Soil resources: What is needed and how do we maintain these resources

The soil as a resouce in potato production must be maintained if potato production is to be sustained into the 21st century. Increased pest resistance, resource scarcity, and increased input costs will all be important in determining the availability of technology in the future. As demands to maintain and improve environmental quality increase, our ability to overcome poor soil management by increased inputs may be restricted. j To sustain soil as a resource more attention must be given to soil organic matter, structure, and water holding capacity. Cropping systems that increase crop residue returned to the soil and reduce tillage can increase soil organic matter levels and improve soil physical properties. Greenmanure crops may also help reduce pathogen populations. Soil compaction, soil erosion, and salinization represent the most significant threats to maintaining the soil resource. Compaction can significantly limit the soil’s ability to supply water and nutrients to the plant by limiting water holding capacity and root growth. Limiting rooting depth increases the potential for nitrates to be leached below the rooting zone. Erosion, through the removal of the most productive topsoil, has the potential to destroy soil productivity. The actual impact of erosion over time is very difficult to measure and has been compensated for by increased inputs. Salinization throughout history has decreased productivity of irrigated soils. The sustainability of the soil resource depends upon the development and use of Best Management Practices that maintain or improve soil physical properties, while minimizing soil compaction and erosion. These practices will have to be developed within the parameters established by changing human needs and expectations.     

Prolonged exclusion of foraging ants (Hymenoptera: Formicidae) from citrus trees using controlled-release chlorpyrifos trunk bands

Abstract

Controlled-release chlorpyrifos trunk bands excluded foraging ants ( Iridomyrmex spp.) from citrus tree canopies for four growing seasons (182 and 211 weeks in two separate trials). The level of exclusion averaged 92.7% over the full period of the trials. Laboratory bioassays of weathered band material showed the bands were still toxic to ants (98 - 100% mortality) after 200 and 229 weeks. In contrast, trunk applications of lambda-cyhalothrin and a chlorpyrifos 'emulsion' were very short-lived (< 14 weeks) in their activity against foraging ants; levels of exclusion over 15 to 18 weeks averaged 46% for lambda-cyhalothrin and 23% for the chlorpyrifos 'emulsion'. The potential of controlled-release chlorpyrifos trunk bands as a practical management strategy for foraging ants in citrus groves is discussed.     

Potential contribution of organosilicon compounds to reduced leaching of biocides in wood protection

? Leaching of biocide treated wood leads to reduced effectiveness and potential threat to the environment.

? Therefore the effectiveness of organosilicons as protective systems of biocides was evaluated. Scots pine sapwood specimens were impregnated with solely organosilicons and biocides as well as with combinations of both.

? The biocides 3-iodo-2-propynylbutylcarbamate, propiconazole and 3-(trimethoxysilyl)propyldimethyloctadecyl ammonium chloride confirmed their effectiveness regardless the addition of an organosilicon. Low leachate toxicities to the crustacean Daphnia magna were found for the organosilicons, whereas significant leachate toxicities were measured for the biocides. Combining both did not considerably diminish the leachate toxicities.

? It must therefore be concluded that under the circumstances as described in this article, organosilicons do not interfere with the efficacy of the biocides, but they do not contribute to a reduced leaching of the biocides either.

     

Soil organic carbon stock in the Belgian Ardennes as affected by afforestation and deforestation from 1868 to 2005

The effects of historical land use changes on the global C cycle have mainly been studied by means of bookkeeping models. Here, we investigate with such models the impact of afforestation and deforestation on soil organic carbon (SOC) stocks. This approach, using field-based estimates of the response of SOC upon land use changes, is applied to a pilot area in the Belgian Ardennes over one and a half century (1868–2005). After a small initial decline during the 1868–1888 period due to deforestation for agricultural use, mean SOC stocks increased steadily up to 1990, due essentially to the conversion of deciduous to coniferous forests (in the study area, deciduous forests stored less SOC than coniferous) and the reclamation of heathland, which occurred both at the turn of the 19th and 20th centuries. Simulations showed that SOC stocks decreased recently (1990–2005) because of the slow down of sequestration in coniferous forests and a reversion of some of the coniferous plantations to deciduous forests. Over the entire period, afforestation resulted in a net sequestration of carbon (0.16 t C ha⁻¹ year⁻¹). Monte Carlo simulations demonstrated that the model was highly sensitive to its inputs (initial SOC stocks for each land use) both in term of predicted SOC stocks and rates of SOC stocks change. However, the sensitivity of the model was not large enough to revert the main trends of SOC changes observed. Compared to the amount of carbon sequestered in the biomass, the contribution of soils to the C sink in forest is small. Despite several sources of errors, a detailed reconstruction of land use changes combined with realistic SOC response curves upon land use conversion are required to be able to quantify the contribution of soils to terrestrial carbon fluxes.     

