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Tomato Yield, Quality and Water Use Efficiency Under Coupling of Irrigation and Nitrogen fertilizer of Greenhouse

Tomatoes in Northern Shaanxi Province

溝灌下水氮藕合對陜北日光溫室番茄 產量、品質及水肥利用效率的影響

Jinjin Xing, Yingying Xing*, Yanfeng WangCollege of Life Sciences, Yan’an University, Yan’an Shaanxi 716000, PR China

ABSTRACT

The objective of this study was to analyze the effects of irrigation levels and nitrogen (N) fertilizer application rates on fruit yield and quality, water use efficiency (WUE) and N-fertilizer partial productivity of greenhouse tomatoes (Solanum lycopersicum) under furrow irrigation in Northern Shaanxi Province. The experiment consisted of two irrigation levels and four N-fertilizer application rates with conventional local water and N-fertilizer management as the control (CK). Two irrigation levels were designed and applied: (1) high irrigation levels (I1: 100% ETc) and (2) low irrigation levels (I2: 75% ETc). We also investigated four N-fertilizer rates, (1) N1: 100 kg N/ha; (2) N2: 200 kg N/ha; (3) N3: 300 kg N/ha and (4) N4: 400 kg N/ha. The results showed that there was a parabolic rise of fruit yield and individual fruit weight with the increase of N-fertilizer application rates. The fruit quality was significantly ( p < 0.05) affected by irrigation levels and N-fertilizer application rates. The increase of irrigation showed a dilution effect on lycopene, vitamin C, soluble sugar, organic acid and nitrate contents, whereas sugar-acid ratio was adverse to irrigation conditions. There was an inverse parabolic trend in lycopene, vitamin C, soluble sugar, organic acid and sugar-acid ratios with the increase of N-fertilizer application rates, but the nitrate content showed a linear increase with the increase of N-fertilizer application rate. Water use efficiency (WUE) decreased with the increase of irrigation levels and increased with the increase of N-fertilizer application rates. Nevertheless, the WUE was more sensitive to irrigation levels than N-fertilizer application rates. Nitrogen partial productivity (PFP) was positively correlated with irrigation levels and negatively correlated with N-fertilizer application rates. The effect of N-fertilizer application rate on PFP was greater than that of irrigation levels. In general, the fruit yield of I2N3 treatment was 89.14% higher than that of CK treatments and the fruit quality in I2N3 treatment was better than that of other treatments. The efficiency of water and N-fertilizer utilization was higher in I2N3 treatment than that of other treatments. Therefore, we recommend that irrigation levels of 75% ETc and an N-fertilizer application rate of N3-N should be adopted in greenhouse tomato production in this region.

Keywords: Solar greenhouse, Tomato, Irrigation level, N-fertilizer application rate, Yield, Quality.

*Corresponding author. E-mail: xingyingying610624@163.com

臺灣水利　第 66 卷　第 3 期民國 107 年 9 月出版

Taiwan Water ConservancyVol. 66, No. 3, September 2018

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1. INTRODUCTION

The tomato (Solanum lycopersicum.) is a fruit, although commonly thought of as a vegetable, that is popular all around the world. It is also one of the characteristic crops for planting vegetables in northwestern China. It has a refreshing taste, is rich in lycopene and vitamin C and has been incorporated into a number of health products thereby further enhancing both its popularity and the economic value of this important crop. With the development of society and rising living standards, increasing attention is paid to the food quality. In recent years, excessive irrigation and fertilizer application rates cause decreases in fruit quality and yield; in addition, potential ecological and environmental problems have also been observed (Li et al., 2017; Zhang et al., 2010). Methods conducive to hypertrophy require high frequency irrigation and copious amounts of other resources; this is not only wasteful and inefficient, but also limits the potential productivity of scarce resources (Cabello M J., 2009; Song et al., 2013). In addition, the biological communities of northwest China are fragile. Therefore, the optimization of water and fertilizer management, thereby balancing crop yield and

quality, is not only beneficial to the ecosystem but also improves water use and fertilizer use efficiency as well as crop quality and yield.

