Application of soil amendments and paclobutrazol to shorten internode and increase rice yields

This study aims to determine the role of soil amendments, Paclobutrazol (PBZ), and varieties as well as their interactions on the growth and yield of rice. This study used a randomized block design (RBD) factorial split-split plot 3 x 2 x 2 with 3 replicates. The first factor was soil amendments as the main plot which consisted of 3 levels: A1= biochar, A2= compost, A3= mixture of biochar, compost, Mycorrhiza, and Trichoderma. The second factor was the concentration of PBZ in the split plot, which consisted of 2 levels: PBZ1 = 500 ppm, and PBZ2 = 700 ppm. The third factor is the variety as a split-split plot consisting of 2 levels: V1 = Sigupai Abdya, V2 = Tangse. The results showed that soil amendments had a significant effect on grain weight, and yield potential. The best yields are found in 50 g pot−1 of compost. PBZ had a very significant effect on grain weight and yield potential. PBZ at 700 ppm, can shorten rice internodes. Varieties have a very significant effect on grain weight and yield potential. The best growth and yields were found in the treatment of 50 g pot−1 compost with PBZ at a concentration of 700 ppm using the Tangse variety.


Introduction
Indonesia is very dependent on rice as a staple food.This is one of the reasons for the importance of various ways to be able to meet the community's need for these food sources.The ways that can be done to meet these needs are improving soil quality, adding nutrients to the soil, and using superior varieties.
Soil amendments are defined as synthetic or natural materials, organic or mineral, in solid or liquid form which can improve soil structure, change soil cation exchange capacity, and improve the soil's ability to hold nutrients.So that water and nutrients are not easily lost, but plants are still able to use water and nutrients.Soil amendments are also used to improve soil chemical properties.Improving soil reactions and neutralizing toxic elements or compounds need to increase soil fertility [1].Materials that are difficult to decompose are better to be used as a soil amendments in improving the biological, chemical, and physical qualities of the soil because they can last longer in the soil [2].These materials can be in the form of biochar, compost, or biological fertilizers [3].
Biochar is a soil amendment that can increase cation exchange capacity, high ion of organic matter, large surface area, and a porous structure made from carbon-rich [4].The use of biochar has been widely studied to increase soil pH, nutrient and water resistance, and plant productivity.Biochar can last a long time in the soil, has relatively long residues, and resistant to microorganisms.So that the decomposition process is slow, the effect of biochar residues can last up to 3-4 growing seasons [5].The other soil amendment is compost which also can increase nutrient availability.It can maintain soil fertility, increase crop yields, and reduce soil and water pollution [6].In addition, compost also stimulates beneficial microbial activity, nutrient retention, water-holding capacity, and CEC, which also improves soil yield through positive effects on soil structure [7].Efforts to increase rice production sustainability need to be carried out, while maintaining soil organic matter content through the use of compost.Compost can improve the availability of nutrients and micronutrients for plants [8].
Biofertilizers can also be used as soil amendments such as mikotrico (Mycorrhiza and Trichoderma spp.).Mikotrico contains microbes that can increase production and reduce synthetic fertilizers.Mycorrhiza's function helps the availability of nutrients for plants.In addition, Mycorrhiza is used to reduce biotic and abiotic stress in plants [9].Trichoderma spp. is an antagonistic fungus that is used to control pathogens, but this fungus also functions to stimulate plant growth.Trichoderma spp.can also help plants absorb certain nutrients, especially phosphate [10].
Paclobutrazol (PBZ) is one of the plant growth regulators (PGR) that works to inhibit the biosynthesis of gibberellins in plants.The use of PBZ also functions as a fungicide that affects plant growth and productivity.The application of PBZ to rice can inhibit the Gibberellin hormone (GA), especially GA 3 , causing shorter plant, but increasing crop productivity [11].
Varieties have different responses to environmental stress.Each national and local superior variety has a comparative advantage [12].National superior varieties with certain advantages are sometimes difficult to find during the growing season.The use of local varieties is an alternative planting material in each area.Local varieties have more stable alleles [13].
The use of PBZ and soil amendments on two rice varieties is expected to enhance knowledge about the appropriate dosage response of soil amendments, the best concentration of PBZ, and varieties that is suitable for growth and yield of rice.It is hoped that this research will become a reference in rice cultivation.Based on the description above, to increase rice yields, it is important to understand the response of soil amendments and PBZ application on two varieties of rice.This study gave an alternative strategy for increasing rice resistance to environmental stress in agronomic treats by applying soil amendment, PBZ, and appropriate varieties.

