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英文文献：Evidence of Temporal Variation in Site-Specific Crop Response to Fertilizer Inputs-特定地点作物对肥料投入的响应时间变化的证据
英文文献作者：Oishi, Kikuo,Hurley, Terrance M.,Malzer, Gary L.
英文文献摘要：
Precision agriculture (PA) in crop production refers to the management approach in which inputs are applied according to the site-specific demand and timing in order to improve efficiency of inputs and farm profitability. Among the variety of techniques under the concept of PA, variable rate application (VRA) of both phosphorus and nitrogen fertilizers, and temporal as well as spatial variability of corn crop response to these fertilizers were studied for the potential contribution of VRA of fertilizers to farm profitability. The crop response data were generated by an on-farm experiment in Windom (Cottonwood County, Minnesota) in 1997, 1999, and 2001, using a commercially cultivated field of 10 ha area, where corn and soybean were rotated. Using a fractional factorial design, three phosphorus fertilizer rates (0.0, 56.2, and 112.3 kg ha-1) and five N-fertilizer rates (0.0, 67.4, 112.3, 157.3 and 202.2 kg ha-1) were applied to the field before corn planting. The observed yields were regressed on these treatment rates and site-specific crop response functions (SS-CRFs) were estimated using maximum likelihood estimation. The SS-CRFs were employed for the optimization problem and the site-specific economically optimal rates (SS-EORs) of phosphorus and nitrogen were obtained as the solution of the profit maximization problem. The temporal as well as spatial variations in these SS-EORs were observed; the estimated SS-EORs of phosphorus and nitrogen fertilizers varied among 33 sites from 0.0 to 112.3 kg ha-1 and from 0.0 to 202.2 kg ha-1, respectively in each year. Moreover, the results indicate that applying the SS-EORs could have been more profitable than uniform rate. The total gains from changing to the SS-EORs from the uniform rates (P = 56.2 kg ha-1 and N = 157.3 kg ha-1) would have been $63.58 ha-1, $64.34 ha-1, and $117.42 ha-1 in 1997, 1999, and 2001, respectively. This study indicates that VRA of fertilizers potentially improve the profitability of corn production. In order for this technology to become practical, some obstacles need to be removed, such as a less expensive method to obtain SS-EORs than on-farm experiences, less expensive machinery, more accurate functional form for SS-CRFs than quadratic functions. Once VRA technologies advance and become inexpensive, the "potential" gain from VRA can be fully realized.
作物生产中的精准农业(PA)是指根据特定的场地需求和时间投入以提高投入效率和农场盈利能力的管理方法。在PA概念下的各种技术中，研究了磷和氮肥料的可变施量(VRA)以及玉米作物对这些肥料响应的时间和空间变异性，以了解肥料的可变施量(VRA)对农场盈利能力的潜在贡献。作物响应数据是由1997年、1999年和2001年在Windom(美国明尼苏达州卡顿伍德县)进行的一项农场试验获得的，使用的是一块10公顷的商业耕地，玉米和大豆轮作种植。采用部分因子设计，玉米种植前田间施3种磷肥(0.0、56.2和112.3 kg ha-1)和5种氮肥(0.0、67.4、112.3、157.3和202.2 kg ha-1)。观察到的产量在这些处理率上进行回归，并使用最大似然估计估计位点特异性作物响应函数(SS-CRFs)。将SS-CRFs用于优化问题，得到了特定地点的磷和氮经济最优率(SS-EORs)作为利润最大化问题的解。观察了这些SS-EORs的时间和空间变化;33个地点每年磷肥和氮肥的估计标准差分别在0.0 ~ 112.3 kg ha-1和0.0 ~ 202.2 kg ha-1之间变化。此外，研究结果表明，采用SS-EORs可能比采用统一费率更有利可图。1997年、1999年和2001年，从统一费率(P = 56.2 kg ha-1和N = 157.3 kg ha-1)变化到SS-EORs的总收益分别为63.58美元ha-1、64.34美元ha-1和117.42美元ha-1。这项研究表明，肥料的VRA可能提高玉米生产的盈利能力。为了使这项技术成为现实，需要消除一些障碍，如获得SS-CRFs的方法比农场经验更便宜，机器更便宜，SS-CRFs的函数形式比二次函数更精确。一旦VRA技术进步并变得便宜，VRA的“潜在”收益就可以完全实现。
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