Tomato yield and water use efficiency change with various soil moisture and potassium levels during different growth stages
Tomato yield and water use efficiency change with various soil moisture and potassium levels during different growth stages
Jie LiuID 0 1 2
Tiantian Hu 0 1 2
Puyu Feng 0 1 2
Li Wang 0 1 2
Shuohuan Yang 0 1 2
0 College of Water Resources and Architectural Engineering, Northwest A&F University , Yangling, Shaanxi , China , 2 Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas of Ministry of Education, Northwest A&F University , Yangling, Shaanxi , China
1 Editor: Ricardo Aroca, Estacion Experimental del Zaidin , SPAIN
2 Natural Science Foundation of China , 51279169
Faced with the scarcity of water resource and irrational fertilizer use, it is highly important to supply plants with water and fertilizer at desiderated stages to improve yield with high water use efficiency (WUE). A pot experiment was conducted to investigate the effects of growth stage-specific water deficiency and potassium (K) fertilization on tomato yield and WUE. The entire growing season of tomato was divided into 5 stages: vegetative growth stage (VG), flowering and fruit setting stage (FS), early fruit growth stage (FG), fruit development stage (FD) and fruit maturity stage (FM). Three soil moisture (W) and three K fertilization levels were set up. W levels included W1, W2 and W3, indicating that soil water was maintained at 60-70% field capacity, 70-80% field capacity, and 80-90% field capacity, respectively. K levels included K1, K2 and K3, indicating that 0 g K2O per kg soil, 0.46 g K2O per kg soil and 0.92 g K2O per kg soil was applied. All combinations of the three W and three K levels were solely imposed at each of the five growth stages, for other four stages, plants were watered to 80-90% field capacity without K fertilizer (W3K1). The permanent W3K1 over the entire growth stage was taken as control (CK). The results showed that W deficiency imposed at all stages significantly affected tomato yield (P<0.01), except for VG stage in which W deficiency did not cause yield loss. K fertilization level during FS or FM stage had a significant effect on yield (P<0.01). A significant interaction effect of W and K on yield was only observed during FM stage. For WUE, significant effect of W deficiency at FS, FD and FM stages were observed, and a significant effect of K levels at FS, FD and FM stages was observed. Specifically, K fertilization was necessary during specific growth stage of tomato (i.e. FS and FM). During FS stage, even if a sufficient water supply seems necessary, a deficit irrigation with K fertilization could be applied as K fertilization could alleviate the negative effect of soil water deficit, however, excess of K fertilization during FM stage should be avoided to maintain tomato yield and WUE.
Data Availability Statement: All relevant data are
within the paper and its Supporting Information
Competing interests: The authors have declared
that no competing interests exist.
In large areas of tomato (Lycopersicon esculentum) cultivation, rainfall could not meet crop
water needs, and surface irrigation is mainly adopted by farmers in practice, which may lead
to water waste [
]. Meanwhile, too much fertilizer applied in pursuit of high yield resulted in
lower quality [
], soil salinization and groundwater contamination [
]. Therefore, a better
understanding of plant periodical response to soil moisture and fertilizer is highly important
to water and fertilizer management in practice. To cope with water scarcity, which is the
primary constraint for high crop yields in many arid areas, deficit irrigation (DI) has been widely
]. DI allows the crop to experience a certain extent of water stress either by
applying less irrigation during the entire crop cycle or by withdrawing irrigation at certain stages,
without compromising yield too much. DI is demonstrated to increase water productivity and
optimize water use efficiency (WUE) [
Crops are drought-sensitive at certain growth stages [
], whereas they are
drought-tolerant at other phenological stages [
]. In previous works, water stress imposed during
fruit growth and maturity stages reduced tomato marketable yield [
], and the most sensitive
period was the fruit maturity stage [
]. However, some researchers insist the most sensitive
stage to water is the flowering and fruit setting stage [
]. Although DI has been extensively
investigated for many crops, the effect of DI applied at specific stages remains largely unknow.
