Suelo y La Nutricion[1]

7/30/2019 Suelo y La Nutricion[1]

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DIVISION S-4SOIL FERTILITY& PLANT NUTRITION

Salinity and Nitrogen Rate Effects on the Growth and Yield of Chile Pepper Plants

Magdalena Villa-Castorena, April L. Ulery,* Ernesto A. Catalan-Valencia, and Marta D. Remmenga

ABSTRACT and increase the negative effects of soil salinity onplant performance.Salinity and low soil N availability are important growth limiting

Studies of plant growth responses to N andsoil salinityfactors for most plants. Our objective was to determine the influenceduring the whole plant life cycle are important to revealof different N fertilization rates and soil salinity levels on the growth

and yield of chile pepper plants (Capsicum annuum L.) grown in a whether the amount of N applied alleviates or aggra-greenhouse in sandy loam soil for 2 yr. The targeted soil salinity levels vates the detrimental effects of salinity during specificwere 1.3, 3.5, and 5.5 dS m1 in 1999, and 1.3, 3.0, 4.5, and 6.0 dS m1 growth stages. In addition, examining plant growth dur-in 2000 as electrical conductivity of the saturated paste extract (EC e). ing the whole growing season provides informationTotal N application rates were 80, 140, and 200 kg ha1 in 1999, and about crop salt tolerance over time. Plant response to30, 90, and 150 kg ha1 in 2000. Nitrogen rates of 140 kg ha1 or more

salinity changes with age, plant development, and growthincreased soil salinities, in some cases by as much as 4 dS m1. Soil

stage (Maas, 1993). For example, Arshi et al. (2002)salinity decreased plant relative growth rate (RGR) up to first maturereported that senna (Cassia angustifolia Vahl.) was mostpod stage. After this growth stage however, salinity increased the

sensitive to salinity at the post-flowering stage.RGR. Low and medium N rates produced the maximum RGR up to Relative growth rate allows one to make more appro-the first mature pod stage. After this growth stage, the maximumRGR was achieved with the medium and the high N rates tested in priate comparisons of plant growth among salinity treat-1999 and 2000, respectively. Increasing N rates and salinity levels ments than absolute growth rate (Cramer et al., 1994).interacted to reduce chile pod yield in 1999, and acted independently The RGR gives a relative basis on which to comparein 2000. This study indicates that over-fertilization during early plant growth rates of plants since it takes into account bothdevelopment may contribute to salinity and decreased pod yield. the initial and ending plant weights over a specified timeWhile salt-stressed chile performs well when adequately fertilized, N

period (Hunt, 1990). The RGR is a function of theshould be applied in amounts that increase with plant need over the

net assimilation rate (NAR), which is an index of thegrowing season.photosynthetic-assimilatory capacity of the plant perunit leaf area, and the leaf area ratio (LAR), which isan index of the leafiness of the plant (Hunt, 1990).

Soil salinity is an important growth-limiting factor Chile pepper is one of the three most important sola-for most non-halophytic plants. Salts inhibit plantnaceous vegetable crops in the world (Hedge, 1997) asgrowth by osmotic stress, nutritional imbalance, andwell as being a major crop in New Mexico and otherspecific ion toxicity (Alam, 1994; Jacoby, 1994; Gunessouthwestern states (Johnson, 1999). It is classified as

et al., 1996; Cornillon and Palloix, 1997). Soil salinity ismoderately sensitive to soil salinity (Maas and Hoffman,

being progressively exacerbated by agronomic practices1977). Studies on chile pepper responses to salinity and

such as irrigation and fertilization, especially in aridto fertilizer application under saline conditions through-regions. The proper use of N fertilizer in all soils isout the growing season are scarce. Therefore, the objec-

important, but particularly so in saline soils where Ntive of this work was to determine the influence of

might reduce the adverse effects of salinity on plantdifferent N fertilization rates and soil salinity levels on

growth and yield (Shen et al., 1994; Soliman et al., 1994;the growth, evaluated at three different plant growthAlbassam, 2001; Flores et al., 2001) depending on plantperiods, and yield of chile pepper plants.species, salinity level, or environmental conditions

(Grattan and Grieve, 1999). On the other hand, overMATERIALS AND METHODSfertilization with N may contribute to soil salinization

This study consisted of two greenhouse experiments con-ducted at New Mexico State University during the 1999 and

M. Villa-Castorena and E.A. Catalan-Valencia, CENID-RASPA-INI- 2000 growing seasons. Sandia chile pepper seedlings thatFAP Apartado Postal No. 41, Cd. Lerdo, Dgo., Mexico 35150; A.L.were 6 wk old and 15 cm tall were transplanted on 29 May

