Page 12 - Volume 2, Issue 1, January 2009

Hellenic Plant Protection Journal

2:

11-13, 2009

SHORT COMMUNICATION

Comparison of two methods for the determination of soil

nitrate nitrogen in the field

Y.E. Troyanos

1

, E. Roukounaki

1

and G. Gomoli

2

Summary

A “test strip” method (Merck quant®) was compared against the standard (hydrazine nitrate

reduction) method for measuring soil nitrate nitrogen (NO

3

-

- N) concentrations in soil samples from

processing tomato fields in the area of Ilia. The agreement between the “test strip” and standard meth-

od was tested by using regression analysis and a simple “graphical” method. The regression analysis

showed that the “test strip” method overestimated the mean soil NO

3

-

- N concentrations ([NO

3

-

- N]) by

approximately 12% compared to the standard method. However, analysis of the results according to

a more precise “graphical” method revealed that the maximum differences that could be expected to

occur when the “test strip” method is used in the field are 10 ppm above or 6 ppm [NO

3

-

- N] below the

standard method. This discrepancy is acceptable for “on-farm” measurements of soil N and the “test

strip” method could be used with adequate confidence to evaluate the soil [NO

3

-

- N] in fields.

out using correlation or regression analysis.

However, the correlation coefficient (r) mea-

sures the strength of the relation, not the

agreement between the methods where-

as, regression analysis has drawbacks since

both the dependent (“test strip” method)

and the independent (standard method)

variables are measured with error. To over-

come these problems, a simple “graphical”

method has been suggested by Altman and

Bland

(1). In this study both the regression

analysis and the simple “graphical” method

were used to compare the two methods.

Soil cores were taken randomly between

the drippers from 0-20 and 20–40 cm depth

from processing tomatoes fields. The cores

were bulked in a composite sample from

each soil depth that contained approxi-

mately 10 soil cores per hectare. The com-

posite samples were placed in a refrigerator

until NO

3

-

- N analysis. A total of 67 compos-

ite soil samples were sent to the laborato-

ry for analyses. According to the standard

method (hydrazine reduction method) (2),

2 sub-samples (25 g each) were taken from

each composite sample, whereas one sub-

sample was taken for the “test strip” meth-

Efficient nitrogen fertilization management

is essential to achieve optimum yields. A

technique available to manage in-season N

inputs efficiently, in terms of economic and

environmental concerns, can be accom-

plished by monitoring the in-season NO

3

-

- N status of the soil. Τhe “quick test” Mer-

ck quant® method described by Hartz

et al.

(4) is currently used in California as an “on

farm” procedure to manage the nitrogen

fertilization of vegetables. Soil samples from

processing tomato fields in the area of Ilia

(Peloponnissos) were collected in order to

compare the “quick test” method with an es-

tablished method (e.g. hydrazine sulfate re-

duction method) for [NO

3

-

- N] determina-

tion.

It is well known that comparisons of dif-

ferent analytical methods could be carried

1

Laboratory of Non Parasitic Diseases, Department of

Phytopathology, Benaki Phytopathological Institute,

8 St. Delta str., GR-145 61 Kifissia (Athens), Greece.

2

Kyknos S.A., 72 km Patra – Pyrgos, Savalia, GR-272 00

Amaliada, Greece

Corresponding author:

Y.Troyanos@bpi.gr

Abbreviations:

NO

3

-

- N; nitrate nitrogen, [NO

3

-

- N]; ni-

trate nitrogen concentration