The effect of NPK fertiliser on oil palm coefficient as a baseline water management during the nursery phase

The Indonesian government views the oil palm industry as a promising sector for poverty alleviation. The germination process of seeds is influenced by water, requiring careful management. This study investigated the impact of NPK application and NPK fertiliser on the crop coefficient value of Tenera variety oil palm seedlings. The entisol soil used had a sandy clay texture, with sand comprising 81.00% of the soil composition. The soil texture, organic matter, bulk density, particle density, porosity, evapotranspiration, potential evaporation, percolation, moisture content at field capacity, and oven-dried root weight were measured with and without fertiliser to 50 oil palm trees at 3 to 6 months of age. The results show that NPK application has affected oil palm’s crop coefficient and growth. The highest dry root weight and plant coefficient obtained without fertiliser and with fertilisers at six months were 24.76 gr and 33.89 gr, 0.626 and 0.65, respectively. Root biomass, a sign of plant health and nutrient uptake, shows fertilization’s long-term effects. Six-month-old plants, especially fertiliser ones, have more extensive root dry weights, indicating persistent nutrition uptake and long-term resistance. Nutrient management is crucial to agricultural productivity, affecting the current crop and future growth phases.


Introduction
Oil palm (Elaeis guineensis Jacq.) is a significant oil crop crucial in global vegetable oil production and economic growth in tropical regions.During the nursery phase, young seedlings develop the foundation for future productivity, laying the foundation for optimal growth and vigour in oil palm plantations.Nutrient management is essential for healthy seedling development, optimal crop coefficients, and plant health and water need indicators.Water is a critical resource for the successful growth and establishment of oil palm seedlings during the nursery phase, as it directly affects the seedlings' ability to establish a strong root system and achieve optimal growth, which subsequently impacts crop coefficients [1].
Water is vital for the successful nursery phase, but striking a balance between water availability and appropriate irrigation practices is essential to prevent waterlogging and potentially detrimental effects on seedling health.Efficient water use and management are critical for conserving this precious resource, optimising nutrient absorption, and minimising the risk of diseases caused by excessive moisture in the nursery environment [2,3].
Nitrogen (N), Phosphorus (P), and Potassium (K) are essential nutrients for supporting numerous physiological processes in plants.Nitrogen is necessary for chlorophyll formation and protein synthesis, contributing to leaf and stem development.Phosphorus is essential for energy transfer and root development, facilitating nutrient and water absorption.Potassium influences osmotic equilibrium, stomatal regulation, and overall plant health, increasing a plant's resistance to environmental stresses [4,5].
Understanding the relationship between NPK fertiliser applications and crop coefficients is crucial for optimising oil palm nursery practices [6].A proportionate and appropriate administration of NPK fertilisers during the nursery phase can significantly affect crop coefficients, influencing water needs and seedling health.Numerous studies have shown that appropriate NPK fertilisation positively influences crop coefficients, increasing water use efficiency and enhancing crop yield.Studies on other oil crops, such as soybean and rapeseed, have shown that NPK fertiliser application significantly enhances crop coefficients and water use efficiency [7,8].Several studies have investigated the effects of NPK fertilisation on oil palms at different growth stages.These investigations have demonstrated the positive impact of appropriate nutrient management on crop yield and overall oil palm productivity [9,10].However, relatively limited research has focused explicitly on the influence of NPK fertiliser application during the nursery phase of Tenera variety oil palm.Understanding the relationship between NPK fertiliser application and crop coefficients is essential for optimising nutrient management strategies and promoting healthy seedling establishment and future yield in oil palm plantations.
Therefore, this study aims to examine the effect of NPK fertiliser application on crop coefficients of oil palm seedlings of the Tenera variety during the nursery phase, emphasising the relationship between nutrient supplementation and the water needs of oil palm seedlings.By quantifying the effect of NPK fertilisation on key growth parameters and crop coefficients, this research aims to contribute to developing optimised nutrient management strategies, thereby promoting the healthy seedling establishment and future yield in oil palm plantations; however, more research is needed to focus specifically on the influence of NPK fertiliser application during the nursery phase of Tenera variety oil palm.

