Superior Fertilizer

Superior Fertilizer is the most efficient fertilizer for Trays. Aside from giving the highest output, it is the only fertilizer that consumes 2 seeds less than normal.

It doesn't provide the minimal time between harvests (it only increases growth rate by x2, while Pesticide increases it by x3), but the overall yield (results of harvest) compensates for that.

Trivia

 * Superior Fertilizer is the only fertilizer that allows to grow Violiroot without constantly losing seeds. This plant returns (on average) 1.5 seeds from 3 harvested plants, which means that you can't afford to spend 2 seeds (which other fertilizers would require) to grow these 3 plants. You can only afford to spend 1 seed, and Superior Fertilizer allows that.
 * Superior Fertilizer can be automatically produced using Precursor Duplicator.
 * It takes 6 different resources to craft Superior Fertilizer (counting the components of Methyl Iodide), which makes its production notoriously difficult to automate. Overcoming this is a popular challenge amongst those players who enjoy complex automation (see screenshot for an example).