OAR@UM Collection:

Recapping and mite non-reproduction in the endemic honey bee subspecies of Malta : Apis mellifera ruttneri

Wed, 01 Jan 2025 00:00:00 GMT

Title: Recapping and mite non-reproduction in the endemic honey bee subspecies of Malta : Apis mellifera ruttneri Abstract: Scientific literature concerning Apis mellifera ruttneri, the endemic honey bee of the Maltese Islands is still limited. Recently, its behaviour and development gained an increasing attention particularly in relation to Varroa resistant traits. Nevertheless, the effect of recapping on mite reproduction remains controversial. In October 2021, a standardized study was set up for the evaluation of two resistant traits: recapping and mite non-reproduction (MNR). In total 40 colonies (A.m.ruttneri n = 20, and Buckfast n = 20, sister queens) of approximately the same size, were distributed across two apiaries, one in Wardija and the other in . Hygienic behaviour evaluated by the pin-test method was higher in the Buckfast than in A.m.ruttneri, but this was not significant. In contrast, A.m.ruttneri produced significantly more honey than the Buckfast group. MNR is very restricted for analysis due its strict requirements in the right number of mites in relation to the brood. A Varroa treatment in December 2021 was applied to reduce mite loads, subsequently the first MNR/recapping assessment occurred in June 2022 and continued until April 2023. The measurements were repeated three times across a ten-month period, but samples could not be further collected due to insufficient mite infestation and colony losses emerging from to constant strain of the mites. High recapping rates and low mite reproductive success were consistent in A.m.ruttneri. In the Buckfast group, both at the colony level and at the cell level elevated rates of recapping were linked with MNR. However, this direct outcome of recapping on mite reproduction was not observed in A.m.ruttneri. Even though, both traits seem to mainly be driven by seasonality and apiary environment, this effect was stronger in A.m.ruttneri. Brood infestation related to an increased non-targeted recapping in A.m.ruttneri but not in the Buckfast. Despite brood infestation was relatively high, most colonies preceded by A.m.ruttneri still survived until the end of the study, and afterwards. All this implies that A.m.ruttneri shows a certain degree of tolerance and resistance expressed both through MNR and an extensive mite infestation tolerance. This is likely due to a combination of recapping and possibly other traits such as VSH, physiological adaptations along with the rhythm of brood dynamics amalgamated to the seasonal changes of to the Maltese Islands. Description: M.Sc.(Melit.)

Electrical conductivity modelling in calcareous soils of the Maltese Islands : developing a soil:water suspension to saturated paste conversion model

Wed, 01 Jan 2025 00:00:00 GMT

Title: Electrical conductivity modelling in calcareous soils of the Maltese Islands : developing a soil:water suspension to saturated paste conversion model Abstract: Soil salinity is a critical factor influencing soil health and agricultural productivity, typically measured through the electrical conductivity (EC) of a saturated soil paste extract (ECe). However, this standard method is time-consuming, and alternative soil: water suspension methods (EC(soil : water)) offer quicker results, though conversion models are often soil-specific. This study aimed to develop models to convert EC (1:1, 1:2, and 1:5) to ECe for Malta's calcareous soils, while also assessing the impact soil texture, carbonate, and organic matter content have on model accuracy. Moreover, the effect these variables have on soil salinity in the field was also investigated. A total of 134 soil samples with varying textures, carbonate, and organic matter levels were analysed. The results indicate a considerable variability in salinity levels among the sampled soils with a mean average of 3772 µS/cm. Out of the different soils analysed, 104 can be classified as non-saline, with an electrical conductivity (e) less than 4,000 µS/cm. This study produced generalized models (ECe = 10(a(logEC(soil))+b)) with strong correlation coefficients (r² = 0.91-0.93, p < .001). Models specific to fine- and medium-textured soils, soils with 35-50 % carbonate content, and those with 2.5-4.2 % organic matter demonstrated even higher accuracy (mean r² = 0.96). Validation using 22 independent samples confirmed the reliability of these models (RMSE = 0.93-0.97 dS m⁻¹; NSE = 0.95-0.97), except for coarse-textured soils. These findings suggest that general models can be reliably applied to most of Malta’s soils, with exceptions for high sand content soils. This methodology was also applied to analyse metal concentrations, and the resulting general model can estimate the concentrations of key metal ions Na⁺, Ca²⁺, Mg²⁺, and K⁺ in the soil saturation extract (ECe) using measurements derived from soil:water suspensions at 1:1, 1:2, and 1:5 ratios. No significant correlation between ECe and the levels of sand, silt, and clay was observed, nor were significant differences in EC found across contrasting textural classes (p = .465). Weak positive correlations were detected between EC and both carbonate (rs = 0.216, p < .05) and OM content (rs = 0.269, p < .05). These results suggest that salinity in these soils is not primarily governed by physical properties like texture. Organic matter levels, when plotted against sand and clay content, showed no significant correlation, indicating that other factors such as soil management practices and environmental factors seem to have a more pronounced impact on soil salinity. Description: M.Sc.(Melit.)