Ulery, Dep. of Agronomy and Horticulture, New Mexico State Uni-1999 and 12 May 2000 into 15-L (4-gal) black polyethyleneversity, MSC 3Q, P.O. Box 30003, Las Cruces, NM 88001; M.D. Re-pots. This chile cultivar is long-fruited, of medium maturationmmenga, New Mexico State University Statistics Center, MSC 3CQ,time, and commonly used in local industry. Each pot wasP.O. Box 30003, Las Cruces, NM 88001. Contribution of the New

Mexico Agricultural Experiment Station with additional funding by filled with 20 kg of non-saline Brazito sandy loam soil (Mixedthe New Mexico Chile Commission. Received 9 Nov. 2001. *Corre-sponding author ([email protected]).

Abbreviations: DAT, days after transplanting; ECe, electrical conduc-tivity of the saturated paste extract; LAR, leaf area ratio; NAR,Published in Soil Sci. Soc. Am. J. 67:17811789 (2003).

Soil Science Society of America net assimilation rate; RGR, relative growth rate; TDM, total drymatter yield.677 S. Segoe Rd., Madison, WI 53711 USA

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1782 SOIL SCI. SOC. AM. J., VOL. 67, NOVEMBERDECEMBER 2003

thermic Typic Torripsamment) collected fromthe upper 15 cm Plants were cut at the soil surface, stems and leaves wereof a local agricultural field before starting each experiment in individually collected, and roots were separated from the soil1999 and 2000. One chile plant was grown in each pot. with a gentle spray of tap water. Leaf area was measured for

Different rates of N and salinity levels were tested in both each plant with a LI-COR LI-2000 portable leaf area meteryears. In 1999, the rates of N were 80, 140, and 200 kg ha1, (LI-COR Inc., Lincoln, NE). Each plant component waswhich correspond to 2.1, 3.7, and 5.4 g N per plant in terms washed with distilled water, dried in a forced air oven at 80Cof plant population density. These amounts of N were esti- for 48 h, and weighed.mated with a population density of 37 000 plants ha1. Com- Plant growthwas evaluatedin terms of RGR, andits compo-

mercial grade NH4NO3 was used as the N source and was nents of NAR and LAR. These were estimated as mean valuesapplied in the irrigation water in four equal quantities at 0, over the time interval T1 to T2 according to Hunt (1990) using15, 35, and 65 d after transplanting (DAT), according to com- the following equations:mon field practices used by local farmers.

The salinity levels, measured as the ECe, were created with RGR ln(W2) ln(W1)

T2 T1[2]

NaCl and CaCl2, which were dissolved in deionized water atan equivalent ratio of 1:1, and applied to each pot 1 d beforetransplanting. In 1999, the intended salinity levels were 1.25(no salts added), 3.5, and 5.5 dS m1. These values changed NAR

(W2 W1)[(ln(LA2) ln(LA1)]

(T2 T1)(LA2 LA1)[3]

throughout the plant-growing season due to the addition ofN fertilizer and the uptake of salts by plants. There was nodrainage or leaching through the pots.

LAR 0.5 LA1W1 LA2W2

[4]In the 1999 experiment, the high N rate contributed to soilsalinity and had a detrimental effect on plant performancewhile the low and medium N rates produced similar plant where LA, T, and Wrepresent leaf area per plant (cm2), time

responses to each other. Therefore, to investigate a lower N (days), and total plant dry weight (g) respectively. Subscriptsrange, the N treatments were reduced to 30, 90, and 150 kg 1 and 2 refer to the values of the variable measured at twoha1 in the 2000 experiment, corresponding to 0.8, 2.4, and successive harvests (1 initial, 2 final). Relative growth4.0 g N plant1. An additional soil salinity level was also added rate is expressed in mg g1 d1, NAR in mg cm2 d1, andfor a more detailed coverage of this factor. The target ECe LARin cm2 g1. Chile pods were collected between the secondvalues tested in 2000 were 1.25, 3.0, 4.5, and 6.0 dS m1. and the third growth stages to evaluate marketable yield.

