有机配体、竞争阳离子和pH对土壤中Zn分解的影响

A series of experiments were conducted to examine the interactive effects of an organic ligand, a competing cation, and pH on the dissolution of zinc （Zn） from three California soils, Maymen sandy loam, Merced clay, and Yolo clay loam. The concentrations of soluble Zn of the three soils were low in a background solution of Ca（NO3）2. Citric acid, a common organic ligand found in the rhizosphere, was effective in mobilizing Zn in these soils; its presence enhanced the concentration of Zn in soil solution by citrate forming a complex with Zn. The ability of Zn to form a complex with citric acid in the soil solution was dependent on the concentration of citric acid, pH, and the concentration of the competing cation Ca^2＋. The pH of the soil solution determined the extent of desorption of Zn in solid phase in the presence of citric acid. The amounts of Zn released from the solid phase were proportional to the concentration of citric acid and inversely proportional to the concentration of Ca（NO3）2 background solution, which supplied the competing cation Ca^2＋ for the formation of a complex with citrate. When the soil suspension was spiked with Zn, the adsorption of Zn by the soils was retarded by citric acid via the formation of the soluble Zn-citrate complex. The dissolution of Zn in the presence of citric acid was pH dependent in both adsorption and desorption processes.     

Efficacy of fermented prawn shell waste as a feed ingredient for Indian white prawn, Fenneropenaeus indicus

Prawn shell waste collected from shrimp‐processing plants in Cochin, India, was subjected to fermentation using 20 chitinoclastic and proteolytic/non‐proteolytic bacterial strains. The products generated were analysed for protein, lipid, total sugars, N‐acetyl glucosamine, free amino acids and ash. Shrimp diets were prepared using these 20 fermented products and a control diet using raw prawn shell waste. Feeding experiment was conducted with postlarvae (PL21) of Indian white prawn, Fenneropenaeus indicus for a period of 21 days. Biogrowth parameters such as mean weight gain, feed conversion ratio, specific growth rate and protein efficiency ratio were estimated and the animals were challenged with white spot virus orally via diet. Enhanced growth could be observed in prawns fed F134 and F124, incorporated with the fermentation products generated using Bacillus spp., C134 and C124 respectively. The percentage survival of prawns after 7 days of challenge was found to be highest for groups fed diet F111 incorporated with fermentation product generated using Bacillus sp. These products of bacterial fermentation hold promise as growth enhancers and immunostimulants in aquaculture.     

Antifungal activity of bergenin, a constituent of Flueggea microcarpa

The antifungal activity of bergenin against some plant pathogenic fungi, namely, Alternaria alternata , A. brassicae , A. carthami , Fusarium udum , F. oxysporum f.sp. ciceri , Curvularia lunata and Erysiphe pisi , was studied. Bergenin as its monosodium salt was effective against all the fungi and the effective dose for complete inhibition of spore germination varied from 15 μg mL⁻¹ for F. udum to 125 μg mL⁻¹ for E. pisi . Experiments on the effect of bergenin on powdery mildew development under glasshouse conditions revealed that it can control powdery mildew of pea at 2000 μg mL⁻¹ by postinoculation treatment, the results being comparable with those of carbendazim (1000 μg mL⁻¹) and wettable sulfur (2000 μg mL⁻¹). It affected hyphal elongation and the number of primary and secondary branches.     

A note on the dispersal of seeds of blackberry (Rubus procerus P.J. Muell.) by foxes and emus

The monthly variation in the number of seeds of blackberry (Rubus procerus P. J. Muell.) in fox (Vulpes vulpes) faecal droppings was measured at two sites in Victoria, Australia. The maximum percentage of droppings containing seeds (89% at Dartmouth and 55% at Sherbrooke) and the maximum monthly average for the number of seeds per dropping (570 at Dartmouth and 390 at Sherbrooke) occurred in March. Droppings of emu (Dromaius novaehollandiae) collected at Dartmouth contained a mean of 2460 blackberry seeds per dropping. Blackberry seed obtained from berries, fox droppings and emu droppings was tested for germination over a 1O-month period. Germination commenced in spring and ranged from 22 to 35%. It is concluded that foxes and birds are probably responsible for dispersing blackberry over large areas of Victorian bushland.     