Potassium (K) is one of the cationic minerals in most demand by tomato. K participates in
plant photosynthesis, enzyme activation, protein synthesis and other biochemical and
physiological processes [
]. A deficiency of K causes direct disorder to these activities, which
leads to a decrease in the growth rate of plant, accelerates leaf senescence and even leads to
plant permanent wilting [
]. Additionally, K increases plant resistance to stress factors, such
as drought, alkalinity and salinity [
]. K has a significant effect on the yield and its
components of tomato [
]. With K applied during the flowering stage, tomato yield and quality
improved significantly [
], and when applied during the reproductive stage, positive
effects of K on vegetable dry biomass are observed [
]. However, increasing K application in
field trials or nutrient solutions does not always improve tomato yield [
], but can
decrease the economic benefit because excess K supply can reduce the mobility of calcium
(Ca) thereby induced the occurrence of blossom-end rot [
Both water and K fertilizer are critical resources in agricultural production. Many studies
have been conducted on the effect of irrigation [
18, 34, 35
] or K fertilizer [
27, 36, 37
] on tomato
yield and WUE. The combined effect of these factors has also been investigated on soybean,
beet, potato, wheat, barley and maize [
]. Nevertheless, few literature reports concern
combined effect of irrigation and K fertilizer on tomato, much less referring to different
We hypothesized the response of tomato to water deficiency and K fertilization largely
depended on the phenological stage. The objective of this study was 1) to assess at which
growth stage water and K fertilizer levels are critical, and 2) to investigate the combined effect
of soil moisture and K fertilizer and applied timing on tomato yield and WUE.
Materials and methods
Site description and materials
The pot experiment was conducted under a rain shelter at the Key Laboratory of Agricultural Soil
and Water Engineering in Arid and Semiarid Areas of Ministry of Education, Northwest A&F
University, Yangling, Shaanxi Province, China (34?20@ N, 108?04@ E and altitude of 521 m).
The soil used in the experiment was taken from the 0?20 cm layer in a local field and was
classified as silty clay loam soil. The gravimetric field capacity (?f) was 27%, and the content of
organic matter, nitrate nitrogen, ammonium nitrogen and rapidly available K was 2.46 g kg-1,
7.25 mg kg-1, 3.93 mg kg-1 and 104.9 mg kg-1, respectively. The pots used in the experiment
were 30 cm in height, 25 cm in bottom diameter and 30 cm in top diameter. Each pot was
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evenly filled with 20 kg of air-dried soil sieved through 5 mm diameter mesh, with a soil bulk
density of 1.3 g cm-3. Two polyvinyl chloride (PVC) tubes (2.5 cm in diameter, 30 cm in
length) with 32 holes arrayed in four rows, intertwined by gauze (1 mm aperture) in case of
soil clogging, were installed vertically in each pot to irrigate homogeneously. In this study,
calcium magnesium phosphate (12.0% P2O5) and urea (46.4% N) were used as base fertilizers at
0.2 g P2O5 kg-1 soil and 0.12 g N kg-1 soil. Additionally, an equal amount of urea acted as top
dressing with irrigation at the fruit development stage of the first and second cluster, on May
31 and June14, 2015, respectively. Three clusters of tomatoes were remained. Other
management activities were the same as local practices.
Tomatoes (Lycopersicon. esculentum Mill. Jinpeng 10, local cultivar) were sown on March 12,
and seedlings were separately transplanted to the pots on April 27, 2015, when 4?5 completely
developed leaves appeared. 2 cm thickness of vermiculite was homogeneously spread on the
soil surface to reduce evaporation from the pot. Each pot was irrigated to the field capacity
immediately after transplantation. The tomato growth period was divided into five stages
based on the first cluster of fruits, namely vegetative growth stage (VG, from transplanting to
flowering, 5/5-11/5), flowering and fruit setting stage (FS, from flowering to fruit setting,
12/522/5), early fruit growth stage (FG, from fruit setting to fruit with 4cm diameter, 23/5-29/5),
fruit development stage (FD, from fruit with 4cm diameter to fruit turning white, 30/5-20/6)
and fruit maturity stage (FM, fruit turning from white to red, 21/6-25/7). Three water
deficiency (W) and K fertilization levels were set up. W levels included W1, W2 and W3,
indicating soil water was maintained at 60?70% field capacity, 70?80% field capacity and 80?90%
field capacity, respectively. K fertilization levels included K1, K2 and K3, indicating 0 g K2O
per kg soil, 0.46 g K2O per kg soil and 0.92 g K2O per kg soil was applied, respectively. All
combinations of the three W and three K fertilization levels were solely imposed at each of the five
growth stages, for other four stages, plants were well watered to 80?90% field capacity without
fertilizer (W3K1). The permanent W3K1 over the entire growth stage was taken as the control
(CK). Thus, the total treatments were 3?3?5?4 = 41.
