Biological amendments such as compost can improve soil health but due to the inherent low organic matter, nutrient levels and structural constraints of sandy soils, their capacity to retain benefits of applied biological amendments may be limited. These constraints affect key aspects of soil physical, chemical and biological fertility. A glass house experiment was conducted with a sandy soil to examine the co-application of clay (0 and 5%) and compost (0, 2%, 3% and 4%) on soil aggregate size distribution, chemical properties, changes in fungal to bacterial ratio, taxa abundance, and Kikuyu grass growth. Co-application of 5% clay with compost significantly increased dissolved organic carbon, microbial biomass carbon, and mineral nitrogen while raising soil pH, EC, CEC and exchangeable cations (Ca, K, Na, and Mg) compared to compost application without clay. Addition of compost alone also significantly increased microbial biomass carbon. However, application of clay negatively affected Kikuyu growth, which was not alleviated by co-application of clay with compost. There were no significant differences in soil aggregate size distribution or fungal bacterial ratios among treatments. This study demonstrated the potential of combining the application of clay and compost to this sandy soil for overcoming some chemical constraints, though it had no effect on soil structural limitations. Challenges remain in improving plant growth conditions in sandy soil by optimizing the application of both clays and organic amendments.

Nematodes are widely distributed in soil ecosystems and play a vital role in soil food webs by regulating microbial communities and influencing nutrient cycling. Their susceptibility to environmental changes makes them valuable bioindicators of soil health. While nitrogen availability and soil pH are known to influence nematode community structure, the interactive effects of these factors on free-living nematode (FLN) trophic groups remain underexplored, particularly in Western Australian (WA) agroecosystems. Most nematode studies in WA have focused on plant parasitic species due to their economic impact, leaving a gap in understanding FLN responses to soil chemistry alterations. This study investigated how soil pH, measured using a 1:5; 0.01M CaCl2 solution, and net inorganic nitrogen availability influence net nitrate availability and FLN trophic composition in sandy soils using a microcosm experiment. Soil samples with pH levels ranging from 4 to 7 were subjected to nitrogen application at rates of 50, 100, and 200 kg N/ha, and responses were measured after a 130-day incubation period. Preliminary results indicate that net nitrate availability was enhanced at pH levels above 5. Ammonium accumulation was measured in treatments with pH 4, suggesting acidic conditions inhibited the conversion of net available ammonium to nitrate. Nitrogen application favoured bacterivorous nematodes but suppressed other trophic groups, with application rates above 100 kg N/ha reducing overall nematode abundance. The findings will enhance our understanding of nematode responses to soil pH and nitrogen availability, highlighting their potential as bioindicators for soil health assessment.

Enhancing soil organic carbon (C) sequestration is critical for improving soil health and mitigating climate change. This study explores an innovative strategy of co-composting clay materials with food waste to enhance organic C stability and reduce CO₂ emissions in soil. Bentonite (B) and kaolinite (K) clays were co-composted with food waste (FW), followed by a soil incubation experiment under controlled conditions. Treatments included unamended compost (FW0), bentonite-amended compost (FWB), and kaolinite-amended compost (FWK).
Results showed that clay amendments significantly reduced dissolved organic carbon (DOC) in the soil. FW0 resulted in the highest DOC, which declined in FWB and FWK after 56 days of incubation, confirming enhanced C stabilisation in clay-amended treatments. Microbial biomass carbon (MBC) was higher in FWB (~2200 mg C kg⁻¹) and FWK (~1350 mg C kg⁻¹) compared to FW0 (~750 mg C kg⁻¹), indicating improved microbial activity in clay-amended soils. CO₂ respiration rates were lower in FWB and FWK (150-160 μg CO₂-C kg⁻¹ day⁻¹) compared to FW0 (~207 μg CO₂-C kg⁻¹ day⁻¹), reflecting reduced microbial decomposition and enhanced C protection in clay-amended soils. Clay amendments also influenced nitrogen dynamics; NH₄⁺ concentrations were elevated in soils amended with FWB and FWK, indicative of enhanced nutrient mineralisation and retention. However, NO₃⁻ levels were not significantly influenced by clay type, highlighting a stronger influence of clay on NH₄⁺ stability rather than NO₃⁻ production. Soil pH was positively affected, with clay amendments (particularly FWB) increasing pH (7-8) compared to the consistently acidic FW0 treatment (4-5), suggesting improved conditions for microbial activity and nutrient availability.
Overall, clay incorporation in composts significantly enhances organic C stability by reducing DOC lability, elevating NH₄⁺ availability, and improving soil chemical conditions, thus favouring microbial activity. These findings confirm the potential of clay-amended composts for long-term carbon sequestration, improved nutrient dynamics, and sustainable soil management.