Materials and Methods
Polybags, water, NPK fertilizer, entisol soil with the texture described in Table 1, and 50 three-monthold tenera-variety oil palm seedlings obtained from the Oil Palm Research Center (PPKS) Medan Business Unit were used in this study.Sample rings, microwaves, digital scales, Erlenmeyers, measuring containers, cutter blades, compasses, digital anemometers, solar power meters, digital thermometers, analogue thermometers, and Class A evapopans were utilized in this investigation.This study employs experimental methods and incorporates field observations.The sample consisted of 50 oil palm trees divided into two groups: 25 treated with fertiliser and 25 untreated plants.This study's objective is to analyse data to determine the coefficient value for three-month-old seedlings of the Tenera variety of oil palm.Considering the specific location and quantity of seeds used, this investigation was categorised as a laboratory/screen house study.The manual and periodic application of NPK fertiliser to plants was performed by hand.Five grams are the recommended dosage per plant.Each plant is manually watered with a consistent volume of water to accomplish the intended soil field capacity and evapotranspiration.By the plant's specific water requirements, water is supplied at regular intervals.
Using a ring sample technique, six polybags were utilised to analyse soil physical parameters for oil palm plants.It must be heated at 105 o C for 24 hours to compute the soil's oven-dry weight.In order to ascertain the quantity of oven-dried soil, the soil must be saturated within an Erlenmeyer flask.To ascertain the volume of oven-dried soil, one can subtract the volume of an Erlenmeyer flask from the volume of the water used for saturation.To determine the soil mass density (also known as bulk density), Equation ( 1) can be applied.Similarly, Equation ( 2) can be used to determine the density of soil particles.Last, the porosity can be calculated using Equation (3).The soil texture was determined utilising the hydrometer technique at the Research and Technology Laboratory, Faculty of Agriculture, Universitas Sumatera Utara, and the organic matter content was assessed.
The field capacity water content can be determined by conducting three soil sampling trials.In each experiment, soil samples are saturated with water and left undisturbed for approximately 24 hours to attain field capacity.Field capacity is attained when no water percolates into the soil due to gravitational forces.The water content is then determined using the gravimetric method, specifically Equation (4).Equation ( 5) is utilised to calculate the evapotranspiration of plants.To quantify evaporation, use an evapopan of Class A and then apply the pan coefficient, as demonstrated in Equation ( 6).Use Equation (7) to determine the percolation rate for measurement purposes.Agricultural research and irrigation management employ the crop coefficient as a parameter.Equation ( 8) was used to calculate the crop coefficient.To evaluate the variation in the root weight of oil palm seedlings across multiple measurement periods.The plant's roots were subjected to gravimetric dehydration at 70 o C for 48 hours.If there is a statistically significant difference between the fertilised and unfertilised plants, continue with the t-test.W = M w M s x 100 % (4) Where: W is soil water content field capacity (%); M w is Mass of water (Initial soil weight, under field capacity conditionsoven dry soil weight) (g); M s is Mass of solids (oven dry soil weight) (g) (Susilo, 1987).
Where: p is large percolation (mm day -1 ); h 1 is Initial water level (mm); h 2 is final water level (mm); t 1 is Initial time (days); t 2 is End time (days) [1].

Bulk density, Particle density and Soil Porosity
Sand makes up 81.00% of entisol soil, compared to 4.12% silt and 14.88% clay (Table 1).Large pores and little water retention characterize this soil.The physical qualities of soil depend on its texture.Large particles with tiny particles make coarse soil, medium-textured materials contain smaller particles, and fine-grained materials make fine soil.Water movement, air circulation, and chemical reactions depend on soil texture.Mass density, particle density, and porosity measurements reveal that soil mass density is highest at four months of plant age, 1.0118 g cm -3 , and lowest at six months, 1.094 g cm -3 .Soil texture changes with fertiliser application, peaking at four months and decreasing at six months (Table 2).A plant's soil bulk density was more significant at four months old, at 1.167 g cm -3 , and lower at six months old, with 1.142 g cm -3 .This difference is related to the dry weight of plant roots, which increases with plant age, affecting the mass of soil solids and decreasing soil bulk density.Four-month-old soil particle density was 2.23 g cm -3 compared to 2.17.This age has more soil with plant roots, reducing soil particle density.Agricultural soil particle thickness ranges from 2.2 to 2.8 g cm -3 depending on soil organic matter content and density.The organic matter content in the entisol soil in this study was low, at 1.999%, indicating low stability.The presence of organic matter dramatically affects the density of soil particles, with higher organic matter leading to lower particle density.Higher bulk density and organic matter lead to lower particle density in soil [11,12].
Table 2 shows that 6-month-old plants have lower porosity than 4-month-old plants.Porosity, measured by soil mass and particle density, may explain these phenomena: when soil bulk density and particle density differ more, porosity increases.Table 2 shows that porosity, soil particle density, and soil bulk density are related.When particle density falls, porosity decreases.As soil bulk density rises, porosity decreases, as seen in Equation 3.

