Ladan Heydari; Javad Hamzei; Tahmeineh Ghytasi Ranjbar; Somayeh Bahramian Ragheb; Fatemeh Madineh Khorrami
Abstract
Introduction: Stability of soil aggregates is a result of complex physical, chemical and biological processes in the soil. In many studies, organic matter has been studied as a major factor in formation of aggregates and the effects of symbiosis between mycorrhizal fungi and bacteria largely ignored, ...
Read More
Introduction: Stability of soil aggregates is a result of complex physical, chemical and biological processes in the soil. In many studies, organic matter has been studied as a major factor in formation of aggregates and the effects of symbiosis between mycorrhizal fungi and bacteria largely ignored, however these microorganisms have a great effect in the formation of the aggregates. Plant roots provide a suitable habitat for the activity of many soil microorganisms. In this regard, the symbiosis of plant roots with fungi is one of the most common and long-lived symbiotic relationships that are found in most ecosystems. On the other hand, biological fertilizers can improve soil aggregation through influence the growth of root and plant. Despite the significant effect of fungi and bacteria on the stability of the soil structure, the effect of arbuscular mycorrhizal fungi species Glomus mosseae and Rhizobium species Mesorhizobiumon caesar on the soil structure has been rarely investigated. Therefore, the aim of this study was to evaluate the effect of chickpea inoculation with Rhizobium (Mesorhizobium caesar) and mycorrhizae (Glomus mosseae) on soil structural stability and aggregates size distribution under both greenhouse and field conditions.
Materials and Methods: The present study was conducted as a randomized complete-block design with three replications in both greenhouse and field conditions. The treatments under field condition were mycorrhizal fungus (Glomus mosseae), Rhizobium (Mesorhizobium caesar), mycorrhizae – rhizobium combined treatment and a control (no inoculation). In the greenhouse condition, sterilized mycorrhiza background material and without plant (without inoculation) treatments were also added. Chickpea was planted at both conditions. Soil sampling was carried out after harvesting. The stability of aggregates using wet sieving method and soil organic carbon content were investigated.
Results and Discussion: Greenhouse study results showed that mycorrhizae treatment significantly increased the mean weight diameter of the aggregates by 51.6% and 189.1%, in comparison with the control (without inoculation) and control- without plant (without inoculation), respectively. This treatment increased macro aggregates and decreased the fine aggregates. In the greenhouse condition, soil organic carbon content had a high correlation with the mean weight diameter of the aggregates (R2 = 0.53) and mycorrhizal treatment increased organic carbon content from 0.73% in the control (without plant) to 1.02%. However, the mycorrhizae – rhizobium combined treatment had less effect on the stability of the aggregates than their single effects. The mass of aggregates of 1–2 mm are more sensitive to short-term management. In the greenhouse condition all the three biofertilizer treatments significantly increased the mass of the aggregates of 1-2 mm in comparison with the control treatment without plant (without inoculation). On the other hand, the mean comparison results showed that there was no significant difference between the sterilized mycorrhizal background and the control without plant (without inoculation). This may be due to the lower organic matter content in these two treatments compared to others. In the greenhouse condition, increasing the mass of coarse aggregates of 4-8 mm in diameter indicates the suitability of soil structure. On the other hand, aggregates coarser than 0.25 mm are considered as coarse and stable aggregates. It can be concluded that the application of mycorrhiza and rhizobium increased soil structural stability through the increase of the mass of these classes of the aggregates (2-4 and 4-8 mm), probably by affecting the length and volume of the root and plant yield. Under the field condition, the treatments had no impact on the mass of the aggregates in different size classes.
Conclusion: Bacteria and fungi can be effective factors in improving soil structure through increasing organic carbon in soil. The results of the present study indicated that aggregate stability was affected by biological fertilizer treatments under greenhouse condition so that the treatments containing biofertilizers increased soil aggregate stability and improved the soil structure that was probably due to increasing plant yield and root. Also, the less effect of biofertilizers on the stability of the aggregates and the increase of coarse aggregates under the field condition can be due to the uncontrolled climatic conditions compared to the greenhouse and the short duration of the study. In recent decades, the physical and chemical properties of soils have changed due to the use of chemical inputs in agricultural lands.The use of biological and organic fertilizers is an appropriate solution to these problems. It is recommended further study on the efficacy of other species of mycorrhizal fungi and rhizobium bacteria in improving soil physical and chemical quality, especially at the field scale. Also, considering the implementation of this project in the field condition, it is suggested to study the physical, mechanical and chemical properties of soil in the long term.
