Use of Neem Cake as an Organic Substrate Component
Cody W. Kiefer, Jeff L. Sibley, Dexter B. Watts, H. Allen Torbert,
Glenn B. Fain, Charles H. Gilliam
Auburn University Department of Horticulture
101 Funchess Hall, Auburn University, AL 36849
Index Words: neem, urease, nitrification
Significance to Industry:
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. This preliminary study investigates the impact of neem
on substrate gas release and provides a starting point to further investigation regarding
neem use as a substrate component.
Nature of Work:
Fertilizer is an expensive part of any nursery’s program and environmental safety is
becoming an increasingly important subject. Therefore, any cost-effective method that can
reduce the volume of fertilizer needed is a valuable product. Now the question arises: How
is fertilizer lost? Nitrogen is often viewed as the “limiting factor” in plant nutrition, and
while there are many forms or sources of nitrogen, our study focused specifically on urea.
Urea breaks down into ammonium with the aid of an enzyme known as urease. Ammonium
then further breaks down into ammonia, which then undergoes volatilization. Therefore,
slowing down this catalysis of urea could, in theory, prolong substrate nitrogen supplies.
Since urease in soil is a byproduct of bacteria, limiting urease production by affecting the
enzyme itself or its bacterial producers could inhibit the breakdown of urea.
Neem cake (neem) is a product derived from Azadirachta indica A. Juss (the neem
tree). With over 140 chemical compounds isolated from the neem tree, uses for neem have
been numerous (everything from an analgesic to an anti-fungal and insecticidal agent) (1).
One chemical in particular is azadirachtin, a compound found in many insecticides used in
the United States. Only a few studies have evaluated neem products’ effect on nitrification
within mineral soils. Mohanty et al (5) reported on the potential inhibitory effects of neem
seed kernel powder on urease in three mineral soils native to India, showing slight
suppression of urease activity when applied to acidic soils. Méndez-Bautista et al (4)
studied the effects of neem leaf extracts on greenhouse gas emissions and inorganic
nitrogen in urea-amended soil and reported that the leaf extract had no significant effect on
urease, but may limit nitrification. Majumdar et al (3) coated urea with neem before adding
to rice fields in North India, resulting in slight nitrification inhibition. Kumar et al (2) used
neem oils to coat urea and added it to sandy-loam soils resulting in some nitrification
inhibition as well.
Mineral soils and soilless potting media, though, are two different worlds.
Therefore, we tested neem’s effect on urea within a standard pine bark mix. The study
consisted of three groups of treatments: pine bark (PB) + neem, PB + poultry compost (PC)
+ neem and PB + PC + urea + neem. Within each of these groups are several treatments
with varying concentrations of neem and/or fertilizer. Within the PB + neem group are four
pine bark treatments containing 0, 1, 2 and 3 percent neem. The second group also contains
four treatments, but also included 20 percent poultry compost in the pine bark media and
the same percentages of neem (0, 1, 2 and 3 percent). Group three contained the same pine
bark and poultry compost stock mix as in group two, with the addition of Scott’s Osmocote
Classic 19-6-12 at nine pounds per cubic yard.
Each of the twelve treatments contained four replicates for a total of 48
experimental units. The substrate was placed in trade-gallon containers without plants and
placed in a glass greenhouse at the USDA Soil Dynamics Laboratory, Auburn University,
Alabama. The substrates were watered as needed, but without leaching. Moist conditions
were necessary to mimic rhizosphere microenvironments in order to facilitate microbial
growth. Data were taken at regular intervals beginning in May 2010 and ended in August
2010. Data was collected for 3 days per week for the first two weeks and then once per
week for the next 7 weeks. After that, data was collected once every two weeks. In order to
determine substrate microbial activity, we relied on a secondary factor, gas emissions. Data
collection consisted of an airtight gas chamber large enough to accommodate one pot each.
The top of the gas chamber was outfitted with a rubber septum through which a needle
could penetrate. Four evacuated collection vials were needed for each experimental unit,
each one representing a time within the 15 minutes of collection (times 0, 1, 2 and 3
represent initial time and 5, 10 and 15 minutes, respectively). Gas samples were pulled for
each experimental unit for each of the aforementioned times and results were analyzed
using a gas chromatograph. Constituents of the gas samples tested for were: carbon dioxide
(CO2), methane (CH4) and nitrous oxide (N2O), which will be representative of microbial
respiration. Acid-coated glass tubes were also placed in hangers inside of each gas chamber
to absorb any volatilized ammonia released from the substrate. Volatized ammonia, though,
will not be presented in this paper. CO2, CH4 and N2O data were analyzed using Tukey’s
Studentized Range Test in SAS Statistical Software (alpha = 0.05).
