英文文献：Barriers For Development In Zambian Small- And Medium-Size Farms: Evidence From Micro-Data-赞比亚中小型农场的发展障碍:来自微观数据的证据
英文文献作者：Kimhi, Ayal,Chiwele, Dennis K.
英文文献摘要：
The objective of this paper is to identify factors which limit the ability of Zambian farmers to increase Maize productivity and/or diversify their crop mix. Both may enable wealth accumulation, investments, and further expansion. Specifically, we link variations in agricultural decisions, practices, and outcomes, to variations in the tightness of the different constraints. We model crop production decisions as having recursive structure. Initially, farmers decide on land allocation among the different crops, based on their information set at planting time. Then, as new information (weather, market conditions) is revealed, farmers can change output by influencing the yield. This recursive structure enables to separate the effects of the constraints on the different stages of production. We therefore conduct estimation in two stages: we first estimate the fraction of land allocated to Maize as a dependent variable that is censored from below and from above, so that its predicted value is necessarily between zero and one. The yield of Maize is estimated in the second stage as a linear function of calculated land allotment (to avoid simultaneity bias) and the other state variables. Environmental and demographic variables also serve as explanatory variables in each stage. The first-stage results indicate that crop diversification can be promoted by rural road construction, developing markets for agricultural products, increasing the availability of seeds, draught animals, and farm machines, increasing women's farm work participation, and increasing the size of landholdings. Specialization in Maize can be promoted by increasing the availability of credit, fertilizers, hired permanent workers, and irrigation knowledge, and improving the timeliness of input delivery. The second-stage results show that the yield of Maize is inversely related to the area of Maize cultivated and to the operator's age, and is lower in female-headed farm households. Maize productivity can be improved by increasing the availability of seeds, fertilizers, labor, draught animals, machines, and credit.

本文的目的是找出限制赞比亚农民提高玉米产量和/或使作物组合多样化能力的因素。两者都可能促进财富积累、投资和进一步扩张。具体来说，我们将农业决策、实践和结果的变化与不同约束条件的紧密程度的变化联系起来。我们将作物生产决策建模为具有递归结构。首先，农民根据种植时的信息集决定不同作物之间的土地分配。然后，随着新的信息(天气、市场条件)的披露，农民可以通过影响产量来改变产量。这种递归结构能够分离生产不同阶段的约束的影响。因此我们分两个阶段进行估计:首先将分配给玉米的土地比例作为因变量进行上下截尾估计，使其预测值必然在0到1之间。在第二阶段，玉米产量被估计为计算的土地分配(以避免同时偏倚)和其他状态变量的线性函数。环境和人口统计变量也是每个阶段的解释变量。第一阶段的结果表明，可以通过建设农村公路、发展农产品市场、增加种子、役畜和农业机械的供应、增加妇女参与农业工作和增加土地持有规模来促进作物多样化。可以通过增加信贷、肥料、雇用固定工人和灌溉知识的可得性以及提高投入的及时性来促进玉米的专业化。第二阶段的结果表明，玉米产量与种植面积和经营者年龄呈负相关，在女性户主农户中产量较低。可以通过增加种子、化肥、劳动力、役畜、机器和信贷来提高玉米产量。