The amount of each salt required to generate each salinity Plants were irrigated by hand with deionized water (EClevel was estimated by the following equation: 0.015 dS m1) every other day at the beginning of the growing

season, and daily during the period of high evaporative de-mand. Two or three pots of each treatment were weighedA

(10ECe)(EW)(PSV)

2[1]

daily to determine the amount of water needed to raise thesoil water content to field capacity and to prevent drainage.

where A was the amount of each salt (NaCl or CaCl2) added Plant growth and yield data collected at each growth stageto the pot in mg, ECe was the intended or target salinity in were subjected to analysis of variance as a factorial experi-dS m1, the constant 10 is an empirical factor used to convert

ment. Because of the large number of pair-wise tests that wereECe in dS m

1 to total dissolved salts in the soil saturatedperformed, Duncans tests at 0.05 were made to determinepaste extract in meq L1 (Dudley, 1994), EW is the equivalentdifferences among treatments of plant dry matter accumula-

weight of each salt in mg meq1, and PSV is the pot soiltion, RGR, NAR, and LAR. Analysis of correlation between

saturation volume in liters. Since two salts were used, weRGR and the variables NAR and LAR were made to deter-

divided the numerator by 2 to consider the contribution ofmine the most influential physiological processes determining

each salt to ECe. The PSV was calculated from soil porosity, plant growth. Statistical analysis was performed using PROCwhich was estimated from the measured soil bulk density (Jury

GLM and PROC CORR from SAS software version 8.0 (SASet al., 1991).

Institute Inc., 1992).A randomized complete block design with nine replications

was used as the experimental design in both years. Each blockincluded nine treatments in 1999 (81 pots), and 12 treatments RESULTS AND DISCUSSIONin 2000 (108 pots), as a 3 3 and 3 4 factorial arrangement,respectively. At each of three growth stages, three blocks (for Nitrogen Application Rate Affects Soil Salinitya total of 27 pots in 1999 and 36 pots in 2000 at each stage)

Nitrogen fertilizer treatments affected soil salinitywere randomly selected to obtain ECe and plant data (de-measured as ECe (Fig. 1). Increasing N rates increasedscribed below). The plants were harvested at the onset ofsoil salinity levels measured at three plant growth stagesflowering, first mature pods, and onset of leaf senescence.in both years. In 1999, N rates of 140 and 200 kg ha1Plant flowering onset occurred at 35 and 40 DAT; first mature

pods started at 65 and 70 DAT; and leaf senescence began at increased the initial soil salinity by an average value of110 and 120 DAT, respectively for 1999 and 2000. Ten seed- 0.8 and 1.5 dS m1 respectively at flowering onset, andlings were collected at transplanting time to establish a control 2 and 4 dS m1 at first mature pod stage. However, bybaseline for plant data. the time of leaf senescence, soil salinity had returned

A composite soil sample was taken from each of the above to the initial values in the medium N rate while it wasselected pots to determine ECe. Five soil subsamples were still 2 dS m1 above the initial values in the highest Ncollected from the whole soil pot depth with an auger, com-

treatment (Fig. 1). In 2000, the highest N rate of 150bined, and air-dried. The ECe was determined with an Accu-kg ha1 increased soil salinity by 0.8 dS m1 at floweringmet conductivity meter 50 (Fisher Scientific, Pittsburg, PA),onset and 1 dS m1 at first mature pod stage, but hadafter extracting solution from a saturated soil paste using the

method of the U.S. Salinity Lab Staff (1954). no effect during leaf senescence (Fig. 1). This result was


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VILLA-CASTORENA ET AL.: SALINITY, N RATE, AND CHILE PEPPER PLANTS 1783

Fig. 1. Soil salinity measured as electrical conductivity of saturated soil paste (ECe) in response to targeted salinity treatments and three Napplication rates at (a) flowering onset, (b) first mature pod stage, and (c) leaf senescence stage in 1999 and 2000. Every point is the averageof three replications and the bars are SE.

comparable with that produced by the medium N rate ment than in 1999 as indicated by the distance fromof 140 kg ha1 in 1999. the 1:1 line in Fig. 1. The higher average maximum

Within the same-targeted salinity treatment, there temperatures in the greenhouse (35C in 1999 comparedwas an increase in salinity as a result of N fertilization with 31C in 2000) may have exacerbated the combinedat rates of 140 kg ha1 and higher. The N rates of 80 osmotic effects of added salts and NH4NO3 fertilizer.and 90 kg ha1 tested in 1999 and 2000, respectively, To account for this microclimatic effect, results fromprovided chile plants with adequate N up to the first the 2 yr will generally be reported separately in themature pod stage. Higher N rates left residual N that

following discussion.accumulated with that applied in subsequent fertiliza- Excessive applications of chemical fertilizers havetions and increased temporarily the soil salinity above

been reported as a factor contributing to soil salinitythe targeted values. By the end of the season, N rates

(Rhoades, 1990; Alam, 1994). Optimal rates of N forin excess of 150 kg ha1 contributed to soil salinities

maximum chile pepper yields vary from 70 (OSullivan,above the targeted levels.1979) to 180 kg ha1 (Moreno et al., 1996), dependingDrainage from the pots was prevented to retain theon soil N availability. We tested N rates under and overinitial salts applied to the pots, which also allowed usthese recommended levels and found that 200 kg ha1to investigate the contribution of high fertilization rateresulted in salt accumulation at the end of the growingto salinity and resultant stress. Differences were notedseason. Thus, fertilization above plant requirements notbetween 1999 and 2000 with respect to the influence ofonly increases costs, but can also have detrimental ef-N rate on soil salinity (Fig. 1). In the 2000 experiment,

the targeted and measured salinities were more in agree- fects on the environment such as soil salinity accumula-


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Table 1. Total plant dry matter (TDM in g per plant) as affected by soil salinity and N rate at three plant growth periods in 1999 and 2000.

