Optimizing substrates, composts, and fertilizer additions for organic transplant production

Optimizing substrates, composts, and fertilizer additions for organic transplant production

Summary

Four experiments have been conducted to determine the performance of organic potting media for seed germination and overall transplant growth and health in tomato. The first experiment was conducted in the early spring of 2004 beginning March 17th. This study sought to get a baseline comparison between a sample grower recipe, a conventional commercial potting mix, and an organic commercial potting mix. The sample grower recipe included 20% vermicompost, 310 mL feather meal, and 133 mL kelp meal added to a .04m3 base of an 80:20 mix of peat and perlite. The second experiment was conducted in late spring of 2004 beginning May 24th. This experiment included the three treatments from experiment 1 as well as an additional treatment that was a variation of the sample grower mix containing the same ingredients but with the percentage of vermicompost reduced to 10%. The treatment that was the variation of the grower mix was included after it was observed that seeds planted in the original grower mix had a reduced rate of germination and was based on the hypothesis that vermicompost was the cause of the reduced germination. The third experiment was a summer experiment that began on July 15th. This experiment sought to gain additional information regarding each ingredient included in the sample grower mix by including treatments that were made up of the .04m3 peat / perlite base and one of the individual ingredients from the original grower recipe in the same quantity as the complete mix. A mix of base plus vermicompost and feather-meal without the kelp meal was also included as were all treatments from experiment 4. Two additional commercial organic potting mixes were also included in this study. The fourth experiment was conducted in the fall of 2004, beginning on October 19th. This study sought to determine the most appropriate rate of feather-meal for the custom potting mix by including treatments including 10% vermicompost and five rates of feather-meal. These treatments were compared to the original grower’s mix, the commercial conventional potting media, and the original commercial organic media.

Objectives/Performance Targets

The objective of this study is to develop an efficient and cost-effective combination of ingredients for a custom organic potting mix that would provide equivalent plant health to commercial organic and conventional potting mixes as well as minimize the need for addition of soluble organic fertilizer. This includes determining which materials are most appropriate in terms of overall plant growth and nutrition as well as cost of those materials, and determining appropriate rates of those materials. A further objective is to develop protocols allowing growers to test and refine their own mixes.

Accomplishments/Milestones

Results between experiments have been variable both in terms of seed germination and transplant growth. Some of the variability in terms of transplant growth has been due to differences in environmental conditions resulting from conducting experiments during different times of the year. Another source of variability has been watering as different methods for watering have been attempted in order to determine if one method was more effective than another. Watering methods that appear best for germination appear to lead to variability in terms of transplant growth so all aspects of transplant production must be taken into consideration. The primary source of variability is the variability in organic amendments that occurs both over time if amendments are stored and between batches if materials utilized are obtained at different times. For example, there is a great deal of variability in vermicompost prepared in different batches even from the same supplier. As much of this variability is somewhat inevitable with this type of production system, identifying the sources of variability should enable us to advise growers the best approaches for minimizing variability and maximizing the quality of their transplants. For example, regular testing of potting mixes as well as organic amendments utilized is essential in determining what nutrition will be provided to the crop.

Impacts and Contributions/Outcomes

An additional experiment is currently underway and further analysis of results is still required however at this point we have found that organic potting mixes blended by growers provide growth and nutrition comparable to commercial potting media through a four week transplant production period. Soluble fertilizer additions may be required in the fourth week, particularly in order to provide sufficient nitrogen. Substitution of kelp meal with another potassium source would be recommended for developing an overall mix. The amount of salt contained in kelp meal for the amount of nutrition provided is very high (376 parts per million). While sufficient nutrition may be provided by this transplant production method, one drawback of this method is the overall lack of control over plant growth as a result of all of the nutrition being incorporated into the potting media. As a result, should a grower’s planting date be delayed for whatever reason, it is not possible to withhold nutrition for a few days in order to delay plant growth to hold them to a particular size prior to planting.

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