Mehdi Kousehlou; Mehdi Rahmati; Iraj Eskandari; Vali Feiziasl
Abstract
Introduction: Soil is one of the nonrenewable resources (in human being life time scale) that is important to be protected. Tillage operations are carried out in a variety of ways, which in general can be divided into two comprehensive classes of conventional and conservation tillage practices. The tillage ...
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Introduction: Soil is one of the nonrenewable resources (in human being life time scale) that is important to be protected. Tillage operations are carried out in a variety of ways, which in general can be divided into two comprehensive classes of conventional and conservation tillage practices. The tillage has a very important impact on soil physical, chemical and biological properties. Different tillage systems can have conflicting effects on soil physical properties, which is thought to reflect the impact of different weather conditions. Therefore, it seems necessary to study the effects of different tillage practices on the soil attributes in different climatic conditions.
Materials and Methods: This experiment was conducted for five years from 2011 to 2016 in a randomized complete block design (RCBD) with repeated measurements in two different locations and four replications. The applied tillage practices included no-till in standing residue (NT1), no-till in entire residue (NT2), chisel plow plus disc harrow (CH), minimum tillage with mulch cultivator (MT) and conventional plowing with moldboard plowing (CT). The experiment was carried out at Dryland Agricultural Research Institute (DARI) in Maragheh. Soil samples were taken at the end of fifth year and then soil texture were determined by hydrometer method, weight and geometric means of aggregates diameters by wet-sieving (MWDwetو GMDwet) and dry-sieving (MWDdry GMDdry) procedures, the stability of 1 to 2 mm aggregates (WAS) by wet-sieving, total soil organic carbon (TOC) by wet oxidizing method, dissolved soil organic carbon (DOC) using carbon analyzer and mass fractal dimension aggregates using Tyler and Wheatcraft model. The soil bulk density (Db) was also measured by intact samples (from two depths of 0-15 cm and 15-30 cm) prepared from the study area using sampling cylinders with a diameter of 5 and a height of 4 cm.
Results and Discussion: In general, the results showed that the interaction of depth and location on Db was significant at 5% probability level. The measured Db in 15-30 cm was greater than the measured Db in a depth of 0-15 cm. Also, in spite of the significance of the main effects of location and tillage and the interaction of tillage-location on soil dissolved organic carbon (DOC), tillage treatments and their interaction effects on total organic carbon (TOC) were not significant. The results showed that conventional tillage, CT, had the highest amount of DOC. However, no-till in entre residue (NT2) and minimum tillage (MT) showed the lowest amount of DOC. Further, the main effects of tillage practices on MWDdry and GMDdry were significant at 5% probability level. No-till (NT1 and NT2) practices had the highest MWDdry with values of 1.17 and 1.25 mm. Tillage practices and location had no significant effect on WAS, Dm, and MWDwet and GMDwet.
Conclusion: It seems that the reason that DOC content of CT was higher than conservation tillage practices is due to the preservation of crop residues on the soil surface in conservation and no-till systems and less mixing of them with soil and consequently their less decomposition. While in conventional tillage, plant residues were mixed with soil, and the effect of biological degradation increased soil DOC. The greater MWDdry in NT1 and NT2 practices suggests that tillage, even at a minimum or reduced state, breaks down the aggregates and produces smaller particles or aggregates. It also seems that the main reason for GMDdry reduction in minimum tillage is due to the further degradation of aggregates by the tillage agent. Therefore, to better and more accurately observe the effects of different types of tillage, sampling should be done at the end of each growing season.
A. Golestani Fard; H. Mirseyed Hosseini; Gholam Reza Savaghebi; Gh.R. Savaghebi
Abstract
In this research chemical forms of lead and zinc in bulk and rhizosphere soil of different cultivars of maize and canola were determined by sequential and single step extraction methods. Some factors affecting chemical transformation of the two elements such as pH, dissolved organic carbon (DOC), their ...
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In this research chemical forms of lead and zinc in bulk and rhizosphere soil of different cultivars of maize and canola were determined by sequential and single step extraction methods. Some factors affecting chemical transformation of the two elements such as pH, dissolved organic carbon (DOC), their uptake by plant and also cation exchange capacity in the rhizosphere and bulk soil were also assessed. Rhizosphere was obtained with gentle shaking and separating the soil around plant roots. Results showed that zinc uptake was more than lead in both plant cultivars. Zinc and lead accumulation in all cultivars roots were also more than shoots. Translocation index (The ratio of element concentration in shoot to root) in the corn cultivars was higher than canola cultivars (significant correlation= 1%) while the ratio was higher for lead in canola cultivars. Metal concentration in shoots to total metal concentrations in soil (Accumulation factor) showed a similar trend like the translocation index. In total, the corn ability in zinc and lead absorption and extraction in soil was higher compared to canola. There weren’t any significant changes in rhizosphere pH compared to bulk soil. Dissolved organic carbon in the rhizosphere of different cultivars was more than bulk soil and the amount of it in canola was significantly more than corn cultivars. Among each plant cultivars, the absorption rate increased with increasing root exudates. The results of sequential and single step extraction methods showed that the general trend and the soil system tendency (Root-Soil interface) is toward zinc availability in the rhizosphere. The amount of lead in rhizosphere showed no significant changes to bulk soil with none of the extractants in single step extraction method but with regards to the results of sequential extraction method, rhizosphere processes tend to reduce the availability of this element in both plant cultivars.
