Group Title: NFREC Research Rpt.
Title: Plant sap tests for nitrogen and potassium in tomatoes
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 Material Information
Title: Plant sap tests for nitrogen and potassium in tomatoes
Series Title: NFREC Research Rpt.
Physical Description: 8 leaves : ill. ; 28 cm.
Language: English
Creator: Rhoads, Fred ( Frederick Milton )
North Florida Research and Education Center (Quincy, Fla.)
Publisher: North Florida Research and Education Center
Place of Publication: Quincy Fla
Publication Date: 1994
Subject: Tomatoes -- Fertilizers -- Florida   ( lcsh )
Potassium fertilizers   ( lcsh )
Nitrogen fertilizers   ( lcsh )
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
Bibliography: Includes bibliographical references.
Statement of Responsibility: F.M. Rhoads ... et al..
General Note: Cover title.
 Record Information
Bibliographic ID: UF00066124
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 71187916

Full Text

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Florida Agricultural Experiment Stations
Institute of Food and Agricultural Sciences
University of Florida, Gainesville


NFREC Res. Rpt. 94-10



Production of staked tomatoes on plastic mulch with drip
irrigation requires relatively large seasonal applications of
nitrogen (N) and potassium (K). A single large application of N
and K fertilizers mixed within the bed or as a surface band before
putting plastic mulch in place has the potential of causing injury
to plants from soluble salts, resulting in reduced plant stand.
Nitrogen in the nitrate (NO0-) form is easily leached from the root
zone of all soils if excessive water occurs either from rainfall or
irrigation and excessive water also can move a large portion of K
out of the root zone of sandy soils. To avoid these problems,
extension specialists recommend that small applications of N and K
be injected through drip irrigation systems into the root zone of
tomatoes several times during the growing season (Hochmuth and
Clark, 1991; and Hochmuth et al., 1991).
Monitoring the tissue concentrations of N and K in tomato
plants using tissue sampling and analysis can improve precision and
efficiency of fertilizer management. However, traditional
laboratory analysis of plant tissue cannot provide results to
growers on a timely basis for the most efficient fertilizer
management. An alternative procedure is the use of plant sap quick
test kits. Two of these kits have been calibrated for tomatoes,
one uses a colorimeter and the other uses test strips that change
color to quantify results (Hochmuth et al., 1991). Sufficiency
ranges, using the above kits, for NO -N in tomato petiole sap from
the fifth or sixth leaf from the tip are 600 to 800 ppm between
transplant and 1-inch fruit size, 400 to 600 ppm from 1-inch fruits
to first harvest, and 300 to 400 ppm during main harvest.
There are several approaches to precision fertilizer
management in tomatoes. All of the fertilizer can be applied in
several applications through the drip system with application
amounts varying as plant growth rate changes or by using a constant
amount for each application. Part of the N and K (40 to 60% of
total) can be applied to the bed before putting on the plastic with
the remainder applied in several small applications with
irrigation. Again, amount of fertilizer injected at each
application date can vary with plant growth rate or remain
constant. Also, the interval between injections of fertilizer can
be varied as needed.
A relatively new sap test kit that uses specific ion
electrodes to measure NO3- and K+ in plant sap directly is now
available. We chose to use the specific ion electrode kit to
compare the influence of several N application procedures on NO3-
and K+ concentration of petiole sap of tomatoes at several sampling
dates and on yield and grade of tomato fruit.


Tomato plants were transplanted 22 March, 1993 in a research
block located at the North Florida Research and Education Center,
Quincy. The production system included drip irrigation, black
polyethylene mulch, and stakes to support and maintain plants in an
upright position when plants were tied to the stakes with twine.
Recommended cultural and pest control practices were applied
uniformly to all treatments (Hochmuth, 1988). There were 8
fertilizer treatments including a control treatment that received
no fertilizer. The remaining 7 treatments each received a total of
175 lb. N/acre. Source of N was ammonium nitrate (NH4NO3) for 6
treatments while one treatment received N from a mixed fertilizer
(13% N 4% P205 13% K20). Two treatments received no N preplant;
one of these received 14.6 lb. N/acre per week injected into drip
irrigation tubing for 12 weeks. The other treatment received 8.75
lb. N/acre each week for the first 2 wk, 13.13 Ib./wk the 2nd 2 wk,
17.5 lb./wk the next 6 wk, and 13.13 lb./wk the last 2 wk. Three
treatments received 40% of N (70 lb./acre) applied broadcast to
beds before polyethylene was applied. One of these received 8.75
lb. N/acre per wk injected into drip tubing for 12 wk. The second
received 5.25 lb. N/wk in first 2 wk, 7.88 lb./wk second 2 wk, 10.5
lb./wk next 6 wk and 7.88 lb./wk last 2 wk. The third treatment
receiving 40% of N preplant received 8.75 lb. N/wk injected into
drip tubing for 12 wk as above plus 5 lb. K20/wk (as KC1), also
injected for 12 wk. The seventh treatment received 100% of N as
NH4NOz preplant before applying plastic. The eighth treatment
received 1350 lb./acre of 13-4-13 preplant before laying plastic
mulch; this is equivalent to 175 lb. of N/acre, 54 lb. of P205/acre,
and 175 lb. of K20/acre.
Rows of tomato plants were 6 feet (ft) apart, width of mulched
bed was 3 ft, each single-row plot contained 18 plants 20 inches
apart, the 12 center plants were harvested for yield. There were
two harvests and tomatoes were graded into medium, large, and extra
large fruit. The experimental design was a completely randomized
block with 4 replicates. Analysis of variance procedures were used
to compare treatment mean yields (Freed et al., 1989).
The fifth or sixth leaf from the tip of 10 tomato plants was
obtained from each plot before injection of fertilizer in wk 4, 5,
6, 8, 10, 12, and 14 following transplanting. Petioles were
chopped, the sap expressed with a hydraulic press, and a few drops
were placed on the micro electrodes of each specific ion meter (
one for N and one for K) to determine NO3- and K ion concentrations
in the sap. Whole leaves were dried and ground for traditional
laboratory tissue analysis for N and K. Simple regression analysis
was employed to determine the correlation coefficient between fruit
yield and sap NO or K+, also correlations between total N and K
in the tissue anA yield were examined (Freed et al., 1989).