Total N appliedTarget soil

Year Plant growth period salinity 80 kg ha1 140 kg ha1 200 kg ha1 Mean

dS m1 g plant1

1999At flowering onset 1.3 6.8 9.2 5.6 7.2 a

3.5 4.7 2.6 2.5 3.3 b

5.5 4.4 1.9 1.7 2.7 bMean 5.3 a 4.6 ab 3.3 b

At first mature pods 1.3 75.5 56.1 39.6 57.1 a3.5 44.5 16.8 6.0 22.4 b5.5 25.3 8.9 5.5 13.2 c

Mean 48.4 a 27.3 b 17.0 cAt leaf senescence 1.3 105.8 117.4 100.0 107.7 a

3.5 95.4 103.4 60.6 86.5 b5.5 74.7 47.9 30.3 51.0 c

Mean 92.0 a 89.6 a 63.6 b

2000 30 kg ha1 90 kg ha1 150 kg ha1

At flowering onset 1.3 13.7 16.7 10.6 13.7 a3.0 12.9 14.4 9.0 12.1 ab4.5 9.4 12.8 8.3 10.1 bc6.0 8.1 10.9 7.0 8.7 c

Mean 11.0 b 13.7 a 8.7 cAt first mature pods 1.3 24.2 49.5 38.6 37.5 a

3.0 23.0 31.8 31.0 28.6 b

4.5 20.5 35.3 24.5 26.8 b6.0 16.6 31.7 22.7 23.7 b

Mean 21.1 c 37.1 a 29.2 bAt leaf senescence 1.3 55.4 91.5 153.6 100.2 a

3.0 49.8 111.3 137.4 99.5 a4.5 45.4 95.5 109.4 83.5 b6.0 44.4 95.5 91.1 77.0 b

Mean 48.8 c 98.5 b 122.9 a

Means followed by the same letter are not significantly different within rows and column according to Duncans test (P 0.05, n 3) for each yearand growth stage.

tion or conversely, ground water contamination by onset or first mature pods stage, but at leaf senescence,an interaction was found. The TDM was reduced byleaching.salinity levels of 4.5 dS m1 and above at flowering onsetand leaf senescence and by salinity levels higher than orSoil Salinity and Nitrogen Effects on Total Plantequal to 3.0 dS m1 at first mature pods stage (Table 1).

Dry Matter Accumulation However, the TDM decrease due to soil salinity wasSalinity andN rate both affected total plant drymatter less in 2000 than in 1999 and may have been because

(TDM) accumulation at flowering onset, first mature of lower air temperatures in the greenhouse. The effectspods, and leaf senescence growth stages in 1999. How- of N rate on TDM differed with plant growth stage.ever, no interaction between salinity and N rate was The N rate of 90 kg N ha1 produced the maximumdetected, that is, the effects caused by the N rates did TDM value at flowering onset and first mature podnot depend on the salinity levels and vice versa. Salinity stages. On the other hand, TDM increased with increas-reduced TDM at all three growth stages (Table 1), but ing N rates during leaf senescence, except for the highestat the end of the growing season, at leaf senescence, salinity level of 6.0 dS m1.the relative TDM reductions caused by salinity werelower than those produced at earliergrowthstages. Thus

Soil Salinity and Nitrogen Effectsit appears that the observed recovery of plant growthon Green Pod Yieldtoward the end of theplant cycle is a possible mechanism

of plant adaptation to soil salinity. Increasing amounts In 1999, both salinity and N rate affected pod yield

and an interaction was detected between these factorsof N had a detrimentaleffect on TDM in all plant growthstages in 1999 due to the contribution of N fertilizer to (Fig. 2). Target salinities of 1.25 and 3.5 dS m1 had

similar pod yields, which were higher than the yieldsoil salinity as described in the previous section (Fig. 1).This effect was more pronounced at the first mature obtained with 5.5 dS m1 at the lowest N rate of 80 kg

ha1. However, increasing salinity reduced pod yieldpods stage when the contribution of fertilizer to soilsalinity, specifically N rates of 140 and 200 kg ha1, was much more in soils treated with higher rates of N such

as 140 and 200 kg ha1. This was because high N rateshighest. Thus, high N rates applied during early plantdevelopment may have detrimental effects on dry mat- increased soil salinity beyond the targeted values by up

to 2 and 4 dS m1, respectively, as previously discussed.ter production of chile grown in saline conditions.Salinity and N rate effects on TDM were also ob- In 2000, when the applied N rates were lower than

those tested in 1999, salinity and N rate also affectedserved for the 2000 growing season. No interaction be-tween these two factors was detected at the flowering pod yields but an interaction between them was not