Each treatment was replicated three times. Each pot was weighed daily during the
experimental period to measure and control the soil water condition. K fertilizer was dissolved in
water and applied with the irrigation water through the PVC tubes according to the above
Tomato fruits were picked and weighed when individual fruits reached maturity, and total
yield (kg plant-1) was calculated as the sum of the weights of all fruits for each plant.
WUE (kg m-3) was calculated as the ratio of tomato yield and water consumption during
the entire growth stage. We use this measurement as a proxy to tomato WUE in order to
express water productivity of tomato. Seasonal water consumption was calculated as the sum
of irrigation and the changes in soil water content between transplanting and harvesting (listed
in S1 Table).
The SPSS Statistics 21 software package (Version 21.0; IBM SPSS, Armonk, NY, USA) was
used for analysis of variance (ANOVA). The significance of the effects of W, K fertilizer rates
and their interaction was statistically evaluated at P<0.05 and P<0.01 significance levels.
Duncan?s multiple range test was used for any significant differences among treatments [
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Single effect analysis was performed when the interaction was significant. Graphs were plotted
using Microsoft Excel 2016 (Microsoft Corporation, USA).
General effects of timing and level of applied water and K fertilizer on yield and WUE
Tomato yield. Table 1 showed that as a whole, water and K fertilizer supplied stage had
significant effect on tomato yield (P<0.001). Tomato yield was lowest when treatment was
applied during FM stage, which was 15.77%, 14.36% and 14.51% lower than that applied
during VG, FS and FG stages, respectively. Soil moisture level had significant effect on tomato
yield (P<0.001). Plants grown under W1 possessed the lowest yield, which was 15.69% and
23.23% lower than W2 and W3, respectively. The effect of K fertilizer rate on yield was not
significant (P>0.05). Stage ? W level and stage ? K fertilizer rate interactions were both
significant (P<0.01), meaning the effect of W or K on tomato yield was closely related to the supply
period. Generally, W level ? K fertilizer rate, stage ? W level ? K fertilizer rate interactions had
no significant effect on tomato yield (P>0.05).
WUE. Water and K fertilizer supplied stage significantly affected tomato WUE (P<0.001,
Table 1). Plants with W and K fertilizer controlled during FM stage had minimum WUE,
16.64%, 14.20%, 14.73% and 12.42% lower than those controlled during VG, FS, FG and FD
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stages, respectively. The effect of W level on tomato WUE was highly significant (P<0.001,
Table 1). Plants grown under W1 had decreased WUE, 8.63% and 11.80% lower than those
grown under W2 and W3, respectively. The effect of K fertilizer rate on tomato WUE was
significant (P = 0.01, Table 1). Tomato WUE increased by 9.14% at K2 compared to K1.
Stage ? W level and stage?K fertilizer rate interaction were both significant (P<0.01, Table 1),
meaning the effect of W or K on tomato WUE depended on the supply period. Globally, the
effects of W level ? K fertilizer rate, stage ? W level ? K fertilizer interactions on tomato WUE
was not significant (Table 1).
Effects of W level and K application rates at different growth stages on tomato yield
Vegetative growth (VG) stage. At the VG stage, the effect of W and K fertilizer on fresh
yield was not significant (Fig 1A). Tomato yield varied from 0.65 to 1.08 kg plant-1 without
significant differences between CK and treatments. Nonetheless, yield tended to decrease with the
increase in K level when W was maintained at 80?90%?f, and the decrease was not significant.
Fruit setting (FS) stage. At the FS stage, both W and K fertilizer had a significant effect
on tomato yield (P 0.01), but their interaction was not significant (P>0.05, Fig 1B).
When soil water content was at W1, with the increasing application of K, tomato yield
increased gradually, and compared with K1, K3 increased tomato yield by 63.29% (Fig 1B).
However, no significant difference in the yield occurred among varied K-rate treatments when
Fig 1. Tomato yield as effected by soil moisture and K supply during vegetative growth (VG, a) stage, flower and fruit setting (FS, b) stage, fruit early growth (FG,
c) stage, fruit development (FD, d) stage and fruit maturity (FM, e) stage. W1, W2 and W3 denote three soil moisture levels, i.e., 60?70% ?f, 70?80% ?f and 80?90% ?f,
respectively. K1, K2 and K3 denote three K application rates, i.e., 0 g K2O kg-1 soil, 0.46 g K2O kg-1 soil and 0.92 g K2O kg-1 soil, respectively. Error bars indicate standard
error of the mean (n = 3 or 2). Fw, Fk and Fw?k are the F values of the variance analysis for soil moisture, K rate and their interaction effect, respectively. The symbol of
and indicate significant effect at 0.05 and 0.01 level, respectively.