Marketable yield was about 900 boxes/acre (30 lb./box) with no
fertilizer N or K (Fig. 1.). Maximum yield (2132 boxes/Acre)
occurred with 100% of fertilizer N applied preplant. There was no

Tomato Fruit Yield








1 2 3 4 5 6 7 8
Fertilizer Treatment

Figure 1. Marketable yield of tomatoes receiving different
fertilizer management strategies. As indicated, either
0,40% or 100% of N was applied preplant (pp). "Even"
indicates that amounts of N were equal in 12 weekly drip
applications (DA) of fertilizer injected into the
irrigation system. Growth curve (GC) means that amounts
of N in 12 weekly fertilizer injections were varied from
week to week in proportion to plant growth rate.
Nitrogen management was varied in treatments 1 through 5
while both N and K were applied to treatments 7 and 8.
Ammonium nitrate is 34-0-0 and 13-4-13 contains 13% N, 4%
P20s, and 13% K20

M 100 % N pp 13-4-13
40% N pp even N&K
EI No Fertilizer
CI] 100% N pp 34-0-0
l 40% N pp GC DA
r-I 40% N pp even DA
S0 N pp GC DA
f 0 N pp even DA

significant difference in yield between weekly N application that
varied with plant growth rate and weekly N application that
remained constant. All N treatments received 175 lb of N/acre but
applying all of the N through the drip system in 12 weekly
increments reduced yield (P < 0.01) in comparison to 40% and 100%
of N applied preplant (Fig. 2.). The yield increase between 40 and
100% preplant N was also highly significant. There was no yield
advantage to applying N via the drip irrigation system. This is in
agreement with previous research results (Locascio, et al., 1989,
and Rhoads, et al., 1988). No evidence was apparent that leaching
of preplant N occurred, otherwise the drip applied N should have
produced the highest yield. Preplant N may have supplied a higher
amount of N03-N than drip applied N because the NH4-N in preplant
NH4NO3 had more time to be oxidized to NO3- than that in drip
applied NH4NO3. It has been shown that excessive NH4-N can be toxic
to tomatoes. It may be that drip applied N would have been more
effective in maximizing yield if all had been applied in the first
8 wk of growth. This application method would have increased NO3-N
concentration in the root zone from both larger applications of
NH4NO3 and allowing more time for NH4-N to be oxidized while plants
were actively absorbing N.
All fertilizer treatments had petiole NO3- levels greater than
4500 ppm (1016 ppm N) at 4 wk after transplanting (Fig. 3.)
However, at 5 wk petiole nitrate dropped to about 1000 ppm (225 ppm
N) in the no fertilizer treatment while all other treatments
remained above 4000 ppm. Petiole NO3- dropped faster in treatments
receiving no preplant N than those receiving either 40 or 100% of
N preplant. At 8 wk after transplanting, petiole NO3- in
treatments with no preplant N were below 2000 ppm, but it ranged
from 3000 to 4500 ppm in those with preplant N. Petiole nitrate
had dropped below 2000 ppm (450 ppm N) in all treatments by 12 wk
after transplanting.
Petiole NO3- levels are of little value unless they are highly
correlated with yield. Simple regression analysis to determine
correlation coefficients (r) of yield versus petiole NO3- was
performed for each sampling date using total market yield, extra
large fruit yield, large fruit yield, and medium fruit yield (Fig.
4.). The effect of each harvest on correlation was also evaluated.
The highest correlation was obtained with total market yield
followed by extra large and large fruit yield. Medium fruit yield
was not correlated with sap NO3-. The correlation was higher for
the second harvest than for the first but it was no better than for
total market yield. Correlation for yield versus petiole NO3- was
significant only between 5 and 10 wk after transplanting (Fig. 4.)
Values of r less than 0.5 account for <0.25 of the variation and
were of little value in establishing sufficiency ranges for petiole
NO3-. Therefore, sap tests made before 5 wk and after 10 wk from
transplanting were of little value for managing N fertility of
Graphs showing a plot of yield (treatment means) versus sap
NO concentration were constructed to estimate sufficiency ranges
between 5 and 10 wk after transplanting (Fig. 5.). The estimated
sufficiency level of sap NO3- between 5 and 8 wk was 4000 ppm (900
ppm N) or more whereas it was 3000 to 4000 ppm (700 to 900 ppm N)







Yield (Boxes/Acre)

Orthogonal Contrasts
0 vs. 40 and 100; F 15.90**

40 vs. 100; F 10.72**

0 40 100
Nitrogen Applied Preplant (% of total)
Figure 2. The influence of preplant nitrogen level on yield of
tomatoes. All treatments received 175 lb. N/Acre.

