تأثیر کشاورزی حفاظتی بر برخی خصوصیات خاک در اراضی دیم شهرستان آق‌قلا، استان گلستان

Background and objectives: The primary goal of soil research is to reassess agricultural ecosystems to achieve sustainable production and profitability while ensuring soil conservation as a non-renewable resource, supporting household livelihoods, and protecting natural resources in the best possible way. The type of cropping system creates countless changes in soil properties (physical, chemical, and biological properties of the soil). Rainfed areas are prone to land degradation and face periods of drought and water scarcity. Thus, selecting appropriate tillage methods and properly managing available resources are critical steps in empowering agriculture in line with sustainable farming principles. Due to minimal soil manipulation and preservation of crop residues in conservation agriculture, the soil as a growth and development environment can have different conditions in conservation and conventional agriculture in terms of physical and chemical properties. Conservation Agriculture (CA) is a set of management agricultural methods that can increase carbon sequestration in soils, improve soil conditions to increase crop growth, use nutrients and soil organic carbon (SOC). Accordingly, the present research was aimed to investigate the effect of conservation agriculture on some soil properties in rainfed lands.
Materials and methods: The present study was conducted as a randomized complete block design with three replications in two regions of Golestan Province, in Aq-Qala County, located in the northern part of the province at a latitude of 37°00' N and a longitude of 54°27' E. The experiment started on October 30, 2022, and ended on October 31, 2023. The characteristics of Region One (suburban area) and Region Two (Section Seven) are as follows, respectively: long-term average rainfall of 250–350 mm and 130–210 mm; average annual evaporation of 1800 mm and 2400 mm; long-term average minimum and maximum temperatures ranging from −5 to 39°C and −12 to 49°C; elevation above sea level of −16 m and −6 m; soil texture ranging from silty clay loam to silty loam and clay loam or silty clay loam. The total area of the studied lands was 70 hectares in Region One and 80 hectares in Region Two. The dominant crop in Region One was wheat, while barley was the dominant crop in Region Two. The experimental treatments included conventional tillage in region one (CT1), no-till for first year + residue conservation + no rotation in region one (NT11), no-till for second year + residue conservation + no rotation in region one (NT12), no-till for second year + residue conservation + rotation in region one (NT12R), no-till for third year + residue conservation + rotation in region one (NT13R), conventional tillage in region two (CT2), no-till for first year + residue conservation + no rotation in region two (NT21), and no-till for second year + residue conservation + no rotation in region two (NT22). In order to examine the effect of sampling depth on soil physical and chemical properties as well as soil permeability and infiltration rate, soil samples were collected from four depths (0-5, 5-10, 10-20, and 20-30 cm) adjacent to the double-ring infiltrometer test sites to enhance the accuracy of permeability and infiltration tests in both conventional and conservation agriculture fields. Each sample was coded independently and transferred to the laboratory for analysis. Soil properties, including organic carbon content, electrical conductivity, porosity, and bulk density, were measured and calculated, while soil moisture, cumulative infiltration, and infiltration rate were assessed in the field. For soil moisture measurement, composite samples were collected at two growth stages -late stem elongation and early grain filling-for wheat in region one and barley in region two. After collection using an auger, soil samples were weighed, oven-dried at 105°C for 24 hours, and reweighed to determine the gravimetric moisture content. Soil infiltration was measured using the double-ring infiltrometer method in a 10-meter radius at three randomly selected locations, with three replications per site, in late July 2023. Suspicious or erroneous data encountered during testing were excluded from the final results or retested. At the end of this stage, the final infiltration permeability values were recorded in centimeters per hour for each individual replication. Following laboratory and field calculations, the collected data were statistically analyzed using SAS software (version 9.4), and mean comparisons were performed using Duncan’s multiple range test.
Results: The results showed that the highest amount of soil organic carbon with averages of 1.54, 1.46, 1.42 and 1.36 percent, at depths of 0-5, 10-5, 10-20 and 20-30 cm, respectively, the highest soil porosity with averages of 61.00, 33.67, 57.59 and 54.33 percent, at depths of 0-5, 10-5, 10-20 and 20-30 cm, respectively, the lowest soil electrical conductivity with averages of 1.25, 1.36 and 1.88 dS/m, at depths of 0-5, 10-5 and 10-20 cm, respectively, and the lowest soil bulk density with averages of 1.24, 1.26 and 1.28 g/cm3, at the same depths, respectively, was observed in the NT13R treatment. In addition, the organic carbon content in the conventional tillage treatment (CT1) at the depths of 10-20 cm and 20-30 cm was higher than in some no-tillage treatments. The NT12R treatment, however, had the lowest porosity at all measured depths. According to the results, only at the deepest soil depth (20-30 cm) the NT12 treatment exhibit the lowest electrical conductivity, while the highest electrical conductivity at all depths belonged to the conventional tillage treatments. Moreover, the minimum bulk density in the 20-30 cm soil depth was found for the CT2 treatment, and there was no significant difference between this treatment and the NT13R, NT12, and NT12R treatments. Also, the highest soil moisture content with averages of 13.49 and 17.48 percent at depths of 0-10 and 10-30 cm, respectively, was observed in the NT12R treatment. Notably, soil moisture in the no-tillage treatments NT12R (Region 1) and NT22 (Region 2) increased compared to the conventional tillage treatments for these regions (CT1 and CT2) by 46.3% and 85.4%, respectively, at the 0-10 cm soil depth, and by 37% and 35.9%, respectively, at the 10-30 cm soil depth. On the other hand, the highest cumulative infiltration and water infiltration rate in the soil with averages of 20.50 cm and 84.83 mm/h, respectively, were observed in the CT1 treatment.
Conclusion: The results of the present study indicated that observing the three interconnected principles of conservation agriculture, including no-tillage + residue preservation + rotation, improved most soil properties over time, except for cumulative infiltration and water infiltration rate in the soil during the implementation of this study. The water infiltration rate in the soil may also increase with the passage of time and a longer history of conservation agriculture. Therefore, it can be concluded that no-tillage treatment has positive effects on soil properties, as it leads to an increase in soil organic carbon, a decrese in soil electrical conductivity, and a rise in soil moisture. However, achieving better results requires a multi-year period, which can even impact on crop yield. Overall, the findings of this study regarding soil chemical indicators revealed that conservation agriculture demonstrates different behaviors depending on various regions and climates. It is recommended that future research consider a variety of different environmental factors (such as rainfall, temperature, and heat) and management practices (such as different planters, tillage methods, crop varieties, and planting dates) to better explain the mechanisms of processes affecting soil chemical properties under conservation agriculture.