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soil moisture was W2 or W3 (Fig 1B), indicating that K fertilizer at this stage could help to
improve tomato yield under a water stress condition but not under situations of adequate soil
The result was similar for the effect of W on yield during the FS stage (Fig 1B). Compared
with CK, W1K1 and W2K1 decreased yield by 40.88% and 14.31%, respectively. For the K
fertilizer rate of K2, compared with W1, W3 increased tomato yield by 35.02%. For K3 no
significant difference in yield occurred among different W levels (Fig 1B).
Early fruit growth (FG) stage. The influence of W at the FG stage on tomato yield was
significant (P<0.01). Compared with W1, tomato yield increased by 27.23% and 33.86% at W2
and W3, respectively. K fertilizer and the interaction were not significant (P>0.05, Fig 1C).
During the FG stage, there was no significant difference in yield obtained by CK, W1K1
and W2K1. (Fig 1C). In the condition of K2, W2 significantly increased the yield (by 41.83%)
compared to W1. Similarly, when the K fertilizer rate was K3, tomato yield acquired at W3
was 39.40% higher than that at W1.
No significant difference in tomato yield caused by K fertilizer rate was observed when soil
moisture was W1 or W3. When the soil moisture was W2, yield tended to increase a little and
then decreased sharply by 27.32% with increasing K application, and tomato yield reached the
maximum (1.13 kg plant-1) under the W2K2 treatment, indicating that moderate soil moisture
and K application helped yield formation.
Fruit development (FD) stage. W at the FD stage had a highly significant influence on
tomato yield (P<0.01, Fig 1D), which increased significantly with increasing W independent
of the K fertilizer level (Fig 1D). Furthermore, compared with the tomato yield obtained at the
soil moisture of W1, yield harvested at W3 increased by 46.00%, 35.22%, and 56.30% at the
three different K rates, revealing that sufficient irrigation at the FD stage was vital to yield
Neither the K fertilizer amount nor the interaction with W had a significant effect on yield
(P>0.05, Fig 1D). Regardless of the soil moisture status, no difference in yield was detected
among the treatments with varying K rates (Fig 1D).
Fruit maturity (FM) stage. At the FM stage, the main effects of both W and K application
rate were highly significant (P<0.01), and their interaction was significant (P<0.05, Fig 1E).
Based on the significant interaction, single effect analysis was performed to explore the
influence of different levels of W or K fertilizer on tomato yield (Table 2). At the FM stage, a
significant difference in tomato yield occurred among K fertilizer treatments regardless of W status
(P<0.05), and the difference was highly significant when soil moisture was W2 or W3
Note: W1, W2 and W3 denote three levels of soil moisture, i.e., 60?70%, 70?80% and 80?90% ?f, respectively. K1, K2 and K3 denote three rates of K fertilizer, i.e., 0, 0.46
and 0.92 g K2O kg-1 soil, respectively.
indicates a significant effect (P<0.05), and
indicates a highly significant effect (P<0.01).
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(P<0.01). When soil moisture was at W1, compared with the K1 rate, K2 increased tomato
yield by 29.78% remarkably, whereas no difference in yield was observed between W1K3 and
W1K1 treatments (Fig 1E). When the soil moisture was at W2, compared with the K-absence
treatment, K2 increased tomato yield by 13.71%, whereas K3 decreased yield by 17.34%. For
W3, no significant difference in yield was observed between CK and W3K2 treatment; however,
compared with CK, the yield obtained by W3K3 was reduced by 24.82%. Single effect analysis
also indicated that the difference in yield among W treatments was highly significant (P<0.01).
Regardless of the K rate, tomato yield increased significantly with the increase in soil moisture
(Fig 1E), indicating that sufficient water supply was conducive to tomato yield formation.
Fig 1E also shows that the maximum yield (1.107 kg plant-1) was obtained when soil
moisture was W3 and the dose of K fertilizer was K2, with yield increasing by 103.49% compared
with the minimum yield (0.544 kg plant-1) obtained by W1K1.