Drought stress remains a major constraint to crop productivity, especially in sandy soils with inherently low fertility. Sustainable amendments like black soldier fly larvae (BSFL) frass and biochar, rich in nutrients and carbon, offer promise, but their combined effects under drought conditions are poorly understood. A glasshouse experiment was conducted over 10 weeks using bell pepper (Capsicum annuum L.) to evaluate the impact of different frass types (vegetable- and manure-derived), biochar (with and without), and water regimes (well-watered at 70% and water-stressed at 35% field capacity). Each treatment was replicated four times. Plant growth was significantly higher with vegetable-derived frass than manure-derived frass, but only under well-watered conditions (p < 0.001 for shoot dry weight, p < 0.01 for root dry weight). Frass application improved soil pH, ammonium-N, nitrate-N, and nitrogen uptake. Biochar increased shoot dry weight (p < 0.001) and nitrogen content (p = 0.026), and when co-applied with manure-derived frass, further enhanced soil pH (p = 0.03). Soil pH was also higher with vegetable-derived frass under well-watered compared to water-stressed conditions (p = 0.01). Notably, the combined application of frass and biochar under drought stress enriched the relative abundance of beneficial bacterial genera including Devosia, Sphingomonas (Alphaproteobacteria), and Catenulispora (Actinobacteria), indicating a shift in rhizosphere bacterial communities linked to improved resilience. These findings demonstrate that integrating BSFL frass and biochar can enhance soil fertility, plant growth, and microbial community structure, even under water-limited conditions. Such strategies hold the potential to improve the drought resilience of crops in sandy soils and contribute to more sustainable agricultural systems.

Agricultural expansion, in the form of monocropping systems, for rural economic improvement is considered the most significant driving force of changes across the Cambodian rural landscape. This transition causes soil fertility decline, which is found widely in sandy soil landscapes of Cambodia. This study aimed to determine how different agricultural land use practices affected soil fertility decline. In this study we selected four different land use classes of: paddy rice, mango, fallow lands and forest to investigate the decline and changes in soil fertility and physical properties. We collected soil samples from non-disturbed forest as the baseline for comparison. The study selected Haong Samnam and Reaksmei Sameakki Communes located in Aoral District, Kampong Speu Province. Random sampling methods were adopted to select 76 locations across the landscape. Soil sampling was completed in 24 paddy fields, 14 mango fields, 19 fallow lands, and 19 forest lands. Statistical analysis of soil organic carbon (SOC) and soil bulk density (BD) indicated there were significant differences between all types of land use classes and forest land at P<0.01. The soil of mango (SOC:0.48%; BD:1.7 g cm-3), paddy rice (SOC:0.38%; 1.6 g cm-3) and fallow (SOC:0.59%; BD:1.6 g cm-3) had lower soil organic carbon and higher soil bulk density compared to forest land (SOC:0.76%, BD: 1.4 g cm-3). Soil fertility and physical properties change over time; thus, we also integrated remote sensing to investigate the changes in land use and land cover classification between 2000 and 2022. Social interview methods were also used to support this investigation. This study confirms that the transition from forest cover to agricultural land use caused a decline in soil fertility parameters. Improved soil management and modifications of the cropping system may need to be considered for sustainable use of agricultural lands in the sandy soil landscapes of Cambodia.

