This Is AuburnElectronic Theses and Dissertations

Evaluation and Use of Neem (Azadirachta indica A. Juss) as an Organic Substrate Component




Kiefer, Cody

Type of Degree





With “green-mindedness” increasing in popularity, the use of organic substrates has become even more important in the retail horticultural market. Multiple experiments were conducted to evaluate commercially available bagged substrates. The effects of eleven commercially available substrates on plant growth were evaluated using four species of plants. In experiment one, Jungle Growth® organic substrates outperformed other commercial potting substrates and were only slightly inferior in performance to the best-ranking substrate, Miracle-Gro® Moisture Control®. The second experiment revealed that, where different, the Jungle Growth® substrates outperformed all other substrates tested (though not statistically greater than Sta-Green® Flower and Vegetable mix when used on tomatoes and petunias). The search for beneficial amendments for horticultural soilless media is a constant and ongoing process. Neem (Azadirachta indica A. Juss) cake powder is currently being used as a substrate component, but its full effects on the rhizosphere and subsequent plant biomass have yet to be explored. Therefore, a third study was conducted to evaluate neem at varying percentages ranging from 0-5% in two stock substrates – one containing poultry protein compost and the other containing peat in place of the compost and receiving nutrients via fertigation. Results show the benefit of the addition of neem, especially at 5%, in the compost-containing treatments. The same cannot be said of the non-compost treatment. Plants grown in 0-1% neem treatments within the non-compost mixes had results that outperformed any of the compost treatments and often outperformed other non-compost treatments. Therefore, neem appears to be beneficial when amended into poultry protein compost-containing substrates, but antagonistic when added to standard mixes that will be fertigated. Nursery and greenhouse growers continue to seek materials to decrease costs of plant production while maintaining environmental stewardship. Incorporation of neem cake as a substrate component could potentially impact nitrogen release as a result of altering substrate bacterial activity. A preliminary study investigated the impact of neem on substrate gas release and provides a starting point for further investigation regarding neem use as a substrate component. With three substrate groups being tested with varying percentages of neem, this study reports on both across-group results as well as within-group results. Across all three groups, 3% neem within the pine bark + poultry protein compost + neem group was significantly greater in CO2 production than all treatments within the pine bark + neem group as well as zero percent neem within its own group and the pine bark + poultry protein compost + 19-6-12 + neem group. Nitrous oxide emission was significantly greater in the pine bark + poultry protein compost + 19-6-12 + neem group than all other treatments. Within-group comparisons reveal that three percent neem had greater CO2 emission than zero percent neem for both the pine bark + neem and pine bark + poultry protein compost + neem groups. Three percent neem also produced significantly greater CH4 than zero percent neem in the pine bark + poultry protein compost + neem group – and within the same substrate group, two percent neem had significantly greater N2O emission than zero percent neem. There were no significant differences among treatments within the pine bark + poultry protein compost + 19-6-12 + neem group for all three gases analyzed.