Tools and materials
Tools used in this research are 108 pots with a capacity of 10 kg soil pot -1 , sieves, seed trays, measuring tape, scale, measuring cup, SPAD Minolta 502, digital camera, and stationery.Materials used in this research are two varieties of rice seeds Sigupai Abdya and Tangse, Entisol soil, rice husk biochar, leaves compost, PBZ at concentrations of 500 ppm and 700 ppm, NPK fertilizer, zeolite substrate Mycorrhizal inoculum, and Trichoderma sp.

Experimental design
This research used a randomized block design factorial split-split plot of 3 x 2 x 2 with 3 replications.There were 108 pots of culture used.The first factor is the soil amendment (A), which consists of 3 levels: A 1 = Biochar 50 g pot -1 , A 2 = Compost 50 g pot -1 , A 3 = Biochar 25 g pot -1 + compost 25 g pot -1 + mycorrhiza 10 g pot -1 + Trichoderma spp.20 g pot -1 .The second factor was the concentration of paclobutrazol (PBZ) which consisted of 2 levels: PBZ 1 = 500 ppm, PBZ 2 = 700 ppm.The third factor is varieties (V) which consists of 2 levels: V 1 = Sigupai Abdya, V 2 = Tangse.Both varieties are local varieties with good rice taste and can be grown as rice in lowland and rainfed.Both varieties are highstemmed, so easily lodging.

Seed sowing
The seeds used were Sigupai Abdya and Local Tangse rice varieties.250 seeds were selected per variety and soaked for 24 hours.Then drain and put in a wet cloth to germinate for 2 x 24 hours.The nursery media consists of soil and compost 3:1 (3 parts soil and 1 part compost) and is watered every day.After germination, the seeds are sunk in trays to germinate and plant at 14 days old seedling.

Preparation of planting media
Entisol as planting media was used 10 kg pot -1 .The total soil used is 1080 kg.The planting medium is filled to 108 pots.After the soil was filled in pots, biochar and compost were added according to the treatment (A 1 , A 2 , and A 3 ), then saturated with water for one day then stirred to form a mud structure.The mud structure was maintained for 2 weeks, 2 cm flooded steady state.Then 3 rice seedlings were planted for each pot together with micotrico.Watering was done every day in the morning and evening using tap water.

Application of PBZ solution
PBZ solution according to the concentration of 500 ppm (dissolved in 0.5 ml L -1 water) and 700 ppm (dissolved in 0.7 ml L -1 water) in the treatment of each pot.The plants begin to enter the reproductive phase 70 days after sowing (DAS) and before entering the heading and anthesis phase 90 days after sowing (DAS).The solution was sprayed on the entire leaves of rice sufficiently using a hand sprayer with the same quality of solution according to the number of leaves at the time sprayed.

Fertilization
Fertilization was done using NPK compost fertilizer at a dose of 750 kg ha -1 (equivalent to 3.75 g for 10 kg of soil or 1.25 g application -1 ).This fertilizer was applied 3 times, at 0, 30, and 42 days after planting (DAP).

Maintenance
Maintenance carried out consists of watering and weeding.Watering is done every morning and evening with tap water from the same water source until the water in the pot is 2 cm and floods stagnant until harvest.The weeding is done every week manually.

Harvesting
Rice harvest using cutting tools at the bottom of the rice stem.Then put it in a plastic bag, label each plant, and dry it.After that, the plants are counted and measured according to the parameters below.

Plant height (cm).
Measured from the base of the rice stem above the ground surface to the tip of the highest leaf in cm.measured at 60, 75, and 90 days after planting (DAP).

Internode Length (mm).
It is measured by measuring the height of the stem from the ground surface to the growing point and then dividing by the number of leaves.

Grain weight.
Grain per weight hill was observed after harvest by selecting the filled grains and then separating them from the panicles and drying them until the water content was 13%.It was weighed using an analytical balance.

Biomass fresh weight (g).
Biomass fresh weight is measured after harvest.

Biomass dry weight (g).
Biomass dry weight was measured at the time of harvest after being dried in the oven to a constant weight.Yield potential = Grain Weight (g pot -1 ) x Total Population ha -1 x 0,85 (constant) 2.11.Data analysis.Data processed from the average of each parameter were analyzed using the standard of variant analysis (ANOVA) with the average values compared using the DNMRT test at P≤ 0.05 level.Data analysis was using SPSS 26 software packages.

