J. AMER. Soc. HORT. SCI. 115(2):245-251. 1990.
Nitrogen Fertilizer Management Practices to
Enhance Seed Production by ‘Anaheim Chili’
J.O. Payerol and M.S. Bhangoo2
Califomia Agricultural Technology Institute, California State University, Fresno, CA 93740
National Forage Seed Production Research Center, Agricultural Research Service, U.S.
Department of Agriculture, 3450 SW Campus Way, Oregon State University, Corvallis, OR 97331
Additional index words. Capsicum annuum var. annuum, reproductive development, pure-live seed, seed germination,
nitrogen-use efficiency, petiole nitrate-nitrogen
Abstract. The effects of six applied N treatments differing by rates and frequencies of application on the yield and
quality of pepper (Capsicum annuum var. annuum L. ‘Anaheim Chili’) grown for seed was studied. The timing of N
applications was based on crop phenology, leaf petiole nitrate-nitrogen concentrations (NO3-N) minimum thresholds,
and scheduled calendar applications of fixed amounts of N. Solubilized NH4NO3 was applied through a trickle-
irrigation system to ensure uniform and timely applications of N. Rate of mature (green and red) fruit production
was unaffected by any treatment except weekly applications of 28 kg·ha-l of N, which stopped production of mature
fruit before all other treatments. Early season floral bud and flower production increased with increasing amounts
of N. The two highest total N treatments produced more floral buds and flowers late in the season than the other
treatments. Total fruit production was maximized at 240 kg N/ha. Differences in total fruit production due to frequency
of N application resulted at the highest total N level. Red fruit production tended to be maximized with total seasonal
applied N levels of 240 kg·ha-1 and below, although weekly applications of N reduced production. Total seed yield
was a function of red fruit production. Pure-1ive seed (PLS) production was a function of total seed production.
Nitrogen use efficiency (NUE) for red fruit production also decreased with N rates >240 kg·ha-1, but PLS yield and
NUE decreased in a near-linear fashion as the amount of total seasonal applied N increased, regardless of application
frequency. Season average NO3-N (AVE NO3-N) values >4500 mg·kg-1 had total seed and PLS yields less than those
treatments <4000 mg·kg-l. Six-day germination percentage was reduced with weekly N applications of 14 kg·ha-1.
Seed mass was reduced with weekly N applications of 28 kg·ha-1. Final germination percent, seedling root length
and weight, and field emergence were unaffected by any of the N treatments. These findings indicate that different
N management strategies are needed to maximize seed yield compared to fruit yield and, therefore, there may be an
advantage to growing ‘Anaheim Chili’ pepper specifically for seed.
It is well-established that N influences the growth and de-
velopment of pepper grown for fruit. This effect-depends on the
available N in the soil and on the amount of applied N (Cochran,
1936; Maynard et al., 1962; O’Sullivan, 1979; Panpruik et al.,
1982; Piazza and Venturi, 1971; Relwani, 1963; Somos et al.,
1976; Stroehlein and Oebker, 1979; Sundstrom et al., 1984).
However, results are related to production region. Maximum
fruit production has been achieved with applications as low as
70 kg.ha-l (O’Sullivan, 1979) to as high as 224 kg.ha-l (Lo-
cascio and Fiskell, 1977).
Recommendations for N fertilization of peppers grown in Cal-
ifornia are 170–225 kg·ha-1 (Sims and Smith, 1984). ‘Anaheim
Chili’ peppers respond to 224 and 336 kg·ha-1
, depending on
the amount of N already present in the soil (Ririe, 1977). De-
pending on specific location conditions, commercial producers
of ‘Anaheim Chili’ peppers in California use between 56 and
336 kg·ha-1 (C. Mouwen, personal communication, 1989).
Received for publication 5 June 1989. Contribution of California Agricultural
Technology Institute, California State Univ., Fresno, and USDA/ARS. Cali-
fornia Agricultural Technology Institute technical paper no. 900605. This study
was supported in art by a grant from Gentry Foods Corporation. Mention of
trade names in this publication does not imply endorsement by California State
Univ. or USDA/ARS. The cost of publishing this paper was defrayed in part
by the payment of page charges. Under postal regulations, this paper therefore
must be hereby marked advertisement solely to indicate this fact.
lForrner Graduate Research Assistant.
2Professor. Dept. of Plant Science and Mechanized Agriculture, California State
Univ., Fresno, CA 93740.
