yield. The interactions of chemical and biological fertilization resulted in significant effects on grain Zn, Fe, P, and N as well as soil Fe, K and N. The highest rate of grain nutrient uptake was resulted by the combined use of biological fertilization and the medium level of chemical fertilization. Interestingly, with decreasing the rate of chemical N fertilization, rice nutrient use efficiency increased indicating how biological fertilization can be efficient in providing plants with its essential nutrients such as N. However, the highest rate of soil and straw nutrient concentration was related to the combined use of biological fertilization and the highest rate of chemical fertilization. We conclude that biological fertilizer, (mycorrhizal fungi and H. seropedicae) can significantly improve wetland rice growth and yield (resulting in the decreased rate of chemical fertilizer), especially if combined with appropriate rate of chemical fertilization, by enhancing nutrient uptake (fortification) and root growth.