For each of these factors and aspects, numerical correction factors
are provided for adapting the actual fertilization practice (Flisch et al.,
2009). Many of these aspects need to be considered at a time horizon
broader than just one vegetation period. This reveals that the nutrient
availability and uptake of individual crops are not only determined by
fertilization activities starting with seedbed preparation. Instead, activities
taking place months and even years before growing the considered
crop significantly affect its quantity and quality (Flisch et al., 2009). Because
this situation applies for all crops, one could state that the same
error is acceptable for all of them — but one must acknowledge that
each crop has different nutrition requirement profiles; thus, different
situations may have different effects on different crops.
Besides removal of crop residues from the field and thus their associated
nutrients, many further aspects contribute to crop-rotation effects.
For example, changing the crop cultivated in a certain field helps to improve
phytosanitary conditions. Also, the use of nutrients, water from
different soil horizons and improvements in soil structure increases
soil fertility and yields. Most of these examples of positive effects are
plant-specific and have been supported by long-term field experiments.
Even though the previously described approaches are suitable for
integrating the shift of nutrients from one crop to a subsequent crop
in LCA, they do not seem to be widely used in agricultural LCA practice,
and they fail to integrate the entire range of positive crop-rotation
effects such as:
• Facilitated timing of farming activities,
• Improved phytosanitary conditions and reduced amounts of agrochemicals
needed,
• Reduction of the probability of harvest failures and improved conditions
for soil organisms,
• Improved soil texture, soil structure, root penetration and water
availability,
• Improved soil fertility and increased yields.