Use of plant tissue N concentrations provides a means to
evaluate the N nutrient status and effectiveness of applied N in
relationship to that available in the soil. Several accounts relate
plant tissue N concentration in pepper to plant growth, devel-
opment, and fruit maturity. These reports are difficult to com-
pare because different plant parts were sampled for total N or
NO3-N analysis. Young leaves and leaf petioles tend to contain
higher NO3-N than older leaves and other plant parts. Addi-
tionally, varying plant tissue NO3-N were obtained with similar
amounts of applied N, indicating that different amounts of N
were available to the crop from the soil N reserve in addition
to the applied N. Also, geographical location appears to greatly
influence the findings. Thus, Thomas and Heilman (1964) re-
ported that, under greenhouse conditions, the critical total leaf
N concentration (including NO3-N) was 40,000 mg·kg-1
enz and Tyler (1983) in California specified deficient and suf-
ficient leaf petiole NO
-N that relate to early growth (first bloom),
early fruit set, and full fruit size. The recommended ranges were
5000-7000, 1000-1500, and 750-1000 mg·kg-1
Another report from California showed that 224 to 336 kg·ha-1
of applied N was required to meet these recommended leaf
petiole NO3-N levels (Ririe, 1977). In Arizona, stem tissue NO3-
N of 8000–10,000 mg·kg-1 at heavy fruit set were reported not
sufficient to produce high yields of fruit. This level was achieved
with a minimum of 100 kg applied N/ha. Nitrogen deficiency
was noted when NO3-N fell below 2000 mg·kg-1 (Stroehlein
and Oebker, 1979). Panpruik et al. (1982) indicated that leaf
petiole NO3-N should be maintained at 4000 mg·kg-1 through
J. Amer. Soc. Hort. Sci. 115(2):245-251. 1990.
mid-season to avoid fruit yield reductions in New Mexico.
O’Sullivan (1979) in Ontario, Canada, showed that fruit yields
were reduced when leaf petiole NO3-N fell below 4000 mg·kg-1.
This level was achieved with 35 to 70 kg·ha-1. Thomas and
Heilman (1967) reported from Texas that total plant dry matter
production was restricted below 40,000 mg·kg-1 as a result of
<134 kg·ha-1 of N being applied before planting.
Little research has been done to determine the effects of N
fertility on the yield and quality of pepper grown for seed. Gill
et al. (1974) reported that an increase in applied N from 0 to
370 kg·ha-1 did not produce a proportional increase in seed
yield. Since the production of seed is not of concern when
producing market fruit, it is important to understand the effects
of N fertilization on pepper grown specifically for seed. Much
of the ‘Anaheim Chili’ pepper seed produced is a bypass product
from commercial food product processing (C. Mouwen, per-
sonal communication). This study was undertaken to determine
the effect of N treatments on the reproductive development and
seed production of ‘Anaheim Chili’ peppers grown specifically
for seed. The treatments used were based on crop phenology,
leaf petiole NO3-N minimum thresholds, or calendar application
schedules of fixed N amounts.
Materials and Methods
Field experiment and analyses. The study was conducted on
a Hanford sandy loam soil (coarse-loamy, mixed, thermic Typic
Xerothent) at California State Univ., Fresno. The experimental
area had been uniformly cropped with carrot grown for seed the
previous season. ‘Anaheim Chili’ pepper seeds were planted 16
May 1986 (day 136) in two rows 20 cm apart on preshaped 1-
m-wide beds. Each plot consisted of four beds 14 m long. The
experimental area was sprinkle-irrigated until seedling emer-
gence. The plants were thinned to 25 cm within each planting
row on 11 June (day 162). Irrigation water was then applied by
a Netafim drip irrigation system (Fresno, Calif.) consisting of
laterals placed on the center of each bed with in-line, turbulent-
flow emitters spaced every 50 cm along the lateral, each dis-
charging 2 liters·hr-1. Water applied to each treatment was mea-
sured using 19-mm flow meters to ensure uniform water and
fertilizer applications to the various treatments. Irrigation water
was applied when tensiometer readings were between 0.030 and
0.035 mPa at 40-cm soil depth, about every 5 to 7 days, de-
pending on the weather.