Survival of Ralstonia solanacearum and Ralstonia pseudosolanacearum in drain water

The survival in drain water of two strains of Ralstonia solanacearum and three strains of Ralstonia pseudosolanacearum, including two strains able to cause wilt in roses, was determined. Water draining from drip‐irrigated rock wool mats on which roses were grown was supplemented with the pathogen and survival was monitored at 4, 12, 20 and 28°C for up to 112 days. All strains were able to survive for at least 112 days in drain water at 12 and 20°C, but at 4°C maximum survival was 56 days. At 28°C, the survival period was strain dependent, but was at least 56 days. Populations declined gradually in non‐sterile drain water to a low level (maximum 100 cfu mL^?1 after 112 days). In sterile drain water (autoclaved prior to addition of populations), no or only a limited decline in populations was found at 112 days, dependent on strain and temperature. Drain water that tested negative for Ralstonia in the dilution plating assay was tested for the presence of cells in a viable but non‐culturable state (VBNCs). Tomato plants were inoculated, but no symptoms developed, and plants sampled 22 days post‐inoculation were negative in a plating assay. Therefore, no indications were found that VBNCs were present.     

Field performance of three real-time moisture sensors in sandy loam and clay loam soils

The study was conducted to evaluate HydraProbe (HyP), Campbell Time Domain Reflectometry (TDR) and Watermarks (WM) moisture sensors for their ability to estimate water content based on calibrated neutron probe (NP) measurements. The three sensors were in-situ tested under natural weather conditions over a 3-yr period in a sandy loam and clay loam soils planted to grass. The HyP, TDR and WM sensors were evaluated for their ability to estimate soil moisture contents by comparing their outputs with those of NP measurements. Results showed that HyP, TDR and WM provided different estimates of soil moisture contents in both soils. Nevertheless, our work suggests that soil moisture sensors including those used in this study can be made suitable for irrigation scheduling without in-situ calibrations by simply setting the upper and lower irrigation trigger limits for each sensor and each soil type. The upper trigger point occurs directly after irrigation event (near field capacity) and the lower trigger point is based on about 50% depletion of available water in the crop rootzone and is occurs prior to irrigation refill. This approach can significantly help irrigators to achieve their irrigation scheduling and productivity goals without consuming any time onsite or soil specific calibrations.     

Administration of Lactobacillus johnsonii FI9785 to chickens affects colonisation by Campylobacter jejuni and the intestinal microbiota

1. Campylobacter jejuni is the most common bacterial cause of human food-borne gastroenteritis in the world. A major source of human infection is the consumption of contaminated meat, particularly poultry. New control measures to reduce or eliminate this pathogen from the animal gastrointestinal tract are urgently required, and the use of probiotics as competitive exclusion agents is a promising biocontrol measure to reduce C. jejuni in the food chain.

2. In this study, we assessed the potential of Lactobacillus johnsonii FI9785, which has shown efficacy against Clostridium perfringens, to combat C. jejuni. The effect of prophylactic administration of L. johnsonii on the ability of C. jejuni to colonise chickens was determined.

3. Two doses of L. johnsonii given a week apart led to a reduction in C. jejuni colonisation in the caecal contents, but this biocontrol seemed reliant upon a high level of initial colonisation by the probiotic.

4. The microbial composition in the chicken gut was significantly altered by the probiotic treatment, as shown by denaturing gradient gel electrophoresis of 16S rRNA gene amplicons.

5. Together these results demonstrate the potential of this probiotic strain to be tested further as a competitive exclusion agent in poultry against C. jejuni.