The Effect of Nitrogen Fertilizer Based on Pocket Fertigation on Growth and Production of Tomato (Solanum lycopersicum L.)

INTRODUCTION

Tomato (Solanum lycopersicum) is one of the most important horticultural crops on earth and is one of the most consumed vegetables (Bai et al., 2021). Tomato fruit has a nutritional content rich in minerals, vitamins, essential amino acids, sugar, fiber, iron, phosphorus, and lycopene, known as an antioxidant. In Indonesia, tomato plants are one of the strategic horticultural commodity crops.

According to data from the Central Statistics Agency (BPS RI, 2020) in the 2019 Horticulture Statistics, tomato production in Indonesia 2019 reached 1,020,330 tons, showing a significant increase for five consecutive years. With a harvested area of 107,380 ha, the export value and imports in 2019 compared to 2018 showed improvement of

11.54% and 10.39%, respectively. This high tomato production is inseparable from the role of agriculture as a production unit. Struggles to improve crop production can be executed by optimizing factors that affect plant growth, such as nutrient and water requirements.

Water and nitrogen (N) are two factors that play a beneficial role in vegetable crop production. Using nitrogen (N) fertilizers as fundamental fertilizers or additional fertilization in vegetable production causes the supply of N to be uncoordinated (Luo & Li, 2018). Applying high- nitrogen fertilizers can cause subsequent NO₃−N leaching (Ullah et al., 2017) and ultimately disrupt the nitrate content in tomato fruit (Wang et al., 2015).

At the same time, significant water application will encourage fertilizer leaching, which can worsen the ARTICLE INFO

Keywords:

Climate Nitrogen Plant growth Pocket fertigation Tomato

Article History:

Received: November 28, 2021 Accepted: August 9, 2023

*⁾ Corresponding author:

E-mail: bayu.tep@ugm.ac.id

ABSTRACT

The tomato (Solanum lycopersicum) is considered a significant horticultural crop in Indonesia and is widely consumed by the local population. It should be cultivated by more efficient water irrigation methods, such as pocket fertigation. This study aims to determine the effect of pocket fertigation-based nitrogen fertilizer treatment on the growth and yield of tomato plants. Three different treatments of fertilizers, including without chemical fertilizer as control (P0), 200 kg/

ha of urea fertilizer (P1), and 200 kg/ha of ZA fertilizer (P2), are applied by utilizing pocket fertigation. The tomato plant is cultivated under 24- 30^oC of daily air temperature, 25.6-28.9^oC of soil temperature, and 68- 201 W/m² of solar radiation recorded by an automatic weather station.

The results show that treatments do not significantly affect plant height, number of branches, root volume, number of fruits, fruit weight per plant, fruit color index, fruit hardness, Brix, and consumption index. However, P1 increases yield and fruit quality more efficiently, while P2 effectively increases plant weight. Further research needs to regard the optimal dosage of Urea and ZA in optimizing the yield and quality of fruits.

ISSN: 0126-0537Accredited First Grade by Ministry of Research, Technology and Higher Education of The Republic of Indonesia, Decree No: 30/E/KPT/2018

Cite this as: Nugroho, B. D. A., Arif, C., Wibisono, Y., & Ansari, A. (2023). The effect of nitrogen fertilizer based on pocket fertigation on growth and production of tomato (Solanum lycopersicum L.). AGRIVITA Journal of Agricultural Science, 45(3), 443–455. http://doi.org/10.17503/agrivita.v41i0.3639

The Effect of Nitrogen Fertilizer Based on Pocket Fertigation on Growth and Production of Tomato (Solanum lycopersicum L.)