Water and fertilizer are important factors that affect the growth and development of crops and are therefore a central means by which to enhance crop yield and quality. The growth of the tomato plant is characterized by physiological and reproductive growth; which ensue simultaneously during certain phases of development thereby increasing the demand for water and fertilizer (Hou et al., 2014; Wu et al., 2017). Many scholars (Li et al., 2017; Huo et al., 2017; Liang et al., 2017) have shown that water and fertilizer have significant effects on tomato growth, yield, quality, water, and fertilizer use efficiency. For example the study of Niu et al., (2017) showed that reducing irrigation can increase tomato yield and water use efficiency in solar greenhouse; Zhang et al., (2016) showed that appropriate irrigation can improve the quality and water use efficiency of tomato. Conversely, tomato yield, vitamin C, and lycopene first rises and then falls with increasing N application in greenhouse settings (Xing et al., 2015). The study of Shi (2016) shows that N application can be characterized as shortfall or oversupply, either of which can lead to

摘　　　　　要

通過日光溫室番茄栽培試驗，研究陝北地區溝灌下不同水氮配比對番茄產量、品質和水肥利用效率的影響，以期探索出適合該地區設施番茄種植的水肥管理措施。以“巨豐美粉863”番茄為供試材料，以當地常規水肥管理為對照，設置2個不同灌水(高水I1:100% ETc，低水I2:75% ETc)和4個施氮水準(N) (N1: 100 kg/hm2，N2: 200 kg/hm2，N3: 300 kg/hm2，N4: 400 kg/hm2)。番茄產量和單果重隨施肥量的增加呈拋物線形上升變化趨勢。番茄品質受灌水量和施氮量的影響較為明顯( p < 0.05)。灌水量的增加對番茄紅素、維生素C、可溶性糖、有機酸和硝酸鹽均表現出“稀釋作用＂；番茄紅素、維生素C、可溶性糖、有機酸和糖酸比隨施氮量增加呈開口向下拋物線形趨勢，硝酸鹽則呈施氮量的增加呈線性關系。水分利用效率(WUE)隨灌水量的增加而減小，隨施氮量的增加而增大，灌水量對WUE的影響作用大於施氮量，而且隨著施氮量增加WUE的變化趨于平緩；氮肥偏生產力(PFP)與灌水量正相關，與施氮量負相關，施氮量對PFP的影響作用大於灌水量。灌水量和施肥量的過多或者不足對番茄產量、品質和水肥利用效率都有顯著的影響。綜合而言，I2N3處理番茄產量為CK的89.14%，且品質均優於其他處理，水肥利用效率較高。推薦在該地區溫室番茄種植中採用75% ETc-N3的水肥管理措施。

關鍵詞： 日光溫室，番茄，灌水量，施氮量，產量，品質。

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significant reductions in tomato root length, yield and water use efficiency. The study of Zhou et al. (2013) has shown that appropriate N application increased the content of soluble sugar and vitamin C; Wang et al. (2017) showed that water and fertilizer coupling has significant interactions with vitamin C, nitrate, and lycopene content in tomato.

In recent years, research on the efficient use of resources involved in cultivation has attracted increasing attention as rapid expansion and development of conventional and traditional cultivation practices has continued. Although there is a large body of research on the influence of water and fertilizer on the growth, yield, and quality of tomatoes, most research has focused on drip irrigation methods. Despite this, excessive costs of drip irrigation preclude it as an option for most farmers in northern Shaanxi. Therefore, furrow irrigation and fertilization methods remain the most widely used method. Unfortunately, there is little research on the effects of water and fertilizer on the growth, yield and quality of tomato under regional furrow irrigation.

In this study, we used the tomato as a test crop to analyze the effects of water and nitrogen coupling on crop yield, quality, as well as water and nitrogen utilization efficiency under furrow irrigation in solar greenhouse settings. In order to provide technical and theoretical support for irrigation and fertilization management based on scientific methodologies, we explore water and fertilizer application patterns suitable for high crop yield and quality in solar greenhouse given the particularities of regional settings.

