Sequential Adoption of Site-Specific Technologies and Its Implications for Nitrogen Productivity: A Double Selectivity Model

This paper analyzes the sequential decision to adopt two site-specific technologies, soil testing and variable rate technology, and the impact of adoption on nitrogen productivity. The results indicate that while farm location was a key variable influencing adoption of soil testing, farm size, human capital, and innovativeness of farmers had a significant impact on adoption of variable rate technology in four Midwestern states. A double selectivity model applied to correct for sample selection bias shows that adoption leads to significant gains in nitrogen productivity for farms with below average soil quality but statistically insignificant gains for farms with above average soil quality.  

Stochastic Technology, Risk Preferences, and Adoption of Site-Specific Technologies

A model of farmer decision making is developed to determine the extent to which uncertainties about soil fertility and weather affect the value of site-specific technologies (SSTs) using jointly estimated risk and technology parameters. Uncertainty can lead risk-averse farmers to apply more fertilizers and generate more pollution than in the certainty case. Ignoring uncertainty and risk aversion would overestimate the economic and environmental benefits of SSTs and underestimate the subsidy required to induce adoption. Accounting for uncertainties and risk preferences might explain the low observed adoption rates of SSTs. Improving the accuracy of SSTs would increase the incentives for adoption.  

Temporal and spatial variability of agricultural land loss in relation to policy and accessibility in a low hilly region of southeast China

The temporal and spatial patterns in land use change in a low hilly region in southeast of China was analyzed from maps of converted agricultural land for 1999–2006. The factors driving farm land conversion was analyzed using logistic regression models. The amount of agricultural land loss varied temporally, and the spatial distribution of converted agricultural land patches decreased from low to high altitudes in the study area. Analysis using logistic regression models showed that good accessibility sped up the conversion of agricultural land to other uses, the elevation of a parcel lowered the risk of conversion, and agricultural land conversions are highly correlated with its adjacent or neighboring parcels’ land use, with the probability of being converted decreasing as the distance to nearest construction land increases. In addition, land use policy, especially the land use regulation policy issued by the central government decreased the agricultural land loss, and the more stringent regulation on cultivated land conversion lowered the possibility of conversion from cultivated land to other use.  

城市扩张与集约农业背景下浅层地下水重金属污染特征空间分析

地下水是城乡结合部和农村地区的重要饮用水源之一，城市的扩张和农业集约经营对地下水的影响日益明显。本文以典型区—沈阳沈北新区为例，以地下水重金属为评价指标，采用经典统计和地统计的方法，分析城乡交错地区地下水污染程度和空间分异性特征，旨在为类似地区土地利用规划和地下水环境管理提供科学依据。结果显示：Fe、Mn超标率较高，分布范围较广；Cd、Hg分布集中，受城镇化的影响较为明显；Pb与集中养殖产业分布关系密切；As 的分布与当地化工企业有关；Fe、Mn空间变异性强，空间异质性主要受自然条件等结构性因素控制； Cd、Pb、Hg空间变异性中等，As空间变异性弱，Cd、 Pb、Hg、As这四种元素空间异质性的形成主要受人为活动等随机因素的影响；初步发现Fe和Mn，Mn和As有相似的来源。