Bayu Dwi Apri Nugroho^1*), Chusnul Arif²⁾, Yusuf Wibisono³⁾ and Andrianto Ansari⁴⁾

1) Department of Agricultural and Biosystem Engineering, Universitas Gadjah Mada, Yogyakarta, Indonesia

2) Department of Civil and Environmental Engineering, IPB University, Bogor, West Java, Indonesia

3) Department of Agricultural Engineering, Faculty of Agricultural Technology, Universitas Brawijaya, Malang, East Java, Indonesia

4) Department of Agronomy, Faculty of Agriculture, Universitas Gadjah Mada, Yogyakarta, Indonesia

environment due to the loss of N to water sources (Li et al., 2018; Sebilo et al., 2013). Too much fertilization causes decreased efficiency of fertilizer maneuver, increased production costs, and higher nutrient loss causing significant environmental problems such as greenhouse gas emissions and nitrate contamination of groundwater. Efficient management strategies are essential to reduce fertilizer loss and soil degradation and increase efficiency in water use, nitrogen, yield, and quality of production towards agricultural sustainability (Delang, 2017; Quemada & Gabriel, 2016).

Fertigation is a technology that combines irrigation systems with the provision of nutrients.

Fertigation can replace fertilization in plants by dissolving nutrients into crop irrigation. Compared to providing water and nutrition separately in conventional irrigation and fertilization, Fertigation applies to water and nutrients simultaneously through an irrigation system around active roots to facilitate water absorption and increase soil nutrient bioavailability. Fertigation allows the application of the required dose of nutrients during a particular growing season with more precise adjustments to water and nutrient management for plants, crop growth, yield, water, and nutrient use efficiency under Fertigation is upgraded compared to conventional fertilizer application (Qin et al., 2016; Zhou et al., 2017²). Several advantages of Fertigation over usual fertilization methods are uniform nutrient application, reduced nutrient loss through seepage or run-off, reduced soil compaction, and mechanical damage to growing plants (Bryla & Machado, 2011;

Wang et al., 2018).

Drip irrigation can minimize water loss due to evaporation and percolation, and the rate and time of water application can adjust to eliminate run- off (Tribowo, 2014). Applying fertilizers under the recommended dose during Fertigation increases yields and water use efficiency (Jayakumar et al., 2017; Sinha et al., 2017). Drip fermentation can reduce the total irrigation water supply, fertilizer application rate, nitrogen leaching, and emissions (Lv et al., 2019; Wang et al., 2021; Zhao et al., 2021). Compared to conventional irrigation and fertilization, drip fertigation increased tomato yield by 24.8%, accompanied by an increase in tomato fruit quality, including the ratio of soluble solids, vitamin C (Vc), and soluble solids of 9.6, 25.2, and 31.2%, respectively (Bai et al., 2015; Rasool et al., 2020).

Drip fermentation increased tomato yield and fruit Vc

by 46.9 and 61.8%, respectively, compared to furrow irrigation and fertilization (Xing et al., 2015). Dip irrigation fertilization on tomatoes and cucumbers also shows that Fertigation can save water and reduce fertilizers, increasing yields and income. The utilization rate of nitrogen fertilizer can reach 58.9%.

If the numbers are the same, drip irrigation and fertilization can save 25.4% of chemical fertilizers than watered fertilization (Fan et al., 2020¹).

Various nitrogen fertilizers are based on the composition and levels of N. Urea and ZA (ammonium sulfate), which farmers commonly use. Urea fertilizer has a higher N content (46%) than ZA (21%). Urea is also hygroscopic, easy to absorb by plants, easy to wash with water, and not easy to denitrify. ZA fertilizer is more acidic because of the sulfur content, so that it can lower the soil pH. In contrast to urea, ZA is not easy leaching into the water, absorption works rather slowly, and plant roots cannot absorb it with groundwater but must get it directly. Treatment of nitrogen fertilizers, including urea and ZA, at a dose of 187.5 kg/ha increased fresh plant weight and yield (Saparso et al., 2019). This study aimed to determine the effect of nitrogen fertilizer treatment, namely Urea and ZA, with a simple drip fertigation method, namely pocket fertigation, on the growth and yield of tomato plants.

MATERIALS AND METHODS Research Location and Materials

The research was conducted on July 15 – October 13, 2021, at the Tri Dharma Experimental Garden, Faculty of Agriculture, Universitas Gadjah Mada. Fortuna tomato seed was cultivated using a planting box measuring 1.5 x 1 x 0.4 m under the plot of land in a net measuring 5 x 4 x 2 m. The treatment variations consisted of the treatment without chemical fertilizer (P0) as control, 200 kg/ha of Urea Fertilizer (P1), and 200 kg/ha of ZA Fertilizer (P2). The fertilizer treatment was selected based on the prior experiment (Arief et al., 2016; Ministry of Agriculture, 2021). The automatic weather station (AWS) was used for climate monitoring systems.

