Overload-controlled cultivation shanks under static loads

Cultivators for stony soils have to be protected to prevent breakage. Draft forces of cultivator shanks in hard clod-forming soils are higher than in the temperate soils of wet areas. Load-control devices are used to prevent breakage, but most of them cannot maintain constant depth in hard soils.

Load-controlled light cultivator shanks and chisel plows were tested to define their behaviour under high soil resistances and obstacles. The shanks were loaded with horizontal forces to simulate soil resistances as found in cultivating hard clod-forming soils.

The variations in the depth, the lift angle and the backward deflection were measured. The maximum stresses on the shanks were calculated.

It was found that only the light cultivator shank with a pre-loaded special design moment control device can till hard soils with small reasonable depth variations and still run over an obstacle without being broken.

Only the heavy chisel plow with the rear spring load control device can run over an obstacle without being broken, but it loses cultivation depth under too low a soil resistance, compared with the maximum draft that it can hold.     

Intensification of redclaw crayfish Cherax quadricarinatus culture: II. Growout in a separate cell system

In the process of exploring ways to intensify crayfish culture, a growout system of individual cages (cells) was designed to determine the effects of gender and cell size on the growth of the red claw crayfish Cherax quadricarinatus. Cells of three different diameters—large (25 cm), medium (20 cm) and small (16 cm)—were used. When crayfish were stocked at a mean weight of approximately 10 g, growth rate of males was significantly higher than that of females. The growth rate of the males in the large cells was 0.31±0.14 g/day, while that of the females was 0.18±0.09 g/day. The size of the cell had significant influence on the weight of males. Male crayfish in the large and medium cells grew better than those in the small cells. When males were stocked at a higher mean weight (about 23 g), their mean weight after 206 days was higher in the large cells (69.28±15.72 g) than in the small cells (58.11±12.66 g), suggesting that the growth of large males was also affected by cell size. Regardless of cell size, male animals of this species grew faster than females under conditions of individual cells. This intensive culture method appears to present a powerful improvement in yields, by as much as two orders of magnitude, in comparison with communal cultures.     

Economic Conflicts in Plant Protection: Individual Versus Social Decisions1

We are becoming increasingly aware of the unintended harm caused by the use of chemical pesticides to man, crops, livestock, and the environment. The major side-effects of pesticides are ecosystem disruption, increasing pest resistance and environmental pollution. Market structure (prices) does not include these effects and, for this reason, the individual farmer has no incentive to consider them in his pest control decisions. This leads to conflicting economic interests between the individual farmer who uses excessive pesticides to maximize profits, and society, which considers environmental quality and other external effects as part of the costs of pesticides, and thus desires lower levels of pesticides. A case study of resistance to pesticides by the Egyptian alfalfa weevil shows that the farmers' pest control decisions lead to faster development of resistance than would be deemed desirable by the society. Economic analysis of the costs of resistance serves as the basis for estimating needed investment in new pest control means, of which the most desirable ones are environmentally neutral: some form of biological control and/or host-plant resistance.     

Combining physical, chemical and biological methods for synergistic control of postharvest diseases: A case study of Black Root Rot of carrot

Combining different control methods can improve control efficacy, increase the spectrum of controlled pathogens and reduce the possibility of resistance development. To be successful, however, the different methods need to be compatible: the first treatment should not have any deleterious effect on the succeeding one; preferably, it should contribute to its efficacy. In the last few years, carrot growers in Israel have begun to brush carrots before storage to remove the outer peel of the root. In the present study we show that this practice enhances the appearance of Black Root Rot during storage, a postharvest disease caused by the fungus Thielaviopsis basicola. The chemical fungicide iprodione is usually applied before storage to reduce the development of postharvest diseases. We evaluated the efficacy of combining physical, low-residue chemical and biological control agents as an alternative to the conventional chemical control approach. A technology for the precise application of steam and combined application with stabilized hydrogen peroxide (Tsunami^® 100) or a yeast commercial product (Shemer™) were tested. Used alone, both the steam and Tsunami were highly effective at reducing disease decay but were phytotoxic to the roots. Application of combined treatments of sublethal steam followed by a sublethal dosage of Tsunami or Shemer improved efficacy and disease control by 80 and 86%, respectively. These combinations showed a synergistic effect as compared to each of the treatments alone. The same pattern, effecting up to 54% disease control, was observed with the non-compatible combination of applying Tsunami first, washing it off with water and then applying Shemer. Thus disease-control agents can potentially be used for a short period, then washed off, if needed, and efficiently followed by application of a biological control agent. The biological pathway and mode of action are still under investigation but to the best of our knowledge, this is the first study to mathematically demonstrate synergistic effects of sublethal treatments applied sequentially to control postharvest disease as a potential method to reduce the use of chemicals in fruit and vegetables.     