Field capacity, potential evapotranspiration (E T0 ), Crop evapotranspiration (E Tc ) and Crop coefficient of oil palm (Kc)
The field capacity of sandy loam soil was measured with and without fertilisers, with a water content of 37.77% and 43.95 %, respectively (Table 3).Every seven days, this was used to provide water for planting polybags.Due to its coarse texture and limited organic matter content, the soil's water-retention capacity is average.Texture, soil structure, and organic matter affect a soil's capacity to store and conduct water.Rapid absorption of water by organic substances.Because sandy soil has large pores, it dries out plants faster than clay-textured soil.This field's water retention capacity is average because entisol soil could retain more water.According to Arifin [13], entisol soil has a comparatively coarse texture because it is granular and low in organic matter, so the water holding capacity is inadequate; the particle structure to grain ratio causes the soil to travel through water rapidly and to be readily lost due to percolation.
Table 3 shows the evapotranspiration, evaporation, and plant coefficient values for oil palm plants aged 4 to 6 months.As the plants grow, their water demand increases, with the highest evapotranspiration value for fertiliser-fed plants at six months being 1.365 mm day -1 and the lowest at four months being 0.81 mm day -1 .The evapotranspiration of plants without fertiliser was greatest at six months, 1,315 mm day -1 , and lowest at four months.
The average potential evaporation rate is highest at six months old and lowest at four months, at 1.87 mm day -1 .As the plants mature, their coefficient value increases, with the crop coefficient (kc) value ranging from 0.82 (for Leaf Area Index < 2) to 0.93 (for Leaf Area Index > 5) for plants over seven years has a Leaf Area Index value spanning from 4.9 -5.1 [14].The coefficient value for fertiliser-using plants is highest at six months and lowest at four months.The coefficient value for oil palm plant fertiliser is greater than without fertiliser.Nutrients are essential for plant growth, specifically N, P, and K. N is needed to synthesize carbohydrates, proteins, lipids, and organic compounds, while P aids in plant reproductive structures [15].This study describes the complex interaction between soil bulk density, particle density, and porosity during oil palm growth, which helps optimize fertiliser administration for sustainable production.The findings emphasize the importance of soil parameters, nutrient levels, and plant age in developing techniques that improve crop productivity and environmental sustainability.Soil bulk and particle densities fluctuate during four to six months of age, demonstrating soil-plant dynamics.At four months, soil bulk density was increased, suggesting a denser soil structure that may affect nutrient and water availability.The reduced soil particle density at six months, especially with fertiliser, indicates a more porous soil, improving aeration and root development.Fertilization affects soil water dynamics, highlighting its environmental impact.Field capacity and evapotranspiration rates show the delicate balance between nutrient availability and water consumption, especially in sandy loam soil with high water content.Sustainable water management requires improving these characteristics to reduce water stress and boost environmental resilience.