The research location is open land at an altitude of 102 meters above sea level, with the vegetation around the land being grass and other crops, such as corn and cucumbers. Paranet was used to minimize the influence of pests and climate influences such as wind. The physical condition of the soil was the texture of dusty clay soil with a volume weight ranging from 1.3-1.5 g/cm³. The

specific gravity ranged from 2.0 to 2.2 g/cm³, while the porosity ranged from 29 to 36.3%.

The utilization of pocket fertigation as the primary drip irrigation system was based on the prior treatment of Arif et al. (2022), which could minimize the actual evapotranspiration, better land usage, and good water productivity. In addition, pocket fertigation was subsurface irrigation that was more effective in water use (de Oliveira et al., 2021).

The provision of water was carried out once every morning daily by the amount of water categorized into 4 phases. Phase 1 was in the first two (2) weeks as much as 200 ml/plant/day; phase 2 was in the next two (2) weeks as much as 300 ml/plant/day;

phase 3 was in the next four (4) weeks as much as 500 ml/plant/day; and finally phase 4 in the last five (5) weeks in one harvest stage.

Pocket Fertigation Design

Drip fertigation extends to pocket fertigation was chosen because drip fertigation boosted tomato yields with higher fruit weight and several fruits per plant (Fan et al., 2020²). The design of pocket fertigation is an 80 cm long threaded hose, which is perforated with uniform diameter and distance, then given the stove wick as a porous medium. The two ends of the hose are connected using a pipe and a T pipe to form a circle. Then, the installation of a 1.5-liter bottle of mineral water in the top hole of the T, which functions as a fertilizer bag. Before use, a droplet uniformity test carries out on each pocket unit, and the average pocket droplet uniformity was 85.55%. The application of pocket fertigation to plants is shown in Fig. 1.

Fig. 1. Design of pocket fertigation

Experimental Design

Tomatoes were sown in containers with a soil-based planting medium, irrigated adequately, and transferred 14 days after sowing. The land was prepared by preparing the soil to a depth of at least three-quarters of the planting box’s height in a 1.5 x 1 x 0.4 m planting box. Tillage is accompanied by adding fertilizer base and manure to the soil in a ratio of 1:1. The spacing used for cultivation in a planting box was 40 cm by 40 cm. Each treatment was cultivated with three replicate plants. The plant was watered daily using pocket fertigation under the plant’s requirements and the local climate. In the control condition, only compost fertilizer and no additional chemical fertilizer were used. Chemical fertilization was accomplished with a concentration of Urea and ZA for each as high as 200 kg/ha (Arief et al., 2016) by dissolving in water and applying 1000 ml of water for each phase, except for phase 1, which utilized only 500 ml of water through a pocket. The tomato harvest was complete when the tomatoes reached harvest age according to the manually determined maturity level of the variety.

Data Observation and Analysis

Plant growth and yield parameters, including plant height, number of leaves, number of branches, root volume, fresh weight and dry weight of plants, number, weight, and diameter of fruit, fruit RGB color index, fruit hardness, and Brix index, and consumption index were recorded during cultivation and harvesting. Physical observation measured plant growth parameters using a caliper, weight balance, the computer vision system (CVS) method, refractometer, and penetrometer. The data obtained were analyzed by one-way analysis of variance (ANOVA) and Duncan’s Multiple Range Test (DMRT) as the further tests at a 5% significance level. EM50 data logger records climate data, including air temperature, humidity, rainfall, solar radiation, wind speed, temperature, and soil moisture.

RESULTS AND DISCUSSION Environmental Conditions During the Study

Environmental parameters are important factors in tomato cultivation. Rainfall, temperature, and humidity seriously affect tomato plants’ growth and yield (Santi et al., 2016). The daily temperature during the cultivation period fluctuated with a temperature range of 24–30°C. This temperature value was optimal for tomato plants› photosynthesis

process, which requires temperatures ranging from 25–30°C to form fruit sets at 22–25°C (Zhou et al., 2017¹). Air humidity increased and decreased with temperature changes, recorded between 73-89%

throughout the growing season. Solar radiation during the planting period ranged from 68-201 W/

m². The highest solar radiation was at the early planting period at 200.2 W/m², and the lowest was at week 11 at 68.1 W/m².

