Technical Efficiency of Shrimp Farming in Bangladesh: An Application of the Stochastic Production Frontier Approach

This study estimates the levels and determinants of farm‐level technical efficiency of shrimp farmers, using the stochastic production frontier function involving a model for technical inefficiency effects. A sample of 90 brackish water shrimp farms were surveyed in the region of Shyamnagar Upazila of the Satkhira District, Bangladesh, to study their economic efficiencies. Data were collected, using a questionnaire survey from September to October 2011. The mean technical efficiency level of the shrimp farmers was estimated at 82%, and thus, farmers operate 18% below the production frontier. The results suggest that the inefficiency effect is significant, and that education, age, non‐farm income and distance of the farm are significant determinants of technical inefficiency. By operating at full technical efficiency levels, shrimp production can increase from the current yield of 225.56 to 265.28 kg/ha. Besides improving technical efficiency, technological progress and extension services (such as dissemination of proper information of the technological practices and further adoption of technological practices) can also contribute to increased shrimp production levels. Finally, quality feed and fingerling at affordable prices need to be ensured to further promote shrimp production.     

Oxidation of Chlorophenols in Aqueous Solution by Excess Potassium Permanganate

A simple spectrophotometric method was developed to quantify chlorophenol (CP) concentrations after reaction with potassium permanganate and quenching with sodium sulfite. Other quenching agents (peroxide, sodium thiosulfate and hydroxylamine hydrochloride) were found to create absorbance in the spectral range required for CP quantification. Analysis at pH 12 gave greater absorption and sensitivity for the method compared with pH 5.6. The calibration curves of the proposed methods were linear in the concentration ranges 0.0061–0.61 and 0.0078–0.78 mM with detection limit of 0.0006 and 0.0008 mM for dichlorophenols and monochlorophenols, respectively. The oxidation kinetics of five chlorophenols in aqueous solution with excess potassium permanganate were evaluated using the analytical method. The pseudo-first-order reaction rates were found to be relatively rapid 1.42 × 10⁻³ to 0.024 s⁻¹ and followed the sequence 2-chlorophenol (2-CP) > 2,6-dichlorophenol (2,6-DCP) > 4-chlorophenol (4-CP) > 2,4-dichlorophenol (2, 4-DCP) > 3-chlorophenol (3-CP). The apparent second-order rate constant was calculated from the measured pseudo-first-order rate constant with respect to CP with initial KMnO₄ concentration (1.5 mM) and follows the same sequence of pseudo-first-order rate constant. This shows that chlorine atoms in the structure of chlorophenol had a significant influence on the oxidation of chlorophenols by potassium permanganate. Permanganate can be used for the treatment of chlorophenol-contaminated soil and groundwater.     

Aphanomyces pea root rot disease and control with special reference to impact of Brassicaceae cover crops

Abstract

Pea root rot disease caused by the pathogen Aphanomyces euteiches deserves increased attention, since peas are an important cash crop and also improve the N balance in temperate agriculture. However, due to pea root rot it is difficult to cultivate peas as frequently and successfully as desired. In the search for biological measures to overcome this problem, attention has been drawn to the use of Brassicaceae plants as cover crops between main crops, since these can be effective catch crops for nutrients and also exert allelopathic effects. Many species within the Brassicaceae contain glucosinolates (GSLs). Their hydrolysis products, the volatile isothiocyanates (ITCs), have been shown to suppress soil-borne plant pathogens such as A. euteiches. In addition, Brassicaceae biomass releases water-soluble toxic substances such as oxazolidine-2-thione and supplies nutrients and organic matter. Overall, this influences the soil microbial community and the final suppression of pathogens. Due to the unpredictability of the control effect of Brassicaceae biomass incorporation into soil on the pathogen, there is a need to define the mechanisms behind suppression in the field situation. This review focuses on how incorporation of Brassicaceae biomass suppresses A. euteiches under field conditions and the effect on the emerging pea. Different factors influencing the severity of field pea (Pisum sativum L.) root rot disease are also discussed. One conclusion is that suppression of pea root rot depends on the quality and quantity of incorporated Brassicaceae biomass.     

