1. nitrogen isotopic composition of N-sources, vegetables and soil from two organic farming systems.
C.T. Inácio (Embrapa)
S. Urquiaga (Embrapa)
P.M. Chalk (Univ. Melbourne)
M.G.F. Mata (UFRRJ)
P.O. Souza (UFRRJ)
Good afternoon
The title of my presentation is Nitrogen Isotopic Compostion of Nitrogen-sources, vegetables, and soil from ‘diferent’ farming systems. This research have been carried out by Embrapa (The Brazilian Corporation for Agricultural Research) and The Federal Rural University of Rio de Janeiro with the contribution of Dr. Phillip Chalk, former professor from the University of Melbourne.

2. Background and Objectives
d15N signatures of N-sources
Synthetic N fertilizers
(e.g. urea, ammonium salts)
Slightly depleted or
slightly enriched in 15N
Organic fertilizers
(e.g. manure, compost)
Enriched in 15N
Green manures
(e.g. BNF -legumes)
Slightly depleted or
slightly enriched in 15N
Crops and agricultural soils tend to show variations in d15N values regarding N-fertilizers types having different 15N composition or signatures.
Synthetic fertilizers are slightly depleted or slightly enriched in 15N, while organic fertilizers, as manures and composts, are enriched in 15N.
On the other hand, green manures as legumes which are able to promote the biological nitrogen fixation in association of microorganisms, tend to be also slightly depleted or slightly enriched in 15N.
Therefore, different farming systems regarding the type of N-source may show different d15N signatures in their plant products and soils.
d15N of Soil and Plants

3. Background and Objectives
Thus, the d15N signature of plants has been suggested as a tool to differentiate mode of production i.e. conventional vs. organic, despite some confounding factors.
Thus, the d15N signature of plants has been suggested as a tool to differentiate mode of production i.e. conventional vs. organic. However, there are some confounding factors that could make it not straightforward.

4. Background and Objectives
The aim of this study was to elucidate factors affecting the d15N values of vegetables grown in two distinct organic systems.
The aim of this study was to elucidate factors affecting the d15N values of vegetables grown in two distinct organic systems and compare these values with one conventional farming system.
One organic farming system is based on the use of compost of manures, and in the other farming system there isn’t use of manure or compost of manure in the soil, the main N-sources are green manures and fermented products made from plant residues.
Distinct organic N-sources!

5. Materials and Methods Farms Samples Samples
In-conversion Organic Farm (Org.A)
Organic Farm (Org.B)
Conventional Farm
Hydroponic Farm
Dried at 60°C
Ball mill
Samples
We chosen two organic farms. The first na In-conversion organic farm which we called Organic Farm A, and the second organic farm which is a 3-years experimental farming system.
Additionally, We chosen one typical conventional farm and one hydroponic farming system.
Samples of Soil, Organic Inputs and Lettuces were taken and sent to a Isotope ratio mass spectrometer to determine the d15N values.
Soil (0-20cm)
Organic Inputs (N-sources)
Lettuce
Tin
capsules
d15N ‰ values
EA-IRMS

6. Results and Discussion
Organic N-sources
Farm
Organic N-source
N-total (%)
d15N (‰)
Org.A
Horse manure
1.8 and 1.2
+11.8 and +14.6
Poultry manure
3.0
+13.9
Compost
1.7
+13.1 to +14.9
Org.B
Gliricidia
4.5
+0.0
Mucuna
6.2
+2.5
Crotalaria
4.6
+1.4
Elephant grass
0.6
+4.3
Maize
+10.0
Fermented product
4.0
+7.9
Vermicompost
2.7
+8.8
Mulch
3.6
+6.5 and +7.6
Green-manure
2.1
+2.2 and+5.4
This table shows the variaty of organic inputs in each organic farm.
In the organic farm A we have manures and compost showing enriched d15N values beteween 11 and 15 deltas. In the organic farm B we have legumes species as N-source with d15N close to zero or slighlty enriched in 15N. However, we found also a enriched d15N (arround to 8 deltas) for the fermented products applied to soil and vermicompost which is used in the bedding of lettuce.

7. Organic N-sources (d15N)
Results and Discussion 2
Organic N-sources (d15N) 1
These graphs ilustrate the d15N signatures of the organic inputs in each farm.
Here, we include a third farm, a conventional farm.
It is clear the differenc beteeen the two organic farms in relation to the mean of d15N signatures of the organic inputs. However, there isn’t differenc beteewen the organic inputs of the conventional famr and the organic farm A. The convetional farm uses manure as organic source besides synthetic fertilizers as N-source. Such vegatable farming is very typical in many farms in Brazil.
In the figure number 2, we have the histograms and it is also clear the array of sources and wide range of d15N values available in the organic farm B.

8. Results and Discussion
Soil
Does the soil signature
reflect organic inputs?
Here we have the d15N values of soil samples. The pattern showed here is quite similar to the pattern we see before for the organic inputs. Thus, we could say that in some extend the soil signature reflects the signature of organic inputs.

9. Results and Discussion
Plant
Without Manure
With Manure + soil
Well, for the plant delta 15N values we introduced samples from a Hydroponic farming system, which has as N-source only synthetic sources, and there isn’t influence of N from soil indeed.
So, we see 3 important matters here.
First, the difference between the two organic farms
Second, the difference between the soil-based farming systems and the hydroponic system.
Therefore, the use of manure as N-source appears to drive the d15N values of lettuce samples.
Third, despite the differences in N-sources between the organic farm B and the conventional farm, we found a overlapping of d15N signatures of lettuce.
Overlapping of
d15N values. Why?

10. Results and Discussion
N-Recovery
Compost as N-source
Low recovery of N from Green manures (?)
Comparing the d15N values of soil, organic inputs and lettuce in each farm is possible to make a qualitative analysis of the N-recovery or N use efficiency on the system.
In the organic farm A the mean values of d15N signatures of organic inputs and lettuce are similar and suggest the nitrogen from compost as source.
In the organic farm B the mean values of d15N signatures of organic inputs and lettuce are different. This mismatch suggests a low recovery of N from green-manures in this farming system. An issue that needs to be further investigated under controlled experiments.
In the conventional farm the mean value of d15N of lettuce is lower than the signature of organic inputs; suggesting the influence of synthetic Nitrogen fertilizers as source.
Influence of synthetic N-fertilizers

11. Conclussion
The array of N-sources available for different organic farms shows a wide range of d15N signatures (from +0.0 to +14.9‰).
However, organic amendments (manure, composts and fermented products) seem to influence the d15N signatures of plants and soil more than BNF inputs (legumes mulching and green manure), which might imprint lower d15N values in vegetables than were found.
Therefore, in this study the (....) and (however) organic amendments...

12. Further consideration
The d15N signatures may be a qualitative or semi-quantitative tool to evaluate the N-recovery from organic inputs (e.g. compost, manure, green manure).
However, We need to be aware of the discrimination processes of 15N.
Our data also suggest that (...) However (....)

13. Caio Teves Inácio caio.teves@embrapa.br
Thank you
Caio Teves Inácio