Soil conditions also play a dominant role in the growth of tomato plants. The ideal soil temperature and moisture can support the extension of tomato plants well. During the study, there were obstacles in recording the data of soil moisture and temperature, so the temperature and soil moisture data started to calculate from the 4^th or 21^st week of day after transplanting (DAT) until the last week. During planting season, soil temperature with time seems to fluctuate between 25.6-28.9°C.

This soil temperature value tended not to differ much from the air temperature. Soil moisture also seemed to fluctuate with more regular increases and decreases. The soil moisture value in units of m³/m³ ranged from 0.09 to 0.26 m³/m³. The amount of influence temperature and soil moisture by environmental conditions, such as rainfall and solar radiation. Heavy downpours can increase soil moisture and reduce temperature. Watering treatment also affects the soil, such as the effect of rain. Meanwhile, solar radiation can increase soil temperature and decrease soil moisture.

Treatment Effect on Crop Water Productivity The value of plant water productivity is obtained as shown in Table 1. Table 1 shows that the highest water productivity values come in the treatment without fertilizer (P0), followed by the ZA treatment (P1), and the last is the Urea treatment (P2). The value of water productivity in this study is directly proportional to the amount of tomato plant production because irrigation water use is the same in all treatments, so the highest water productivity gain is P0. The production value of tomato plants ranges from 0.37 to 0.45 kg/plant.

According to Maulana (2010), the actual production value of tomato plants per hectare nationally at the farmer level averages 2.65 tons in the lowlands to the potential production per hectare from several research results reaching 12-30 tons in the lowlands.

The value of water productivity in this study is low compared to the value of water productivity of

tomato plants in general. It is because water use is relatively low with a small production value.

Tomato Plant Growth in Several Treatments of Fertilizer Application

Plant height is one of the parameters of plant growth. Cell division and enlargement indicate plant growth has occurred. Based on Fig. 2, the tomato plant height increased in the early growth phase, decreased, and remained nearly constant until harvest. Generally, tomato plants run into a vegetative stage up to 45 days after planting and come to a generative phase 45 to 90 days after planting. According to Sumbayak et al. (2018), ammonium urea treatment resulted in significantly higher plant height than ammonium sulfate.

However, based on the ANOVA and Duncan’s test (Sig. > 0.05) indicated that treatment of P1 and P2 had no significant effect on the final plant height compared with control.

Another parameter that was measured in this study was the number of leaves. Fig. 3 shows that the number of leaves of tomato plants increases in the early growth stage, afterward decreases, and is close to constant until harvest. According to Sumbayak et al. (2018), ZA fertilizer can increase the number of leaves. However, based on the ANOVA and Duncan’s test (Sig. > 0.05) indicated that the P1 and P2 had no significant effect on the final number of leaves compared with the control treatment.

Table 1. Tomato plant productivity in various treatments

Treatment Parameter

Crop production (kg/m²) Irrigation water use (liters) Irrigation water productivity* (kg/m³)

P0 (Control) 2.81^a 56^a 7.96 ± 3.95^a

P1 (Urea) 2.31^a 56^a 6.65 ± 2.13^a

P2 (ZA) 2.44^a 56^a 7.01 ± 1.58^a

Remarks: ^a Numbers with the same letter on each parameter indicated a non-statistically significant difference between treatments in the DMRT test at 5%; * = The data consist of an average of 3 samples

Remarks: ^a,b = numbers with a different letter on each parameter indicated a statistically significant difference between treatments in the DMRT test at 5%

Fig. 2. Plant height against time

Remarks: ^a,b =numbers with a different letter on each parameter indicated a statistically significant difference between treatments in the DMRT test at 5%

Fig. 3. Number of leaves against time

Remarks: ^a,b =numbers with a different letter on each parameter indicated a statistically significant difference between treatments in the DMRT test at 5%

