Evaluation of nutrition status and fertilization recommendations for lowland paddy (Case study in Merigi Kelindang District, Bengkulu Central Regency)

Farmer fertilization doses are generally insufficient compared to the recommended doses therefore causing low productivity of rice plants. This study aims to evaluate soil nutrient status to determine site-specific fertilization recommendations in Merigi Kelindang District, Central Bengkulu Regency. This study was carried out in February-April 2022 in Merigi Kelindang District, Central Bengkulu Regency, Bengkulu Province. Data was collected by taking composite soil samples at random after harvesting or before the first tillage. Determination of nutrient levels of N, P, K, and soil pH using the at Paddy Soil Test Kit. Data were analyzed descriptively comparatively. The results showed that the nutrient status of paddy fields in Merigi Kelindang District was low N 72%, medium N 14%, high N 7%, and very high 7%. P nutrient status was medium at 93% and low at 7%. High K nutrient status 100%. Meanwhile, pH status is acidic at 7% and slightly acidic at 93%. Recommendations for fertilizer usage in the Merigi Kelindang sub-district as follow; Urea 300 kg/ha for sandy soil (clay content < 20%) or 250 kg in clayey soil (clay content >20%); SP-36 fertilizer (100 kg/ha); KCl (50 kg/ha) without the use of paddy straw as compost and no KCL needed if 5 t/ha paddy straw compost used. Recommendations for soil management with a soil pH value of 5-6 (slightly acidic) are conventional drainage systems and the application of urea as N fertilizer.


Introduction
Opportunities for increasing rice productivity in Bengkulu Province to increase national production continue to be carried out through optimizing land resources and managing site-specific nutrients.The growth, development, and production of rice depend on the availability of nutrients in the soil [1], so the yield of rice in various agroecosystems still varies between locations and is not optimal.This was caused by low fertilization efficiency and nutrient deficiency of macro and microelements.Increasing 1297 (2024) 012005 IOP Publishing doi:10.1088/1755-1315/1297/1/012005 2 nutrient efficiency is very important to increase the use of fertilizers and rice yields [2].Optimization of rice productivity can be achieved through the application of technology in accordance with its agroecological characteristics [3].
Important components of the agroecology of rice farming in paddy fields include soil type, chemical fertility, and nutrient management [4].Rice plants require nutrients in sufficient quantities, the use of fertilizers is in accordance with soil nutrients, and the need for good plant growth and adequate yields, but the dosage must be appropriate to reduce the impact on the environment [5].Continuous application of inorganic fertilizers with doses that exceed plant needs can disrupt the nutrient balance in the soil due to a decrease in soil pH and the accumulation of P and K nutrients, resulting in nutrient disorders [6], as well as reduction rice yields up to 40% [7].
Nutrient management in rice cultivation can provide benefits for increasing soil fertility and sustainable crop productivity.For growth, development, and production, plants need all nutrients in balance [1].Balanced fertilization is one of the key factors to improve and optimize agricultural land productivity in accordance with plant needs and nutrient availability in the soil [8]; [6].A limiting factor for plant growth that is commonly encountered is low nutrient content in the soil, especially macronutrients N, P, and K [8].To overcome this, it is necessary to determine the dose of fertilizer given in the type and amount in accordance with recommendations based on soil nutrient status and soil fertility [3] to increase crop productivity [9].
Determination of a balanced fertilizer dose in paddy fields based on soil tests requires data on N, P, and K status, as well as pH status to determine soil management recommendations that are set before planting.By knowing the nutrient status of soil, the amount of fertilizer needed by plants to achieve optimal production can be calculated.Determination of balanced fertilization rates for lowland rice can be done quickly using the Paddy Soil Test Kit which has been developed by Soil Research Institute, Agricultural Research, and Development Agency to determine soil nutrient status and fertilizer recommendations for lowland rice [10].
Paddy Soil Test Kit is a practical, efficient soil testing instrument and can be carried out directly in the field [11].Test results using this instrument determined levels of nutrients N, P, and K, and soil pH in three classes, namely low, high, and medium classes.In addition, PUTS also sets recommendations for fertilization in accordance with the results of testing for several nutrient levels and pH [8].Paddy Soil Test Kit method is one of the practical ways to be applied in determining the nutrient needs of lowland rice plants [3].The use of PUTS needs to be encouraged nationally to increase the efficiency of fertilizer use [12], rice productivity, and farmers' income [10].
Each rice field location has different agroecosystem characteristics, which causes nutrient content of the soil to differ from one area to another.Evaluation of the nutrient status of paddy fields in each area needs to be done as a reference in determining site-specific fertilizer dosage recommendations because what is happening at this time is that the application of fertilizer recommendations by farmers is still general, so fertilizers applied are not in accordance with soil nutrient status and plant needs.Therefore, this study aims to evaluate soil nutrient status and determine the recommended dose of lowland rice fertilizer based on PUTS in Merigi Kelindang District, Central Bengkulu Regency.