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tion between these two factors detected (Table 2). Dur-ing the first growth period, from transplanting to flow-ering onset, salinity levels greater than or equal to3.5 dS m1 decreased the RGR. From flowering onsetto first mature pods, the RGR was reduced by the targetsalinity ECe of 5.5 dS m1. Conversely, salinity had apositive effect on RGR in the last development period,

from first mature pods to leaf senescence. However,this apparent beneficial effect of salinity on RGR latein the plants life cycle may be because salt-stressedplants delayed their early growth and development andsubsequently continued growing longer into the season,resulting in a higher RGR while nonstressed plants hadalready reached leaf senescence. It is known that salinitystress retards plant growth due to osmotic and specificion effects on metabolic processes such as nutrient up-take and photosynthesis (Alam, 1994). Increasing Nrates from 80 to 200 kg ha1 also reduced the RGRduring the early and middle development periods. Incontrast, N rates of 140 and 200 kg ha1 both increasedthe RGR with respect to 80 kg ha1 toward the end

of the growing cycle, from first mature pods to leafsenescence period (Table 2).

In 2000, soil salinity reduced the RGR during earlyplant development but then caused an increase in RGRduring the last development period (Table 2). Soil salin-ity of 4.5 dS m1 or above decreased the RGR duringtransplanting to flowering onset, but salinities of 3.0 dSm1 or more tended to increase the RGR from firstmature pods to leaf senescence. These results are similarto those found in 1999 with respect to differences in salttolerance among plant growth periods. However, thesalinity levels that were required to reduce the RGR in2000 were higher than those in 1999 possibly due to

Fig. 2. Chile green pod yield response to soil salinity as affected by temperature differences as discussed earlier. Other stud-N rate applied in 1999 and 2000. Every point is the mean from ies have also pointed out the strong influences of airthree replications and the bars are SE. The arrows indicate the

temperature on the responses of plants to soil salinitytarget salinity levels for each experiment.(Maas, 1993).

There was no interaction detected between soil salin-detected. Target salinities of up to 4.5 dS m1 caused ity and N rate for any of the plant growth periods inno decrease in pod yield, but at 6 dS m1 yields were 2000 (Table 2). Increasing the N rate from 30 to 90 kgsignificantly lower. Contrary to 1999, increasing N rates ha1 increased the RGR during transplanting to flow-resulted in increased pod yields in the 2000 experiment. ering onset and from flowering onset to first mature

Soil salinity decreased chile pod yield more in 1999 pods. But at the end of growing season, an increasethan in 2000 at similar N rates (Fig. 2). That is, the from 30 to 150 kg N ha1 was needed to produce thedecrease in pod yield as a function of ECe was more highest RGR. These results were in agreement withabrupt in 1999 for plants treated with 80 or 140 kg N those found in 1999 when 80 and 140 kg N ha1 wereha1 than in 2000 when comparable N rates of 90 or enough to satisfy plant N requirements from trans-150 kg ha1 were applied. The difference in greenhouse planting to first mature pod and from first mature podtemperature for the two growing seasons was the only to leaf senescence periods, respectively. Thus, it mayparameter observed that might have caused this exag- be possible to improve chile plant yields by supplyinggerated osmotic effect as it is known that plant response N fertilizer in amounts that increase with plant sizeto salinity varies with many factors such as climate, soil instead of in four equal application rates since salt stressconditions, agronomic practices, and stage of growth was intensified by over-fertilization during times of low(Rhoades, 1990; Maas, 1993). fertilizer requirements.

Soil Salinity and Nitrogen Effects Soil Salinity and Nitrogen Effects on Neton Relative Growth Rate Assimilation Rate

The RGR was affected by soil salinity and N rate Soil salinity affected the NAR throughout the grow-ing season in 1999 but N rate only affected NAR afterduring all plant growth periods in 1999 with no interac-


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Table 2. Relative growth rate (RGR in mg g1 d1) as affected by soil salinity and N rate over three plant growth periods in 1999 and 2000.

