January 28, 2014

Lettuce Seedling Trials: Do fertilizers and probiotics affect lettuce germination and growth rates?

Mengli Shi

Mengli Shi

Research Assistant, Aquaponics

Johns Hopkins Center for a Livable Future

aquaponics-seedling-trial-2014All plants start out from seeds on the farm. We raise seedlings in coconut coir media and after 2-4 weeks we plant them in net pots in hydroponic beds. The healthy establishment of our seedlings is vital to the aquaponics system. High germination rates and vigorous seedlings growth rates help conserve valuable farm resources, like space, time, and money.  This fall, I studied methods to improve germination rates and seedling growth of lettuce by testing whether watering with natural fertilizers and probiotics affected seedlings differently than watering with a control of aquaponics system water.

To test this hypothesis we set up a study that we informally dubbed the “Seedling Trials.” We used three different nutrient solutions: Rock Phosphate Fertilizer (Dr. Earth, Winters, CA), EM-1 Microbial Inoculant (EMRO, city), and homemade compost tea as the treatments. The Rock Phosphate Fertilizer consists of small pellets, which contain phosphates, an essential nutrient that benefits plant growth. The EM-1 Microbial Inoculant is a solution that contains many beneficial microorganisms, which synthesize nutrients for the seed and seedling roots. Our compost tea was made from vermicompost, or worm poop, which was prepared with molasses and aerated for 24 hours. The compost tea solution contains many vital nutrients such as potassium, nitrate, sodium, calcium, magnesium, and chloride (Khan and Ishaq 2011), as well as beneficial microorganisms. Nutrient solutions were dissolved in a fixed amount of aquaponics system water to standard concentrations. The aquaponics system water served as a control. We seeded one lettuce seed (grand rapids variety) per cell of an 84-cell plant tray, and one tray per treatment. Trays were watered daily for three weeks with each type of nutrient solution Meanwhile, every day we watched for new seedlings and recorded each one’s date of germination.

By the end of the three weeks, there were clear differences among the four treatments. Figure 1 shows the frequency of germination for each treatment. The compost tea produced the greatest germinated rate (51%) and the system water had the lowest germination rate (23%). Rock phosphate and EM-1 treatments were only slightly more successful than the system water (germination rates of 32% and 29%, respectively). There were significant differences between germination rates for the compost tea treatment compared to Rock Phosphate (p = 0.01), EM-1 (p = 0.003), and system water (p = 0.0001). The overall germination rates were lower than expected, which could be due to the age of the seeds and the conditions in which they were stored. For example, old seeds generally have low germination rates.

Seedling Trails Fig 1

In addition to recording germination rates, 10 randomly selected seedlings from each tray were analyzed for weight (the weight of leaves, stem and roots). Figure 2 shows the average weight of seedlings in each treatment group. We found that there were no significant differences in average weight among all treatments (p = 0.2). Variation in weights can be explained, in part, by the difficulty of isolating the seedlings and root hairs from the planting media.

Seedling Trials Fig 2

Stay tuned for more results from this study.  Currently, another 10 randomly selected lettuce seedlings from each treatment are growing in the plant beds, slowly but steadily in the colder weather. We want to see if fertilizing seedlings early in their development will lead to larger lettuce heads at harvest. Keep posted for new updates in the future!

One Comment

  1. Posted by bandu silva

    Dear; pleas let me know the best organic hydroponic fertlizer for letuce. Do you recomend the fertlizere name “biowish” and also inorganic fertilizer name master blend N.P.K.4.18.38 + calcium nitrate and magnesium sulpate.(master blend 10 grams+epsum salt 5 grams+calcium nitrate 10 grams per 5 galon water) Thank you.bandu

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