| چکیده انگلیسی مقاله |
Introduction
Tillage is the most significant agricultural practice worldwide, playing a crucial role in soil quality, the environment, and crop yield. In the majority of Iran's rainfed farmlands, tillage is performed using moldboard plows and along the slope gradient. Due to its role in organic carbon depletion, soil erosion, and reduced crop yield, this method is considered the most detrimental form of tillage. Based on numerous studies worldwide, conventional tillage using a moldboard plow severely damages key soil properties, reduces moisture retention, increases costs, leads to nutrient loss, decreases crop yield, and causes numerous off-site consequences such as sedimentation, flooding, water pollution, and organic carbon depletion, these impacts are exacerbated under climate change, making it a distinct and critical issue in soil erosion, specifically termed tillage erosion. The aim of the study was to determine the effects of tillage methods on bulk density, aggregate stability, and soil erodibility, conducted at the Sararoud Dryland Agricultural Research sub-institute over a five-year period (2017–2022).
Materials and methods
This research was conducted at the Sararood research station (Dryland Agricultural Research sub-institute). The station is located 15 km east of Kermanshah city and 3 km from the main Kermanshah-Tehran road. This research was conducted as a split-split plot experiment based on a randomized complete block design with three replications. The experiment consisted of four main treatments (conventional tillage, combined tillage, chisel tillage, and no-tillage) and three sub-treatments (no plant residue, 33% plant residue, and 66% plant residue). To evaluate the long-term effects of the treatments, the locations of the main and sub-treatments remained fixed throughout the study period, with only the crop rotation being altered. Soil samples were collected from the 0-20 cm depth layer and analyzed for bulk density, organic carbon, and aggregate stability (using the wet sieving method). The erosion factor was calculated by determining the erodibility factor (K) in the Universal Soil Loss Equation, based on five parameters: organic matter content, percentage of silt + very fine sand (0.05–1 mm), percentage of coarse sand (1–2 mm), soil structure, and permeability. Statistical analysis of the data was performed using SAS software.
Results and discussion
The mean bulk density in the main treatments, including control (conventional tillage), combined tillage, chisel tillage, and no-tillage, was 1.62, 1.45, 1.40, and 1.37 g/cm³, respectively, with a significant decrease (p < 0.05) observed in the no-tillage treatment. The sub-treatments (crop residue levels) also had a significant effect on bulk density, with both 33% and 66% straw (crop residue) rates significantly reducing it. The effect of treatments on bulk density became significant from the third year onward. The statistical analysis also revealed the effects of tillage methods and crop residue levels on soil organic carbon. In the main treatments—control (conventional tillage), combined tillage, chisel tillage, and no-tillage—soil organic carbon content was 1.20%, 1.50%, 1.40%, and 1.70%, respectively, these values showed significant differences (p < 0.05), with no-tillage having the greatest effect on increasing soil organic carbon. The sub-treatments (crop residue levels) also had a significant effect on soil organic carbon, with both 33% and 66% straw (crop residue) rates significantly increasing it. The proportion of very fine aggregates was significantly lower in the no-tillage treatment with the highest crop residue level. The amount of medium-sized aggregates did not differ significantly among the treatments. The proportion of very large aggregates was significantly lower in conventional tillage and the sub-treatment without crop residue. The size of soil aggregates became significant in the third year and predominantly in the fourth year. In other words, an increase in large and very large aggregates and a corresponding decrease in fine and very fine aggregates were observed from the third year onward. The results indicate the effective role of various conservation tillage methods in reducing soil erodibility compared to conventional tillage. The results of this study showed that the three conservation tillage methods played an effective role in improving the evaluated soil properties. Certainly, the role of no-tillage (without plowing) was more prominent in this process. As indicated in the results, over time following the implementation of the study, organic carbon and the proportion of large (1–2 mm) and very large (2–4.6 mm) aggregates gradually increased in the conservation tillage treatments.
Conclusions
Conservation tillage combined with retaining crop residues significantly improved the most important measured soil quality properties, including organic carbon, bulk density, and the proportion of large soil aggregates. No-tillage (direct seeding) with one-third crop residue (33%) is recommended as the most suitable tillage method under rainfed conditions and wheat-chickpea rotation, which is common in most semi-arid regions of the country, and is proposed as the optimal treatment in this study.
|