Total N applied

Year Plant growth period Target soil salinity 80 kg ha1 140 kg ha1 200 kg ha1 Mean

dS m1 mg g1 d1

1999From transplanting to flowering onset 1.3 105.4 115.5 99.4 106.8 a

3.5 88.0 76.0 77.6 80.5 b

5.5 93.2 70.5 67.8 77.2 bMean 95.5 a 87.4 ab 81.6 bFrom flowering onset to first mature pods 1.3 82.1 60.4 67.6 70.0 a

3.5 84.5 65.6 28.7 59.6 ab5.5 58.2 46.8 33.9 46.3 b

Mean 74.9 a 57.6 ab 43.4 bFrom first mature pods to leaf senescence 1.3 6.2 13.3 16.4 12.0 b

3.5 14.0 33.1 42.7 30.0 a5.5 20.7 32.9 33.1 30.8 a

Mean 13.6 b 26.5 a 30.8 a

2000 30 kg ha1 90 kg ha1 150 kg ha1

From transplanting to flowering onset 1.3 89.6 93.7 82.9 88.7 a3.0 88.2 90.6 79.2 86.0 ab4.5 80.8 88.0 78.0 82.2 bc6.0 77.8 84.3 74.6 78.9 c

Mean 84.1 b 89.1 a 78.7 cFrom flowering onset to first mature pods 1.3 22.0 43.9 53.5 39.8 a

3.0 23.22 31.61 50.49 35.11 a

4.5 30.71 40.61 44.05 38.46 a6.0 28.27 42.55 46.07 38.96 a

Mean 26.06 b 39.66 a 48.52 aFrom first mature pods to leaf senescence 1.3 20.89 15.40 34.45 23.58 b

3.0 19.29 31.28 37.77 29.45 a4.5 20.52 24.96 37.45 27.64 ab6.0 24.77 27.88 35.44 29.37 a

Mean 21.37 b 24.88 b 36.28 a

Means followed by the same letter are not significantly different within rows and column according to Duncans test (P 0.05, n 3) for each yearand development period.

the onset of flowering (Table 3). No interaction between In 1999, increasing N rates from 80 to 200 kg ha1

reduced NAR during flowering onset to the first maturesalinity and N rate was detected for any plant growthperiod. Target salinities of 3.5 and 5.5 dS m1 reduced pod stage (Table 3). This indicates that over-fertilizationNAR by about 30% compared with the unsalinized is detrimental for plant growth and may be due to thetreatment during the period of transplanting to flow- osmotic effect caused by added fertilizer. In contrast,

ering onset. These salinity levels also reduced NAR by during the period of first mature pods to leaf senescence,approximately 35% compared with unsalinized treat- the NAR positively responded to increases in N ratements from flowering onset to first mature pods stage. from 80 to 140 or 200 kg ha1. In 2000, the NAR wasIn contrast, perhaps as a consequence of plant growth not affected by salinity at any plant growth period. Thedelay caused by salinity, the NAR was increased about NAR did increase in response to N rates of 150 kg ha1

two-fold by the salinity treatment of 3.5 and 5.5 dS m1 during the two latter growth stages, flowering onset toduring the last development period. leaf senescence.

The NAR, which represents a balance between thephysiological processes of photosynthesis and respira- Soil Salinity and Nitrogen Effectstion of the whole plant, decreases due to reductions in on Leaf Area Ratiophotosynthesis or increases in maintenance respiration

Salinity and N rate affected LAR primarily during(Cramer et al., 1990). Several studies have shown reduc-the first mature pod to leaf senescence period in 1999tions in photosynthesis due to salt stress (Myers et al.,(Table 4). No interaction was detected between salinity1990; Tiwari et al., 1997), which has been attributed to

and N rate. The targeted salinity treatment of 5.5 dSdecreased stomatal, and mesophyll conductance to CO2m1 increased the LAR by 34% with respect to thediffusion (Delfine et al., 1999) as well as the inhibition ofunsalinized treatment. Salinity has also been shown tobiochemical reactions and reduced carboxylase activityinduce higher LAR in sweetclover (Melilotus segetalis(Ungar, 1991). In addition, reduced photosynthesis inBrot Ser.) (Romero and Maranon, 1994). In addition,saline conditions has been correlated with leaf Na oran increase of similar magnitude in LAR was also pro-Cl accumulation (Bethke and Drew, 1992). There isduced by the high N rate of 200 kg ha1.also evidence that salt stress increases maintenance res-

In 2000, there was no effect due to salinity during thepiration (Gonzalez-Moreno et al., 1997) which is mainlyfirst plant growth stage (Table 4). From flowering onsetattributed to additional energy expenditures requiredto first mature pods, only the 3.0 dS m1 salinity treat-for the salt economy of the cell, that is, pumping outment increased LAR with respect to the less saline treat-ions from the cytosol into the vacuole (Semikhatova et

al., 1993). ment. During the last growth stage, salinity treatments


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Table 3. Net assimilation rate (NAR in mg cm2 d1) as affected by soil salinity and N rate over three development periods in 1999and 2000.

