Changes in the technology of harvesting timber in the United States: Some implications for labour

The parameters of the production technology for the United States timber harvesting industry were estimated from models based upon the production function and a flexible dual cost function. The results were remarkably similar, and suggested that the constant elasticity of substitution (CES) production function was consistent with the data for the period 1951–1974. The elasticity of factor substitution was estimated to be less than unity. Technological progress, primarily in the form of labour-saving mechanical harvesting equipment, has been responsible for the decline in labour's relative share of income. In this respect, forestry is structurally similar to agriculture. From the standpoint of public policy, continued technical advancement in the form of mechanical harvesting equipment will displace additional workers and, for developing countries, could have undesirable consequences for trade balances and the functional distribution of income. Recent efforts to increase labour productivity using intermediate technologies could do much to mitigate the displacement of labour that accompanies the adoption of highly capital-intensive technologies.     

区域灌溉需水量时空变化特征及其影响因素研究——以鲁西北地区为例

【目的】探寻鲁西北地区灌溉需水量时空分布特征及影响因素。【方法】选取冬小麦为研究对象,利用Penman-Monteith公式对鲁西北地区灌溉需水量进行计算,应用Mann-Kendall突变检验法分析其变化趋势,得出鲁西北地区灌溉需水量的时间分布规律,使用反距离权重插值法得出灌溉需水量空间分布规律,并利用Pearson相关分析法对各气象因素对灌溉需水量的影响程度进行分析比较。【结果】(1)鲁西北地区的年平均灌溉需水量为339 mm,年际变化呈上升趋势;(2)灌溉需水量空间变化呈带环状分布,各生育期内规律不相同;(3)相对湿度和日照时数是影响鲁西北地区灌溉需水量较为重要的因素,分别呈极强负相关与较强正相关。【结论】鲁西北地区冬小麦灌溉需水量逐年缓慢上升,由东北到西南递增;各站点降水量在播种期、返青期和拔节期内均不满足需水要求,需要人工灌溉补给。     

Prospects for grass-clover swards in beef production systems: A computer simulation of the practical and economic implications

A mathematical model of herbage production and utilization on grass and grass-clover swards in the context of an 18-month beef system is described. Using the model the potential costs and benefits of replacing grass by grass-clover mixtures are examined. It is projected that gross margins per hectare will be higher on grass-clover swards receiving little or no fertilizer N than on grass swards receiving 300kg N ha⁻¹. The higher average profits from grass-clover systems must be set against a higher year-to-year variation in the financial returns. To some extent the financial risk associated with the more variable annual profits may be reduced by only allocating a proportion of the forage area to grass-clover and continuing to devote the rest of the area to fertilized grass swards.These conclusions, which are at variance with other studies, are influenced by three key assumptions within the model. First, dry-matter intakes by beef cattle are presumed to be about 10% higher on grass-clover than on grass swards. Secondly, the metabolizable energy value of clover is assumed to be 5% higher than grass. Thirdly, the model projects that the available forage is utilized more efficiently on grass-clover swards, due to the more uniform seasonal pattern of herbage production. If some or all of these assumptions are rejected, the economic advantage moves in favour of grass-based production systems. Since confirmation of these assumptions awaits experimental work, the findings of the model can be seen as little more than informed speculation.