Nonlinear Dynamics and Structural Change in the U.S. Hog–Corn Cycle: A Time-Varying STAR Approach

The linearity of the U.S. hog–corn cycle has been questioned by Chavas and Holt (1991) . Even so, attempts have not been made to model the potential nonlinear dynamics in the hog–corn cycle by using regime-switching models. One popular alternative is Teräsvirta's smooth transition autoregressive (STAR) model, which assumes regime switching is endogenous and potentially smooth. In this article, we examine monthly data for the U.S. hog–corn cycle, 1910–2004. A member of the STAR family, the time-varying STAR, is fitted to the data and its properties examined. We find evidence of nonlinearity, regime-dependent behavior, and time-varying parameter change.     

The Term Structure of Implied Forward Volatility: Recovery and Informational Content in the Corn Options Market

Using a flexible method, we develop the term structure of volatility implied by corn futures options with differing maturities, and evaluate its ability to predict subsequent realized price volatility. The implied forward volatilities anticipate realized volatility well. For the nearby interval, the implied forward volatilities provide unbiased forecasts, and are superior to forecasts based on historical volatilities. For more distant intervals, early-year options predict the direction and magnitude of future volatility changes about as well as a three-year moving average and better than a naïve forecast. However, later-year options display less forecast power in part due to reduced trading activity.     

清代中晚期山地种植玉米引发的水土流失及其遏止措施

清代中晚期，我国渭河至黄河下游一线以南、青藏高原以东范围内，人们广泛开垦山地，种植玉米，许多地方出现了“遍山漫谷皆包谷”的景象。大面积的山地开垦和玉米种植，破坏了原有的自然植被，引发严重的水土流失。在不同地区，官方和民间对开山种玉米的利弊有不同认识。在四川、湖北、湖南等省，政府对开辟荒山种植玉米的行为基本上是听之任之；但在浙江、皖南和陕南等地，政府和民间曾采取多种积极措施，遏止山地种植玉米引发的水土流失，并取得了一定成效。     

Is Site-Specific Yield Response Consistent over Time? Does It Pay?

This study examines the profitability and stability of site-specific (SS) nitrogen fertilizer recommendations using an empirical model of SS yield response to controlled inputs, stable site characteristics, and time-varying weather factors. Using a three-year panel of on-farm corn yield experiments and new, continuous variables to describe site characteristics, both spatial and ordinary least squares regression models show clear evidence of SS corn yield response to nitrogen fertilizer. Yield response is predictable only on irrigated fields. Even there, bootstrapped confidence intervals for profitability gains on selected fields indicate that SS nitrogen application would rarely cover its costs.     

Evaluation of USDA Interval Forecasts of Corn and Soybean Prices

USDA World Agricultural Supply and Demand Estimates (WASDE) price forecasts are published as an interval, but are typically analyzed as point estimates. Thus, all information about uncertainty imbedded in the forecast is ignored. The purpose of this article is to evaluate the accuracy of WASDE corn and soybean price forecasts using methodology suitable for testing judgmental interval forecasts. Accuracy tests suggest that WASDE forecasts are not calibrated at the 95% confidence level for both commodities and generally not calibrated for corn, but calibrated for soybeans, at the implied confidence level elicited from the survey of forecast providers.     

玉米保护地栽培技术

阐述了玉米保护地立体栽培技术,该项技术是当前农业生产投资少、见效快、受益大的新举措,有可行性、重演性、可操作性,符合推广法要求,前景广阔。本文介绍了玉米保护地立体栽培的由来、技术模式、产量效益等。     

Examining crop price effects on production decision and resource allocation: an ex-ante approach

This article examines the output price effects on the US crop production, employing an ex-ante approach to the differential systems of input demand and output supply. The estimation results of the differential input demand show that the expansion of crop production leads to an increase in acreage (i.e. extensive margin) and a proportional rise in input usage improving yield per acre (i.e. intensive margin). The substitutable relationship between fertilizer and land supports that crop producers have an option to choose either intensive or extensive margin in response to changes in their relative prices. In addition, the estimation results of the differential output supply highlight that the composition of crop supply can be altered by changes in ex-ante crop prices. The estimation results suggest that crop producers substitute corn supply for the supply of cotton, wheat and soybeans or vice versa. Based on the estimated elasticities, the decompositions of profit-maximizing input demand are conducted, which reveals that a change in ex-ante crop prices is associated closely with resource reallocation.     

复合交联淀粉制备工艺研究进展

综述了氧化交联淀粉、醚化交联淀粉、酯化交联淀粉等复合交联淀粉制备工艺的研究进展,重点讨论了各种复合交联淀粉的研究热点,并展望了其今后的发展前景。     

用磷酸法制备玉米秸杆活性炭的研究

介绍了以玉米秸杆为原料，用磷酸法生产活性炭的方法。用正交试验法考察了影响玉米秸杆制活性炭之亚甲蓝脱色力的因素，提出了制备玉米秸杆活性发适宜的工艺条件。制得的玉米秸杆活性炭之亚甲蓝脱色力最高可达16ml／0．1g。     

Managing the Risk of European Corn Borer Resistance to Bt Corn

New pesticidal crops are taking advantage of advances in geneticengineering. For example, corn has been engineered to express Bt proteinsthat are toxic to the European corn borer. These crops are effective pestmanagement tools for United States growers. However, there is concern thatpests will develop resistance to these crops resulting in the increased useof more hazardous pesticides. The purpose of this paper is to develop astochastic dynamic bioeconomic simulation model to help guide regulatorypolicy designed to mitigate the threat of resistance to new pesticidal crops.The model is used to evaluate the insect resistance management guidelinesmandated by the United States Environmental Protection Agency for theuse of Bt corn in the Midwestern United States.