Assessing Spatial and Temporal Variability for Some Edaphic Characteristics of Mediterranean Rainfed and Irrigated Soils

Soil organic carbon in irrigated agricultural systems: A meta-analysis

Over the last 200 years, conversion of non-cultivated land for agriculture has substantially reduced global soil organic carbon (SOC) stocks in upper soil layers. Nevertheless, practices such as no- or reduced tillage, application of organic soil amendments, and maintenance of continuous cover can increase SOC in agricultural fields. While these management practices have been well studied, the effects on SOC of cropping systems that incorporate irrigation are poorly understood. Given the large, and expanding, agricultural landbase under irrigation across the globe, this is a critical knowledge gap for climate change mitigation. We undertook a systematic literature review and subsequent meta-analysis of data from studies that examined changes in SOC on irrigated agricultural sites through time. We investigated changes in SOC by climate (aridity), soil texture, and irrigation method with the following objectives: (i) to examine the impact of irrigated agriculture on SOC storage; and (ii) to identify the conditions under which irrigated agriculture is most likely to enhance SOC. Overall, irrigated agriculture increased SOC stocks by 5.9%, with little effect of study length (2-47 years). However, changes in SOC varied by climate and soil depth, with the greatest increase in SOC observed on irrigated semi-arid sites at the 0-10 cm depth (14.8%). Additionally, SOC increased in irrigated fine- and medium-textured soils but not coarse-textured soils. Furthermore, while there was no overall change to SOC in flood/furrow irrigated sites, SOC tended to increase in sprinkler irrigated sites, and decrease in drip irrigated sites, especially at depths below 10 cm. This work sheds light on the nuances of SOC change across irrigated agricultural systems, highlights the importance of studying SOC storage in deeper soils, and will help guide future research on the impacts of irrigated agriculture on SOC.

Temporal Variations of Soil Organic Carbon and pH at Landscape Scale and the Implications for Cropping Intensity in Rice-Based Cropping Systems

Landscape scale assessment of temporal variations in soil organic carbon (SOC) contents and soil pH and the implications for long-term agricultural sustainability was determined using legacy datasets collected over two periods separated by 20 years: the 1990s and 2010s. Soil data on SOC and pH were categorized according to the prevailing land types (based on inundation as highland (HL), medium highland (MHL), and medium lowland (MLL)), and physiographic types (i.e., Himalayan Piedmont plain, Tista Floodplain and Barind tract/Terrace) to determine which variable or combination of variables was more influential in spatial and temporal changes of these properties. SOC contents in the physiographic types were generally found to be low, varying between 8 to 12 g/kg. While, SOC contents were significantly higher in MHL and MLL compared with HL that experienced less inundation. The change in SOC contents over 20 years was significant with a 14.5% increase of SOC. There was a greater influence of land type compared with physiography on SOC contents over time. Inundation land types and associated cropping intensity were considered likely to influence SOC of soils under rice-based cropping systems. Furthermore, the levels of soil pH decreased by 0.5 units over 20 years with an approximately 50% increase in soils within a pH category of 4.6–5.5. The majority of soil pH results shift from slightly acidic to strongly acidic in the intervening 20-year period between samplings. Soil acidification is potentially a combination of inefficient and excess use of ammonium-based fertilizers with higher application rates and low input from residues. We conclude that acidification may continue with more intensive land use. However, trends in SOC contents over time under certain combinations of physiography and land type either increased slightly or showed a significant loss and in the latter, specifically, the role of land management is not clear. The legacy datasets would be useful for monitoring spatial and temporal soil quality trends at a regional scale, but has limited capacity to capture field level variations in soil properties as data on smallholder cropping practice and management were not collected. Therefore, future research examining the role of management in SOC and pH dynamics at the field-scale would guide the use of fertilizers, crop residue management, and amelioration of acidic soil, to improve the sustainability of rice-based cropping systems in Bangladesh.

The Relationship between the Physicochemical Properties and Permeability of the Fluvisols and Eutric Cambisols in the Zagreb Aquifer, Croatia

The physicochemical properties of soil and the unsaturated zone can have a large influence on the infiltration of precipitation into an aquifer. Soil permeability presents soil property that can be very variable. The main objectives of this study were to estimate differences in soil permeability in two dominant types of soils—Fluvisols and Eutric Cambisols—in the area of the Zagreb aquifer and determine the relationship between the physicochemical properties and the permeability of the analyzed soils. For this purpose, the particle size distribution, soil water retention curves (SWRCs), hydraulic parameters, and chemical properties of soils (i.e., electrical conductivity (EC), pH, carbonate content, cation exchange capacity (CEC), and total concentration of zinc (Zn)) from six soil profiles were observed. In general, the results show that Fluvisols have a smaller amount of clay and a higher amount of sand. Furthermore, particle size distribution indicates that Eutric Cambisols have smaller permeability and a slightly higher capacity for retention. In Eutric Cambisols, the percentages of clay, silt, and sand generally do not change with depth. On average, Fluvisols and Eutric Cambisols become impermeable when they reach different values of water content and effective saturation. All results suggest that Fluvisols generally have to desaturate more than Eutric Cambisols to become impermeable. The proportions of sand and Ks increases through the depth of all analyzed soils, while CEC, EC, and Zn decrease. The total Zn generally decrease with depth, which can be attributed to the aerodeposition in the surface horizons of the analyzed soils and their higher availability for binding/sorption elements. Generally, it can be seen that most Zn concentrations increase until 80 cm in depth, after which they decrease. This result indicates that, in these specific locations, the groundwater body is not under the influence of a potentially toxic metal, in this case Zn. Statistical analysis shows a strong correlation between Zn concentrations and some soil properties, such as soil texture and CEC. This may point to the prevalence of Zn retention. Furthermore, statistical results show that silt has a higher influence on the permeability of Eutric Cambisols than Fluvisols.