Effects of W and K application rates at various growth stages on WUE of tomato
The interaction of stage?W and stage?K rate were both significant (P<0.01, Table 1).
During the VG or FG stage, W and K application rate had little effect on WUE of tomato,
and the interactions were also not significant (P>0.05, Fig 2A and 2C).
During FS stage, the effect of W levels on tomato WUE was significant (P<0.01, Fig 2B).
W3 plants possessed 13.78% higher WUE than W1 plants. The effect of K rates on WUE was
Fig 2. Tomato water use efficiency (WUE) as effected by soil moisture and K supply during vegetative growth (VG, a) stage, flower and fruit setting (FS, b) stage,
fruit early growth (FG, c) stage, fruit development (FD, d) stage and fruit maturity (FM, e) stage. W1, W2 and W3 denote three soil moisture levels, i.e., 60?70% ?f,
70?80% ?f and 80?90% ?f, respectively. K1, K2 and K3 denote three K application rates, i.e., 0 g K2O kg-1 soil, 0.46 g K2O kg-1 soil and 0.92 g K2O kg-1 soil, respectively.
Error bars indicate standard error of the mean (n = 3 or 2). Fw, Fk and Fw?k are the F values of the variance analysis for soil moisture, K rate and their interaction effect,
respectively. The symbol of and indicate significant effect at 0.05 and 0.01 level, respectively.
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also significant (P<0.01). Compared to K1, K2 and K3 improved WUE by 14.43% and 24.52%,
respectively. The interaction of W and K application was significant (P<0.05). With soil water
deficit at W1 level, in relation to K1, K2 and K3 enhanced WUE by 28.19% and 58.14%,
respectively. With K level at K1 rate, compared with W1, W2 and W3 increased WUE by
32.04% and 38.52%, respectively.
During the FD stage, W had a significant effect on tomato WUE (P<0.01, Fig 2D). Plants
grown with soil moisture at W3 possessed 26.49% and 17.68% higher WUE than those grown
at W1 and W2, respectively. The effects of K fertilizer rate and the interaction with W were not
significant (P>0.05, Fig 2D). Tomato WUE was highest in treatments W3K2 (27.44 kg m-3)
and W3K3 (27.82 kg m-3) and lowest in those of W1K1 (19.91 kg m-3) and W1K3 (20.46 kg
m3), suggesting that increasing soil moisture at the fruit development stage was helpful for
During the FM stage, both W and K fertilizer rate affected WUE significantly (P<0.01),
whereas their interaction was not significant (P>0.05, Fig 2E). At K1 level, WUE increased
from 15.61 kg m-3 to 23.67 kg m-3 with increasing soil moisture. The maximum value was
obtained for W2K2 (25.93 kg m-3), which was 30.27% and 34.70% higher than that of W2K1
and W2K3, respectively (Fig 2E).
Yield change by soil moisture varies with the controlled growth stage
Irrigation plays a vital role in tomato yield formation, and the effect varies from stage to stage.
In this study, soil moisture (W) at the vegetative growth (VG) stage had little effect on tomato
yield (Fig 1A). This result could be explained by that during this period, the temperature was
relatively low and plants only had 5?6 leaves, resulting in low evapotranspiration. Thus, soil
moisture of 60~70%?f was adequate to meet the demand of water for tomato plants [
water-saving strategies are recommended at this stage.
In this research, soil moisture at the flowering and fruit setting stage (FS), early fruit growth
stage (FG) and fruit development (FD) or maturity stage (FM) had highly significant effects on
tomato yield (Fig 1B?1E). This result was in consistent with that of Chen et al, who reported
that excessive and insufficient soil moisture during FS stage had negative effects on tomato
yield, while increasing soil moisture during the last three stages could significantly promote
tomato yield [
]. Additionally, soil water deficit during flowering and/or yield formation
stages sharply reduces the marketable yield of tomato [
]. For non-K or moderate K
treatments at the FS stage, low soil moisture (60?70% ?f) significantly decreased tomato yield (Fig
1B). This decrease could be explained by the fact that leaf stomatal conduction declines and
stomatal resistance increases when soil moisture was 60?70% ?f, which inhibits the rate of
photosynthesis . The demand of tomato for water is high from the FS stage to the FM stage,
particularly at the FD and maturity stage when water is a limiting factor for tomato plant
growth. Soil water deficit during the fruit development and ripening stage restricts the
movement of calcium from soil to fruit and results in blossom-end rot and yield loss [
]. In this
study, with the decrease in soil moisture at the FD and FM stages, tomato yield decreased
significantly (Fig 1D and 1E), which was consistent with the findings of Marouelli & Silva [
The decline in yield by DI at the FD and FM stages could be caused by inhibited cell
multiplication and expansion and restricted translocation of assimilates from leaves to fruit [
Moreover, water deficit could influence the fruit setting and development of the second or
third cluster of fruits resulting in reductions in fruit weight and fruit number (S2 Table),
which is consistent with the results obtained by Nangare et al. [
]. Furthermore, sufficient
water supply at these two stages is crucial to meet the demand of water for high-intensity
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evapotranspiration induced by high temperatures and flourishing leaf area, and vital for
enlargement of fruit cells and metabolism of fruit nutritional substances; therefore, single fruit
weight increased in treatments with sufficient water supply compared with those exposed
under soil moisture deficit (S2 Table).
