Competitiveness of tomato (Lycopersicon esculentum Mill.) with weeds at various nitrogen doses and weed free periods

The research objectives were to determine the effect of nitrogen dose and weed-free period on the competitiveness of tomato plants with weeds. The research used 6 x 4 Factorial Randomized Group Design. The first factor was the weed-free period (P) which consisted of six levels, namely weeds during tomato growth (P0), weed-free two weeks after planting (P1), weed-free four weeks after planting. (P2), weed-free six weeks after planting (P3), weed-free eight weeks after planting (P4), and weed free until harvest (P5). The second factor was the dose of nitrogen (N) consisting of 4 levels, namely: without fertilization (N0), fertilizing 50 kg N ha−1 (N1), fertilizing 100 kg N ha−1(N2) and fertilizing 150 kg N ha−1 (N3). The variable of observation was analyzed univariately using the F test and continued with the (Student-Newman-Keul) SNK test with a test level of 0.05. The plants growth rate weeds were analyzed by regression in the form of a curve as a function of time to see the dynamics of weed growth. The amount of competition between weeds and tomatoes were done through the competition index value approach. The results showed that the was a change in the value of competition between tomato plants with weeds at each level of nitrogen dose and weed-free period, this change decreased with increasing nitrogen dose. The highest yield was obtained when weed-free during tomato growth, namely 25.88 tons ha−1 with a fertilizer dose of 100 kg ha−1.


Introduction
The presence of weeds in tomato plantations has a major contribution in reducing production.Weeds can cause up to 75% loss of tomato yields if not controlled [1].The magnitude of this decrease shows how important good weed management is to save crop yields.However, controlling weeds during plant growth is an inefficient method.The using the right fertilizer can reduce weed disturbance to plants [2].The changes in the level of soil fertility can affect the level of crop competition with weeds, depending on the type and density of weeds [3].Most of the agricultural weed species are more responsive to fertilizers than staple crops [4]; Increasing the dose of fertilization can increase the competitiveness of weeds against plants and reduce or eliminate the positive effect of fertilization on plants [4][5][6].
Nitrogen is a nutrient that is easily leached and often occurs on agricultural land so that its availability is in limited quantities [7,8].Limited availability allows for competition between plants and weeds.Weeds are able to absorb nitrogen more than plants at high nitrogen levels [9,10].The increasing crop competitiveness is a form of integrated weed management [11,12].Efforts to increase the competitiveness of tomato plants against weeds can be done by controlling weeds at the beginning of plant growth.Early stages in the plant growth cycle should be free of weeds [13].The critical period for tomato plants is estimated to be around 3.3-5.8weeks after planting [1].The aim of the research was to 1253 (2023) 012030 IOP Publishing doi:10.1088/1755-1315/1253/1/012030 2 see the level of competition between weeds and tomato plants and yield loss at various nitrogen doses and weed-free periods.

Materials
The research was conducted at the Experimental Garden of the Indonesian Vegetable Research Institute, Lembang, West Java.The materials used were tomato seeds, urea, Triple superphosphate, potassium chloride, insecticides and fungicides.

Research design
The research used 6 x 4 Factorial Randomized Group Design.The first factor was the weed-free period (P) which consisted of six levels, namely weeds during tomato growth (P0), weed-free two weeks after planting (P1), weed-free four weeks after planting.(P2), weed-free six weeks after planting (P3), weedfree eight weeks after planting (P4), and weed free until harvest (P5).The second factor was the dose of nitrogen (N) consisting of 4 levels, namely: without fertilization (N0), fertilizing 50 kg N ha -1 (N1), fertilizing 100 kg N ha -1 (N2) and fertilizing 150 kg N ha -1 (N3).Each treatment series was repeated three times.

