The production impact of agricultural residues are generally not accounted for in LCAs when they are given a second life as feedstocks for bio-fuels/plastics/fertilizers. Such is the case for the organic fertilizers manure and blood meal (stemming from livestock) used in organic cultivation. This raises questions on how realistic comparisons are between conventional cultivation systems and organic systems: the flows of resources and associated impacts are not represented equivalently in both systems. The aim of this study is to conduct sensitivity analyses for different possible allocation procedures and to select the most preferable one.

The cultivation of organic apples in Flanders is used as case study. Considering no production impacts for organic fertilizers was firstly assessed as it is the generally used approach in LCA. In system expansion, the production impacts of two products: a mineral fertilizer and an organic plant-based fertilizer, are allocated to apple cultivation as a substitute for the organic fertilizers. For mass and economic allocation, the production impact is considered as a fraction of the impacts of the livestock system based on mass flows and economic value, respectively. Several possible allocation factors were assessed and price variations were considered.

The different allocation procedures lead to diverging results, underlining the importance of selecting an appropriate procedure. Accounting no production impact is not advised since organic growers do not carry any environmental burden for a product they need for fertilization. System expansion causes too much uncertainties, needing to make speculative scenarios for factors lying outside the studied system. Economic allocation causes the impact of a product to change with its price while production stays the same. Therefore, mass allocation is preferable – though more harmonization research is needed - since no parameters from outside the system are needed, leading to a stable and close approximation of reality.

For this case study, the amount of N available in fertilizers as a fraction of live weight and the mass of N in manure, is chosen as the least worse option. Our general recommendation is that the allocation factor needs to be chosen such that it is a representation of the function of the organic fertilizers and is comparable between different fertilizers.

当农业废弃物作为生物燃料/塑料/肥料的原料获得第二次生命时，通常不会在 LCA 中考虑其对生产的影响。有机栽培中使用的有机肥料粪肥和血粉（来自牲畜）就是这种情况。这就提出了一个问题，即传统栽培系统和有机系统之间的比较现实性如何：资源流动和相关影响在两个系统中的表现并不相同。本研究的目的是对不同的可能分配程序进行敏感性分析，并选择最优选的分配程序。

以法兰德斯的有机苹果种植为例进行研究。考虑到有机肥对生产没有影响，首先评估了它是 LCA 中常用的方法。在系统扩展中，将矿物肥料和有机植物肥料这两种产品的生产影响分配给苹果种植，作为有机肥料的替代品。对于质量和经济分配，生产影响被认为是畜牧系统影响的一部分，分别基于质量流量和经济价值。评估了几个可能的分配因素并考虑了价格变化。

不同的分配程序导致不同的结果，强调了选择适当程序的重要性。不建议考虑不影响生产，因为有机种植者不会为他们需要施肥的产品带来任何环境负担。系统扩展会导致太多的不确定性，需要对研究系统之外的因素进行推测场景。经济分配导致产品的影响随价格而变化，而产量保持不变。因此，质量分配是可取的——尽管需要更多的协调研究——因为不需要来自系统外部的参数，从而导致稳定和接近现实。

在本案例研究中，肥料中可用的氮含量占活重的比例和粪肥中的氮质量，被选为最不差的选择。我们的一般建议是，需要选择分配因子，使其能够代表有机肥料的功能，并且在不同肥料之间具有可比性。