Esmaeil Esfandiary Ekhlas; Mohsen Nael; Mohsen Nael; Javad Hamzei; Ali Akbar Safari Sinegani
Abstract
Introduction: Soil is a finite natural resource and non-renewable under agricultural production without implementation of sustainable management practices. Ecological sustainability of agroecosystems can be comparatively assessed by soil quality evaluation, which in turn is assessed by soil quality indices. ...
Read More
Introduction: Soil is a finite natural resource and non-renewable under agricultural production without implementation of sustainable management practices. Ecological sustainability of agroecosystems can be comparatively assessed by soil quality evaluation, which in turn is assessed by soil quality indices. Soil quality is the general term used to refer to “the continued capacity of soil to function as a vital living system, within ecosystem and land-use boundaries, to sustain biological productivity, maintain the quality of air and water environments, and promote plant, animal, and human health”. Conservation tillage and use of cover crops are some of the sustainable agriculture practices that can improve the soil quality by adding organic matter and nutrients, and by acting as scavengers to trap leftover nutrients that otherwise might leach out. Cover crops are used as ground cover, mulches, green manure, nurse crops, smother crops, and forage and food for animals or humans. Given the significant role of tillage practices and crop residue management in soil quality improvement and crop production, a four-year field experiment was conducted to determine selected soil quality indices and Cucurbitapepo yield under different tillage and legume cover crop managements in Hamadan.
Materials and Methods: A four-year field experiment (2011-2014) was carried out at Bu-Ali Sina University experimental field in Dastjerd, Hamadan, as a factorial experiment in randomized complete block design with three replications. The area is located at 37 km of Hamadan, on 35◦ 01' N latitude and 48◦ 31' E langitude with 330 mm annual rainfall and 1690 m altitude. The treatments consisted of three levels of tillage practices (NT: no-till (direct seeding), MT: minimum tillage (chisel plowing + disk) and CT: conventional tillage (moldboard plowing + disk)) and two levels of cover cropping (C1: with legume cover crop (lathyrus sativus) and C0: without cover crop). These treatments were applied for four consecutive years in a way that lathyrus sativus as cover crop were planted in late winter for each year and returned to the soil surface with a trowel when 30% of the field was flowered. One week later, and prior to the cultivation of main crop, the mentioned tillage treatments were implemented. In the fourth year of the project,Cucurbita pepo was planted as the main crop. Soil and plant (Cucurbita pepo) were sampled early autumn (2014) and were analyzed for soil organic carbon, soil active carbon, macro and micro-aggregate carbon, mean weighted diameter of water stable aggregates, soil bulk density, basal microbial respiration and grain yield. Obtained data were analyzed using statistical software SAS 9.4 and the means were compared using LSD multiple range test at 5 percent level.
Results and Discussion: The results revealed that total organic carbon, active carbon, aggregate carbon, mean weighted diameter of water stable aggregates, bulk density, porosity and basal respiration were significantly affected by cover crop and tillage system so that the highest amount of these indicators were obtained in no-tillage system with cover crop treatment (NT-C1) and the lowest amounts were observed in the conventional tillage without cover crop (CT-C0). For instance, mean soil organic carbon increased from 0.4 percent in CT-C0 to about 0.7 percent in NT-C1. For majority of soil quality indices, no significant difference was observed between minimum and no-till; moreover, the application of cover crop in conventional tillage improved some aspects of soil quality. For instance, MWD was the highest (2.14 mm) in NT-C1, and was not significantly different with that of MT-C1 treatment. On the contrary, this index was significantly the lowest (0.48 mm) in CT-C0. The C. pepo grain yield was also significantly affected by tillage system, cover crop and their interactions. The highest grain yield (142.1 g.m-2) was obtained in MT-C1 treatment, which did not show significant difference with NT-C1 treatment. The lowest C. pepo grain yield (115.3 g.m-2) was observed in conventional tillage without cover crop (CT-C0) treatment, but it was in a same statistical group with NT-C0, MT-C0 and CT-C1 treatments. Cover crop increased organic carbon, active carbon, porosity, bulk density, microbial biomass activity and MWD by enhancing soil organic matter, probably; conservation tillage on its part further improved these effects by preventing the rapid decomposition of organic matter by reduced soil destruction, which eventually increased soil organic carbon, active carbon and production of stable aggregates.
Conclusions: Generally, after four years of applying different tillage practices and cover cropping, it was demonstrated that the integrated management of the conservation tillage (either no-tillage or minimum tillage) with legume cover cropping was the most appropriate management in the semi-arid region of Hamadan in view of selected soil quality indices and crop yield improvements.