Research implementation
The soil preparation was carried out by plowing, then loosening and applying manure at the rate of 20 tons/ha.Experimental plots were made with a size of 2 m x 3 m and sprayed with insecticides and fungicides before planting.Planting tomato seedlings with a spacing of 60 cm x 40 cm after 2-3 leaves have been produced, and before planting, basic fertilization was carried out at a dose of 75 kg ha -1 P2O5 and 100 kg ha -1 K2O.While the application of nitrogen fertilizer according to the treatment dose at the time of planting as much as 1/3 of each treatment dose and 2/3 at the age of one month after planting.Weeding as an interpretation of the weed-free period is carried out according to the treatment, namely weeds during plant growth, 2 Week After Planting (WAP) weed free, 4 WAP weed free, 6 WAP weed free, 8 WAP free of weeds and weed free during plant growth.

Parameters and data analysis
Parameters observed included the composition of weeds that grew during the growth of tomatoes, weed dry weight, tomato root decay ratio, and yield per hectare.All observation parameters were analyzed univariately using the F test and followed by the (Student-Newman-Keul) SNK test with a test level of 0.05.While plants growth rate weeds were analyzed by regression in the form of a curve as a function of time to see the dynamics of weed growth.

Plant and weed competition
The amount of competition between weeds and tomatoes is done through the competition index value approach, namely by using formula [5]: Y = a + bx, where Y = tomato yield; a = intercept; b = regression coefficient; x = weed free period.From this equation it will be possible to calculate the crop competition index with the formula: b1 = b.a-1 where b1=competition index; b = regression coefficient and a-1 = intercept of the regression equation.

Lost yield
The yield loss of tomatoes due to growing together with weeds is calculated using the formula [14]: where L = amount of yield loss; A = crop yield in the weed-free period and B = crop yield in weed conditions.

Optimum dosage
The optimum dose of nitrogen fertilizer for each level of the weed-free period is calculated based on the response curve technique in the form of results through the derivative technique with the following equation model:

Dominant weed
The types of weeds that grew on the tomato plantations during the study were

Weed dry weight
Based on the results of statistical analysis followed by the 5% SNK test, the that interaction between the weed-free period and nitrogen fertilizers significantly affected the dry weight of weeds.The average weed dry weight in various weed-free periods and nitrogen doses is presented in Table 1.
Table 1.Average Weed dry weight (g) in various weed free periods and nitrogen doses.

Weed free periods (WAP)
Nitrogen doses (kg.ha - Table 1 showed the that dry weight of weeds increased with increasing doses of nitrogen, while the longer the weed-free period showed the that a decrease in the dry weight of weeds.The highest weed dry weight was at a dose of 150 kg N ha -1 with a weed-free period of 83.23 g.At a dose of 150 kg N ha - 1 , the dry weight of weeds in the no weed period was different from the other weed free periods.While in the weedless period, the dry weight of weeds at a dose of 150 kg N ha -1 was different from the other doses.This showed the that increase in weed dry weight at increased nitrogen doses was made possible by the native of weeds which are quite responsive to nitrogen fertilization compared to plants.Weeds are able to absorb nitrogen more than plants at high nitrogen levels [9,10].According [15], that with an increase in nitrogen levels, there will be a significant increase in the dry matter of broad and narrow leaf weeds.
The weed-free period generally reduces weed dry weight.It was can be understood that plants were free from weeds at the beginning of their growth will provide opportunities for plants to dominate the growing space, making them more competitive compared to weeds.According to [16], that plants should be weed-free at the start of growth, because the presence of weeds in that period indicates stronger competition than plants and conversely plants have a low ability to compete with weeds.

