转Bt基因棉籽仁中脂肪酸的分析

采用气相色谱法测定了 1 0个品系转 Bt基因棉籽仁的脂肪酸组成及其相对百分含量。样品所含主要脂肪酸为棕榈酸、油酸、亚油酸。其中亚油酸的相对百分含量最高 ,为 5 9.2 8%～ 65 .2 8%。与美国转 Bt基因棉籽仁及普通棉籽仁进行了对比 ,结果表明 ,脂肪酸组成一致 ,相应组分含量相近。     

Impacts of Market Reform on Spatial Volatility of Maize Prices in Tanzania

Maize is one of the major staples and cash crops for many Tanzanians. Excessive volatility of maize prices destabilises farm income in maize‐growing regions and is likely to jeopardise nutrition and investment in many poor rural communities. This study investigates whether market reform policies in Tanzania have increased the volatility of maize prices, and identifies regional characteristics that can be attributed to the spatial price volatility. To achieve the objectives, an autoregressive conditional heteroskedasticity in mean (ARCH‐M) model is developed and estimated in this study. Results show that the reforms have increased farm‐gate prices and overall price volatility. Maize prices are lower in surplus and less developed regions than those in deficit and developed regions. Results also show that the developed and maize‐deficit regions, and regions bordering other countries have experienced less volatile prices than less developed, maize‐surplus and non‐bordering regions. Our findings indicate that investments in communication and transportation infrastructures from government and donor countries are likely to increase inter‐regional and international trade, thereby reducing the spatial price volatility in Tanzanian maize prices in the long run.     

The impact of conservation tillage on maize yield and input demand: the case of smallholder farmers in north‐west Ethiopia

This study analyses the economics of conservation tillage (CT) with respect to its effect on maize yield and chemical fertiliser, herbicide, and female and male labour demand. We estimate production and input demand functions using seemingly unrelated regressions on plot‐level cross‐sectional farm household data collected in the north‐west of Ethiopia. A two‐step control function is applied to address potential endogeneity bias due to the inclusion of the CT adoption decision as an explanatory variable. Our results show that CT increases maize yield and chemical fertiliser demand. Additionally, the results show that the adoption of CT reduces female and male labour required for crop production. However, this is achieved through the increased use of herbicides, which might have an undesirable health and environmental effects.     

Measuring Farm and Market Level Economic Impacts of Improved Maize Production Technologies in Ethiopia: Evidence from Panel Data

While it is often recognised that agricultural technology adoption decisions are intertwined and best characterised by multivariate models, typical approaches to examining adoption and impacts of agricultural technology have focused on single technology adoption choice and ignored interdependence among technologies. We examine farm‐ and market‐level impacts of multiple technology adoption choices using comprehensive household survey data collected in 2010/11 and 2012/13 in Ethiopia. Economic surplus analysis combined with panel data switching endogenous regression models are used to compute the supply shift parameter (K‐shift parameter), while at the same time controlling for the endogeneity inherent in agricultural technology adoption among farmers. We find that our improved technology set choices have significant impacts on farm‐level maize yield and maize production costs, where the greatest effect appears to be generated when various technologies are combined. The change in maize yield and production costs results in an average 26.4% cost reduction per kilogram of maize output (the K‐shift parameter). This increases the producer and consumer surpluses by US$ 140 and US$ 105 million per annum, respectively. These changes in economic surplus help to reduce the number of poor people by an estimated 788 thousand per year. We conclude that deliberate extension efforts and other policies that encourage integration of technologies are important for maize technologies to yield their full potential at both farm and market levels.     

Ecosystem impacts of pesticide reductions through Bt cotton adoption

This article examines the ecosystem impacts of transgenic Bt cotton technology resulting from reduced chemical pesticide use. Employing unique panel data from smallholder farmers in India, negative environmental and health effects of pesticide use are quantified with the environmental impact quotient (EIQ), with and without Bt technology. An environmentally sensitive dynamic production function is estimated, treating the environmental risk of pesticide toxicity as an undesirable output in the production process. Negative externalities are significantly lower in Bt than in conventional cotton. The reduction in EIQ through Bt technology adoption has increased from 39 per cent during 2002–2004 to 68 per cent during 2006–2008. Bt adoption has also contributed to higher environmental efficiency. Environmental efficiency is influenced by the quality of Bt technology: high‐quality Bt seeds are associated with higher environmental efficiency than lower‐quality seeds.     

