Progress Report Series No. 93
Agricultural Experiment Station
AUBURN UNIVERSITY
E. V. Smith, Director
Auburn, Alabama
Soil Fertility Experiments with Tomatoes
CLYDE E. EVANS, W. A. JOHNSON, and DALLAS HARTZOG'
A COOPERATIVE RESEARCH program between to-
mato growers in Geneva County, Alabama, and Au-
burn University Agricultural Experiment Station
was begun in 1970.2 Purpose of this continuing re-
search is to better define the fertility requirements
and to improve soil test calibration for tomatoes.
Four experimental test areas were located in to-
mato fields of cooperating 
growers: Billy Adkison,
James Bedsole, H. D. Green, and Leon Keel. Each
grower prepared the land, layed off rows, subsoiled,
planted, cultivated, and sprayed for disease and in-
sect control in the experimental test area just as he
did in the remainder of his tomato field. The authors
applied fertilizer and harvested tomatoes from the
test area.
Each test area was marked off into 24 single-row
plots 6 feet wide and 15 feet long. Each test included
six treatments replicated four times. Rates of N were
0, 50, 100, and 160 pounds per acre from ammonium
nitrate. Except for one P "check" plot that got no
phosphorus and one K "check" treatment that got no
potassium, all plots received 80 pounds P (180 pounds
1 Associate Professor, Department of Agronomy and Soils; Assis-
tant Professor, Department of Horticulture; and Research Associ-
ate, Department of Agronomy and Soils.
2 Successful establishment of the research program was made
possible through efforts of the Geneva County Extension Chairman.
P
2
0
5
) and 150 pounds K (180 pounds K
2
0). All plots
had gypsum applied at 1,000 pounds per acre and
the recommended rate of a nematicide was applied
in the furrow during row preparation.
Approximately one-third of the nitrogen, all the
phosphorus, one-half of the potassium, and all the
gypsum were applied before planting. It was applied
on a 3-foot strip centered on the row and incorpo-
rated with the soil using a rototiller. The remaining
nitrogen and potassium were sidedressed at all test
areas on April 17, 1970.
During the harvest period, ripe, 
pink, and mature
green tomatoes were picked once each week for a
total of 5 weeks. These were sorted into marketable
and non-marketable fruit and weighed.
INDIVIDUAL EXPERIMENTS
Keel farm (Table 1). Tomatoes at this location
were staked and supplemental irrigation was applied
during dry periods. Plots that received no phos-
phorus fertilizer made the lowest yield-67 per cent
of the top yields. On plots that got no potassium, the
yield was 88 per cent of the highest yield. Soil-test
P and K were both "low" at this location. Highest
yields were on plots receiving 100 or 160 pounds of
TABLE 1. EFFECT OF FERTILIZER TREATMENT ON TOMATO YIELDS, LEON KEEL'S FARM, 19701
No. Treatment, lb. /acre Marketable fruit per acre'
N P K June 10 June 17 June 25 July 1 July 7 Total
Lb. Lb. Lb. Lb. Lb. Lb. Pct.
1 0 80 150' 2,860 2,420 2,100 4,660 6,430 18,460 11
2 50 80 150 4,090 2,930 2,470 5,010 4,950 19,440 8
3 100 80 150 3,550 3,470 2,710 6,060 7,830 28,620 5
4 160 80 150 3,170 2,440 2,440 5,230 11,490 24,740 10
5 160 0 150 2,690 2,450 2,080 4,480 4,940 16,630 8
6 160 80 0 3,520 2,800 3,000 5,700 6,870 21,890 10
1 Soil test P = 48 (low); soil test K = 75 (low).
2 Variety, Floradel.
' 80 pounds P = 180 pounds P
2
0.
150 pounds K - 180 pounds K
2
0.
January 1971
TABLE 2. EFFECT OF FERTILIZER TREATMENTS ON TOMATO YIELDS, H. D. GREEN'S FARM, 1970
No. Treatment, lb./acre Marketable fruit per acre
2
N P K June 4 June 10 June 17 June 24 June 30 Total
Lb. Lb. Lb. Lb. Lb. Lb. Pct.
