Conservation agriculture as a sustainable option for the central Mexican highlands

Tropical highlands of the world are densely populated and intensively cropped. Agricultural sustainability problems resulting from soil erosion and fertility decline have arisen all over this agro-ecological zone. Based on selected soil quality indicators, i.e. time-to-pond, aggregate distribution and stability (expressed as the mean weight diameter (MWD) for dry and wet sieving, respectively) and soil moisture, from a representative long-term sustainability trial initiated in 1991 in Central Mexico (2240 masl; 19.31°N, 98.50°W; Cumulic Phaeozem), some insights into the feasibility of conservation agriculture (CA) as part of a sustainable production system in the tropical highlands are given. Zero tillage plots with crop residue removal showed low aggregate distribution (average MWD = 1.34 mm) and stability (average MWD = 0.99 mm) resulting in top layer slaking, increased erosion and low time-to-pond values. Retaining the residue in the field with zero tillage avoided the above-mentioned negative evolution for both aggregate distribution as stability (average MWD = 2.77 and 1.51 mm, respectively) and even improved the physical conditions of the soil as compared to conventional practice. Throughout the growing season the lowest soil moisture content was found in zero tillage without residue (average over the entire growing season = 20.5% volumetric moisture content), the highest in zero tillage with residue retention (average = 29.7%) while conventional tillage had intermediate soil moisture values (average = 27.4%). Zero tillage without residue retention had most days of soil moisture values under permanent wilting point, while zero tillage with residue retention had the least. Taking into account these results, zero tillage with residue retention can clearly be a part of an integrated watershed management scheme towards sustainable agriculture in the tropical highlands. It is clear that to develop new management practices to improve water use, reduce erosion and enhance human labor/animal power focus must be on the use of conservation agriculture both for rainfed as well as irrigated production systems and be fine tuned for each system.     

The structure-activity relationship of DDT analogs in crayfish giant axons

The effects of 14 DDT analogs on the resting and action potentials of the crayfish giant axon were investigated using the intracellular microelectrode technique. These analogs can be classified into three groups, excitatory, blocking, and dualist. An excitatory analog tends to increase the excitability of the axonal membrane, and has hydrophobic side chains on the para positions whose optimal size equals that of the ethoxy group. A blocking analog suppresses the action potential without affecting the resting potential, and has hydrophilic side chains capable of forming hydrogen bonds. A dualist has both excitatory and blocking actions, and the latter may be related to restriction in rotation imposed by the grouping on the benzylic carbon. However, the dividing lines between these categories are not sharp, the compounds tending to fall along a spectrum between pure excitatory and pure blocking activity.     

Assessment of the repeatability of a milk Ostertagia ostertagi ELISA and effects of sample preparation

An indirect Ostertagia ostertagi ELISA on milk is a promising diagnostic tool in bovine parasitology. Interpretation of the test results requires a good knowledge of the test characteristics. In this study, border effects, the repeatability of the ELISA and the effect of different factors such as storage, skimming and freeze–thaw cycles of the milk samples were investigated. The border effects trial showed that significant border effects can occur. The repeatability trial was conducted over 3 days. An alternative graphical technique to assess the repeatability over a large number of ELISA plates measured over different days was developed. From these graphs, it was obvious that the ODR values obtained on the third day were deviating from the values on the first and second day. On the third day, also abnormal control values were observed. When the control values were normal, 94% of the variability was explained by the milk sample and 6% by assay variability. The expected 95% range of the difference of 2 ODR readings of the same sample on the same plate and the same sample on different plates was −0.14 to 0.14 and −0.16 to 0.16. No extra variability was observed when samples were tested on a different day, however these results are based on the measurement of 2 days. Storage for 2–4 days at 4 °C, using whole milk instead of skimmed milk and up to 2 extra freeze–thaw cycles of the milk samples did not significantly affect the test results.     

Effect of the Host and Temperature on the Formation of Defective RNAs Associated with Broad bean mottle virus Infection

ABSTRACT Previously, we demonstrated that Broad bean mottle virus (BBMV), a member of the genus Bromovirus, could accumulate RNA 2-derived defective interfering (DI) RNAs during infection. In this work, we study how host and environmental factors affect the accumulation of DI RNAs. Serial passages of BBMV through selected plant species reveal that, with low-multiplicity inocula, some systemic hosts (Vicia faba, Nicotiana clevelandii, and N. tabacum cv. Samsum) support DI RNA accumulation after the first passage cycle but other hosts (Phaseolus vulgaris, Pisum sativum, and Glycine max) do not. However, several passages with the high-multiplicity inocula can generate DI RNAs in pea plants. Local lesion hosts (Chenopodium quinoa, C. amaranticolor, and C. murale) remain free of the DI RNA components. The size of the de novo-formed DI RNAs depends on the host and on environmental conditions. For instance, broad bean plants cultivated in a greenhouse or in a growth chamber at 20 degrees C accumulated DI RNAs of 2.4 or 1.9 kb in size, respectively. A reverse trend was observed in pea plants. Lower temperatures greatly facilitated the formation of DI RNAs in broad bean and pea hosts after the first passage. The importance of these findings for the studies on DI RNAs are discussed.     

