Soil properties following studied communes
Data from Table 3 indicated that soil samples from 6 communes had soil texture belonging to the group of clay loam to clay. Soil texture was more significantly clay in A Luoi town and Son Thuy commune than in the remaining communes. The pHKCl was acidic and ranged from 4.95 to 5.44 with no significant differences in studied communes. Organic carbon (OC) was from 1.48% to 1.90% with the highest value in correlation with the clay content (48.74%) in A Luoi town. Similarly, N content was found higher significant differences in the A Ngo commune than in Hong Thai and Quang Nham communes. Most of the available phosphorus content was poor level (<10 mg/100 g) (
MONDRE, 2024). The highest values of total potassium were observed in A Luoi town and Hong Bac commune from 0.56-0.59%. The lowest mean value of CEC is observed in Hong Thai (4.25 cmolc kg
-1) and the highest in Son Thuy (7.47 cmolc kg
-1). Our evaluation revealed the correlation among clay, organic carbon and cation exchange capacity (CEC) levels.
Specifically, in A Luoi town and Son Thuy commune, higher clay content was associated with increased organic carbon and CEC levels. This trend can be partially attributed to the increased cation exchange sites facilitated by soil organic matter (
Deng et al., 2018;
Nguyen et al., 2024).The findings align with the studies conducted by
Pham et al., (2018), Nguyen et al., (2024) and
Nguyen et al., (2024), whichhig hlighted the soil characteristics in the A Luoi district of Thua Thien Hue province in Central Vietnam. alsohighlighted.
Discrimination of soil properties following cropping pattern
One main objective of this study is to evaluate possible relationships between soil use and soil properties in the mountainous zone of the province. Indeed, mountainous soils naturally lack fertility and therefore the choice of adapted crops is more crucial than in more favored contexts. Other constraints for local agriculture result from adverse weather conditions. Therefore there is a great diversity of crops and cropping systems in the mountainous zone to cope with these difficulties and to increase the land use index per year
(Jamala et al., 2013; Tahat et al., 2020).
Table 4 substantiates this visual observation and provides detailed information regarding the differences in mean properties between rice soil and other types of crop soils. Notably, all ten properties exhibit significant differences between the different soil types. These variations arise not only from inherent soil characteristics, particularly texture and organic matter content, which are crucial in influencing other properties but also from agricultural practices. The waterlogged conditions prevalent in paddy fields lead to soil reduction and initiate a series of physico-chemical and biological processes. Following submersion, the pH of acid soils tends to rise; however, the soluble ferrous iron released from Fe (III)-oxyhydroxides competes with exchangeable bases for adsorption sites
(Fahmi et al., 2018).When paddy soils undergo re-aeration, Fe(II) transforms back into Fe(III), leading to the re-protonation of liberated sites or the incorporation of aluminum. This phenomenon accounts for the notably lower pH levels observed in dried paddy soils compared to other soil types
(Gu et al., 2019). Additionally, rice soils exhibit a higher cation exchange capacity (CEC), enabling them to retain a greater quantity of exchangeable bases. However, it is important to note that the overall content of exchangeable bases remains quite low, with the retention of essential nutrients like potassium being particularly
vital(Fahmi et al., 2023; Yang et al., 2024).
The breakdown of soil or added organic material occurs relatively quickly in aerobic environments where oxygen serves as the electron acceptor. In contrast, submerged conditions present a limited or nonexistent supply of free oxygen, leading to the decomposition of organic matter being reliant on the presence of alternative electron acceptors such as ferric iron or sulfate. Furthermore, these alternative electron acceptors, including ferric oxyhydroxides or sulfate, are less effective in degrading organic matter compared to oxygen. As a result, the decomposition process is notably slower and less complete in flooded or anaerobic soil environments
(Bi et al., 2023). This phenomenon may contribute to the elevated levels of organic carbon found in paddy soils, alongside other factors such as the increased clay content that helps stabilize humic substances.