Weed growth rate
Weed growth rates in various weed-free periods were analyzed by quadratic regression at each nitrogen dose.The relationship between the weed growth rate and the time period of observation for each weedfree period forms a real squared line.Based on the alignment and proximity tests in Figures 1, 2, 3 and 4, the regression line equations for each weed-free period at each nitrogen dose level show differences between the lines, except for the regression line between weeding periods during plant growth (P0) and the weed-free regression line 2 WAP (P2) showed no difference at each nitrogen dose (0, 50, 80 and 100 kg ha -1 ).
Weed growth rate at 45 to 66 DAP showed the that same pattern on the five regression lines.At the beginning of growth to a certain age weed shows an increasing growth rate, but the increase begins to decrease due to the increase in weed dry weight which is getting smaller.The decrease in the dry weight gain of weeds as a result of the increasingly shady canopy of the tomato plants, so that the amount of sunlight reaching the weed surface decreases.Light plays an important role in regulating plant growth and development.Rapid plant canopy formation can reduce light intensity, thus negatively impacting weed growth.Plants grown under reduced radiation conditions had a higher leaf area ratio and a lower relative growth rate [17].Interception of light at an early growth stage is critical for reduction of weed pressure [18].

Tomato root loss ratio
The results of the statistical analysis followed by the 5% SNK test showed the that interaction between the weed-free period and the increasing dose of nitrogen significantly increased the root removal ratio.The average of root removal ratios in various weed-free periods and nitrogen doses are presented in Table 2.     Table 2 showed that increasing the dose of nitrogen in each weed-free period significantly increased the root removal ratio.The highest tomato root decay ratio was at a dose of 150 kg N ha -1 with a weed-free period of 10 WAP, was found 10.92.At a dose of 150 kg N ha -1 , the root loss ratio of tomatoes in the weed free period of 10 WAP was not different from the other weed free periods except for the weed free period of 8 WAP.While in the weed-free period of 10 WAP, the ratio of tomato root decay at a dose of 150 kg N ha -1 was not different from the other doses except without nitrogen.Plants that get a lot of nitrogen usually have green and dense leaves, with a stunted root system, so that the root loss ratio is high [19].According to [20] and [21], that the availability of N can affect the development of plant roots and water absorption.The weed free period significantly increased the root shoot ratio.This showed that tomato plants can increase nitrogen uptake during the weed-free period which is getting longer during plant growth, thereby affecting the ratio of shoots and roots.N application had a significant effect on the R:S ratio, shoot dry weight in moderate nitrogen application increased significantly by 10.7 -13.3% compared to no nitrogen and nitrogen application significantly reduced root dry weight [22].

Yield per hectare
The results of the statistical analysis followed by the 5% SNK test showed that the interaction between the weed-free period and the increased dose of nitrogen significantly increased tomato production.The average production per hectare in various weed-free periods and nitrogen doses is presented in Table 3. Table 3 showed that the weed-free period during plant growth for all levels of nitrogen doses gave the highest yields and was no different from the weed-free period eight weeks after planting.The highest yield per ha of tomatoes was obtained at a dose of 100 kg N ha -1 with a weed-free period during plant growth, namely 25.88 tons ha -1 .At a dose of 100 kg N ha -1 , the yield per ha in the free period during plant growth was not different from the other weed free periods except the weed free period of 8 WAP.Meanwhile, in the weed-free period of 10 WAP, the yield per ha of tomatoes at a dose of 100 kg N ha -1 was different from the other doses.The weed-free period can increase tomato crop yields as a result of reduced competition between plants and weeds.The maximum yield of tomatoes can be achieved if they grow without competing with weeds in fighting for resources that are in limited quantities, so that control is carried out at the beginning of plant growth which needs attention.
According to [23] stated that factors that affect the ability to compete between plants and weeds include types of weeds, weed density, duration of competition, plant varieties and soil nutrient content.The competitive ability of a species is largely determined by the space it can control at the start of growth.This response can be attributed to the slow development of the plant canopy in the early stages of growth, so that light penetration can stimulate seed germination and weed growth in the early growth stages [24].Increasing the dose of nitrogen up to a dose of 100 kg ha -1 was able to increase the yield of tomato plants, but at a dose of 150 kg ha -1 there was a decrease.Nitrogen is a constituent of protein and other important compounds in sustaining plant life.Nearly 70% of total nitrogen was contained in the chloroplasts where the photosynthetic process takes place, but excess can disrupt metabolic processes in plants and will further affect production [25].