1 0 80" 150 590 1,190 2,940 2,830 6,900 14,450 14
2 50 80 150 940 1,430 3,790 2,070 10,590 18,820 12
3 100 80 150 500 1,270 3,860 1,970 9,150 16,750 9
4 160 80 150 490 1,760 3,510 1,770 10,900 18,430 12
5 160 0 150 990 900 4,320 2,410 8,480 17,100 11
6 160 80 0 900 1,170 2,820 2,290 9,200 16,370 11
1 Soil test P = 145 (medium); soil test K = 80 (low).
2 Varieties, Manapal and Floradel.
3 80 pounds P = 180 pounds P
2
0s.
150 pounds K = 180 pounds K
2
0.
N per acre (treatments 3 and 4). The combined yields pounds of N to a high of 14 from 0 N. The 
other
of the first four harvests from 50 and 100 pounds of fertilizer rates had either 11 or 12 per cent culls.
N per acre were as high or higher than from the Adkison farm (Table 3). Tomatoes at this location
160-pound N rate. Therefore, early production was were not staked or irrigated. Nitrogen had little 
or
delayed from use of a high rate of N. At the last no effect on total yields, and there was little yield
harvest, the yield from 160 pounds N was consider- response to phosphorus or potassium. However,
ably larger than that for any other N rate. added phosphorus did improve early growth and
The relative amounts of culls were 5 per cent from early yield. Soil-test P was "low" and soil-test K was
100 pounds N, 11 per cent from 0 N, and 8 or 10 per "medium."
cent from the others. The number of cull tomatoes was quite large be-
Green farm (Table 2). Tomatoes at this location cause of excess rainfall following an extended
were staked but not irrigated. The yield from 50 drought during fruit production. Over half of the
pounds of N was as high as that from 160 pounds, culls occurred at the peak harvest on June 11, the
but the 0 N treatment made the lowest yield. With- first harvest after the heavy rain. Most culls were
out applied phosphorus, the yield was 93 per cent the result of cracking. Total culls ranged 
from 25 to
and without applied potassium it was 89 per cent. 33 per cent of the total crop. The 0 N rate had 25
Soil test P was "medium" and K was "low." The per- per cent culls, the 0 potassium plots 
had 33 per cent,
centage of culls ranged from a low of 9 from 100 and the others were 28 or 32 per 
cent.
TABLE 3. EFFECT OF FERTILIZER TREATMENTS ON TOMATO YIELDS, BILL ADKISON'S 
FARM, 1970'
No. Treatment, lb./acre Marketable fruit per acreC
N P K May 28 June 4 June 11 June 17 June 24 
Total
Lb. Lb. Lb. Lb. Lb. Lb. Pct.
1 0 80 1504 710 3,130 6,320 5,690 
7,230 23,080 25
2 50 80 150 1,830 5,010 8,410 
4,190 5,140 24,580 28
3 100 80 150 1,320 5,160 6,460 
3,630 5,700 22,260 32
4 160 80 150 1,820 5,430 7,430 4,080 
3,340 22,100 32
5 160 0 150 1,570 2,300 6,460 5,160 
6,160 21,640 28
6 160 80 0 1,600 4,420 6,320 3,180 
5,510 21,020 33
Soil test P = 38 (low); soil test K -- 236 (medium).
Variety, Homestead 24.
S80 pounds P - 180 pounds P205.
150 pounds K - 180 
pounds K
2
0.
TABLE 4. EFFECT OF FERTILIZER TREATMENTS ON TOMATO YIELDS, JAMES BEDSOLE'S FARM, 1970'
No. Treatment, lb./acre Marketable 
fruit per acreC
N P K June 4 June 10 June 16 
June 25 June 30 Total
Lb. Lb. Lb. Lb. Lb. 
Lb. Pct.
1 0 80" 150' 390 1,730 
4,470 2,940 5,510 15,030 13
2 50 80 150 330 1,110 4,480 
2,610 4,860 13,400 13
3 100 80 150 560 930 4,420 
2,350 6,440 14,690 8
4 160 80 150 460 1,000 4,220 
2,360 5,880 13,930 14
5 160 0 150 170 850 
2,990 2,760 5,740 12,500 11
6 160 80 0 50 1,610 3,510 
2,830 6,700 14,690 10
Soil test P - 56 (medium); soil test K - 148 (medium).
2 Variety, Manapal.
280 pounds P - 180 pounds P
2
0.
150 pounds K - 180 pounds K
2
0.
Bedsole farm (Table 4). Tomatoes at this location
were staked but not irrigated. Rates of N had no
effect on yield. Without phosphorus fertilizer the
yield was 90 per cent, but omitting potassium fertil-
izer had no effect. Soil-test values for both P and K
were "medium."