Nitrate Sap Test- Tomatoes

Thousands (ppm nitrate)

---- I

1 ~ ~ 1 1

0 N pp even DA
-4- 0 N pp GC DA
-- 40% N pp even DA
--- 40% N pp GC DA
--- 100% N pp 34-0-0
---- No Fertilizer
- 40% N pp even N&K DA
S100 % N pp 13-4-13

0 2 4 6 8 10 12 14 16
Weeks After Planting
GC growth curve, DA drip application
pp preplant, Total N 175 lb/A
Figure 3. Nitrate sap test levels in tomatoes at seven sampling
dates for 8 fertilizer management treatments. All
treatments except the no fertilizer treatment received
175 lb-N/Acre. See figure 1 for further treatment

Correlation: Yield vs Sap Nitrate

Correlation (r values)






0 2 4 6 8 10 12 14 16
Weeks After Planting

Figure 4. Correlation coefficients (r) for total yield, yield of
extra large fruit, large fruit, and medium fruit versus
sap nitrate of tomatoes at seven sampling dates.

Tomato- Yield vs 8Sp Nitrate
Week 6
Total Fruit Yield (Boxes/A)


1500- r



0 10 20 30 40 60 60
Petiole Sap Nltrate (ppm/100)
Multiply by 10O to convert to ppm

Tomato- Yield vs Sap Nitrate
Weak 8
Total Fruit Ylied (Boxes/A)




0 10 20 30 40 50
Petlole Sap Nitrate (ppm/100)
Multiply by 100 to convert to ppm

Tomato- Yield v Sap NItnrte
Week 6
Total Fruit Yleld (Boxes/A)

2000 '

1600 z



0 10 20 30 40 61
Petiole Sap Nitrate (ppm/100)
Multiply by 100 to convert to ppm

Tomato- Yield vs Sap Nitrate
Week 10
Total Fruit Y1ild (Boxos/A)





0 10 20 30 40 6C
Petiole Sep Nitrate (ppm/100)
Multiply by 100 to convert to ppm

Figure 5. Total fruit yield plotted against petiole sap nitrate of
tomatoes at four sampling dates. Each data point is the
average of four replications and represents a treatment
mean. The trend line is part of the computer graphics
program. Multiply x-axis by 100 to convert to ppm


--- Total Market Yield

- Extra Large

- Large

- Medium

between 8 and 10 wk. These values are higher than those found for
tomatoes in the guidelines for testing petiole sap (Hochmuth,


Petiole sap NO3- concentration in tomatoes was correlated with
yield during the period of 5 to 10 wk after transplanting. The
sufficiency level for this period was greater than 3000 ppm NO3-
(700 ppm N). There was no yield response to K fertilizer addition
nor was sap test K+ correlated with tomato fruit yield. However,
total K concentration in tomato tissue was reduced significantly
(P 0.01) with no N fertilizer compared to other treatments.


Freed, R. D., S. P. Eisensmith, E. H. Everson, M. Weber, E. Paul,
and D. Isleib. 1989. Mstat-c a microcomputer program for the
design, management, and analysis of agronomic research
experiments. Mich. State Univ. East Lansing.

Hochmuth, G. J., D. Maynard, C. Vavrina, and E. Hanlon. 1991. Plant
tissue analysis and interpretation for vegetable crops in
Florida. Univ. of Fla. IFAS. Florida Cooperative Extension,
Special Series Report. SS-VEC-42.

Hochmuth, G. J., and G. A. Clark. 1991. Fertilizer application and
management for micro (or drip) irrigated vegetables in
Florida. Univ. of Fla. IFAS. Florida Cooperative Extension,
Special Series Report. SS-VEC-45.

Hochmuth, G. J. 1993. Petiole sap testing guidelines. Vegetarian

Hochmuth, G. J. 1988. Tomato production guide for Florida. Univ. of
Fla., IFAS. Coop. Ext. Serv. Circular 98 C.

Locascio, S. J., S. M. Olson, and F. M. Rhoads. 1989. Water
quantity and time of N and K application for trickle-irrigated
tomatoes. J. Amer. Soc. Hort. Sci. 114(2):265-268.

Rhoads, F. M., S. M. Olson, and A. Manning. 1988. Nitrogen
fertilization of staked tomatoes in North Florida. Soil and
Crop Sci. Soc. of Fla. Proc. 47:42-44.


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