The Impact of Alfalfa Cultivation and Maize–Wheat Rotation on Soil Quality in Semi-Arid Agroecosystem

Document Type : Research Article

Authors

O. Eghbali

H. Emami

R. Khorassani

Department of Soil Science, Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad, Iran

https://doi.org/10.22067/jsw.2025.95221.1498

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 of 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 understanding of soil status, which is essential for developing effective management strategies and long-term planning for sustainable land use. This study was performed to assess soil quality under alfalfa cultivation and compare it 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 two 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 harvesting the crops and were taken from three depths (0–10, 10–20, and 20–30 cm). Eleven 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 MDS.
 
Results and Discussion
Using 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 the alfalfa and the maize–wheat rotation, four components explaining more than 80% of the total variance were selected. In the alfalfa, the selected variables included organic carbon, total nitrogen, calcium carbonate equivalent, and MWD of wet and dry sieving. In the maize–wheat rotation, the selected variables included organic carbon, EC, calcium carbonate equivalent, and MWD under both wet and dry sieving conditions. The observed EC in this rotation system likely reflects the influence of evaporation and fertilization practices on soil salinity. Evaluation of SQI across different soil depths and two agronomic management systems revealed that soils under the 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 the deep layers, whereas soils in the alfalfa system had relatively higher SQI values even at the 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 the 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 that improved soil quality were OC, TN, CCE, and MWD. The presence of continuous plant cover, biological nitrogen fixation, and reduced tillage in the alfalfa cultivation played vital roles in increasing soil OM, reducing erosion, and improving SI. The application of 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, in enhancing soil quality and sustainability in semi-arid agroecosystems. Long-term monitoring of soil quality under alfalfa monoculture is recommended for sustainable land management.
 

Keywords

Agronomic management

Rotation

Soil quality index (SQI)

Subjects

• Soil science

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Authors retain the copyright. This is an open access article distributed under Creative Commons Attribution 4.0 International License (CC BY 4.0).

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