Yield change by K fertilizer rate varies with the controlled growth stage
In this study, tomato yield had highly significant response to K application at the FS stage or
the fruit maturity stage, whereas little response was observed at the VG, FG or FD stage (Fig
1A?1E). Han et al. also reported that potash applied at the flowering phase not only increases
plant height and stem width but also increases yield, whereas potash applied at the fruit
enlarging phase had no statistical effect on yield [
]. At the FS stage, when soil moisture was 60?
70% ?f, yield tended to decline with decreased K application (Fig 1B). This decline could be
explained by that K deficiency at FS stage decelerates the photosynthesis rate and translocation
of assimilates from source (e.g., leaves) to sink (e.g., fruits) [
], which contributed to the
decrease in fruit weight (S2 Table). At FM stage, the medium K rate helped to obtain the
greatest yield, while sufficient K fertilization appeared to decrease tomato yield (Fig 1E). Similar
results were reported by previous studies [
26, 33, 45
]. This result might be related to that high
K supply reduced the mobility of Ca and consequently, increased the occurrence of
blossomend rot . Excess application of K fertilizer could also reduce boron (B) absorption, thus
inducing tomato fruit microcracks and sacrifice quality [
]. Additionally, the benefit of K
fertilization under soil moisture stress was only shown in FS stage. Thus, it?s beneficial to apply
adequate K fertilizer during FS stage if water is limited, but not necessary during FM stage,
and in this study for plants with three clusters, the K in the soil could meet plants demand
under adequate soil moisture status.
Interaction of W and K fertilizer on tomato yield
During the FM stage, the interaction of W and K fertilizer occurred (Fig 1E), indicating the
ability of K to improve tomato yield was closely associated with soil moisture. During the FM
stage of the first cluster, the second and third clusters of fruits were at the stage from FS to FD,
which contributes much to the yield. Moreover, the temperature and evapotranspiration were
high, leading to a high demand for water. Increase of soil moisture (i.e., W2 and W3)
significantly improved yield, especially at K1 and K2 status (Fig 1E). As K is an important osmoticum
in determining cell turgor and stomatal aperture for plants [
], plant osmotic adjustment
and photosynthesis are directly related to K nutrition status. K fertilizer can alleviate the
negative effect of soil water deficit (Fig 1E) [
], while adequate K may lead to ion antagonism (i.e.
K and magnesium), resulting an unbalanced nutrition status in soil, which in turn affect crop
]. Additionally, overuse of K may reduce Ca mobility and induce the bottom-end rot
]. In this study, medium K supply improved tomato yield in regardless of soil water status,
this could be related to that medium K enhanced osmotic adjustment and sustained cell
expansion, increasing drought resistance potential for plants [
], and consequently, determined
yield at the critical stages of yield formation .
During FS stage, when soil moisture was limited as W1, the increased K supply improved
yield. When soil moisture was sufficient as W3, tomato yield was constant with increased K
supply (Fig 1B). This indicated the interaction of W and K fertilizer occurred during this stage
despite that it is not significant as a whole according to analysis of variance (Fig 1B). At FS
stage plant was more sensitive to soil water deficit (Fw = 11.240) than K fertilizer (Fk = 6.401)
(Fig 1B). Lower soil moisture may lead to the flower abortion and fewer fruits (S2 Table).