Materials and methods
This research was conducted in Merigi Kelindang District, Central Bengkulu Regency, Bengkulu Province in Februari-April 2022.This research was carried out using a field survey method and soil sample testing using Paddy Soil Test Kit.Determination of location was done purposively with consideration that the study location is a rice field where the level of application of technology, especially in determining the dose of fertilizer carried out by farmers is still conventional and the productivity level of rice is still low are shown in table 1.
Composite soil samples were taken randomly are shown in figure 1, and soil was taken after harvest and before the first tillage.Prior to sampling, the uniformity of the area/overlay and the intensity of land management in the study area should be considered.Things that need to be considered include the state of the land slope, soil texture and colour of soil, drainage, plant conditions, and land management.
Composite soil samples were taken using a drill with a depth of 0-20 cm from the soil surface [13].The sample of the test soil taken was then analysed using the Paddy Soil Test Kit method with the following procedure [13]:  The solution was then allowed to stand for ± 10 minutes.Next, soil N nutrient status was read by comparing the colour that appears in the clear solution on the soil surface.

Determination of soil P status
A spoonful of soil sample was put into a test tube, then tested with P reagent in the PUTS package.The solution was then allowed to stand for ± 10 minutes.Furthermore, the blue colour that appears from the clear solution on the soil surface is compared with the soil P colour chart.

Determination of soil K status
A spoonful of soil sample was put into a test tube, then tested with K reagent in the Paddy Soil Test Kit package.The solution was then allowed to stand for ± 10 minutes.Furthermore, the yellow color that appears in the clear solution on the soil surface was compared with the soil K color chart.

Nutrient Status of Rice Fields in Study Area
The results from soil samples analysis using Paddy Soil Test Kit consisted of qualitative levels of N, P, K, and pH showed that the nutrient status of N, P, K, and pH of paddy fields in Merigi Kelindang District from 14 soil samples tested had class diversity, that the nitrogen status was low to very high, phosphorus nutrients were low to moderate, high potassium nutrients, and pH status from acid to slightly acidic are shown in table 2. Soil nutrient status was diverse in values.In N status, most of the N is low in an area of 363 ha or about (80.13%) of the total paddy field area in Merigi Kelindang District (453 ha).In P status, an area of 412 ha (90.95%) has a low P status, while the overall K status is high.Meanwhile, the pH status of the soil, acidity status was in all areas but dominated by slightly acidic status covering an area of 436 ha or about (96.25%) of the total paddy field area in the study area.
The diversity of nutrient status values showed that most of the nutrients, especially N and P dominant in the study area, were not available enough for the growth and development of rice plants.The low nutrient content in the soil is a limiting factor for plant growth [8].Therefore, additional nutrients from external are needed in the form of inorganic and organic fertilizers such as animal manure or compost and the application of these materials must be in a mature condition [14].