2. MATERIALS AND METHOD

2.1. Experimental sites

Experiments were performed from February 2017 to June 2017 in a solar greenhouse at Yan’an University Life Science Research Demonstration

Base. The si te is located at E36 o38'7" and N109o26'56" with an elevation of 953 m. The annual average temperature is 8.6oC, the average annual duration of sunshine is 2,478.7 h, and the temperature difference between day and night is large with an average annual frost-free period of 190 days and an average annual rainfall of 426.3 mm. The test soil type is loess. Before the experiment, important properties of the 0 to 20 cm soil horizon were as follows: the bulk density was 1.28 g/cm3, the field capacity was 22.3%, the organic matter was 5.47 g/kg, the nitrate content was 110.57 mg/kg, the available nitrogen was 112 mg/kg, the rapid available phosphorus was 3.75 mg/kg, the available potassium was 54.5 mg/kg, and the pH was 8.2. The greenhouse has a small weather station that automatically records atmospheric pressure, temperature, PAR, relative humidity and solar radiation.

2.2. Experimental material

The fertilizers used in the experiment were urea (N≥46%) from Shandong Rising Chemical Co., Ltd., superphosphate (P2O5≥12%) from Hubei Xiangyun Chemical Co., Ltd., and potassium sulfate (K2O≥52%) from Chemical Co., Ltd. production. Jufeng Seed Co., Ltd. Provided the test tomato cultivar – Ningxia Jufeng Meifen 863. A number of notable cultivar traits included: unlimited growth-type fruit, a uniform size, resistance to TY virus and Ye Mei disease, and overall suitability for conservation cultivation.

2.3. Experimental design

We investigated two factors, including irrigation levels and N application rates with full irrigation and local recommended fertilization as CK (100% ETc, N400 kg/ha), respectively. The irrigation factor consisted of two levels: high water I1 (conventional irrigation, 100% ETc) and low water I2 (75% conventional irrigation, 75% ETc). The N application factor consisted of four

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application rates: N1 (25% conventional nitrogen application, 100 kg/ha), N2 (50% conventional nitrogen application, 200 kg/ha), N3 (75% conventional nitrogen application, 300 kg/ha) and N4 (conventional nitrogen application, 400 kg/ha). The experiment was carried out with a complete randomized design, with 8 treatments, namely I1N1 treatment, I1N2 treatment, I1N3 treatment, I1N4 (CK) treatment, I2N1 treatment, I2N2 treatment, I2N3 treatment, I2N4 treatment. The experiment was conducted with three replicates per treatment, giving a total of 24 cells. Each cell had an area of 8.4 m2 (7.0 m wide and 1.2 m wide) with a ridge width of 75 cm and plant spacing of 50 cm with row spacing of 50 cm. Each plot was planted in two rows with 14 plants per row. In order to prevent surface water loss and increase ground temperature, plots and compartments were all covered with mulch (LDPE). During the experiment, the application rates of phosphate fertilizer (160 kg/ha) and potash fertilizer (560 kg/ ha) were the same on each treatment. Before planting, 50% of phosphate and potash fertilizers and 40% of all N fertilizers were applied as basal fertilizer to the tillage layer. The remaining P, K and N fertilizers were applied at the first panicle, the second panicle, the third panicle, in a 1 : 1 : 1 ratio via ditch irrigation. Throughout the growth period, topping was performed on each tomato plant. Other farming management measures

were carried out by local management.On February 20th, planting commenced and

plant seedlings were filled with 40 mm of irrigation water. The average daily evapotranspiration was collected by a small weather station (HOBO event logger, USA) during the period of treatment. We determined irrigation levels based on the Penman-Monteith correction formula (Chen et al., 2007) along with necessary measurements taken before and during the experiment. The irrigation and fertilizer levels in each growth period are shown in Table 1.

2.4. Collection and measurements

1) Yield measurements are based on 3 replicates for each treatment plot and 6 plants for each replicate. Yields for each plot are calculated by area weighting at harvest.

