Document Type : Research Article
Authors
1 Soil Science, Faculty of agriculture, Ferdowsi university of Mashhad
2 Soil Science, Agriculture, Ferdowsi University of Mashhad, Mashhad, Iran
3 Soil Science, Agriculture. Ferdowsi University of Mashhad, Mashhad, Iran
Abstract
Introduction
Agronomic management is a set of field practices that not only influence plant growth and yield but also affect the soil physical, chemical, and biological properties. The selection the crop species and cropping systems -monoculture or crop rotation-significantly affects soil attributes and plays an important role on enhancing nutrient cycling, increasing organic matter content, reducing erosion, and ultimately promoting the sustainability of agricultural ecosystems. Therefore, an appropriate cropping strategy can be regarded as a key strategy for sustainable soil management. Evaluating soil quality through physical, chemical, and fertility indicators provides a comprehensive knowledge of soil status, which is essential to develope effective management strategies and long-term planning for sustainable land use. This study was performed to assess soil quality under alfalfa cultivation and to compare with a maize–wheat rotation in a single cropping season.
Materials and Methods
This study was conducted during the 2020–2021 cropping season at the research farm of Ferdowsi University of Mashhad, located in Khorasan Razavi Province, northeastern Iran. Two adjacent fields with different agronomic management systems were selected: (i) alfalfa (Medicago sativa L.) monoculture, which had been continuously cultivated for several years without rotation, and (ii) a maize–wheat (Zea mays L.–Triticum aestivum L.) rotation system, a typical cereal-based cropping pattern in the region. These different systems were chosen to evaluate the long-term effects of continuous legume cultivation versus crop rotation on soil quality attributes. The experimental design was a randomized complete block design (RCBD) with three replications. Soil samples were collected after the harvesting the crops and taken from three depths (0–10, 10–20, and 20–30 cm). 11 soil properties including pH, electrical conductivity (EC), calcium carbonate equivalent (CCE), total nitrogen (TN), available phosphorus (P), available potassium (K), mean weight diameter (MWD) of soil aggregates (both wet and dry methods), soil structure stability index (SI), saturated hydraulic conductivity (Ks), and organic carbon (OC) were measured. The minimum data set (MDS) was identified using principal component analysis (PCA). Subsequently, the soil quality index (SQI) was calculated based on both the total data set (TDS) and the minimum data set (MDS).
Results and Discussion
Using the Minimum Data Set (MDS) approach, the number of soil properties was reduced, and the most important variables were selected. Among the principal components (PCs), only those with eigenvalues greater than one were retained. For both alfalfa and the maize–wheat rotation, four components explaining more than 80% of the total variance were selected. In alfalfa, the selected variables included organic carbon, total nitrogen, calcium carbonate equivalent, and mean weight diameter (MWD) of wet and dry sieving. In the maize–wheat rotation, the selected variables were organic carbon, electrical conductivity (EC), calcium carbonate equivalent, and MWD under wet and dry sieving. Regarding the EC in the rotation system reflects probabily the influence of evaporation and fertilization practices on soil salinity. Evaluation of the Soil Quality Index (SQI) among the different soil depths and two agronomic management systems revealed that soils under alfalfa monoculture exhibited higher quality compared to the maize–wheat rotation, particularly in the surface layer (0–10 cm). These findings emphasize the crucial role of continuous plant cover in maintaining soil organic matter, reducing surface erosion, facilitating nitrogen fixation through rhizobial symbiosis, improving soil aggregate stability, and enhancing soil biological activity in perennial systems such as alfalfa. These processes may improve nutrient availability and foster long-term soil sustainability. Soil depth significantly influenced SQI trends. The decline in SQI with increasing depth in the maize–wheat rotation reflects reduced biological activity and limited nutrient availability in deep layers, whereas soils in alfalfa system had the relatively higher SQI values even at deep depths, indicating the potential of deep-rooted legumes to enhance subsoil quality through extended root penetration and associated biological processes.
Conclusion
This study revealed that alfalfa monoculture considerably enhanced soil quality compared to the maize–wheat rotation, particularly at the soil surface (0–10 cm). The most important soil properties improved soil quality were organic carbon, total nitrogen, calcium carbonate equivalent, and aggregate stability (MWD). The presence of continuous plant cover, biological nitrogen fixation, and reduced tillage in alfalfa cultivation played vital roles in increasing soil organic matter, reducing erosion, and improving soil structural stability. The application of the Minimum Data Set (MDS) approach proved to be a reliable, efficient, and cost-effective method for soil quality evaluation. These findings highlight the potential of perennial legume-based systems, such as alfalfa, to enhance soil quality and sustainability in semi-arid agroecosystems. Long-term monitoring of soil quality and alfalfa monoculture is recomended for sustainable land management.
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