Total N applied


dS m1 mg cm2 d1

1999From transplanting to flowering onset 1.3 1.08 1.53 1.19 1.27 a

3.5 0.98 0.68 0.96 0.87 b5.5 0.95 0.76 0.87 0.86 bMean 1.00 a 0.99 a 1.00 a

From flowering onset to first mature pods 1.3 1.53 1.10 1.11 1.25 a3.5 1.15 0.96 0.49 0.87 b5.5 1.04 0.68 0.58 0.77 b

Mean 1.24 a 0.91 ab 0.73 bFrom first mature pods to leaf senescence 1.3 0.23 0.55 0.50 0.42 b

3.5 0.64 1.25 1.07 0.99 a5.5 0.69 0.86 0.83 0.80 a

Mean 0.52 b 0.89 a 0.80 a

2000 30 kg ha1 90 kg ha1 150 kg ha1

From transplanting to flowering onset 1.3 1.00 1.18 1.11 1.09 a3.0 1.19 1.07 0.86 1.04 a4.5 1.16 1.04 0.99 1.06 a6.0 1.02 1.12 1.04 1.06 a

Mean 1.09 a 1.10 a 1.00 aFrom flowering onset to first mature pods 1.3 0.32 0.60 0.68 0.53 a

3.0 0.36 0.37 0.55 0.43 a4.5 0.49 0.49 0.52 0.50 a6.0 0.43 0.56 0.57 0.52 a

Mean 0.40 b 0.51 ab 0.58 aFrom first mature pods to leaf senescence 1.3 0.56 0.38 0.85 0.59 a

3.0 0.47 0.71 0.87 0.69 a4.5 0.48 0.59 0.82 0.63 a6.0 0.57 0.62 0.74 0.65 a

Mean 0.52 b 0.58 b 0.82 a

Means followed by the same letter are not significantly different within rows and column according to Duncans test (P 0.05, n 3) for each yearand development period.

Table 4. Leaf area ratio (LAR in cm2 g1) as affected by soil salinity and N rate over three development periods in 1999 and 2000.

Total N applied


dS m1 cm2 g1

1999From transplanting to flowering onset 1.3 112.38 98.96 102.78 104.71 ab

3.5 116.73 125.21 99.39 113.77 a5.5 94.77 106.70 96.55 99.34 b

Mean 107.96 a 110.29 a 99.57 a

From flowering onset to first mature pods 1.3 66.44 58.29 63.94 62.89 a3.5 78.05 72.10 63.63 71.26 a5.5 57.27 75.89 61.34 64.83 a

Mean 67.25 a 68.76 a 62.97 a

From first mature pods to leaf senescence 1.3 28.75 31.25 38.45 32.82 b3.5 32.66 32.25 46.75 37.22 b5.5 37.49 48.99 45.80 44.09 a

Mean 32.97 b 37.50 b 43.67 a

30 kg ha1 90 kg ha1 150 kg ha12000

From transplanting to flowering onset 1.3 97.84 92.57 89.25 93.22 ab3.0 88.43 95.55 99.79 94.59 a

4.5 85.29 94.94 90.51 90.25 ab6.0 89.56 89.25 86.67 88.49 b

Mean 90.28 a 93.08 a 91.056 a

From flowering onset to first mature pods 1.3 71.44 73.31 78.30 74.35 b3.0 65.18 84.66 90.63 80.15 a4.5 63.93 82.28 82.63 76.28 ab6.0 67.65 75.57 79.65 74.29 b

Mean 67.05 b 78.96 a 82.80 a

From first mature pods to leaf senescence 1.3 42.23 48.23 56.02 48.83 b3.0 45.99 57.42 58.77 54.06 a4.5 48.09 54.54 61.17 54.60 a6.0 49.03 55.34 62.60 55.66 a

Mean 46.34 c 53.88 b 59.64 a

Means followed by the same letter are not significantly different within rows and columns according to Duncans test (P 0.05, n 3) for each yearand development period.


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Table 5. Correlation coefficients between relative growth rate (RGR) and net assimilation rate (NAR), and between (RGR) and leafarea ratio (LAR) at three growth periods for 2 yr. Each correlation value was obtained from 9 and 12 pairs of data (number ofsalinity levels times three replications for 1999 and 2000, respectively).