A blanket application of 30N–90P2O5–112K2O (kg·ha-1) in
a concentrated stock solution was made 13 June (day 164) through
the trickle-irrigation system. Six applied N treatments in the
form of NH4NO3, which differed by rates and frequencies of
application, were replicated four times (Table 1). The treatments
were based on crop phenology (70-3X = 70 kg·ha-1 at estab-
lishment, early fruit set, and full fruit size); leaf petiole
NO3-N minimum thresholds (35-5K = 35 kg·ha-1 whenever
NO3-N decreased to 5000 mg·kg-1; 35-2K = 35 kg·ha-1 when-
ever NO3-N decreased to 2000 mg·kg-1; and 70-5K = 70 kg·ha-1
whenever No3-N decreased to 5000 mg·kg-l); or fixed N rates
applied on a calendar schedule (14-W = 14 kg·ha-1. week-1
and 28-W = 28 kg·ha-l·week -1). The total seasonal applied
N for the six treattments was 240, 275, 170, 310, 170, and 310
kg·ha-1, respectively. Solubilized NH4NO3 was injected into
the irrigation system through Venturi injectors to establish the
variable N treatments. The amounts of total applied N corre-
sponded with a range commonly used for ‘Anaheim Chili’ pep-
pers grown in California.
Fifty leaf petioles from fully expanded young leaves (Lorenz
and Tyler, 1983) were sampled at random between 1100 and
1300 HR from each plot about weekly from 8 July (day 189) to
27 Sept. (day 260) for NO3-N determination. One-half gram of
ground material was extracted with 50 ml of 0.1 M aluminum
sulfate for 0.5 hr. Nitrate-N concentration was determined with
an ion selective electrode.
About every 14 days beginning 14 July (day 195) and ending
3 Sept. (day 247), five plants were chosen at random, uprooted,
and the number of flower buds, flowers (fully opened), fruit
buttons (structures formed following pollination when petal fall),
and set fruit (both developing and mature) were counted for
each experimental unit. At maturity (3 Oct., day 276), total
fruit yield (red and green fruits, both full-sized) was obtained
for a once-over harvest from 6 m of row from the two middle
rows of each plot. Red fruits were separated from green and
both were weighed. Seeds were extracted from the red fruits
with a modified version of a mechanical fruit crusher (Wehner
et al., 1983). The seeds were then washed with a seed cleaning
sluice (Steiner and Letizia, 1986), separated into fractions that
either sank or floated, and dried at 31C to constant weight ( 10%
moisture) in a forced-air seed drier. The seeds were then cleaned
using a continuous flow aspirator and weighed to determine total
seed yield and seed mass. Seed germination was determined
according to AOSA rules (Association of Official Seed Ana-
lysts, 1978), with counts made on days 6 (early count germi-
nation) and 14 (final count germination). Pure-live seed was
determined by multiplying seed yield by final count germination
(Copeland and McDonald, 1985). Seedling root length and
seedling dry weight were also determined. Three 100-seed rep-
licates from each experimental unit were seeded 1 cm deep and
2 cm apart on 1-m-wide beds on 1 Apr. 1987 to determine field
emergence. The area was sprinkler-irrigated daily to maintain
uniform soil moisture. Final seedling emergence was deter-
mined when all emerged seedling had reached the first true leaf.
Total and red fruit, and total seed and PLS yield N use ef-
ficiency (NUE) were calculated as the yield of the respective
components per amount of total N applied for each treatment.
Results and Discussion
Reproductive development. Initial flower bud production (day
195) was relatively unaffected by the different treatments (Fig.
la). The number of flower buds present at day 203 was pos-
itively related to the amount of total applied N to that time.
This result agrees with the findings of Cochran (1936) and May-
J. Amer. Soc. Hort. Sci. 115(2):245-251. 1990.
nard et al. (1962) for a first set of fruit, although no effect was
observed for the average over two harvests. Maximum flower
bud and flower load (Fig. lb) was reached by the time of max-
imum fruit set (day 231; Fig. 1c) for all treatments except 70-
5K, which had achieved maximum load by early fruit set (day
217). Flower bud and flower production by day 247 were greater
for treatments 28-W and 70-5K (both receiving the greatest amount
of total applied N for all treatments, 310 kg·ha-1, compared to
all other treatments (Fig. 1 a and b). Maximum new fruit set
(buttons) was achieved by day 231 for all treatments, with the
rate of new fruit production decreasing after this time (Fig. 1c).
The number of fruit that had set (achieved a minimum length
of 2 cm) continued to increase through day 247 for all treatments
except 28-W, which reached maximum fruit production at day
217, the time of initial full fruit sizing (Fig. id). This was the
only substantial modification in plant phenology caused by the
different treatments. The weekly application of N at 28 kg-ha-1
appeared to allow continual initiation of floral structures (Fig.