Fig. 4. Number of branches against time

Fig. 4 shows the number of branching of tomato plants against time in each treatment. Based on the ANOVA and Duncan’s test (Sig. > 0.05), the results indicate that the P1 and P2 have no significant effect on the final number of leaves compared with the control treatment—environmental factors such as water supply, temperature, light, and nutrients support plant growth. According to Cahyono (1998), tomato plants can grow well at an air temperature of 24-28°C with an air humidity of 80%. Based on the current data, the humidity value ranges from 76- 85%, and the ambient air temperature ranges from 26-28°C, which is under the requirements for growing tomato plants. Plant nutrition and water availability affect the growth or expansion of cells, such as vegetative organs or plant fertilization organs.

Treatment Effects on Yield

The data analysis results on several parameters of tomato plant yields are shown in Table 2. The type of nitrogen fertilizer treatment significantly affected plant fresh weight. Treatment with P1 and P2 obtains actual different significant effects on plant lively load, but between P1 and P0, the results were significantly different (unreal). The highest plant fresh weight in P2, P1, and P0 were 794.35, 494.05, and 487.78 g, respectively. Nitrogen-containing fertilizers play a role in stimulating overall growth, especially in the formation of chlorophyll, used in photosynthesis.

The resulting photosynthate is translocated to the vegetative parts of the plant to form new organs.

The larger the plant organs formed, the more water content the plant can bind; the amount of water content will be directly proportional to the plant’s fresh weight (Pramitasari et al., 2016).

Similar to the fresh weight, the dry weight of the plant showed that the effect of nitrogen fertilizer was significantly different from the dry weight of the plant. P1 with P0 was not seriously distinct. The dry weight of the plant is the result of the accumulation of plant assimilation obtained from the total growth and development of the plant during its life (Kusumayati et al., 2015). The highest dry weight came in P2, P1, and the last was P0. The dry weight also influenced the fresh weight of the plant, so the comparison of the effects of the treatment was relatively not much different.

The root volume is related to plants’ absorption extent of nutrients and water in the soil. The test results showed that the effect of nitrogen fertilizer

and no fertilizer was not significantly different on the root volume. In this case, there was a significant difference between P2 and P1, but applying fertilizer and no fertilizer was not significantly different. The highest root volume was found in P2, followed by P0 and finally P1 with 129, 80, and 56.67 g, respectively.

At the P2 roots, there were many root nodules with a relatively larger size than the roots in P1 and P0.

According to Kumalasari et al. (2013), the higher the nitrogen level, the fewer the total root nodules. The following results showed the highest root volume of P2 because the number of root nodules was inversely proportional to the nitrogen level, where nitrogen in P1 was only 21% lower than in P1 (46%).

The number of fruits is an indication of plant productivity. The number of fruits describes the ability of plants to form assimilate products in the form of fruit. The number of fruits in the treatment of nitrogen fertilizer and without fertilizer showed no significant difference. It means that the three treatments produced several fruits that were not much different—the highest number of fruits resulted in the treatment of P1, P2, and P3.

Fresh weight and fruit size reflect the balance between water and carbohydrate influx and water loss caused by reflux and fruit transpiration (Ripoll et al., 2014). Weight per fruit showed significantly different results on the effect of treatment with nitrogen fertilizer and no fertilizer. Fertilizer application had an unusual effect compared to no fertilizer, and the different types of nitrogen fertilizer also had a real impact. The highest weight value per fruit is figured in the P0, P1, and P2 of 50.37, 39.18, and 31.52 g, respectively (Fig. 5).

This value is close to the ideal weight of a tomato variety Fortuna, which is 41 g but is included in the small size category because it weighs under 100 g (Ministry of Agriculture, 2021). The nitrogen fertilizer treatment had a lower fruit weight than the treatment without fertilizer. It is probably due to too much nitrogen supply captured by plants. A result of too much nitrogen received by plants can cause a slowdown in fruit ripening because nitrogen still stimulates the growth of branches, twigs, and leaves (vegetative growth), while the formation of fruit neglected; it can affect the quality of crop yields such as decreased production and fruit quality (BPTP Kaltim, 2017). Compared to the weight per fruit, the overall fruit weight per plant showed that the treatment of nitrogen fertilizer and no fertilizer gave a non-significantly different effect. The difference

between the weight per fruit and the fruit per plant weight can occur due to the diversity of fruit sizes at each harvest stage. Some tomatoes are ripe but

smaller than the ideal size. Many factors, such as nutrient availability, climatic conditions, and pests and diseases, may influence this.

