February 2019 - 24

RESEARCH
80/20
peat/perlite
immediately
after watering
50/50
peat wood
Figure 3. Wicking of
water makes it appear
that a plant needs to
be watered when only
the surface is dry.
12 hours later
Figure 4. Cucumbers and tomatoes are just two of the crops being evaluated at
Utah State University.
for about 25 days from seeding or transplanting. Figure 4 shows a
representative study with cucumbers and tomatoes.
The effect of wood percentage on whole-plant fresh-mass and typical
plant appearance are shown in Figures 5 and 6. The error bars are the 95
percent confidence interval across all species. In each study, there were
two types of controls for a reference: 50/50 peat/vermiculite and 80/20
peat/perlite. Aging the wood improved growth, but the benefit was less
than we expected.
CONCLUSIONS
1. The 50/50 peat/vermiculite (PV) and the 80/20 peat/perlite (PP)
were nearly identical in every study. Vermiculite has excellent nutrient
holding capacity, provides silicon to reduce disease, buffers pH and
is a natural wetting agent. These characteristics did not increase
crop growth in these studies, so the combination of the PV and PP
treatments provided an excellent, double reference for comparison of
the wood treatments.
2. The elevated fertilizer level only slightly increased (less than 10
percent) the growth of the crops in the peat/vermiculite and the
peat/perlite substrates. Fertilizer in excess of plant needs (especially
nitrogen) can increase fresh mass of some plants, but in this study the
plants were leached with about 15 percent of input solution volume at
each watering. This would have replenished the nutrients in the root
zone and provided ample nutrition at 120-ppm nitrogen. The results
also show that over a wide range of plant species a 120-ppm nitrogen
fertilizer solution is ample to meet plant nutritional requirements in
substrates without wood.
3. Elevated fertilizer did increase plant growth in the treatments with
wood, and the benefit increased with increasing fraction of wood (Figure
7). Based on tissue analysis, elevated fertilizer slightly increased N and
phosphorus concentrations in leaf tissue, but the concentrations at
120-ppm nitrogen were adequate to support rapid growth. We do not
yet fully understand the physiological basis for increased growth with
increased nutrients in high wood percentage media.
There may be indirect benefits of elevated fertilizer. The electrical
conductivity (EC) of the leachate from containers with the same input
solution decreased with increasing percentage of wood. This suggests
microorganisms are growing on compounds coming from the wood and
consuming nutrients. This microbial growth may be beneficial if they
break down toxic compounds coming from the wood.
4. The treatments indicated by the one- and three-month labels are
from aged sawdust, both lodgepole from Utah and loblolly pine from
Harold - Western US Rep
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(214) 213-0666
Alan - Eastern US Rep
(931) 607-4170
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GREENHOUSE PRODUCT NEWS
Capture the
Foodie Gardener
p. 28
INSIDE:
Trends in Edibles
Sanitation in the Greenhouse
Researching Cutting Types
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February 2019

Table of Contents for the Digital Edition of February 2019