2) Quality assay is based on mature fruit quality measurements of the first and third panicle. Only those fruit with equivalent developmental status are selected. The tomato quality was determined according to the method of Li (2000). The average measurement is used as the final quality. Soluble sugar was determined by sulfuric acid-enthrone colorimetric method; Vitamin C was determined by molybdenum blue colorimetry; Lycopene was determined by UV-2600 UV-visible spectrophotometer; Nitrate content was

Table 1. The irrigation amount of treatments

TreatmentsNitrogen

fertilizer rate/(kg•hm-2)

Irrigation amount/(mm)

The irrigation amount of each growth period/(mm)Seeding stage/

(mm)Flowering

period/(mm)Fruit inflating stage/(mm)

Mature picking period/(mm)

Total/(mm)

I1N1 100 (40+60) 100%ETc 52.4 48.8 64.5 128.6 294.3I1N2 200 (80+120) 100%ETc 52.4 48.8 64.5 128.6 294.3I1N3 300 (120+180) 100%ETc 52.4 48.8 64.5 128.6 294.3CK 400 (160+240) 100%ETc 52.4 48.8 64.5 128.6 294.3

I2N1 100 (40+60) 75%ETc 39.3 36.6 48.4 96.5 220.8I2N2 200 (80+120) 75%ETc 39.3 36.6 48.4 96.5 220.8I2N3 300 (120+180) 75%ETc 39.3 36.6 48.4 96.5 220.8I2N4 400 (160+240) 75%ETc 39.3 36.6 48.4 96.5 220.8

* Nitrogen in the table in brackets figures represent (basic fertilizer + additional fertilizer).

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determined by UV spectrophotometry; Titratable Acid titration with NaOH.

2.5. Calculation formula

(1) Determine the amount of irrigationETo Solar Greenhouse Penman-Monteith

correction formula, namely:

ETo = [1408Δ(Rn ‒ G) + 1713γ (ea ‒ ed) / (T + 273)] / (Δ + 1164γ) (1)

Where,ETo = the reference crop evapotranspiration

(mm/d)Rn = the net radiation (MJ/(m2•d))G = the soil heat flux (MJ/(m2•d)Γ = the humidity meter constant (kPa/oC)T = the average temperature (oC)ea = the saturated vapor pressure (kPa)ed = the actual vapor pressure (kPa)Δ = the slope of the saturated vapor pressure

curve (kPa/oC)Please note: the parameters represent values

from 24 hours a day readings taken from the indoor greenhouse weather station.

(2) The actual irrigation amount calculation formula (Yuan et al., 2015) is:

ETc = KcETo (2)

In the experiment, the crop coefficient Kc is in accordance with FAO-56 and the values of the different growth stages were 0.5 (seedling stage), 1.15 (flowering and fruit setting stage), 1.15 (fruit enlargement stage) and 0.7 to 0.9 (maturity stage).

ETo = Crop evapotranspiration (mm/d).(3) Coefficient of variation CV is calculated as:

CV = s / Y × 100% (3)

Where,s = the standard deviation of production (kg/

hm2)Y = the output (kg/hm2)

(4) Irrigation Water Use Efficiency (WUE) (kg/m3) is the quantity of economic products produced per unit irrigation water. This is equivalent to the recorded irrigation volume throughout the entire growth period divided by the economic output, which is:

WUE = Y/I (4)

Where,Y = the yield of each treatment during the

growth period (kg/hm2)I = the amount of irrigation (mm)

(5) Nitrogen partial productivity (PFP) (kg/kg):

PFP = Y/N (5)

Where,Y = the tomato yield (kg/hm2) N = the cumulative N application rate (kg/hm2)

2.6. Statistical analysis

Calculations were performed by Microsoft Excel 2007. Visualizations were performed with sigmaplot 10.0. One-way analysis of variance (ANOVA) was performed using SPSS 10.0 statistical software, and Duncan's method was used for comparison if there was a significant difference ( p < 0.05).

3. RESULT AND ANALYSIS

3.1. Effect of water and nitrogen coupling on yield and variation coefficient of tomatoes in greenhouse settings

Reasonable water and fertilizer supply is an important guarantee of high crop quality and yield. Table 2 shows the effects of different irrigation and N-fertilizer treatments on tomato fruit yield. The different irrigation and N-fertilizer application rates have obvious effects on the fruit yield and yield component index. At the same irrigation levels, the tomato fruit yield and individual fruit weight