1a), but hindered further flowering (Fig. 1b) and fruit set (Fig.
1d). This finding has not been noted in other reports were high
N levels were used, and maybe due to the high (weekly) fre-
quency of application.
The relative equal time of initial bud formation and flowering
for all treatments is in agreement with the findings of Thomas
and Heilman (1967), but contrary to Gill et al. (1974), who
found flowering to be delayed with increasing levels of applied
N. The initial increase in number of flower buds and flowers
with increasing amount of N also agrees with Cochran (1932)
and Thomas and Heilman (1967).
At final harvest (day 276), 70-3X produced the greatest amount
of total fruit (red and green) of all the treatments (Fig. 2).
Treatment 28-W was the lowest-yielding, with the remaining
treatments being intermediate and roughly decreasing in order
according to increasing frequency and amounts of applied N.
Treatment 70-5K, which received the same total seasonal ap-
plication of N as 28-W, yielded more total fruit. This result
indicates that frequency of application affected plant perform-
ance and that total fruit yield is not a simple function of total
applied N. The decrease in fruit yield with the higher levels of
N is in agreement with the findings of Ahmed (1984), Piazza
and Venturi (1971), Thomas and Heilman (1967), and Stroeh-
Iein and Oebker (1979). The absence of change in fruit yield,
with differing levels of applied N below 210 kg·ha- 1
with O’Sullivan (1979) and Panpruik et al. (1982).
Red fruit yield was the highest for 70-3X and 35-2K and the
lowest for 28-W. Treatments 35-5K, 70-5K, and 14-W were
intermediate in their responses (Fig. 2). A very weak negative
relationship existed between red fruit yield and total applied N,
with maximum red fruit production at 240 kg·ha-1. Applica-
tions of N in excess of 240 kg·ha-1 decreased red fruit produc-
tion. When N at 170 kg·ha-1 was applied in either weekly
application (as in the 14-W treatment), or when petiole N levels
were 2000 mg·kg-1 (as in the 35-2K treatment), the effects on
fruit production were different. Greater red and total fruit yields
were realized when N was applied to maintain petiole NO3-N
levels >2000 mg·kg-1
Total and red fruit NUE decreased as the amount of applied
N increased (Fig. 3a). Total applied N in excess of 240 kg·ha-1
reduced NUE for both fruit classes. The effect of frequency of
application on total and red fruit NUE was not as clearly defined
as it was for the respective component fruit production.
Seed quality. Six-day germination percent, which is a mea-
J. Amer. Soc. Hort. Sci. 115(2):245-251. 1990.
sure of seedling vigor, was greatest for 70-5K and 35-2K but
least for 14-W (Table 2). The other three treatments were in-
termediate in their early germination response. The frequency
of application for the two highest total seasonal applied N treat-
ments (28-W and 70-5K) did not affect early count germination
percentages (Table 2). However, seedling dry weight, root length,
and field emergence, which also are indicators of seed vigor,
were not affected by the different N treatments. The absence of
a relationship between 6-day germination percent and these other
indicators of vigor suggests that N fertility has little if any affect
on seed vigor. Final germination percent (14-day) was not af-
fected by any of the applied N treatments.
Seed mass was related more to PLS yield (R2 = 0.864) than
total seed yield (R2 = 0.779) (Fig. 4). The 28-W treatment
produced the lightest seeds and had the lowest PLS yield of all
treatments. This relationship indicates that plant N status affects
both seed yield (see Fig. 6 a and b) and individual seed mass
(Fig. 4). Since red fruit production was also greatly reduced in
this treatment (Fig. 2), it appears that the weekly applications
of N at 28 kg·ha-1 were detrimental to ‘Anaheim Chili’ pepper
Seed yield components and seed yield relationships. Produc-
tion of red fruit (which produce viable seeds) was a linear func-
tion of total fruit yield (Fig. 5a). However, both total and PLS
yields were nonlinear functions of red fruit yield and were max-
imized at a yield of 8 t·ha-1 or higher (Fig. 5b). Thus, max-
imum seed yields are not equated with maximum red fruit
production. Since final count seed germination percent was not
affected by any of the treatments, PLS production was a linear
function of total seed production (r2 = 0.977; P = 0.004).
Therefore, maximum PLS yield was obtained by maximizing
total seed production.
Total and PLS yields were functions of total applied N (Fig.
