Evaluation of Alfalfa-Based Organic Amendment in Peat-Compost Growing Medium for Organic Transplant Production

To optimize production system, most vegetable crops are established from greenhouse-grown transplants that are fertilized with amendments or water soluble fertilizer, which would provide N, P, K, and other nutrients to the developing seedlings. Under organic transplant production, nutrient management is a challenge due to unavailability of quality organic fertilizers and amendments. Our research evaluated the incorporation of alfalfa-based amendment in a peat–compost medium for organic tomato transplant production in a greenhouse experiment. The root medium (peat:vermicultite:compost in 2:1:1 v:v:v ratio) was amended with 0%, 0.6%, 1.2%, 1.8%, or 2.4% weight by weight of alfalfa-based organic amendment and incubated for 0, 1, 2, 3, or 4 weeks. Measurements were collected on medium pH, EC, seed germination, transplant dry weight, height, stem diameter, and SPAD values. The addition of alfalfa-based amendment increased medium pH and EC, but they were well within the satisfactory range. Germination percentages were less than 50% in non-incubated and more than three week incubated medium and were greater than 75% at one, two and three week incubations. Unamended medium (transplants grown in peat-compost medium without amendments) had higher germination rates; however, nutrient deficiency suppressed subsequent seedling growth. For one, two, three, and four week incubations, the highest rate of amendment (2.4%) resulted in highest biomass, 7.0, 6.5, 7.6, and 9.1 g total dry weight, respectively. Forty two days after seeding there were no statistically significant differences in stem diameter between amendment rates for one week incubation treatments; however, they were significantly higher than the unamended medium. Transplants grown in amended medium were taller and had higher leaf chlorophyll content and overall transplant health as compared to unamended medium, provided the amended medium was incubated for at least one week. To summarize, the alfalfa based amendment used with compost in this study produced transplants with suitable growth characteristics and met commercially acceptable standards for transplanting and handling, at a reasonable estimated production cost. Growers involved in transplant production exploring means and products to transition or adopt sustainable production practices could benefit from the use of such amendments in producing healthy and robust transplants.