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tended to increase with the increase of N-fertilizer application rates. The variation coefficient first decreased and then increased with the increase of N-fertilizer application rates. The results showed that the decreasing trend of fruit yield with respect to treatment was CK > I1N3 > I2N4 > I2N3 > I1N2 > I2N2 > I1N1 > I2N1. The difference was not significant among CK, I1N3 and I2N4 treatments. The results show diminishing returns as nitrogen fertilizer application increases. The individual fruit weight increased with the increase of N-fertilizer application rate, and there were significant differences among all treatments in individual fruit weight. The coefficient of variation of fruit yield and individual fruit weight showed an upward paraboloid-like trend with the increase of N-fertilizer application rate. At the same N-fertilizer application rate, the tomato fruit yield and individual fruit weight under I2 irrigation were lower than those under I1 irrigation levels. This shows that the increase of irrigation can increase the yield.

3.2. Water and nitrogen coupling on the quality of tomatoes

As tomato quality is strongly affected by water and fertilizer availability, the evaluation of these relationships is attracting increased attention.

The effects of different water and N-fertilizer application rates on lycopene content were significant (except I1N3, CK and I2N2 treatments) ( p < 0.05). Under I1 and I2 irrigation, the lycopene showed a downward parabola trend with increasing

N application rates. In the meantime, under equivalent N application rates, the content of I2 irrigation in lycopene was higher than that in I1 irrigation. The content of lycopene in each treatment was I2N3 > I2N4 > I2N2 > I1N3 > CK > I1N2 > I2N1 > I1N1 and the content of lycopene with N3-N application was the highest in both I1 and I2 irrigation. Among them, the lycopene in I2N3 treatment increased by 23.07% compared with CK. This study shows that both shortfalls and oversupply of water and fertilizer can reduce lycopene content.

Different water and N-fertilizer application rates had significant effects on vitamin C content of tomato fruits (Table 3). The content of vitamin C in I2N3 treatment was the highest, which was 23.29% higher than CK. The content of vitamin C exhibited a downward paraboloid trend with the increasing N-fertilizer application rates and there was a significant difference among treatments (except CK and I1N2 treatments) ( p < 0.05). Under I1 and I2 irrigation levels the content of vitamin C in N3-N was the highest, which was 1.12 times and 1.23 times higher than that of CK. The results showed that nitrogen deficiency or excessive N application could lead to a significant decrease of vitamin C content in fruit. With the same N-fertilizer application rate under the I1 irrigation level vitamin C content was lower than that under I2 irrigation content, but there was no significant difference between the treatments (except N1-N and N3-N) ( p > 0.05).

It can be seen from Table 3 that the content

Table 2. The treatment, yield, weight of individual fruit, and coefficient of variation

Treatment yield/ (kg• ha) Variable coefficient Weight of individual fruit/(g) Variable coefficientI1N1 74,753c 13.15 191.7d 4.80I1N2 86,269b 11.84 208.6c 4.20I1N3 94,884a 8.34 225.2a 3.37CK 97,275a 13.84 227.6a 8.40

I2N1 66,477d 17.84 167.4e 6.84I2N2 75,766c 12.71 200.1cd 4.66I2N3 87,270b 7.61 210.5c 3.54I2N4 90,280a 9.16 217.9b 5.71

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of soluble sugar is positively correlated with the amount of N applied in I1 irrigation. The content of soluble sugar initially increased then decreased with N application in I2 irrigation. Under the same N-fertilizer application rates, soluble sugar content of I1 irrigation levels were significantly lower than that of I2 irrigation levels. The content of soluble sugar in tomato fruits with respect to treatment was I2N3 > I2N2 > I2N4 > CK > I1N3 > I1N2 > I2N1 > I1N1. The content of soluble sugar in I2N3 treatment was the highest, 1.28 times higher than that of CK, which was significantly different from other treatments ( p < 0.05), indicating that soluble sugar in tomato can be increased by decreasing water availability and applying appropriate fertilizer levels.