Estimating the Enduring Effects of Fertiliser Subsidies on Commercial Fertiliser Demand and Maize Production: Panel Data Evidence from Malawi

Most studies of input subsidy programmes confine their analyses to measuring programme effects over a one‐year period. This article estimates the potential longer‐run or enduring effects of fertiliser subsidy programmes on smallholder farm households' demand for commercial fertiliser and maize production over time. We use four waves of panel data on 462 farm households in Malawi for whom fertiliser use can be tracked for eight consecutive seasons between 2003/2004 and 2010/2011. Panel estimation methods are used to control for potential endogeneity of subsidised fertiliser acquisition. Results indicate that farmers acquiring subsidised fertiliser in three consecutive prior years are found to purchase slightly more commercial fertiliser in the next year. This suggests a small amount of crowding in of commercial fertiliser from the receipt of subsidised fertiliser in prior years. In addition, acquiring subsidised fertiliser in a given year has a modest positive impact on increasing maize output in that same year. However, acquiring subsidised fertiliser in multiple prior years generates no statistically significant effect on maize output in the current year. These findings indicate that potential enduring effects of the Malawi fertiliser subsidy programme on maize production are limited. Additional interventions that increase soil fertility can make using inorganic fertiliser more profitable and sustainable for smallholders in sub‐Saharan Africa and thereby increase the cost‐effectiveness of input subsidy programmes.     

A Question of Integrity: Variants of Bt Cotton,Pesticides and Productivity in Pakistan

Bt cotton remains one of the most widely grown biotech crops among smallholder farmers in lower income countries, and numerous studies attest to its advantages. However, the effectiveness of Bt toxin, which depends on many technical constraints, is heterogeneous. In Pakistan, the diffusion of Bt cotton occurred despite a weak regulatory system and without seed quality control; whether or not many varieties sold as Bt are in fact Bt is also questionable. We utilise nationally representative sample data to test the effects of Bt cotton use on productivity. Unlike previous studies, we invoke several indicators of Bt identity: variety name, official approval status, farmer belief, laboratory tests of Bt presence in plant tissue, and biophysical assays measuring Bt effectiveness. Only farmer belief affects cotton productivity in the standard production model, which does not treat Bt appropriately as damage‐abating. In the damage control framework, all Bt indicators reduce damage from pests. Biophysical indicators have the largest effect and official approval has the weakest. Findings have implications for impact measurement. For policy‐makers, they suggest the need, on ethical and productivity grounds, to improve variety information and monitor variety integrity closer to point of sale.     

The Costs of Coexistence Measures for Genetically Modified Maize in Germany

We estimate the perceived costs of legal requirements (‘coexistence measures’) for growing genetically modified (GM) Bt maize in Germany using a choice experiment. The costs of the evaluated ex‐ante and ex‐post coexistence measures range from zero to more than €300 per measure and most are greater than the extra revenue the farmers in our survey expect from growing Bt maize or than estimates in the literature. The cost estimates for temporal separation, the highest in our evaluation, imply that the exclusion of this measure in Germany is justified. The costliest measures of the ones that are currently applied in Germany are joint and strict liability for all damages. Our results further show that neighbours do not cause a problem and opportunities for reducing costs through agreements with them exist. Finally, we find that farmers’ attitudes towards GM crops affect the probability of adoption of Bt maize. Our results imply that strict liability will deter the cultivation of Bt maize in Germany unless liability issues can be addressed through other means, for example, through neighbours agreements.     

河北省夏玉米需水量变化特征及未来可能趋势

基于1963—2015年近50年间河北省夏玉米主产区8个气象站点气象资料,采用联合国粮食与农业组织(FAO)推荐的Penman-Monteith模型和作物系数法计算夏玉米需水量,再结合《IPCC排放情景特别报告》中的两种排放情景RCP2.6(低排放情景)和RCP8.5(持续排放情景)预估的未来气候情景,探讨气候变化下未来河北省夏玉米需水量的时空演变规律。结果表明:1963—2015年河北省夏玉米需水量呈现下降趋势,在空间上大致以黄骅为高值中心,由东北向西南逐渐递减,并在邢台形成低值中心的分布特征;从未来气候变化情景来看,相对于基准时段(2015年),RCP2.6和RCP8.5情景下,在2020年、2030年、2050年、2070年未来4个典型年份夏玉米的需水量均表现出增加的特征。