Adapted thermal imaging for the development of postharvest precision steam-disinfection technology for carrots

Postharvest carrots are brushed, hydro-cooled to 4–6 °C and treated with chemical fungicide before storage to prevent soft rot caused by Sclerotinia sclerotiorum (Lib.) de Bary during storage. Replacement of the fungicide with high-temperature surface heat treatment poses a dilemma: excessive heating will cause damage whereas insufficient heating will result in incomplete disinfection. This problem is further compounded by the difficulty in providing uniform surface heating. To alleviate this problem, a system for the uniform application of high-temperature short-duration steam disinfection was developed using accurate real-time temperature monitoring of individual produce segments by thermal imaging. Uniform short-duration high-temperature heat was delivered from above by steam jets combined with electric steam-drying elements and reflectors. Produce was subjected to rotational and linear motions to expose each surface segment to the same amount of heat. The novel use of thermal imaging to monitor surface temperature in steam systems was essential for determining transferred heat and heating uniformity in a treated object. The resultant, uniform application of short-duration high-temperature steam provided surface heat-disinfection with minimal internal heating and damage. Application of the steam treatment immediately after carrot hydro-cooling reduced post-storage phytotoxic color change by 60–80% and resulted in significantly reduced sensitivity to post-storage soft rots caused by S. sclerotiorum. Carrot sprouting was not increased by the steam treatment, suggesting retention of the hydro-cooling's physiological effect. These results suggest that precise heat treatment can be optimally applied after hydro-cooling to improve postharvest quality of carrots in a procedure that is harmless to man and the environment.     

Complement, polymorphonuclear leukocytes and platelets in acute experimental respiratory reactions to Aspergillus

An experimental complement-dependent model of an acute allergic response to inhalation of Aspergillus spores has been used to examine the roles of polymorphonuclear leukocytes (PMN) and platelets in mediating this reaction as measured by decreases in arterial oxygen tensions (Pa_O2). Normal rabbits selectively depleted of PMN by nitrogen mustard (HN₂) showed a decrease in Pa_O2 later than that observed in untreated animals. The HN₂-treated group also showed a marked decrease in platelets after challenge, not seen in the similarly challenged untreated group or in unchallenged HN₂-treated animals. These data demonstrate the importance of PMN in complement-mediated host responses to aerosols of fungal spores. In the absence of the PMN, platelets appear capable of initiating a similar, albeit delayed, reaction, thus further emphasizing the flexibility of pulmonary defense mechanisms against inhaled particles.     

Reduction of postharvest losses of Galia melon by a short hot-water rinse

A rapid method for simultaneously rinsing and disinfecting fresh harvested produce using a hot-water rinse and brushes (HWRB) was tested on Galia melon ( Cucumis melo cv. reticulatus ) fruit. The optimal treatment to reduce decay while maintaining fruit quality after prolonged storage and marketing simulation was 59 ± 1°C for 15 s. Trial shipments by sea transport to Europe demonstrated that treating melon with a commercial-scale HWRB machine (3 tonnes fruit h⁻¹) maintained significantly better overall quality of treated fruit compared with untreated fruit. Exposing spores of Alternaria alternata and Fusarium solani to 60°C for about 15 s in vitro reduced germination by 48% and 42%, respectively. Employing HWRB resulted in a 3-log reduction in total colony-forming units (CFU) of the epiphytic microbial population, compared with untreated fruit. Scanning electron microscopy (SEM) showed that HWRB removed soil, dust and fungal spores from the fruit surface, and partially or entirely sealed natural openings in the epidermis.