Interaction of soil amendment and PBZ on morpho-agronomic properties of rice
Table 1 shows the interaction between soil amendments and PBZ on plant height, internode length 75 and 90 DAP.Numbers followed by the same letter in the same column and rows show no significantly different results on the DNMRT test (α ≤ 0.05).DAP = days after planting In A 1 , the increase in PBZ concentration caused a decrease in plant height, as well as in A 2 .This is in line with [14] stated that PBZ is a growth inhibitor and fungicide.This is supported by [15] who stated that the application of PBZ in the reproductive phase significantly shortened plant height.There is no interaction between PBZ and NPK on rice yields and quality [16].In addition, PBZ can reduce chlorophyll content [17].
PBZ is a type of plant growth hormone whose working system is to inhibit the biosynthesis of gibberellins in plants [18].Plant growth will be suppressed by PBZ because PBZ compounds inactivate three stages in separate terpenoid pathways in producing gibberellins by binding and inhibiting enzymes that catalyze metabolic reactions [19].[20] also stated that treatment of PBZ with different concentrations resulted in different responses, the higher concentration given, the lower the plant height produced.This is in line with the statement of [21] stating that giving PBZ to rice plants at high concentrations can reduce the area of the flag leaf, but increase the chlorophyll content in the leaf, resulting in increased photosynthesis and an impact on increased production.Reducing plant height and leaf area is an advantage of vegetative changes in plants to increase their productivity [22].
However in A 3 , there was an increase in plant height, this was because A 3 was a mixed amendment, and the effect of PBZ to reduce plant height did not occur.This is because the mixed amendment consisting of Mycorrhiza and Trichoderma affect the soil properties.This is in line with the statement of [23] who revealed that the biological fertilizer Tricoderma spp.can provide a high amount of leaf chlorophyll (41.3 units chl total mm -1 of leave) of rice.This is possible because the amount of N available at this level is sufficient for the needs of rice for the formation of leaf chlorophyll.So that it can increase the growth of rice.Increasing PBZ can inhibit the increase in internode as well as at age and 90 DAP.Likewise for the length of internodes 75 and 90 DAP.The compost had a higher plant height compared to the treatment without compost.This is also because compost can increase plant resistance to environmental stress according to research by [24] which is also in line with [25] which states that the application of vermicompost can increase the plant vigor index and also increase the ability of plants to grow.
The application of PBZ on peanuts reduced the photosynthetic capacity of the leaves, reducing the percentage of yielding.Increase breaking biosynthesis and increase stem resistance.PBZ can induce changes in plant architecture, resistance to lodging, and increases light transmission in the middle and underside of the leaves which causes increased levels of chlorophyll, the rate of photosynthesis in the leaves [26].[27] explained that the PBZ spraying increased the fresh mass of tubers, dry matter content, and specific gravity.Low concentrations of PBZ will increase fresh and dry weight.The result in line with research by [28] stated that the shorter the plant's result the higher the concentration of PBZ given.Application of PBZ to rice plants can reduce plant height, increase seed yields, and increase chlorophyll content [29].Based on the research results of [30] which stated that PBZ treatment of 200-600 ppm was able to increase chlorophyll a and b.This increase in chlorophyll will increase photosynthetic activity which in turn increases plant yields and lodging resistance.

Effect of interaction between soil amendments and varieties on growth and yield of rice
The interaction between soil amendment and drought on dried grain weight, biomass fresh weight, and soil pH is shown in Table 2.
In the Sigupai variety, the highest plant height is in A , while in the Tangse it is in A 2 (compost soil amendments).The same goes for the length of internodes at 75 and 90 DAP.This is in line with the research of [31] which revealed that there were differences in the yield of each variety caused by genetic factors and the growing environment.This shows that it is necessary to select varieties that are resistant to environmental stress to ensure food security.This is in line with [32] Besides [24], [25] also stated that adding compost (A 2 ) can increase plant resistance to environmental stress.Giving organic matter can increase rice tillers [33].
Rice has different resistance to environmental stress [12].The application of compost causes changes in nutrient levels in the root area [24] [34].Provision of compost, which is a natural soil amendment that can be produced from agricultural waste, can be easily obtained in various places.This is an important characteristic of compost that has a comparative advantage over other amendments.The use of compost can increase soil fertility and overcome agricultural waste.The use of compost can overcome the problem of soil fertility.It can also maintain the physical, chemical, and biological properties of the soil to support crop production.The use of compost is an alternative organic amendment for sustainable agriculture [4].
The highest yield potential in Sigupai is found in A 2 as well as Tangse.The highest grain weight and yield potential are found in A 2 Sigupai and Tangse, this is because amendments A 2 (compost) can improve soil fertility.So assimilation goes well and produces assimilate which is used for grain filling.This is in line with [4] and supported by [35] which states that soil density affects rice productivity.The application of biochar affects grain yield, soil-specific gravity, and moisture regime in upland rice.Biochar increases the efficiency of water use by plants.The application of biochar increases the efficiency of water use at various plant spacings and irrigation times.The impact of tillage that occurs in more density levels can be overcome by applying biochar and it depends on soil moisture.3.35 ab 4,32 d Numbers followed by the same letter in the same column and rows show no significantly different results on the DNMRT test (α ≤ 0.05).DAP = days after planting