Results and Discussion:
Overall: Notation for reporting data will adhere to the following guidelines: PB is
pine bark; PC is poultry compost; fertilizer will refer to the Osmocote 19-6-12 urea; and
when entire groups of treatments are referenced, the values that follow are given
chronologically within the group’s treatments. The unit for gas emission values is μmoles
trace gas m-2 min-1. All data is presented in Table 1.
Carbon Dioxide (CO2): Increasing neem percentage (by volume) as a potting media
component appeared to increase CO2 production. However, in the PB + neem treatments,
there is no statistical difference among treatments. Within the PB + PC + neem group, the
3% neem treatment (247.27) is statistically larger than the 0% neem treatment (125.94).
However, there is no statistical difference among treatments in the PB + PC + fertilizer +
Across all groups, PB + PC +3% neem (247.27) has the highest value for CO2
production, though it is not statistically different than: PB + PC + 1 and 2% neem (172.01
and 198.01, respectively). The PB + 0% neem treatment had the lowest value for carbon
dioxide (53.61), but was not statistically different than: any of the PB + neem treatments
(85.39, 97.51 and 126.86), PB + PC + 0% neem (125.94), or PB + PC + fertilizer + 0% neem
Methane (CH4): Methane’s relation to neem percentage does not seem to be as clear-
cut as with carbon dioxide. Three percent neem used in conjunction with PB + PC is
significantly higher than no neem in the same mixture (0.04150 and -0.00494, respectively).
There was no significant difference in methane levels among treatments within the other
two groups tested.
Again, among all groups PB + PC + 3% neem had the highest methane value
(0.04150), but is not significantly different than: PB + 0 and 2% neem (0.01768 and
0.00279, respectively), PB + PC + 1 and 2 % neem (0.01426 and 0.02995, respectively) or
PB + PC + fertilizer + 1, 2 and 3 % neem (0.01013, 0.00687 and 0.01235, respectively). The
PB + PC + 0% neem had the lowest value for methane across all treatments (-0.00494), but
was not statistically different from any treatment other than PB + PC + 3% neem (0.04150).
Nitrous Oxide (N2O): Nitrous oxide results yield that there are no statistical
differences among treatments within the PB + neem group (0.0008, 0.0013, 0.0003 and
0.0006) or the PB + PC + neem group (0.0394, 0.0442, 0.1299 and 0.0993). The PB + PC +
fertilizer + neem group, though, shows that 3% neem (1.7349) is significantly higher than 0
and 1% neem (1.0294 and 1.0998, respectively).
Across all treatments, 3% neem in PB + PC + fertilizer (1.7349) is significantly
higher than all other treatments, other than 2% neem in PB + PC + fertilizer (1.1539). PB +
PC + fertilizer + 2% neem is higher than all treatments from the PB + neem and PB + PC +
neem groups. The 0 and 1% neem treatments within the PB + PB + fertilizer group (1.0294
and 1.0998, respectively) are also statistically higher than all treatments within the PB +
neem and PB + PB + neem groups.
In summary, that data presented in this paper do not arrive to a clear conclusion.
Studies to determine the fate of urease when neem is added are ongoing, with some
supplemental data not having been analyzed yet. It seems reasonable to conclude that
based on the presented data, neem does have an effect on soil respiration, though more
testing to prove the extent to which this occurs is currently underway. Current testing
includes the aforementioned acid-coated tubes for ammonia volatilization, pH and EC, as
well as nutrient composition of the different treatments.
1. Brahmachari, G. 2004. Neem—An Omnipotent Plant: A Retrospective. ChemBioChem
2. Kumar, R., C. Devakumar, V. Sharma, G. Kakkar, D. Kumar and P. Panneerselvam. 2007.
Influence of Physiochemical Parameters of Neem (Azadirachta indica A Juss) Oils on
Nitrification Inhibition in Soil. J. Agric. Food Chem. 55: 1389-1393.
3. Majumdar, D., S. Kumar, H. Pathak, M.C. Jain and U. Kumar. 2000. Reducing Nitrous
Oxide Emission From an Irrigated Rice Field of North India with Nitrification
Inhibitors. Agriculture, Ecosystems and Environment 81: 163-169.
4. Méndez-Bautista, J., F. Fernández-Luqueño, F. López-Valdez, R. Mendoza-Cristino, J.A.
Montes-Molina and F.A. Gutierrez-Miceli, L. Dendooven. 2009. Effect of Pest
Controlling Neem (Azadirachta Indica A. Juss) and mata-raton (Gliricidia sepium
Jacquin) Leaf Extracts on Emission of Greenhouse Gases and Inorganic-N Content in
Urea-Amended Soil. Chemosphere 76(3): 293-299.
5. Mohanty, S., A.K. Patra and P.K. Chhonkar. 2007. Neem (Azadirachta indica) Seed Kernel
Powder Retards Urease and Nitrification Activities in Different Soils at Contrasting
Moisture and Temperature Regimes. Bioresource Technology 99: 894-899.