Cull tomatoes ranged from a low of 8 per cent for
100 pounds of N to a high of 14 per cent for 160
pounds of N. For the other treatments, culls ranged
from 10 to 13 per cent.
SIZES OF TOMATOES
Tomatoes are marketed by sizes according to di-
ameter measurements. Tomatoes in these experi-
ments were sorted into three size categories: 5 X 6
and larger-minimum diameter of 2 11/16 inches;
size 6 X 6-diameter ranging between 2 14/16 and
2 8/16 inches; and size 6 X 7 and smaller -ranging
from 2 10/16 to 2 inches.
The different fertilizer treatments had an effect on
the size of tomatoes produced at some locations, Ta-
bles 5-8. At the Keel farm, for example, the fewest
large tomatoes were on plots receiving no phosphorus
fertilizer. This treatment, together with plots receiv-
ing 0 N, also had the lowest yield of intermediate size
TABLE 5. TOTAL YIELD OF TOMATOES BY SIZES,
KEEL'S FARM, 1970
Marketable fruit per acre
Treatment, lb./acre
No. 
N 
P 
K
0
50
100
160
160
160
80
80
80
80
0
80
150
150
150
150
150
0
Size
and
larger
Lb.
5,640
6,630
6,920
6,150
3,120
5,360
Size
Size 6 X 7
6 X 6 and
smaller
Lb. Lb.
5,020 7,800
5,990 6,820
7,420 9,280
6,440 12,160
4,880 8,630
8,340 8,190
TABLE 6. TOTAL YIELD OF TOMATOES BY SIZES,
GREEN'S FARM, 1970
Marketable fruit per acre
No. 
Treatment, 
lb. /acre
N P K
80
80
80
80
0
80
150
150
150
150
150
0
Size
and
larger
Lb.
1,760
3,850
3,120
,3,060
3,860
2,440
Size
Size 6 X 7
6 X 6 and
smaller
Lb. Lb.
4,910 7,790
6,640 8,320
6,240 7,380
6,990 8,370
6,320 6,920
6,100 7,830
TABLE 7. TOTAL YIELD OF TOMATOES BY SIZES,
ADKISON'S FARM, 1970
No. Treatment, lb./acre
N P K
1
2
3
4
5
6
0
50
100
160
160
160
80
80
80
80
0
80
150
150
150
150
150
0
Marketable fruit per acre
Size Size
5 X 7 Size 6 X 7
and 6 X 6 and
larger smaller
Lb. Lb. Lb.
10,530 8,050 4,510
10,680 9,180 4,720
9,480 8,730 4,050
9,830 8,060 4,200
9,120 7,890 4,630
8,030 8,970 4,020
TABLE 8. TOTAL YIELD OF TOMATOES BY SIZES,
BEDSOLE'S FARM, 1970
No. 
Treatment, 
lb./acre
N P K
0
50
100
160
160
160
80
80
80
80
0
80
150
150
150
150
150
0
Marketable fruit per acre
Size Size
5 X6 Size 6,X7
and 6 X 6 and
larger smaller
Lb. Lb. Lb.
3,280 5,920 5,830
3,180 5,450 4,770
3,010 5,600 6,070
2,520 5,320 6,090
1,950 5,030 5,520
2,440 5,970 6,280
tomatoes (6 X 6). As the N rate was raised from 50
to 160 pounds per acre the yield of small size fruit
(6 X 7) increased. At the Green farm, the 0 N plots
had the lowest yield of large tomatoes, whereas the
0 phosphorus plots and plots receiving 50 pounds of
N had the highest yield of large size fruit. Fertilizer
rates did not appear to affect fruit sizes at the Adki-
son and Bedsole farms.
SUMMARY
Test areas were located on farmers' fields that
tested "low" or "medium" in phosphorus and potas-
sium. An application of phosphorus fertilizer in-
creased yield by as much as 33 per cent on a soil
"low" in P and adding potassium raised the yield by
as much as 12 per cent. That phosphorus or potas-
sium fertilizer improved early growth and produc-
tion of tomatoes was observed at three locations.
The effect of fertilizer nitrogen varied from one
location to another. Overall, the response in 1970
indicated that 100 pounds of fertilizer N was ade-
quate for optimum yields. The 100-pound N rate
was the treatment having the lowest percentage of
culls at three of the four locations.
0
50
100
160
160
160
,,,