Effect of interaction between soil amendment, PBZ, and Varieties on biomass fresh weight
Interactions between soil amendments, PBZ, and varieties on average biomass fresh weight can be seen in Table 3 below.In the biomass fresh weight, biochar soil amendment, the highest was found in the Sigupai variety with a concentration of PBZ 1 (500 ppm).While in A 2 the highest biomass fresh weight was found in the Tangse variety in PBZ 2 (700 ppm), in the A 3 amendment, the highest was in PBZ 2 (700 ppm), at the Sigupai variety.This is in line with the research of [36] stated that biochar has the potential to remediate agricultural soil.In addition, the application of biochar significantly increases N fixation in soil.Biochar changing the C/N ratio stimulated bacteria to release nutrients in the tillering phase of rice and reduced heavy metal poisoning.[26] also stated that the application of biochar and nitrogen could increase rice yields and increase panicles.The addition of biochar increases NH 4 reduces NO 3 also reduces NO 2 and reduces CH 4 .The application of corn straw biochar with 100 kg N can increase rice production and reduce greenhouse emissions.Good soil physical conditions can support the life of beneficial microorganisms for plants [37].Based on the research results of [38] in the stem fresh weight variable, the higher the PBZ concentration, the lower the biomass fresh weight.
The difference in carbon accumulation between Sigupai and Tangse varieties, due to the interaction between soil amendments and PBZ, the highest at Sigupai at PBZ 2 (700 ppm), as well as A 1 , A 2 , and A 3 , are still at PBZ 2 (700 ppm) in Sigupai, as well as the Tangse variety, but the highest at A 3 , is found in PBZ 1 (500 ppm).This is in line with research by [15] stated that the application of PBZ in the reproductive phase can shorten plants.[39] also stated that PBZ can increase the weight of grains, the amount of filled grains, and the weight of filled grains of grass.In addition, PBZ can increase chlorophyll a, b, productive tillers, and panicle length with 600 ppm PBZ.In addition to improving organic matter in the soil and using the right varieties to increase rice yields, the PBZ effect also serves to accelerate the vegetative growth process.Thereby accelerating generative development [19].The inhibition of rice plant height was caused by PBZ blocking the synthesis of gibberellins which function in plant cell elongation.Inhibition of gibberellin production does not inhibit cell division, but the resulting new cells do not grow elongated [40].
In general, in A 1 and A 2 , both varieties increased the biomass fresh weight at PBZ 2 (700 ppm).This shows that increasing the use of PBZ can increase the biomass fresh weight which is the accumulation of assimilate during the vegetative and reproductive phases, which is also a source of assimilate transferred to increase rice yields.This is in line with the statement of [39] who stated that PBZ can increase the weight of grains, the amount of filled grains, and the weight of filled grains of rice.In addition, PBZ can increase chlorophyll a, b, productive tillers, and panicle length with 600 PBZ [41].In addition, soil density also affects rice productivity, this is in line with [35] which states that soil density affects rice productivity.The application of biochar affects grain yield, soil-specific gravity, and moisture regime in upland rice.Biochar increases the efficiency of water use by plants.The application of biochar increases the efficiency of water use at various plant spaces and irrigation times.The impact of tillage that occurs in more density levels can be overcome by applying biochar and it depends on soil moisture.
Compost is a carrier agent for Trichoderma sp. which can be used as a carbon source for saprophytes such as Trichoderma sp.This biological fungus is also capable of producing metabolites that act as growth hormones for plants [42].Produce high leaf area and photosynthesis, thereby contributing to the increase in total biomass dry weight [43].

Conclusions
There is an interaction between soil amendments, paclobutrazol, and varieties on plant height, internode length, wet hull weight, grain weight, and rice yield potential.Compost soil amendment and increasing the PBZ concentration from 500 to 700 ppm can shorten the internodes from 93.23 mm to 81.89 mm.There was an increase in grain weight per pot from 16.72 g pot-1 and 16.75 g pot-1 in the biochar and mixed soil amendment to 18.02 in the Tangse variety with the use of compost amendment.In Sigupai grain weight increased to 21.78 g pot-1 with compost soil amendment, 21.62 g pot-1 with mixed soil amendment, and 16.62 g pot-1 with biochar soil amendment.The use of paclobutrazol can shorten internodes and increase the yield of Sigupai and Tangse rice varieties.This can also be a strategy to increase yields in conditions of environmental stress as a result of global warming impacts like flooding, drought, and others and environmental stress.PBZ can shorten rice internodes and increase, lodging resistance and other abiotic stresses.

Table 1 .
Interaction between soil amendments and PBZ on plant height and internode length 75 and 90 DAP

Table 2 .
Interaction between soil amendment and PBZ on parameters plant height 75 DAP, internode length 75 DAP, biomass dry weight, grain weight, and yield potential

Table 3 .
Interactions between soil amendments, PBZ, and varieties on average biomass fresh weight