Ammonia volatilization is a significant nitrogen loss pathway from agricultural soils, reducing fertilizer use efficiency and impacting environmental sustainability. This study evaluates the effectiveness of slow-release nitrogenous fertilizer in mitigating ammonia volatilization loss compared to urea fertilizer in two soil types. A laboratory experiment was conducted over six weeks using five nitrogenous fertilizers that include urea, NBPT (n-butyl thiophosphoric triamide) and DMPP (3,4-Dimethylpyrazole Phosphate)-coated urea fertilizers, and three urea-based fertilizer which are coated with vegetable oil, water, and organics in different combinations. Soil samples from Shenton Park (Podosol) and Kojonup (Tenosol), which differ markedly in their clay content were used. Results indicate that NBPT (urease inhibitor) and DMPP (nitrification inhibitor)-coated fertilizer consistently reduces ammonia volatilization in both soils. Notably, volatilization rates in Shenton Park soil were approximately six times higher than in Kojonup soil, which is attributed to the much lower clay content in Shenton Park soil (3.7%) than Kojonup soil (18.25%). These findings underscore the importance of the clay content of the soil in nitrogen loss dynamics and highlight NBPT and DMPP-coated slow-release nitrogenous fertilizer as a promising solution for improving nitrogen use efficiency. Further research is warranted to explore its field-scale applicability and long-term benefits across diverse crops on different soil types.

Many agricultural sandy soils in coastal southern Western Australia have a very low capacity to retain phosphorous (P). Due to phosphorus oversaturation from fertilizers and grazing, any additional P can be lost to downstream waterways and cause environmental impacts.

Applying a high-P sorbing material such as Iron Man Gypsum (IMG) improves soil-P retention capacity but is likely to have additional effects on other aspects of fertility. We conducted laboratory-based experiments focusing on reducing free-P and understanding soil phosphorus dynamics to complement existing paddock trials. We measured PRI, PBI, and CaCl2-extractable P (free-P), along with pH, conductivity, sulfur, and trace elements using DTPA and EDTA extraction on soils mixed with 0 to 13% IMG by weight and incubated moist for 2 weeks. These soils were a no carbon sand (NCS), a moderate organic C sand (MCS) and a high organic C sand (HCS).

Small percentages of IMG increase PRI slightly (from <0 to >100) and similarly in the MCS and HCS soils. PBI followed a similar trend but at lower IMG rates. Free-P decreased sharply, with close to 0 mg/kg at 4% IMG. Given the slight liming effect of IMG, pH increased in all three soils. Both conductivity and sulfur increased similarly with IMG addition. DTPA iron was somewhat unchanged in the HCS, slightly increased in the NCS, and significantly decreased in the MCS. DTPA manganese increased in the HCS but varied little with added IMG in the other two soils. EDTA iron increased similarly for the 3 soils but from different background levels whereas patterns of EDTA manganese were similar regardless of the soil.

These investigations show predictable effects of IMG on sandy soil fertility, irrespective of the background organic C, which can be used to interpret effects on soils with farm applications of IMG.

Saudi Arabia’s sustainability mega-projects—ranging from urban greening and national parks to desert agriculture—face persistent challenges due to sandy soils' poor fertility, alkalinity, and limited water-holding capacity. Sustainable soil amendment technologies are essential to overcome these limitations. This study evaluates the potential of engineered biochar (Carbosoil) to support native desert tree establishment compared to conventional soil amendments—compost and peat moss—under varying irrigation regimes. Five native desert tree species were transplanted and grown in sandy soil as-is, or amended with either Carbosoil, compost, peat moss. Carbosoil was applied at five different rates (2-32 L/tree) and preloaded with diammonium phosphate (DAP), while compost and peat moss were applied at a constant 8 L/tree. No additional fertilizer was used.

Six irrigation volumes (V1–V6, from 0.5 to 12.5 liters per irrigation event) and two frequencies (daily and weekly) were tested over six months. Results show that overall, Carbosoil, peat moss, and compost results in an increase in trunk diameter by 11.5%, -2.4%, and 15.5%, respectively. Carbosoil outperformed compost and peat moss in trunk diameter, particularly under low to moderate irrigation volumes (V1–V2). Notably, at higher CarboSoil application rates (16 and 32 L/tree), tree growth increased progressively with irrigation volume when compared to unamended sandy soil under the same irrigation conditions. For instance, 16L CarboSoil resulted in a 7% increase over the control at V2 and a 23.6% increase at V6, suggesting enhanced water-holding capacity. This trend indicates that CarboSoil may not only improve nutrient retention but also extend the availability of water in sandy soils.

These findings highlight the potential of Carbosoil to enhance afforestation outcomes in sandy desert soils by enhancing nutrient and water use efficiency.