Table 2. The tomato plant yield and physical properties in various treatments

No Parameters* Treatment

P0 (Control) P1 (Urea) P2 (ZA)

1 Plant fresh weight (g) 487.783 ± 71.52^a 494.050 ± 118.22^a 794.353 ± 110.34^b 2 Plant dry weight (g) 108.873 ± 8.38^a 109.077 ± 22.98^a 150.890 ± 12.28^b 3 Root volume (ml) 80.000 ± 35.00^ab 56.667 ± 25.17^a 129.000 ± 23.52^b

4 Number of fruit 23.333 ± 7.02^a 34.000 ± 12.00^a 32.333 ± 12.58^a

5 Weight per fruit (g) 50.369 ± 4.51^c 39.175 ± 2.91^b 31.520 ± 2.40^a

6 Total fruit weight per plant (g) 446.024 ± 220.62^a 372.292 ± 119.38^a 392.362 ± 88.13^a

7 Color Index R 0.613 ± 0.018^b 0.605 ± 0.013^ab 0.593 ± 0.014^a

8 Color Index G 0.253 ± 0.008^a 0.265 ± 0.017^a 0.262 ± 0.012^a

9 Color Index B 0.135 ± 0.012^a 0.131 ± 0.021^a 0.146 ± 0.015^a

10 Fruit diameter (mm) 4.248 ± 0.13^b 3.888 ± 0.10^a 3.752 ± 0.09^a

11 Fruit Hardness (kgf/cm²) 1.760 ± 0.02^a 1.570 ± 0.33^a 1.740 ± 0.05^a

12 Brix Index (%) 4.328 ± 0.51^a 5.373 ± 0.73^a 4.960 ± 0.80^a

13 Consumption index 0.469 ± 0.16^a 0.461 ± 0.06^a 0.385 ± 0.04^a

Remarks: ^a,b,c = Numbers with a different letter on each parameter indicated a statistically significant difference between treatments in the DMRT test at 5%; * = The data consist of an average of 3 samples

Fig. 5. The effect of treatment P0 (a - d), P1 (b - e), and P2 (c - f) on the diameters and weight of tomatoes

The RGB color index observed determines the RGB color index by taking an image with a camera on a dark background after the image is processed into the RGB Color Detection application to get the R, G, and B values. The R-value indicates the red, G-green, and B-blue levels. The effect of nitrogen fertilizer type and no fertilizer showed results that were not significantly different for all RGB color indices. The highest R and G index values are in P2, P1, and P0. While, at index B, the highest was P2, P0, and P1, respectively. The value of R will be substantial if the tomato ripeness class increases (Masithoh et al., 2012). The results indicated that the R-value represents the value of tomato pigments in carotene and lycopene, which are synthesized during cooking to increase the red color. The G value of tomatoes will decrease with rising ripeness class because the G value reflects the green color chlorophyll in tomatoes which degrades during ripening. As for the B value, the greater the ripeness class, the B value will decrease with a massive decrease in the Green to Light red maturity class, then it will constantly approach the end of maturity (Red class).

Fruit diameter is a parameter of fruit size, mainly the great weight of the fruit. The diameter also will be greater. The highest diameters in the P0, P1, and P2 were 42.48, 38.88, and 37.52 mm.

This value is still below the diameter value of the Fortuna variety, which is 52 mm (Decree of the Minister of Agriculture, 2006). The diameter of the fruit in this study showed the effect of the type of fertilizer treatment. The control treatment, without fertilizer, gave significantly different results to the diameter of the fruit. Considerably distinct impacts were found between the treatment without fertilizer and the fertilizer application, while the treatment with nitrogen fertilizer was not significantly different.

It shows similar results to the fresh weight of tomatoes because the diameter of the fruit is generally proportional to the load of the fruit. Water accumulation in fruits decreases individually when tomato plants are under heat stress or water deficit (Hernandez et al., 2015; Kuşçu et al., 2014).