Nitrate content in plants reflects not only nitrogen uptake by plants and supply of nitrogen in soil, but is also one of the important indexes for evaluating the safety and quality of fresh vegetables. As can be seen from Table 3, the nitrate content of tomatoes increased from 68.67 to 104.34 mg/kg with the increase of N application rate and decreased with the increase of irrigation. The differences among treatments were significant ( p < 0.05). Among them, the content of nitrate in I2N4 treatment was the highest, 10.48% higher than that of CK, followed by I2N3 treatment. This study shows that none of the treatments exceeded the allowable intake of nitrate in vegetables (≤400 mg/kg), as stipulated in the 2003 national standards. The uppermost safe nitrate

content standard of fresh vegetables in China is 432 mg/kg (Fang et al., 2015).

The water and nitrogen coupling have a significant effect on organic acids in tomato fruits (Table 3). Among them, I2N3 treatment had the highest content of organic acids, which was 24.19% higher than that of CK, followed by I2N4 and I2N2 treatment. Under the condition of I1 irrigation, the content of organic acids showed an upward trend with the increase of N application rate. However, under the condition of I2 irrigation, organic acid content initially increased and then decreased with the increase of N application rates. Under the same N-fertilizer application rate, organic acid content of tomato treated with I1 irrigation was significantly lower than that of I2 irrigation. Therefore, modulation of nitrogen and water deficit levels can increase the organic acid content of tomatoes.

Organic acid content levels have a significant impact on tomato fruit flavor, with optimal taste achieved at intermediate levels taste. Inadequate levels lead to tastelessness whereas excessive levels lead to an overly acidic taste. Therefore, people often take the ratio of soluble sugar and organic acid content in fruit as an index to evaluate the quality of tomato flavor. The smaller the sugar-acid ratio, the poorer the fruit flavor quality. Fruit sugar-acid ratios should generally be above 6.0 (Yuan et al., 2008). Comparison of different treatments on fruit sugar-acid ratio (Table 3) can be seen in the treatment of tomato fruit sugar-acid ratios ranging between

Table 3. Different effect of water and nitrogen coupling on tomato quality

TreatmentLycopene/ (mg•kg-1)

Vc/ (mg•100g-1)

Soluble sugar/ (%)

Nitrate/ (mg•kg-1)

Organic acid/ (%)

Sugar-acid ratio

I1N1 20.68f 22.68f 1.79f 68.67g 0.19g 9.42cI1N2 27.83d 26.45de 2.47cd 73.45f 0.25f 9.88bcI1N3 32.66c 33.30b 2.69cd 82.61e 0.27de 9.96bCK 31.38cd 29.63cd 2.87c 94.47c 0.29cd 9.90b

I2N1 26.54e 24.04e 2.15e 82.76e 0.23f 9.35dI2N2 33.57c 27.35d 3.12b 91.87d 0.32bc 9.75bcI2N3 38.62a 36.53a 3.68a 95.21b 0.36a 10.22aI2N4 35.17b 30.15c 3.01b 104.34a 0.33b 9.12cd

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9.12~10.22, of which the sugar-acid ratio of I2N3 treatment was the highest, followed by I1N3 treatment, and the I2N4 treatment was the lowest. Under the condition of I1 and I2 irrigation, the sugar-acid ratio was the highest in N3-N treatment. Therefore, the appropriate amount of N fertilizer to improve the sugar-acid ratio in fruit is preferred, with shortfalls or oversupplies of N application rates leading to sugar-acid ratios that are detrimental to flavor. Under the same N application rate, the sugar-acid ratio of treatments under I1 irrigation content was higher than that in I2 irrigation (except I2N3 treatment). In addition the I2N3 treatment was significantly different from all other treatments ( p < 0.05). Therefore, the coupling effect of water-fertilizer is the most obvious for I2N3 than other treatments.

In general, the content of vitamin C, lycopene, soluble sugar and organic acid in tomatoes is an important indicator of the nutritional quality of tomato fruits. The content of these molecules determines the nutritional value and taste of tomatoes, which in turn affects the commercial value of crops. As can be seen from Table 3, under the same fertilizer application rate, vitamin C, lycopene, soluble sugar, organic acid and nitrate content of tomato fruits all show an inverse relationship with irrigation levels. The appropriate amount of irrigation can significantly improve the quality of tomato fruit; under the same irrigation conditions, the quality of lycopene, vitamin C and sugar-acid ratio were shown to exhibit an inverted parabolic trend with the increase of N-fertilizer application rate. However, the content of soluble sugar, organic acid and nitrate of tomato under I1 irrigation was linear with the amount of nitrogen application. The quality of tomato treated with I2N3 treatment reached the maximum (except nitrate), indicating that adequate water and fertilizer deficiencies can improve tomato quality.

