What happens if nitrogen from slow release fertilizers is not converted by soil microbes?

The correct choice highlights that if nitrogen from slow-release fertilizers is not converted by soil microbes, plants cannot effectively utilize it. Nitrogen in its natural, inorganic form is often unavailable to plants without microbial action to convert it. Slow-release fertilizers contain nitrogen that must be broken down by soil microbes into forms that plants can utilize, such as ammonium or nitrate. If this conversion process does not occur, the nitrogen remains in a form that plants cannot absorb.

The other outcomes mentioned are not as directly relevant to the primary function of soil microbes in nutrient cycling. For instance, nitrogen doesn't persist indefinitely in an unusable form; plants are unable to access it, which ultimately hampers their growth. While nitrogen can contribute to soil pollution when it leaches into water systems, this is more about excess nitrogen rather than its inherent inability to assist plants. Quick plant growth, on the other hand, is contingent upon the plant's access to usable nitrogen, which is why microbial conversion is crucial.