A Computer-based Extension Delivery System: Progress and Outlook1

The development of pest management programs in extension has placed severe strains upon traditional information delivery systems. The implementation of new monitoring procedures and management strategies has emphasized the need for systems which allow rapid data summarization, interpretation and dissemination to the agricultural community. Thus, new extension information delivery systems have been developed which incorporate modern, high-speed communications technology. Such a system is operational in Michigan. The computer-based aspects of Michigan's system are referred to as PMEX, or the Pest Management Executive System. The objectives, development and structural components of PMEX have been described in the literature. This paper shall only briefly review these aspects to provide a basis for understanding the significance of recent changes. Any useful information delivery system must be designed with flexibility so as to incorporate changes demanded of it. As Michigan's pest management programs evolve from their crude beginnings, they demand more from and put more emphasis on such systems. Three progressive changes in the system are discussed: 1) a new interactive-feedback program providing interpreted reports from specialists to field personnel based on monitoring input; 2) expansion of the environmental monitoring capabilities and 3) a generalized phenology modeling program or PETE and its implementation in an action pest management program in tree fruit production. Finally, the future uses of the PMEX and related systems shall be explored, especially with reference to a holistic view of farm management. Le developpement des programmes de protection integree demande une amelioration des systemes de diffusion d'informations. La mise en ceuvre des nouveaux systemes de recensement et des strategies de management requiert le recours aux procedes permettant une analyse et une interpretation rapides des donnees qui doivent ensuite atteindre I'exploitant dans les meilleurs delais. Profitant du progres de la technologie moderne des communications ultra-rapides, I'Etat du Michigan a passé a un systeme d'information tres perfectionne. Ce systeme, appele PMEX, donc le but et les structures ont ete decrits (Pest Management Executive System) repose sur I'emploi d'ordinateurs. Le present article a pour objet de revoir I'essentiel du procede afin de faciliter la comprehension de la signification des changements qui sont intervenus. Tout systeme de diffusion d'informations doit etre conyavec suffisamment de souplesse afin qu'il soit possible d'y incorporer les modifications necessaires. Avec le developpement des programmes de management au Michigan, le recours a la telematique s'est intensifie et il est question dans le present article de trois     

Efficacy, uptake and distribution of different herbicides in the water hyacinth

Experiment conducted in the glasshouse with water hyacinth plants in pots revealed that 3h.after spraying parquet or 2.4-D at recommendeb herbicida rates, 43 to 53, of the herbicide is found in the plants and the rest is present in the water culture Out of the total [¹⁴Clparaquat applied,38,9,8·8. 32 and 0.9% was found in the leaf blads. petioles, underwater foliage and roots respectively. The corresponding values for [¹⁴C]2, 4-D were 320. 94. 13 and 0.2% As the time interval after spraying increased, a greater accumulation of herbicide in the under-water parts was evident A net loss of 14 and 60%. of the applied 2,4-D was recorded 1 and 2 weeks after spraying respectively the rate of paraquat loss from the plant water system was similar to 2,4-D. Absorption of [¹⁴C]2,4-D from the culture solution by the roots and the floats of the water hyacinth was. evident Translocation of root-absorbed 2, 4-D into the meristematic folrar parts was dernonstrated If the substrates was treated with 2,4-D.a minimal concentration of 1 p. p. m. was required for water hyacinth death In another experiment glyphosite at 2 to 6 kg a 1 ha and 2.4-D.amine at 0–75 2.25 kg a ha gave complete control of water hyacinth Asulam was found to be unsatis factory even at 6 kg a.1 ha the highest rate tried.