3.3. Water and nitrogen coupling on water and nitrogen utilization efficiency

WUE is affected by water and nitrogen coupling (Fig. 1). WUE with respects to treatment was I2N4 > I2N3 > I2N2 > CK > I1N3 > I2N1 > I1N2 > I1N1, among which I2N4 treatment had the highest water use efficiency of 35.30%, an increase of 27.16% compared with CK. This was followed by the I2N3 treatment, which had an increase of 19.60% compared with CK ( p > 0.05). As shown in Fig. 1, WUE decreased with the increase of irrigation and increased with the increase of N-fertilizer application rates. Lower irrigation in conjunction with increased N fertilizer levels were beneficial to WUE of tomato plants. At the same time, it was found that the effect of irrigation on WUE was greater than that of N-fertilizer application rates, with the changes in WUE tending to be less drastic as N application rates increased. Although increases in N fertilizer levels marginally improve the WUE, doing so is neither cost effective, i.e., increases in WUE is not commensurate to costs of increasing fertilizer levels, nor sustainable.

PFP reflects the combined effect of local soil base nutrients and chemical fertilizer application rates. As can be seen from Fig. 2, the PFP of each treatment varied from 231.95 to 747.53 kg/ kg, with an increase of 3.07, 1.77, 1.30, 2.73, 1.56 and

Fig. 1. Effect of water-nitrogen coupling on WUE.

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1.20 times higher than that of CK. Among these, the I1N1 treatment had the highest PFP, followed by I2N1. Both of these treatments were also significantly different from other treatments ( p > 0.05). PFP increased with irrigation and decreased with N-fertilizer application rates, a response that is opposite to WUE. This means that increasing the amount of irrigation and reducing N-fertilizer can increase PFP. In addition, it was found that the effect of N application on PFP was greater than that of irrigation.

As can be seen from Fig.3, the polynomial equation of WUE and PFP with the amount of N applied under I1 irrigation were as follows: y = -7E ‒ 05x2 + 0.054x + 16.51, R2 = 0.998 and y = 0.006x2 ‒ 4.666x + 1145 and R2 = 0.991, respectively. Based on these equations, balanced water and fertilizer use under I1 irrigation was 190~200 kg/ha. As can be seen from Fig. 3, the multinomial equations of WUE and PFP increase with the amount of applied nitrogen under I2 irrigation: y = -4E ‒ 05x2 + 0.052x + 20.25, R2 = 0.991 and y = 0.005x2 - 4.224x + 1021, R2 = 0.987. From this, it can be determined that the nitrogen application rate at the balance of water and fertilizer use efficiency under I2 irrigation is 180~190 kg/ha. The fruit yield and quality were lower at N-fertilizer application rates of 180~200 kg/ha, while the yield, fruit weight, quality and

water use efficiency was higher at N3-N (300 kg/ha). Therefore, we recommend that the nitrogen application rate is 300 kg / ha in this area.

4. DISCUSSION

4.1. Effects of water and nitrogen coupling on yield

In agricultural production, rational management of water and fertilizer is one of the important ways to improve crop yield and quality. Many scholars have shown that tomato yield first increased and then decreased with the increase of water and N application (Dai, 2017; Yu et al., 2017; Jia et

Fig. 2. Effect of water-nitrogen coupling on PFP.

Fig. 3. Water and nitrogen use efficiency under different irrigation (Fig. A is under I1 irrigation; Fig. B is under I2 irrigation).

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al., 2017). Under the experimental conditions investigated here, tomato yield increased with N application rates, whereas the growth trend gradually decreased (Table 2). It can be seen that the yield-increasing effect is obvious at 200 kg/hm2 and 300 kg/hm2 under different irrigation rates, but not obvious at 400 kg/hm2. Therefore, under suitable water and fertilizer conditions, tomato yield and fruit weight increased with increases in irrigation and fertilizer levels. This is in line with the findings of Yu et al. (2017) and Zotarelli et al. (2008). To this end, under different irrigation conditions we recommend to choosing I1N3 and I2N3 treatments to obtain higher yields.