De economie van de bespuitingen in de fruitteelt

Ohne ZusammenfassungVoordracht, gehouden tijdens den Fruitteeltdag (vanwege de Ned. Pomologische Vereeniging, de Ned. Plantenziektenkundige Vereeniging en de Commissie voor Phytopatologie van de Ned. Botanische Vereeniging) van de 8ste Ned. Landbouwweek op 1 October 1937 te Wageningen.     

A survey on biosecurity and management practices in selected Belgian cattle farms

The shift from cure towards prevention in veterinary medicine involves the implementation of biosecurity, which includes all measures preventing pathogens from entering a herd and reducing the spread of pathogens within a herd. In Belgium no studies have considered the implementation of biosecurity measures in the daily management of cattle farms. Therefore the aim of the study was to map the current application of biosecurity measures in Belgian cattle farms in the prevention of disease transmission within and between farms.     

Mercury Emission from Anthropogenic Sources in Poland and Their Scenarios to the Year 2020

We present the concentrations and distribution patterns of nine acid leachable trace metals (ALTMs) Fe, Mn, Cr, Cu, Ni, Co, Pb, Zn, and Cd in the soil samples from the five century old Pachuca-Mineral de Monte mining district of the Central Mexico. The ALTMs do not show any significant correlation with pH, EC, CaCO₃, and organic carbon. The metal concentration indicates three distinct distribution patterns. Fe, Mn, Cr, Pb, and Zn show enrichment in the high altitude region of the northern and central part of the study area. Likewise, Cu and Cd are enriched in the northern mountainous terrains. Both these groups show strong positive correlation with Mn indicating that they are associated with Mn-bearing minerals. However, we relate the first group of metals to excessive vehicular transportation and second group to mining waste dumps. The third group of ALTMs Co and Ni indicates its direct relationship to ore processing activities. Comparison of ALTMs concentrations from this study and various other studies throughout the world suggests the need to take precautionary measures of surface soil in high altitude areas to avoid metal enrichments and its subsequent environmental problems.     

A Bayesian approach for the evaluation of six diagnostic assays and the estimation of Cryptosporidium prevalence in dairy calves

The prevalence of Cryptosporidium in calves and the test properties of six diagnostic assays (microscopy (ME), an immunofluorescence assay (IFA), two ELISA and two PCR assays) were estimated using Bayesian analysis. In a first Bayesian approach, the test results of the four conventional techniques were used: ME, IFA and two ELISA. This four-test approach estimated that the calf prevalence was 17% (95% Probability Interval (PI): 0.1-0.28) and that the specificity estimates of the IFA and ELISA were high compared to ME. A six-test Bayesian model was developed using the test results of the 4 conventional assays and 2 PCR assays, resulting in a higher calf prevalence estimate (58% with a 95% PI: 0.5-0.66) and in a different test evaluation: the sensitivity estimates of the conventional techniques decreased in the six-test approach, due to the inclusion of two PCR assays with a higher sensitivity compared to the conventional techniques. The specificity estimates of these conventional assays were comparable in the four-test and six-test approach. These results both illustrate the potential and the pitfalls of a Bayesian analysis in estimating prevalence and test characteristics, since posterior estimates are variables depending both on the data at hand and prior information included in the analysis. The need for sensitive diagnostic assays in epidemiological studies is demonstrated, especially for the identification of subclinically infected animals since the PCR assays identify these animals with reduced oocyst excretion, which the conventional techniques fail to identify.     

Field testing of a fenbendazole treatment combined with hygienic and management measures against a natural Giardia infection in calves

The need of a combination of animal treatment and environmental measures against a natural Giardia infection in calves between the age of 1 and 6 months was emphasized and evaluated. Ten commercial farms with a total of 94 calves suffering from chronic diarrhea, ill thriving and impaired growth, were included in two subsequent studies. The first study indicated that treatment of all animals with fenbendazole at 15 mg/kg during 3 consecutive days combined with environmental measures on the final day of treatment, which were either removal of bedding, thorough cleaning and ammonia 10% disinfection or relocation of the treated animals to a Giardia free environment, resulted in a total reduction in cyst excretion for at least 2 weeks. In the second study, the immunofluorescence assay (Merifluor Cryptosporidium/Giardia; Meridian Diagnostics Inc., Cincinnati, Ohio) was used quantitatively and confirmed that the combination of treatment and environmental measures resulted in a total reduction of cyst excretion during 2 weeks and in a significant (P<0.05; >or=98.0%) reduction of the cyst excretion until at least 4 weeks after treatment. Furthermore, there was a noticeable improvement of the clinical symptoms in all animals towards day 28 after treatment and 4 months after treatment health in all calves was normal.