Evaluation of Processed Corncob and Paulownia tomentosa as Substrate Components in Horticulture Crop Production

Abstract

The main components in soilless substrates for greenhouse and nursery production include pine bark, peatmoss, and perlite. There have been recent concerns with peatmoss because of availability, and the environmental impact harvesting has on natural peat bogs. There have also been concerns with perlite because of the fine particle dust that is associated with its dry state. These concerns have led researchers to look at alternatives that will be able to provide the same function with less environmental and health concerns. The first study evaluated the use of corncob as an alternative to perlite in the production of greenhouse annuals. Results from physical properties analysis showed that container capacity decreased with increasing percentages of corncob. Growth index and shoot dry weights showed a reduction in growth with an increase in percentage of corncob for all species, similar results were seen in root ratings and bloom counts. Results from this experiment suggest that a possible reason for reduction in growth could be the availability of essential nutrients. A second study was addressed to evaluate the effect of nitrogen fertilizer rates on corncob-amended substrates in the production of Petunia ×hybrida. Peatmoss was combined with soaked corncob, un-soaked corncob, or perlite at an 80:20 (v:v) ratio and mixed with 0.9 (2), 1.8 (4), 2.72 (6), or 3.6 kg•m-3 (8 lbs•yd-3) of slow-release fertilizer. Results showed a higher container capacity and total porosity for substrates containing corncob. Electrical conductivity readings decreased over time for all treatments. Shoot dry weights and growth index increased with an increase in fertilizer rates across all treatments for both experiments. Petunias grown in non-soaked and soaked corncob substrates at the highest rate were similar to perlite at fertilizer rates of 1.8 (4), 2.72 (6), or 3.6 kg•m-3 (8lbs•yd-3). Results from this study showed that an increase in fertilizer had a positive effect on the growth of petunias in a corncob amended substrate. The third study looked at the effects of corncob as a substrate component in the production of container grown perennials. Container capacity and air space of corncob-amended substrates were equal to their perlite amended counterpart. Results from bulk densities indicated that substrates containing corncob were higher than all substrates containing perlite. Results at 30 and 60 days after planting (DAP) of pH for lantana and miscanthus showed substrates with corncob to have a higher pH than perlite substrates. While at 90 DAP there were no differences across all treatments and species; electrical conductivity followed similar trends. Shoot dry weights of salvia and lantana showed a reduction in growth at 35 DAP, but by 90 DAP there were no differences with miscanthus corncob substrates at 10% and 30% were lower in shoot dry weights compared to its PL counterpart, while at 90 days all treatments were equal except for 30% corncob. In conclusion, growth of lantana, salvia, and miscanthus in corncob amended substrates were similar compared to its perlite counterpart at 90 DAP. Results from this study show that corncob might be a viable alternative to perlite. Because of the environmental issues and the availability of peatmoss, a fourth study was conducted to look at the effects of Paulownia tomentosa (PT) as a substrate component in annual production. Results showed substrates containing higher amounts of paulownia had greater air space than substrates containing less amounts of paulownia. Substrate container capacity was greater in the low percentages of paulownia. All substrates containing paulownia had a higher total porosity than the perlite standard (PS). Substrate pH at 14, 21, and 28 DAP was highest for treatments containing 60% to 100% PT. Initial substrate EC was greatest for the PS and the 20% PT substrate, however by 35 DAP, substrate EC was similar among all treatments. Petunia growth index was 63 to 400% greater for plants grown in the PS compared to other treatments. Dianthus tended to respond better to PT as a substrate component than petunia, although dianthus growth index followed a similar trend with GI being 26 to 135% greater in the PS treatment compared to all others. With one exception, all other growth parameters followed similar trends on both species with plants grown in PS having the greatest bloom counts, root ratings, and shoot-dry weights of all treatments.