Year Development period N rate applied NAR LAR

1999 Transplanting to first flowers 80 0.65 NS 0.59 NS140 0.91 ** 0.61 NS200 0.83 ** 0.21 NS

Flowering onset to first mature pods 80 0.49 NS 0.79 **

140 0.91 ** 0.21 NS200 0.98 ** 0.13 NS

First mature pods to leaf senescence 80 0.81 ** 0.88 **140 0.89 ** 0.57 NS200 0.98 ** 0.85 **

2000 Transplanting to first flowers 30 0.16 NS 0.51 NS90 0.60 * 0.13 NS

150 0.50 NS 0.01 NSFlowering onset to first mature pods 30 0.99 ** 0.63 **

90 0.96 ** 0.39 NS150 0.95 ** 0.03 NS

First mature pods to leaf senescence 30 0.91 ** 0.67 **90 0.98 ** 0.79 **

150 0.74 ** 0.62 *

NS not significant or only significant at P 0.05.* Significant at 0.01 P 0.05** Significant at P 0.01.

of 3.0 dS m1

or more caused an increase in LAR. The plants were apparently aggravated by higher averagemaximum temperatures in the greenhouse in 1999N rates of 90 and 150 kg ha1 increased the LAR during

the two last development periods compared with 30 kg (35C) compared with 2000 (31C). Thus increasing Nrates and salinity levels interacted to reduce chile podN ha1.yield in 1999, but acted independently in 2000 whenlower N rates were applied and greenhouse tempera-Correlations between Growth Parameterstures were lower.The NAR and RGR were highly correlated for most

The RGR decreased in response to salinity early inof the N rates and plant growth periods (Table 5). Thus,

the growing season, but was higher during later growthchanges in RGR can be explained by concomitant de-

stages because salt-stressed plants delayed their earlycreases or increases in photosynthesis per leaf area and

growth and development and subsequently continuedrespiration reflected in the NAR. Salt stressed barleygrowing longer into the season while non salt-stressedplants (Hordeum vulgare) (Cramer et al., 1990) andplants had already reached leaf senescence. However

sweet clover (Romero and Maranon, 1994) were alsothe recovery in RGR later in the plants life cycle didshown to have high correlation between NAR and RGR.not compensate for the final pod yield. The N rates ofThe correlation between LAR and RGR was consid-80 and 90 kg ha1 tested in 1999 and 2000 provided theerably lower than that between NAR and RGR for mostplant with enough N to produce the maximum RGRof the N rates and plant growth periods (Table 5). Anup to the first mature pod stage while higher N ratesexception was the greater correlation between LAR andtended to reduce RGR. After the first mature podsRGR at 80 kg N ha1 during reproductive growth instage, the maximum RGR was achieved with the N rates1999. This suggests that leaf expansion was not limitingof 140 and 150 kg ha1 in 1999 and 2000, respectively.the RGR of most of the plants affected by salt stress.

Salt-stressed chile pepper plants can grow and pro-However, leaf expansion appeared to contribute to highduce high pod yields when adequately fertilized by sup-RGR values in salt-stressed plants during the period ofplying N in amounts that increase with plant size. Thefirst mature pods to leaf senescence. The LAR has beenaddition of excess N as NH4NO3 fertilizer did not allevi-shown to be highly correlated with the RGR of salt-ate osmotic stress as hypothesized by some authors,stressed maize (Zea mays) (Cramer et al., 1994) andand in fact, contributed to the overall soil salinity assweet clover (Romero and Maranon, 1994). But LARmeasured by ECe. Therefore, over-fertilization early inwas not correlated with the RGR of salt-stressed barleythe plant life cycle can be both destructive and wasteful.plants (Cramer et al., 1990). Munns and Termaat (1986)

proposed that salt stress acts by increased leaf deathrates, not decreased NAR. The ability to maintain func- REFERENCEStional leaf area by increasing LAR, as seen here, can Alam, S.M. 1994. Nutrient uptake by plants under stress condition.be adaptive. p. 227243. In M. Pessarakli (ed.) Handbook of plant and crop

stress. Marcel Dekker, New York.Albassam, B.A. 2001. Effect of nitrate nutrition on growth and nitro-

CONCLUSIONS gen assimilation of pearl millet exposed to sodium chloride stress.J. Plant Nutr. 24:13251335.Soil salinity decreased plant growth and yield of San-

Arshi, A., A.Z. Abdin, and M. Iqbal. 2002. Growth and metabolismdia chile pepper plants grown for two separate years of senna as affected by salt stress. Biol. Plant. 45:295298.in a greenhouse. High N fertilization rates contributed Bethke, P.C., and M.C.Drew. 1992. Stomataland nonstomatal compo-

nents to inhibitionof photosynthesis in leaves ofCapsicum annuumto soil salinity. The negative effects of salinity on the


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