Polyphenol-induced inhibition of the response of na(+)/glucose cotransporter expressed in Xenopus oocytes

To study the effects of polyphenols on the Na(+)/glucose cotransporter (SGLT1) response, SGLT1 was expressed in Xenopus oocytes by injecting cRNA synthesized from the cloned cDNA of the small intestine cotransporter of rats, and the electrical response elicited by glucose or galactose was measured by a voltage clamping method. Most phenol derivatives had no effect on the response. However, the polyphenols (+)-catechin, (-)-epicatechin gallate (ECg), and (-)-epigallocatechin gallate (EGCg), which are components of green tea, caused an inhibition of the response, which was almost independent of glucose concentration. The inhibition constants were estimated to be 2.3 mM for (+)-catechin and 0.45 mM for both ECg and EGCg, assuming the noncompetitive inhibition mechanism. Saponin prepared from tea seeds also inhibited the response significantly. Tannic acid and aqueous extracts of teas induced nonspecific electrical responses in both cRNA-injected and noninjected oocytes at lower concentrations than those that caused an inhibition of the SGLT1 response when their dose-dependent effects were examined. These results are possibly helpful in the development of a dietary supplement for diabetic patients.     

Effects of fertilizer application and fire regime on soil microbial biomass carbon and nitrogen,and nitrogen mineralization in an Australian subalpine eucalypt forest

The effects of a range of fertilizer applications and of repeated low-intensity prescribed fires on microbial biomass C and N, and in situ N mineralization were studied in an acid soil under subalpine Eucalyptus pauciflora forest near Canberra, Australia. Fertilizer treatments (N, P, N+P, line + P, sucrose + P), and P in particular, tended to lower biomass N. The fertilizer effects were greatest in spring and smaller in summer and late actumn. Low-intensity prescribed fire lowered biomass N at a soil depth of 0–5 cm with the effect being greater in the most frequently burnt soils. No interactions between fire treatments, season, and depth were significant. Only the lime + P and N+P treatments significantly affected soil microbial biomass C contents. The N+P treatment increased biomass C only at 0–2.5 cm in depth, but the soil depth of entire 0–10 cm had much higher (>doubled) biomass C values in the line + P treatment. Frequent (two or three times a year) burning reduced microbial boomass C, but the reverse was true in soils under forest burn at intervals of 7 years. Soil N mineralization was increased by the addition of N and P (alone or in combination), line + P, and sucrose + P to the soil. The same was true for the ratio of N mineralization to biomass N. Soil N mineralization was retarded by repeated fire treatments, especially the more frequent fire treatment where rates were only about half those measured in unburnt soils. There was no relationship between microbial biomass N (kg N ha^-1) and the field rates of soil N mineralization (kg N ha^-1 month^-1). The results suggest that although soil microbial biomass N represents a distinct pool of N, it is not a useful measure of N turnover.     

Effects of a neem-based insecticide on different immature life stages of the leafminerLiriomyza sativae on tomato

The effects of the commercially available neem insecticide NeemAzal-T/S® (neem) (1% azadirachtin) onLiriomyza sativae (Diptera: Agromyzidae) were studied on tomato in Bangkok, Thailand. Neem emulsions were sprayed on the aerial plant parts at five concentrations (from 0.001% to 0.010% a.i.); different aged residues (0, 1, 3, 5, and 7 days) were tested, in both controlled environment rooms and in greenhouses. Irrespective of the residual age of the application, no significant effects on oviposition or egg hatch were detected. However, neem drastically increased larval mortality at the higher concentrations tested. The L1 and L2 larvae were most susceptible. Irrespective of concentration, larval mortality or inhibition of adult eclosion decreased much faster in greenhouses than in controlled environments with artificial light. Nevertheless, our results suggest that neem has potential to controlL. sativae in netted greenhouses.