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1.
稻鳅共生种养模式试验研究   总被引:2,自引:0,他引:2  
[目的]稻鳅共生是典型的稻田综合利用模式,符合生态农业发展方向。通过对稻鳅共生生态系统的生理生态学机制开展试验研究,为进一步推广稻鳅共生种养模式提供科学依据。[方法]采用田间试验方法,以水稻单作为对照,研究了不同泥鳅养殖密度下的稻鳅共生对水稻农艺性状、土壤理化性质、水稻产量构成的影响,并对稻鳅共生种养模式进行了经济效益分析。[结果]与对照处理相比,水稻长势在株高、有效分蘖率、根长等方面有一定提高。养殖田水稻株高增高了3%,有效分蘖率提高了8%~11%,根长提高了8.8%~31.3%。在土壤理化性质方面,与对照相比,土壤容重降低了7.1%~21.2%,孔隙度增加了4.1%~14.7%。实验前后养殖田内土壤有机质增加了3.5%~26.5%,对照田降低了2.5%~5.8%。土壤肥力(氮、磷、钾)减少,但减少幅度小于对照处理。稻鳅共生种养模式下水稻产量提高了5%~25%,同时稻田增收泥鳅1 725~3 375kg/hm2,净收入为1.836 0万~2.307 0万元/hm2,经济效益提高了3.65~4.84倍。稻鳅共生种养模式中泥鳅的养殖密度为30万尾/hm2时稻田的生态效益和经济效益最佳。[结论]稻鳅共生有效改善了土壤理化性质,促进了水稻的生长,提高了稻田产量和产值。  相似文献   
2.
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.  相似文献   
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Following the approach of interpolation, this paper proposes the multiple exponential decay model to fit yield curves for both the U.S. TIPS market and the conventional Treasury security market. Several estimation methods, including the unconstrained/constrained nonlinear minimization, quadratic programming, and the iterative linear least squares, are applied to estimate the unknown parameters according to different curve‐fitting purposes. Comparisons between the proposed model and the alternatives show that the multiple exponential decay successfully (1) adapts to a variety of shapes associated with yield curves, (2) (partially) keeps in line with the economic interpretations of Nelson–Siegel summarized by Diebold and Li ( 2006 ), and (3) dominates the competing models in curve‐fitting performance measured by mean fitted‐price errors over the sample period. In addition, the exact specification of a nonparametric interpolation model is pinned down by applying three statistical tools, which enable us to jointly take into account validity, optimality, and parsimoniousness of the proposed model.  相似文献   
5.
This paper examines the return and volatility spillovers between the foreign exchange and bond markets of India using a bivariate asymmetric BEKK-GARCH (1,1) model for the period 4 April 2005 to 31 March 2017. We find the evidence of bidirectional return and volatility spillovers with asymmetric effects between these two markets. The spillovers are evidenced even during the periods when foreign portfolio investments in the Indian bond markets were relatively low suggests the existence of strong inter-linkages between both the markets.  相似文献   
6.
Nonhub airports are an essential component in the National Plan of Integrated Airport Systems (NPIAS) of the United States in that they connect regional towns and small communities to the air transportation network. Understanding the interplay of operational and spatial factors in determining average passenger yield of nonhub airports provides airlines with valuable information for network planning and revenue management. This study examines factors contributing to the yield variation among nonhub airports in the U.S. Using ordinary least squares (OLS) based econometric models, this study captures the spatial dependence of passenger yield of nonhub airports, which tends to increase with a corresponding increase in distance to the nearest large hub airport. Nonhub airports surrounding large hub airports with higher passenger enplanements and higher average yields also have higher yields than other nonhub airports. In addition, this study finds the effect of Allegiant Airlines in lowering the average passenger yield of the nonhub airports served directly by the airline, which can be termed as ‘Allegiant Effect’. Findings of this study could provide valuable guidance for airlines to analyze network planning strategies and to identify future markets for growth and for policymakers when allocating resources to communities relying on these nonhub airports.  相似文献   
7.
The trend in crop yields and yield variability affects food security and impact agricultural and food policies. Recent studies in this area have either focused only on one country or performed global analysis on a handful of crops. We provide the first worldwide analysis of trend and variability for 8088 country-crop yield series taken from the FAO database, employing a robust estimator to cope with the adverse statistical effects of outliers. More than half of the series display a slowdown in yield growth due to a closing of the gap between realised and attainable yields as well as to agricultural policies promoting more sustainable agricultural practices. Around one fourth of the series show also an increase in yield variability as a consequence of climate change and changes in farm management practices. Yield variability is highest in Eastern Europe, Central Asia and Middle East and North Africa, where food security may be threatened.  相似文献   
8.
The potential presence of jumps and time-varying volatility in convenience yields can lead to abnormally fat tails, which has implications for investment in storage capacity, leasing and drilling for crude oil. In this paper we evaluate the potential for these features in convenience yields. To that end, we analyze the rate of change in convenience yields for five futures prices time horizons (1, 3-, 6-, 9- and 12-month ahead), allowing for the both jumps and time-varying volatility. We find that both features exert a statistically important effect on convenience yields, for each of the five time horizons. We also calculate the implied probability that at least one jump would occur on any date, which reveals a period of relative calm at the start of the fracking boom, when large stockpiles built up at the trading hub for West Texas Intermediate, and a period of considerable churn, after the ban on exporting crude oil was lifted. Both elements underscore a linkage between inventory holdings and convenience yields.  相似文献   
9.
This paper examines the effect of monetary policy on the market value of the liquidity services that financial assets provide, known as the liquidity premium. The theory predicts that money supply and nominal interest rates have positive effects on the liquidity premium, but asset supply has a negative effect. The empirical analysis with U.S. data confirms the theoretical predictions. The theory also proposes that the liquidity properties of assets can cause negative nominal yields when the money holding cost is low and liquid assets are scarce. The suggestive empirical findings in Switzerland to support this theoretical result are presented.  相似文献   
10.
In a 1991–2013 sample of bonds issued by US public firms, we find that the cost of debt (yield spread relative to comparable Treasuries) of suppliers to government agencies is contingent on the strategic importance of the supplier's industry. The yield spreads for strategically unimportant government suppliers are higher than for firms that are not government suppliers. If government contracts serve as tangible evidence of political connections, these higher yield spreads indicate that weaker corporate governance as a cost of political connections outweighs the benefits of said connections. For the subsample of government suppliers from strategically important industries, where the benefits of implicit bailout guarantees and revenue stability outweigh the corporate governance problems, the cost of debt is lower than for firms that are not government suppliers. The higher (lower) cost of debt for strategically unimportant (strategically important) suppliers is confined to contracting with the federal government. Our findings are robust to alternative variable and sample specifications, and to endogeneity concerns.  相似文献   
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