The effect of salinity and soil texture on the degradation and humification of soil organic matter

Wed, 01 Jan 2025 00:00:00 GMT

Title: The effect of salinity and soil texture on the degradation and humification of soil organic matter Abstract: Soil organic matter (SOM) is one of the most critical components of soil, owing to its essential roles in influencing physical, chemical, and biological properties. It is an essential source of energy and carbon for many soil organisms that are highly dependent on its availability. The SOM content and its fractionation vary significantly due to factors such as climate, land management practices, soil properties, redox status and salinity, with the latter emerging as a widespread concern in irrigated agricultural land. The aim of this study was to investigate the effects of soil texture, redox status, and increasing salinity on SOM content and its humification. The study was divided into two phases. In the first phase, a survey of 138 locally collected soil samples was conducted to analyse the relationships between SOM and pH, carbonate content, soil texture, and salinity. In the second phase, three soils; a Luvisol, a Calcisol, and a Vertisol; were amended with 4 % peat and NaCl to achieve electrical conductivity (EC 1:5) levels of 1000 and 3000 µS cm⁻¹, along with an unamended control. The soils were then incubated under both aerobic and anaerobic conditions for 150 days. The results from the 1st phase indicated that SOM dynamics may be influenced by several soil factors, including soil texture, pH, carbonate content, and salinity. However, the observed correlations were generally weak. In contrast, the 2 nd phase demonstrated that SOM content, humification, and the FA:HA ratio are regulated by a complex interaction among salinity, redox conditions, and soil texture. Clay-rich soils under aerobic conditions tend to promote humification, whereas elevated salinity and anaerobic conditions suppress humification, with outcomes varying depending on the specific mineralogical characteristics of the soil. Description: M.Sc.(Melit.)

The impact of tillage on soil organic matter

Wed, 01 Jan 2025 00:00:00 GMT

Title: The impact of tillage on soil organic matter Abstract: This study investigates the impact of long-term tillage on soil organic matter (SOM) content across two soil depths. Soil samples were collected from a number of sites with conventional tillage and from adjacent agricultural land that has remained untilled for over 20 years. Samples were taken at two depths (0–15 cm and 15–30 cm), and SOM was determined using the loss-on-ignition method. Statistical analysis using post-hoc pairwise comparisons (Holm-Sidak method) revealed a highly significant difference (p < 0.001) in SOM between tilled and untilled soils. However, no significant difference was observed between topsoil and subsoil SOM levels (p = 0.178). Within both depth layers, SOM was significantly higher in the untilled soil compared to the tilled soil (p = 0.002 and p < 0.001, respectively). Differences in SOM between depths within the same tillage treatment were not statistically significant (p > 0.2). These findings indicate that tillage is the primary factor influencing SOM content, causing a substantial decline in SOM regardless of soil depth, while depth alone had no significant effect and no interaction between tillage and depth was observed. Description: Dip. Agric.(Melit.)