Scale and scope economies in small household rice farming in Vietnam          下载免费PDF全文

Viet-Ngu HOANG  Trung Thanh NGUYEN  Clevo WILSON  Thong Quoc HO  Uttam KHANAL 《农业科学学报》2021,20(12):3339-3351

The Vietnamese agricultural sector has experienced a dramatic structural change based on increased specialization in rice cultivation. However, small-scale rice-farmers have continued to grow multiple crops, especially in less developed provinces. While the literature advocates crop diversification for reasons of both economic and ecological sustainability, there lacks empirical evidence as to whether crop diversification brings efficiency and productivity gains to small farms. The present study is the first applications of the input-oriented stochastic distance function approach in estimating scale and scope economies using data of multi-crop farming households in Vietnam. We find strong evidence of product-specific economies of scale. Scope economies are also present for rice, vegetable, and other annual crop production. This suggests that crop diversification enhances efficiency and productivity. However, there still exists significant technical inefficiency in crop production, indicating opportunities to expand farm output at the existing level of inputs and technologies. More specifically, our empirical results indicate that it is desirable to expand vegetable and other annual crop production in mountainous areas while rice cultivation can be further expanded in delta and coastal regions.  相似文献   

Effect of grazing pasture with a low selenium content on the concentrations of triiodothyronine and thyroxine in serum,and GSH-Px activity in erythrocytes in cows in Chile     

PA Contreras  F Wittwer  R Matamoros  IM Mayorga  tvan G Schaik 《New Zealand veterinary journal》2013,61(1):77-80

AIM: To determine the effect of grazing pasture that had a low selenium (Se) concentration on serum concentrations of tri iodothyronine (T₃) and thyroxine (T₄), and erythrocyte glutathione peroxidase (GSH-Px) activity in dairy cows.

METHODS: Forty pregnant Friesian cows were grazed on pasture that contained 0.03–0.04 ppm Se on a dry matter (DM) basis. Two months before parturition, 20 cows were randomly selected and treated with 1 mg Se/kg bodyweight subcutaneously, as barium selenate (Group Se-S). The other group (Se-D) was not supplemented. Blood samples were taken before supplementation (-60 days) and 30, 60, 90, 180 and 270 days after parturition, for determination of concentrations of T₃ and T₄ in serum, and GSH-Px activity in erythrocytes.

RESULTS: Erythrocyte GSH-Px activity in the Se-D group was >60 U/g haemoglobin (Hb) throughout the experiment. Supplementation increased (p>0.05) activities to >130 U/g Hb throughout lactation. Mean serum concentrations of T₄ in Se-D and Se-S cows increased from 23.7 (SEM 0.7) and 23.4 (SEM 0.8) nmol/L, respectively, in the prepartum period to 69.6 (SEM 0.1) and 67.6 (SEM 0.2) nmol/L, respectively, at 180 days of lactation (p>0.01), and no effect of Se supplementation was evident. Serum concentrations of T₃ in Se-D cows decreased (p>0.05) from 1.6 (SEM 0.1) nmol/L prepartum to 1.0 (SEM 0.2) nmol/L at the beginning of lactation, and remained lower (p>0.05) than those in the Se-S cows which did not decrease after calving and ranged from 1.9 (SEM 0.1) to 2.4 (SEM 0.2) nmol/L throughout lactation.

CONCLUSIONS: Serum T₃ concentrations decreased during early lactation in unsupplemented cows grazing pastures low in Se (0.03–0.04 ppm) and both serum T₃ and erythrocyte GSH-Px activities were consistently lower throughout lactation compared with Se-supplemented cows. Se supplementation had no effect on serum T₄ concentrations.  相似文献   

Duration of action of a topical anaesthetic formulation for pain management of mulesing in sheep     

S Lomax  M Sheil  PA Windsor 《Australian veterinary journal》2013,91(4):160-167

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建设农民的精神家园——浅议推进“农家书屋”的科学可持续发展     