Single Fertilizer Recommendation
The recommended dose of fertilizer generated from the analysis of paddy soil samples using PUTS describes the overall distribution of fertilizer doses at the study site.Preparation of fertilizer recommendations based on the status of N, P, K, and soil pH.The single fertilizers used were Urea, SP-36, and KCl.Urea fertilizer is a type of fertilizer that is recommended to overcome N deficiency in the soil.In the research area, the N status of the soil is dominated by low N. To overcome this problem, a large supply of N is needed.The high recommended dose of urea fertilizer as an external supplier of N, due to the low soil N status, is also caused by the dynamic nature of N in the soil [8].
Recommendations for the type and dose of specific single fertilizer in Merigi Kelindang District based on pH status, especially for the use of low-status N fertilizer, are in the form of urea with a dose of 300 kg Urea/ha for sandy textured soils (<20% clay), 250 kg Urea/ha for clay textured soil (20-40% clay).Medium N status with a dose of 250 kg Urea/ha for sandy textured soils (<20% clay), and 200 kg Urea/ha for clay textured soils (20-40% clay).High N status with a dose of 200 kg Urea/ha for sandy textured soils (<20% clay), and 200 kg Urea/ha for clay textured soils (20-40% clay).Recommended P fertilizer in the form of SP-36 with low P status using a dose of 100 kg SP-36/ha and medium P status using a dose of 75 kg SP-36/ha.Furthermore, K fertilizer in the form of KCl with a dose of 50 kg KCl/ha (no straw returned into the soil); without KCl fertilizer by returning straw to rice fields as much as 2 tons of straw compost or 5 t of fresh straw per ha.Meanwhile, water management with conventional drainage systems are shown in table 3.
The level of acidity (pH) of the soil from the test results shows a slightly acidic status, namely pH 5-6 where the condition of the Kelindang Village rice fields is irrigated rice fields, and in general irrigated paddy fields have a slightly acidic to neutral pH caused by alternating wet and dry conditions in the long period.This is in line with that stated by [13] that inundation tends to cause soil pH to become neutral.Changes in soil pH to neutral have benefits for optimal levels of soil nutrient availability and alleviate toxic elements for plants.

Recommendations for Single Fertilizers and Compound Fertilizers Based on Yield Targets
One of the efforts that can be made to achieve the target yield is the use of the recommended dose of fertilizer in accordance with the soil nutrient status and yield targets.Based on the research results, recommendations for single and double fertilization with a target yield of 7 t GKP/ha in Kelindang Village, Merigi Kelindang District, Central Bengkulu Regency are shown in table 4 and table 5.The dose of fertilizer must be in accordance with the specifications for nutrient requirements in the soil and based on the target yield.The provision of fertilizers that are in accordance with nutrient requirements will optimize production results from cultivated land.Nitrogen application at 120% of the recommended dose can be a valuable agro-management strategy to maintain relatively high yields [15].
According to [16] that fertilization recommendations are useful in providing the right fertilizer both at the dose, time, and type of fertilizer, therefore, fertilization will be efficient, and farmers' production and income will increase.In addition, fertilizer recommendations also aim to prevent environmental pollution, maintain soil fertility and sustainable rice production, and can reduce the cost of purchasing fertilizers.Benefits and impacts of applying site-specific fertilizers, namely the right dose, on time, and the appropriate type of fertilizer required, fertilization would be more efficient, yields high, and farmers' incomes increased [17; 18; 19].Environmental pollution can be avoided, soil fertility is maintained, and rice production is sustainable.In addition, it can reduce waste by 15-20%.[12]

Figure 1 .
Figure 1.Distribution pattern of random composite soil sampling

Table 2 .
Nutrient status of paddy fields in Merigi Kelindang District

Table 3 .
Recommended dose of single NPK fertilizer in Merigi Kelindang District

Table 4 .
Recommended dose of single NPK fertilizer target yield of 7 t GKP/ha

Table 5 .
Recommended doses of single and compound fertilizers target yield 7 t GKP/ha