Support The advent of chemical fertilizers led the farmers in a certain region to abandon the practice of periodically growing a "green-manure" crop, such as alfalfa, in a field to rejuvenate its soil. Support As a result, the soil structure in a typical farm field in the region is poor. So Conclusion to significantly improve the soil structure, farmers will need to abandon the use of chemical fertilizers.
The author concludes that to significantly improve soil structure, farmers will need to stop using chemical fertilizers.
Why does the author think this?
Because the introduction of chemical fertilizers led farmers in the region to stop the practice of periodically growing a “green-manure” crop for rejuvenating the field. The stopping of this practice led to damage to the soil structure.
We know that the introduction of chemical fertilizers caused, in this one case, farmers to stop growing “green-manure” crops. And this damaged soil structure. But does this prove that in order to improve the soil structure, we need to abandon the use of chemical fertilizers? No — why couldn’t we just get the farmers to start growing “green-manure” crops again? The premises never established that we can’t use both the chemical fertilizers and grow “green-manure” crops.
The author is assuming that we can’t use both — that in order to get farmers to grow “green-manure” crops again, we have to stop using chemical fertilizers.
The argument relies on the assumption that
most, if not all, farmers in the region who abandon the use of chemical fertilizers will periodically grow alfalfa
Not necessary, because alfalfa is just one example of a “green-manure” crop. But other “green-manure crops” could be grown instead. Also, the author doesn’t need to assume that “most” farmers will grow crops. As long as enough farmers grow the crops to improve soil structure, the reasoning still works.
applying chemical fertilizers to green-manure crops, such as alfalfa, has no positive effect on their growth
Not necessary, because even if chemical fertilizers have a positive effect on “green-manure” crop growth, it could still be necessary to abandon their use in order to get farmers to grow “green-manure” crops again.
the most important factor influencing the soil quality of a farm field is soil structure
The argument concerns what’s required to improve soil structure. Whether soil structure influences other things, such as soil quality, is not relevant to the argument. And even if it were, there’s no reason the author must assume that soil structure is the “most” important factor in soil quality.
chemical fertilizers themselves have a destructive effect on the soil structure of farm fields
Not necessary, because the effect of chemical fertilizers was to cause farmers to abandon “green-manure” crops. Even if the chemical fertilizers do not directly destroy the soil structure, they still had the effect of causing abandonment of the practice that rejuvenated soil structure.
many, if not all, farmers in the region will not grow green-manure crops unless they abandon the use of chemical fertilizers
Necessary, because if it were not true — if many farmers in the region WILL grow “green-manure” crops even if they keep using chemical fertilizers — then there’s no reason farmers would need to stop using chemical fertilizers to improve the soil structure. They could keep using the fertilizers and start growing the crops again.
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