Percolation and Root Dry Weight
According to Table 4, percolation uses the most fertiliser at four months, consuming 14.67 mm day -1 , and the least at six months, consuming 11.96 mm day -1 .Percolation without fertiliser was greatest at four months, 14.43 mm day -1 , and was lowest at six months, 11.0 mm day -1 .According to Harto (1993), percolation is the process by which water moves downward by gravity from a layer of soil to the layer beneath it so that it reaches the groundwater surface in a layer saturated with water.The percolation value was more excellent at four than six months (Table 4).
The variance in the amplitude of this percolation is closely related to the variation in soil porosity values (Table 3).When seedlings are six months old, the porosity value decreases, causing the space between soil particles to shrink, and the root density increases, as indicated by the dried weight of the plant's roots (Table 4).This decreases percolation by decreasing the soil's ability to transfer water and increasing its capacity to retain water.The difference in the quantity of percolation is also attributable to the increased need for plant water at six months of age due to the larger plant size.So, the same quantity of water supplied results in less unused water and water lost through percolation.The quantity of water supplied should correspond to the evapotranspiration requirements of the plant, which are determined by the growth rate and climatic conditions.The relationship between percolation and soil texture, and plant age indicates that the soil texture acquired exhibits a substantial proportion of sand particles.According to [15], there is a positive correlation between the age of a plant and the development of roots in the soil, resulting in increased water absorption by the roots.The rate of percolation exhibits a downward trend as the plants mature.Table 4 shows that the dried root weight of fertiliser-treated plants was most significant when the plants were six months old, at 33.89 g, and that it was lowest when the plants were four months old, at 24.5 g.Table 4 reveals that, in the absence of fertiliser, plant dried root weight was greatest at six months of age, at 24.76 g, and lowest at four months, at 21.47 g.Table 4 shows a difference in the weight of the roots of plants using fertiliser and without fertiliser due to differences in the availability of nitrogen, phosphorus and potassium nutrients.The optimal availability of nitrogen, phosphorus, and potassium nutrients for plants can increase chlorophyll.According to [16,17], with increased chlorophyll, photosynthetic activity will increase, producing more assimilation, which supports the plant's dried weight.The difference in root dry weight is because primary roots branch to form secondary roots during the growth period.Typically, secondary roots create tertiary roots, which then branch to form quaternary roots.Consequently, the weight of the oil palm plant's roots will continue to increase as the plant grows, 23% of the total surface area of oil palm roots are absorption roots.Additionally, percolation rates show a complex link between fertiliser application and soil porosity.The decrease in percolation from four to six months and differences in porosity show that fertiliser management affects water movement and soil ecosystem viability.Root biomass, a sign of plant health and nutrient uptake, shows fertilization's longterm effects.Six-month-old plants, especially fertilised ones, have more extensive root dry weights, indicating persistent nutrition uptake and long-term resistance.Nutrient management is crucial to agricultural productivity, affecting the current crop and future growth phases.

Conclusions
The relationship between soil bulk density, soil particle density, and soil bulk density is significant for plants aged 4 to 6 months.Soil bulk density is higher at four months old, while soil particle density is lower at six months old using fertiliser.Six-month-old plants had lower porosity than four-month-old plants, with or without fertiliser.With 37.77% and 43.95% water content, sandy loam soil field capacity was tested with and without fertilisers.The greatest evapotranspiration value for fertiliser-fed plants at six months is 1.365 mm day -1 , while the lowest at four months is 0.815.The coefficient crop value for fertiliser-using plants is greatest at six months and lowest at four months, as is the average potential evaporation rate.Percolation uses the most fertiliser at four months, consuming 14.67 mm day -1 , and the least at six months, consuming 11.96 mm day -1 .The variance in the amplitude of this percolation is closely related to the variation in soil porosity values.The dried root weight of fertiliser-treated plants was highest at six months, 33.89 g, and lowest at four months, 24.5 g.Root dry weight varies depending on plant nitrogen, phosphorus, and potassium availability.This study shows the dynamic relationship between soil qualities, nutrient availability, and plant growth, laying the groundwork for sustainable oil palm production.Understanding and improving these interactions improves crop coefficients and IOP Publishing doi:10.1088/1755-1315/1302/1/0121077 agricultural system sustainability.Context-specific nutrient management strategies incorporating crop health and soil ecosystem resilience are needed.

Table 2 .
Bulk density, particle density and porosity of soil using and without fertilizer

Table 3 .
Field capacity, evapotranspiration, potential evaporation and plant coefficients using fertilizer and without fertiliser

Table 4 .
Results of plant percolation and root dry weight analysis using fertiliser and without fertiliser