Introduction

Human interventions, particularly land-use changes and agricultural management practices, exert a profound and lasting influence on soil quality indicators. Numerous studies have demonstrated that such interventions can significantly alter soil physical and chemical properties. Practices like excessive application of chemical fertilizers often degrade soil quality, while appropriate management techniques such as conservation tillage, crop residue retention, and the use of organic or manure-based fertilizers can help maintain or even improve soil health.
A thorough review of the global literature reveals that the effects of land-use change on soil characteristics are highly dependent on ecosystem type and climate conditions. For instance, findings from temperate and tropical humid ecosystems differ markedly from those observed in arid and semi-arid climates. Meta-analyses have shown that land-use change often has a more pronounced and enduring impact on soil organic carbon (SOC) than climatic variation alone, with reported declines in SOC reaching up to 30% in some cases. The conversion of natural ecosystems such as primary forests or grasslands into agricultural lands has also been associated with significant reductions in SOC, cation exchange capacity (CEC), and increases in soil salinity (EC). However, these impacts vary based on land-use history, soil type, and management intensity.
While long-term land-use changes can lead to either beneficial or adverse outcomes, most evidence suggests that, in the absence of sustainable management, converting natural land to intensive agriculture typically accelerates soil degradation processes, including nutrient depletion, erosion, and reduced water-holding capacity. On the other hand, implementing sustainable agricultural practices may enhance certain soil quality indicators particularly when organic inputs are emphasized.
These findings underscore the need for region-specific assessments, as generalizations from one ecological zone may not be valid in another. In this context, the Jiroft Plain an agriculturally vital region in southern Iran with a dry to semi-arid climate has received limited research attention regarding the impacts of land-use change on soil quality. Given its strategic importance in national food production, this study aims to investigate the long-term effects of different land-use types on key soil chemical properties in the Jiroft region, with the goal of informing sustainable soil and land management strategies.
Materials and methods
Geologically, the Jiroft Plain is situated within the Central Iranian sedimentary basin and is delineated from the Kavir Basin by the Jebalbarez mountain range, which trends northwest to southeast. Additionally, it forms part of the Bazzman-Sahand volcanic belt. The study area is geographically positioned at 28°35′14″N latitude and 57°48′14″E longitude. Within the Jiroft Plain, three agricultural zones characterized by distinct land-use types were selected: rangeland (non-cultivated land adjacent to agricultural areas), arable land (cultivated under an annual potato-onion rotation), orchards (citrus), and greenhouse cultivation (greenhouse cucumber). The selection of these sites was guided by two primary criteria: long-term land-use stability (no changes over several years) and a minimum of 20 years of continuous cultivation following the specified cropping system.
For each land-use category, three composite soil samples were collected, each comprising ten subsamples taken from a standard soil depth. The analyses included determination of soil clay content via the hydrometer method, organic carbon content by the Walkley-Black method, soil pH in saturated paste, electrical conductivity in saturated extract, available phosphorus using the Olsen method, exchangeable potassium by the one-normal ammonium acetate method, and cation exchange capacity (CEC) through ammonium acetate and sodium acetate extractions. Sodium concentration in the saturated paste extract was measured using flame photometry, while calcium and magnesium concentrations were quantified by atomic absorption spectroscopy. Subsequently, the Sodium Adsorption Ratio (SAR) was calculated based on these measurements.
Results and discussion
The analysis of variance results demonstrated that land-use type exerted a statistically significant effect (at the 1% probability level) on all examined soil properties. Comparative analysis of mean pH values revealed that soils under arable and orchard land uses exhibited higher pH levels than those under greenhouse cultivation across all three study regions. Additionally, the comparison of mean values indicated that agricultural management practices, particularly greenhouse cultivation and the cultivation of onions and potatoes, significantly increased soil salinity compared to uncultivated lands in all regions.
Furthermore, although soils under agricultural land uses displayed higher Sodium Adsorption Ratio (SAR) values than uncultivated soils across all study sites, this increase did not reach statistical significance. Organic carbon content varied substantially among the land uses, ranging from 0.06% to 1.34%, with the highest concentration observed in orchard soils within region 2 and the lowest in uncultivated soils in region 3. Cation exchange capacity (CEC) under different land uses ranged from 3.86 to 12.40 cmol(+) kg⁻¹, with orchard lands in region 2 exhibiting the highest values, while the lowest CEC was recorded in uncultivated soils in region 1. The studied land uses also had a significant positive impact on soil phosphorus and potassium contents. The elevated concentrations of these nutrients in greenhouse soils were primarily attributed to the intensive application of chemical fertilizers containing phosphorus and potassium, in contrast to the control (uncultivated) soils. Given phosphorus’s relative immobility in soil, it tends to accumulate rather than leach, especially under excessive fertilizer application aimed at increasing crop yield. The reduced phosphorus levels observed in uncultivated lands were attributed to the absence of fertilizer inputs. Notably, phosphorus toxicity has recently emerged as a challenge in certain greenhouses within the Jiroft region, imposing additional costs on farmers for soil remediation.
Conclusion
Land use and land management practices, particularly over the long term, lead to significant changes in soil properties. Addressing this issue across various regions of the country is essential to prevent uncontrolled soil degradation. Generally, natural land uses, due to the absence of soil disturbance, contribute more effectively to soil conservation compared to other land-use types. Although converting land to agricultural use may enhance certain soil characteristics such as organic matter content, cation exchange capacity, and even soil salinity this improvement does not necessarily imply the absence of soil degradation associated with such changes. The application of fertilizers, especially chemical fertilizers, in agricultural lands can lead to the accumulation of elements like phosphorus in the soil, necessitating careful monitoring. To safeguard soil health, appropriate land management practices must be adopted in the region’s agricultural lands. Furthermore, sustainable soil management in regional agriculture requires regular assessment of soil properties ideally at intervals of a few years to effectively evaluate the impacts of land-use changes.