The primary agricultural products in the examined area consist of rice, maize, cassava, bananas, various vegetables (from home gardens), fruit trees and acacia. The traditional agricultural systems are diverse, having developed in response to the specific soil and climatic conditions, as well as social and ethnological preferences
(Nguyen et al., 2024; Nguyen et al., 2024). It is common for traditional farmers to cultivate multiple crop species within a limited area. Intercropping, which involves the simultaneous cultivation of two or more crops in the same field, is prevalent across tropical regions and is frequently observed in the study area. Additionally, multi-layered homestead gardens, which integrate more than three annual crops and vegetable species alongside tree crops, are typical in humid regions
(Gardarin et al., 2022). In this analysis, we examine seven categories of land use: rice (58 samples), cassava (52 samples), maize (20 samples), fruit tree (24 samples), acacia (54 samples) and other crops (37 samples) (Table 2).
Table 4 indicates that soils utilized for maize and banana cultivation exhibit lower significant clay content (23.39 – 26.55%) and higher sand content (34.12 - 42.21%) compared to other annual crop soil types, while fruit tree and rice soils have higher clay content (36.56 – 41.70%) than other crops. The average organic carbon content is marginally higher in rice soils (OC = 1.84%) and fruit tree soils (OC = 1.94%) than in cassava soils (OC = 1.64%) and acacia soil types (OC = 1.63%). The higher OC could be due to the addition of plant litter to the soil, the increased return of organic residues from nearby family residences, continuous cropping throughout the year and reducing the rate of risk of erosion. However, the lower OC from cassava and acacia soils could be the removal of crop residues, soil erosion and soil disturbances during plowing and harvesting that expose the soils
(Molla et al., 2022). The average pH values are slightly higher in rice and fruit tree soils compared to other soils, which can be attributed to earlier observations regarding the impact of waterlogging and organic matter on soil acidity
(Fahmi et al., 2018; 2023;
Vu Thanh Pham and Quang Minh Vo, 2023). Regarding cation exchange capacity (CEC), the only notable characteristic is the higher average value found in rice soils compared to other soil types, which aligns with the increased clay and carbon content observed in rice soils
(Solly et al., 2020; Yuan et al., 2023).
Certain soil characteristics can be classified as intrinsic properties, while others arise as direct or indirect effects of these intrinsic features. For instance, factors such as texture, organic matter content (as indicated by oxidizable carbon) and pH significantly influence various other properties, including cation exchange capacity (CEC), organic nitrogen and phosphorus, which are typically closely associated with total nitrogen and phosphorus levels. Consequently, we computed correlation coefficients (r) among all soil characteristics, as presented in Table 5.
The most substantial significant correlations were observed between CEC and clay (r=0.71), OC and clay, available P (r=0.73), OC and nitrogen (r=0.62) as detailed in Table 5. This indicates a strong correlation among nitrogen, CEC and organic carbon across all soil samples. Additionally, organic carbon exhibited significant correlations with other characteristics, including pHKCl, phosphorus and potassium. Previous research has noted similar correlations, as reported by
Sang et al. (2013) and
Naikwade et al., (2019). The average carbon-to-nitrogen (C/N) ratio of the 245 soil samples was approximately 16.1, which is indicative of well-humified organic matter. This suggests that the soils under investigation still contained coarse or partially decomposed organic material, potentially linked to low biological activity in acidic sandy soils. Furthermore, many samples were collected from rice fields, where the humification process occurs more slowly in waterlogged conditions compared to aerated soils
(Fahmi et al., 2018). The cation exchange capacity was influenced by organic matter, as evidenced by the significant correlation coefficients between CEC and OC (r=0.71), consistent with findings from
Pham et al., (2018) and
Somchai (2024). Previous studies have indicated that pH typically shows a positive correlation with soil CEC in acidic soils
(Yunna et al., 2018; Zhang et al., 2023). However, our study did not reveal a significant negative correlation between pHKCl and soil CEC (r=-0.39), which may be due to the limited pH range of the soil samples analyzed (acidic, ranging from 4.95 to 5.44, with a mean of 5.34). While clay content is generally associated with a significant positive correlation to soil CEC, our findings are similarto previous studies
(Bi et al., 2023; Nguyen et al., 2024). 