Moreover, K uptake by plant might be decreased at low soil water condition because the
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diffusion of K ion to roots from soil was inhibited [
], and K deficiency may impair
photosynthesis activities and decelerate tomato plant growth and result in reduction in assimilate
translocation to fruits . In low soil moisture condition, sufficient K fertilizer to plants
might enhance resistance to drought stress [
] and alleviate the negative effect of soil
water deficit . This finding needed further investigation.
WUE change by W and K fertilizer varies with controlled growth stage
Management of watering and fertilization not only change plant transpiration by participating
in the fundamental physiological process [
], but also change the surface evaporation of
soil where the plant stands by direct and indirect process [
]. Moreover, the water amount of
plant transpiration and soil evaporation has close interaction with each other [
]. In order to
select agronomic measures to use water resources efficiently, soil evaporation should also be
concerned besides plant transpiration. In other words, water productivity in the whole system
of plant and its soil should be focused on. So, in this paper, WUE was calculated as the ration
of tomato yield and water consumption during the entire growth stage, using this
measurement as a proxy to tomato WUE.
WUE reflects the efficient use of water in crop production. Compared with the entire
growing season, WUE is more sensitive to water during some phenological growth stages [
our study, tomato WUE was defined as the ratio between total yield and seasonal water
consumption (soil evaporation included). As all pots were in the same air condition, evaporation
could be relatively similar for each pot. However, different soil moisture might cause difference
in evaporation, which was linearly related with yield production [
]. Sato et al. [
Adams et al. [
] reported that poor fruit set was observed at high temperatures (more than
26?C). In this study, temperature in the air was higher during the last two stages. For
treatments conducted during FD and FM stage, the maximum values of tomato WUE were
observed at 80?90% ?f and 70?80% ?f, and the minimum values were obtained at 60?70 ?f,
which were consistent with the results of Nuruddin et al. who found that tomato WUE
declined with water stress during fruit growth and ripening stages [
]. This might be related
to the higher temperature in the plant leaf with lower evaporation when soil moisture was 60?
70 ?f. However, during FS or FG stage, low soil moisture did not decrease WUE, which might
be ascribed to the compensation effect resulting from sufficient water supply in FD and FM
]. Additionally, during VG stage, low soil moisture did not increase tomato WUE
(Fig 2A), which is different from the expectation. The reason might be the difference among
the three W levels (60?70% ?f, 70?80% ?f, 80?90% ?f) was not sufficiently large to significantly
affect the total water consumption in this investigation (S1 Table). This should be investigated
The effect of K fertilizer during FM stage on tomato WUE depended on the soil moisture
status, and WUE was highest at 70?80% ?f with 0.46 g K2O kg-1 soil (Fig 2E). For arid and
semiarid areas with a climate similar to that in this experiment, saving water resources during
the fruit growth and ripening stage is important, which generally experiences the longest time
in tomato production. With consideration of K fertilizer, soil moisture of 70?80% ?f is
Our study shows that the effects of soil water deficit and potassium fertilizer on tomato yield
and water use efficiency depended on tomato growth stages. Soil moisture and potassium
fertilizer were generally not limited factors during vegetative growth stage, so deficit irrigation
without K fertilizer at this stage could be recommended. Potassium fertilizer could alleviate
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the negative effect of water stress during flower and fruit setting stage. Sufficient water supply
during fruit development and maturity stage was essential for tomato yield. During fruit
maturity stage tomato yield was enhanced by moderate potassium fertilizer, while decreased by
excess application, indicating moderate level of potassium fertilizer during fruit maturity stage
S1 Table. Water consumption during the entire growth period (m3 plant-1).
S2 Table. Single fruit weight and fruit number per plant of the same combination of W and K as affected by the growth stages of its supply.
The authors thank Delong Yao, Fan Gao, Xia Hong and Shaowu Zhang for the help during the
experiment. And the authors are grateful to the two anonymous reviewers of this journal for
their constructive comments on previous versions of this manuscript.
Conceptualization: Tiantian Hu.
Formal analysis: Jie Liu.
Funding acquisition: Tiantian Hu.
Investigation: Jie Liu, Puyu Feng, Li Wang, Shuohuan Yang.
Methodology: Tiantian Hu.
Project administration: Tiantian Hu.
Supervision: Tiantian Hu.
Writing ? original draft: Jie Liu.
Writing ? review & editing: Jie Liu, Tiantian Hu.
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Wang F., Kang S., Du T., Li F., Qiu R., 2011. Determination of comprehensive quality index for tomato
and its response to different irrigation treatments. Agricultural Water Management 98, 1228?1238.
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