Modelling stochastic crop response to fertilisation when carry-over matters
研究尼日尔农业区农民在不确定条件下如何经济管理土壤肥力，基于农学原理建立动态模型，发现维持土壤磷含量在14 ppm以上需要每年施用12 kg P2O5/ha的过磷酸钙，而氮肥收益低且不稳定。
Soils in a large part of Niger's agricultural area are sandy and very low in nitrogen (N), phosphorus (P) and organic matter. This low soil fertility combined with low and erratic rainfall constitutes a severe constraint on food cropping in the area. Although agronomists have advised chemical fertilization as a means of improving soil fertility, little fertilizer has been used in this area of the world. The economic management of soil fertility in the agricultural area of Niger is analyzed using a dynamic model of farmer decision-making under uncertainty. The model is based on agronomic principles of plant growth and accounts for the carry over of P, an immobile nutrient. At current input prices, a soil P content of at least 14 ppm is found to be desirable. This target is above the natural soil fertility level of about 3 ppm. It can be maintained with a moderate annual application (12 kg P20 5 ha- 1) of simple superphosphate. Results also suggests that returns to N fertilization are too low and variable to warrant the use of this input.