4.2. Water and nitrogen coupling on the quality of tomatoes

Water availability and fertilizer are two key factors that affect the growth and development of crops. The proper application of irrigation and fertilizer is the key to promote plant growth, increase yield and improve quality. The results show that lycopene, vitamin C and sugar-acid ratio increased first and then decreased with the increase of N application rate under I1 irrigation, while soluble sugar, nitrate and organic acid increased linearly with the increase of N application rates (Table 3). Under I2 irrigation, the relationship between lycopene, vitamin C, soluble sugar, organic acid and sugar-acid ratios initially increased and then decreased with increasing nitrogen application rates (except nitrate). Among them, the I2N3 treatment had the highest quality (except nitrate content), and there was a significant difference ( p < 0.05) with other treatments, followed by I2N4 treatment. The results showed that increases in irrigation have a dilution effect on the content of lycopene, vitamin C, soluble sugar, nitrate and organic acid, while increases in nitrogen application had the opposite effect. This is consistent with the study results of Wang et al. (2015).

4.3. Water and nitrogen coupling on water and nitrogen utilization efficiency

Water and nitrogen utilization efficiency of tomato yield, quality and economic benefits are an important impact indicator since they are foundational to achieving high yield and efficiency. This study shows that the effect of N application rate on PFP is greater than that of irrigation ( p < 0.05) (Table 4), which is consistent with the results of the study of transfusion and others (Si et al., 2017). The effects of irrigation on WUE was greater than that of N application ( p < 0.05) (Table 4), which is consistent with the results of Yu et al. (2005). The effect of water-N interaction on WUE and PFP was not significant ( p > 0.05).

5. CONCLUSION

1) In this study, we found that the yield of tomato and the weight of individual fruit showed a parabolic curve with the increase of irrigation amount and N application rate. Excessive or insufficient irrigation and fertilization could significantly affect the yield and fruit weight.

2) Tomato quality is influenced by water and fertilizer levels. The quality of tomato treated with I1 irrigation was lower than that of I2 irrigation. The lycopene, vitamin C, soluble sugar, organic acid and sugar-acid ratio reached their highest levels with initial increases of N application but then decreased, whereas nitrate increased linearly with N supply. These results can assist in the improvement of tomato quality by modulating irrigation and fertilizer levels.

3) The efficiency of water and fertilizer use is drastically affected by the amount of irrigation

Table 4. Tests of between-subjects effects

Source WUE PFPW <0.05 >0.05N >0.05 <0.01

M × N >0.05 >0.05

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and N application. Among them, WUE decreased with increases in irrigation and increased with increases of N application rates. The effect of irrigation on WUE was greater than that of N application and WUE tended to increase only gradually in response to increases of N application rates. PFP was positively correlated with the amount of irrigation and negatively correlated with the amount of N applied. The effect of N application on PFP was greater than that of irrigation.

Achieving high tomato yields, individual fruit weight, high quality and high water and fertilizer utilization efficiency is difficult to attain using the same water and fertilizer management strategy. In general, the increment of tomato yield before N3-N was more obvious with the increase of N application rates. The increase of tomato yield after N3-N was not obvious with the increase of N application rates, and the imbalance between input and output was serious. For this reason, I1N3 and I2N3 treatments seem to be optimal management options. Compared with CK, lycopene, vitamin C, soluble sugar, nitrate, organic acid and sugar-acid ratio of I2N3 treatment reached the maximum, reaching 23.07%, 23.29%, 44.68%, 0.78%, 24.14% and 3.23% higher than that of CK. The WUE and PFP of I2N3 treatment was 19.60% and 19.62% higher than the CK treatment. According to the above analysis, it was found that I2N3 treatment was in good agreement with water saving and fertilizer saving. Therefore, we suggested a 75% ETc-N300 kg/ha water and fertilizer management measure should be adopted when plastic mulching and furrow irrigation is applied in solar greenhouses under conditions similar to this study.

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Received: 107/01/25

Revised: 107/03/27

Accepted:107/05/25