According to Li et al. (2021), the lower water uptake by tomato plants under drip irrigation provides environmental pressure so the weight and size of fresh fruit, especially in the summer cycle.

Fig. 6. The principal component analysis (PCA) result of 13 variables (axes Dim1 and Dim2: 64.2% total variance) for observation levels is shown as a biplot graph. Positive correlations are grouped, while negative correlations are positioned opposite.

The plant’s water status determines fruit firmness; the lower water absorption in drip irrigation leads to a significant increase in fruit firmness (Barbagallo et al., 2013; Nangare et al., 2016).

However, the combination of water deficit and heat stress under drip irrigation might promote tomato fruit ripening in the summer cycle, thereby reducing fruit firmness. Favati et al. (2009) also reported that tomatoes were softer with the same color under higher temperatures. The effect of treatment with nitrogen fertilizer and no fertilizer gave no significant difference in fruit hardness. Based on Fig. 6, the highest hardness value resulted in P0, P2, and P1, respectively, with a tiny difference in hardness.

The value of total dissolved solids in fruit showed by the Brix index (%). Fortuna variety tomato plants have a Brix of approximately 4.5%.

Tomatoes typically have a Brix index ranging from 3.8 to 5.0°Brix in agreement with those reported elsewhere (3.5 and 5.4°Brix) (Vinha et al., 2014). The highest Brix in treating P1, P2, and P0, respectively, is 5.37, 4.96, and 4.33. The treatment of nitrogen fertilizer and no fertilizer had no significant effect on fruit Brix. Microclimate conditions that tend to be homogeneous can affect the dissolved solids of tomatoes because they are related to water availability in the environment.

The Consumption Index describes the ratio between the fresh weight of edible plant parts and the total fresh weight. The consumption part in tomato plants is the fruit, so the consumption index is obtained by comparing the new load of the tomatoes with the total fresh weight. The highest consumption index value gain in the P0, P1, and P2. Overall, treating nitrogen and no fertilizer has no significant effect on the crop consumption index.

According to the direction of the different PCA vectors, it was noticeable that, for example, the consumption index held a solid positive relationship with weight per fruit and total fruit weight per plant.

In contrast, a negative relationship occurred with root volume, color index G, and color index R. On the other hand, the Consumption Index negatively correlated with the number of fruits, Brix index, fruit hardness, plant dry weight, color index B, plant fresh weight, and fruit diameter. The observation biplot allowed a pretty clear separation of three treatments. P0 was confined within two right-hand quadrants. However, no variables significantly contributed to such a precise placement.

On the contrary, P2 was plotted into two left- hand quadrants that mainly contributed to such a precise placement: plant fresh weight and plant dry weight. P1 showed a more erratic location as data were distributed within three quadrants, and values tended to be distributed along the line with fruit hardness and total fruit weight per plant. Moreover, the most critical variables contributing to PCA are plant dry weight and color index B, while fruit diameter and index are the least important.

CONCLUSION AND SUGGESTION

The type of nitrogen fertilizer treatment on the growth and yield of tomato plants with pocket fertigation significantly affects the number of leaves, fresh and dry plants’ weight per fruit, and fruit diameter. However, it does not significantly affect plant height, number of branches, root volume, number of fruits, fruit weight per plant, fruit color index, fruit hardness, Brix, and consumption index.

Urea (P1) is more efficient for increasing yield and fruit quality, while ZA (P2) is more for increasing plant weight. Further research needs to regard the optimal dosage of Urea and ZA.

ACKNOWLEDGEMENTS

This research was funded by BPTNBH of the Research Directorate of Univeristas Gadjah Mada for 2021 Fiscal Year under the “Program Penelitian Kolaborasi Indonesia (PPKI)” Scheme collaboration with IPB University and Universitas Brawijaya. We also thank Badi’atun Nihayah, Umi Hapsari, Kayisa Setyadina, Ultuf Sahila, and Hertiyana Nur Annisa as students of the Department of Agricultural and Biosystem Engineering, Universitas Gadjah Mada who have assisted in conducting this research.

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