6a). Applied N rates >240 kg·ha-l resulted in decreased seed
yields. Treatments 35-2K, 14-W, and 70-3X produced the great-
est amounts of total and pure-live seed, 28-W produced the
least, and 35-5K and 70-5K were intermediate in their re-
sponses. Frequency of application was important only at the
J. Amer. Soc. Hort. Sci. 115(2):245-251. 1990.
high total N level, indicated by the lower total and PLS seed
yield for treatment 28-W compared with 70-5K (Fig. 6a). Total
seed and PLS yields were more closely related to total applied
N (R2 = 0.893 and 0.851, respectively) than total and red fruit
yields (R2 = 0.393 and 0.658, respectively). Both total seed
and pure-live seed NUE decreased in a near linear fashion as
total applied N increased and were not influenced by frequency
of application (Fig. 3b). This result differs from the response
for total and red fruit NUE, which did not decrease until >240
kg N/ha was applied and was affected by frequency of appli-
cation (Fig. 3a). The absence of a positive relationship between
seed yield and N is contrary to the findings of Gill et al. (1974).
Leaf petiole N03-N and its relationship with reproductive
development and fruit and seed yield. Leaf petiole NO3-N gen-
erally increased rapidly within 1 week of application of N at 35
kg·ha-1 or more and then decreased the following week (Fig.
7). Weekly applications of 14 kg-ha-l maintained a relatively
constant leaf petiole N03-N status <2000 mg·kg-1, indicating
a possible maintenance level of N required by the crop through-
out the growing season. Weekly applications of 28 kg·ha-1
resulted in a gradual, steady increase in leaf petiole NO3-N
through the season.
Each single application of 70 kg·ha-1 was adequate to raise
the petiole NO3-N above 5000 mg-kg-1 (treatments 70-3X and
70-5 K). For three cycles of application, two consecutive weekly
applications of 35 kg·ha-1 (treatment 35-5K) were needed to
raise the petiole NO3-N to the 5000 mg·kg -1 level. Single ap-
plications of this same amount (treatment 35-2K) were not suf-
ficient to reach the 5000 mg·kg -1 level at any time during the
experiment, except for the N application during early plant es-
tablishment (day 184).
Previous research has reported critical plant tissue NO3-N
levels of at least 4000 mg·kg-1 to be necessary to maintain fruit
yields (O’Sullivan, 1979; Panpruik et al., 1982). In this study,
AVE NO3-N >4000 mg·kg-1 were obtained with treatments
28-W, 70-5K, 70-3X, and 35-5K (Fig. 1). Treatments with
AVE NO3-N values >4500 mg·kg -1 had total and pure-live
seed yields lower than those treatments <4000 mg·kg-1 (with
the exception of 70-3X PLS, which was intermediate to the two
groups) (Fig. 6b). Treatment 28-W, the most detrimental treat-
ment in regards to both fruit and seed production, had the sec-
ond-highest AVE NO3-N of all treatments. Treatment 70-3X
had the highest total fruit yield and along with treatment 35-2K
the highest red fruit yields.
Overall, leaf petiole NO
-N was unrelated to number of flower
buds, flowers, button fruit, and total fruit on the plant at any
time during the experiment and therefore was not suitable as a
predictor of reproductive status (data not shown). There was
also no relationship between AVE NO3-N and total or red fruit
yield (data not shown). Treatment 70-5K had the highest AVE
NO3-N and received the same total amount of N as 28-W, but
had a higher total and PLS yields (Fig. 6b). This substantiates
that frequency of N application affects pepper plant growth.
Treatments 14-W and 35-2K had the highest seed yields with
treatment 70-3X intermediate to the higher and lower seed-yielding
groups (Fig. 2).
These findings indicate that total seed and PLS yield are af-
fected by both total applied N and frequency of application.
J. Amer. Soc. Hort. Sci. 115(2):245-251. 1990.
Both total and red fruit production appear to be affected more
by timing and frequency of N applications than by total seasonal
applied N. Total fruit yield was maximized at 240 kg N/ha,
while red fruit, total seed, and PLS yields decreased with in-
creasing N. The greatest efficiency of seed production was ob-
tained from 170 kg N/ha or with AVE NO3-N values <4000
. Different N management strategies should be consid-
ered to maximize seed yield and NUE compared to total fruit
yield. Petiole NO3-N content can be used as an indicator of
‘Anaheim Chili’ pepper crop N status for seed production, but
further research is needed to determine exact N fertility strate-
gies needed for maximum seed production by this cultivar.
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