Figure 5.
The optimum dosage of nitrogen fertilizers in various weed free periods.
Longer weed-free periods in tomato cultivation will increase yields and can reduce the use of nitrogen fertilizers.This is made possible by the availability of nitrogen in the soil and is able to be absorbed by plants compared to plants that grow together with weeds.

Competition index
The competition index is a quantity that describes the amount of competition between plants and weeds.Measurement of the competition index was first introduced by [26], which is to see the level of competition between plants and weeds for limited resources.The competition index of plants with weeds in various weed-free periods and nitrogen doses can be seen in Tables 4 and 5.

Table 4. Indices of plant competition with weeds at various nitrogen doses
Nitrogen dosage (kg ha -1 ) Competition index 0 50 100 150 7.42 6.68 6.67 6.27 Table 4 showed that the higher the nitrogen dose, the lower the competition index between plants and weeds.The availability of nitrogen fertilizers in the soil will meet the nutrient needs of both plants and weeds thereby reducing competition between plants and weeds.The competitive ability of a species is largely determined by the space that can be mastered at the start of growth [28].Increasing the dose of fertilizer can reduce competition between plants and weeds for mineral nutrients, especially nitrogen.5 showed that the longer weed free, the competition index value between plants and weeds decreases, this indicates that the competition between plants and weeds decreases.

Yield loss
Yield losses of tomato plants due to weeds in various weed-free periods were calculated using the formula [14] presented in Table 6.6 showed that weeds can reduce tomato yields by up to 58.26% if tomatoes grow along with weeds during growth.Yield losses due to crop-weed competition can range from 10 to 100%, depending on the type of crop and associated weeds [29].Yield loss due to the presence of weeds can be reduced if the plants during their growth are free from weeds, especially at the beginning of plant growth.According to [16], that yield loss can be avoided if weeding was done at the early growth stage of the plant.The results of the same study on cowpea (Vignia unguiculata L.) that increased seed yield by maintaining weed-free conditions up to 60 days after planting, equivalent to 80 days after planting and weed-free throughout crop growth [30].Competition with weeds was the most important of all biological factors that can reduce crop yields, this is mainly because weeds use up resources that should be available to plants.The amount of crop yield loss was influenced by various agronomic and environmental factors, especially weed density and the time of emergence of weeds on plants [31].

Conclusion
There was a change in the competition between tomato plants and weeds at various nitrogen doses and weed-free periods.Yield loss due to the presence of weeds in tomato plantations can reach 58.26 percent.The optimum dose of nitrogen fertilizer in various weed-free periods (0, 2, 4, 6, 8 and 10 WAP were 156, 134, 117, 106, and 97 kg N ha -1 respectively.

Figure 1 .
Figure 1.Weed plant growth rate in various weed-free periods at a dose of 0 kg ha-1.

Figure 2 .
Figure 2. Weed plant growth rate in various weed-free periods at a dose of 50 kg ha-1.

Figure 3 .
Figure 3. Weed plant growth rate in various weed-free periods at a dose of 100 kg ha -1 .

Figure 4 .
Figure 4. Weed plant growth rate in various weed-free periods at a dose of 150 kg ha -1 .

Table 2 .
Average of root removal ratio in various weed-free periods and nitrogen doses.
Noted: Mean numbers followed by the same letter indicate results that are not significantly different according to Duncan's test at the 5% level capital letters read horizontal direction (rows) and lowercase letters read vertical direction (columns).

Table 3 .
Average yield per hectare in various weed-free periods and nitrogen dosage.
Noted: Mean numbers followed by the same letter indicate results that are not significantly different according to Duncan's test at the 5% level capital letters read horizontal direction (rows) and lowercase letters read vertical direction (columns).

Table 5 .
Plant competition index with weeds in various weed-free periods

Table 6 .
Yield losses of tomato plants due to weeds in various weed-free periods.