潘觉敏 《农业图书情报学刊》2011,23(5):158-161,164

从＂农家书屋＂的现状分析,探究＂农家书屋＂建设中所存在的问题,并提出进一步推进＂农家书屋＂科学可持续发展,从而在农村文化建设中发挥更大作用的对策。  相似文献   

The Eucalyptus shoot and leaf pathogen Teratosphaeria destructans recorded in South Africa     

Izette Greyling  Michael J Wingfield  Martin PA Coetzee  Seonju Marincowitz 《Southern Forests》2016,78(2):123-129

Species of Teratosphaeria include some of the most important fungal pathogens of plantation-grown eucalypt trees. During routine disease surveys, symptoms and signs of leaf spot and blight were observed on the foliage of one-year-old E. grandis × E. urophylla hybrids in the Zululand region of KwaZulu-Natal, South Africa. These were distinct from those caused by the well-known and leaf-infecting fungus Teratosphaeria suttonii, which is not considered an important pathogen in the country. Culture and morphological characteristics as well as DNA sequences for three gene regions were used to compare the fungus isolated from the newly emerging symptoms with those for known Teratosphaeria species. DNA sequences were the same as those for T. destructans and this was consistent with the distinctive morphology of the asexual spores and the symptoms on leaves. Teratosphaeria destructans is an aggressive pathogen and actions will be needed to ensure that it does not impart serious losses to the local forestry industry.  相似文献   

应用倒传递类神经网络模拟预测山棕寮地滑地位移之研究     

黄文仁  许中立 《水土保持研究》2009,16(6)

地滑为陡坡地最具破坏之灾害形态之一,藉由实施地滑地监测与评估,可以协助政府拟订适当的管理对策.研究以台东县池上乡山棕寮地滑地为例,利用倒传递类神经网络(BPNN)具有建构高复杂且非线性关系方式预测坡面位移变化.研究所发展之倒传递类神经网络分析系应用MATLAB程序之Levenberg-Marquardt算法求解.网络输入系以直接关系位移之7个物理因子为变数,建构最佳之4层网络.根据监测资料共取12次台风暴雨事件,作为网络训练及模拟测试,并分别以6批次、8批次、10批次等3种情况网络训练对应模拟测试.研究结果显示所需监测台风暴雨事件至少8批次,即可达到13.1%预测位移误差.其误差精度可作为中危害度以上地滑地执行后续监测管理值与利用管理之参考.  相似文献   

小米紅葉病的研究Ⅱ.小米紅葉病的寄主范圍   总被引：1，自引：0，他引：1  

俞大绂  許順根  裴美云 《植物病理学报》1958,4(1):1-7

 上次的报告曾报道了在我国的主要小米产区所发生的小米紅叶病,是一种借蚜虫传播的病毒病害;玉米蚜(Rhopalosiphum maidis Fitch)、麦二岔蚜(Toxoptera graminum Rond)和麦长管蚜(Macrosiphum granarium Kirby)均能传病,其中特別以玉米蚜最为重要,因为这种蚜虫,在自然环境条件下,时常在大田內的小米上面普遍的发生,同时它的传病效能极高。  相似文献   

小米红叶病的研究Ⅰ.红叶病,小米的一个新的病毒病害     

俞大紱  裴美云  許順根 《植物病理学报》1957,3(1):1-18

 最近六年来,在我国的主要小米产区,包括山东、河北、河南和山西四省均报道有小米植株变红的现象,农民称它为红叶病或红丝病。  相似文献   

The effect of oxalacetic acid and pyruvic acid on hypoglycemia and ketonemia in pregnant ewes     

HO P  REBER EF 《The Cornell veterinarian》1957,47(1):131-136

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马铃薯晚疫病中心病株形成的观察   总被引：8，自引：0，他引：8  

林傳光  黄河  王道本  霍守祥 《植物病理学报》1957,3(1):19-29

 自从1953年以来,我们注意到马铃薯晚疫病的流行无例外地是以少数的中心病株的出现并逐步往周围传染而开始的^[1]。去年许多地区应用观察中心病株的方法作为预测预报的根据也都获得了成功^[3]。  相似文献