A Site-Specific Fertilizer Recommendation Based on the Phosphorus and Potassium Status in Mempawah District, West Kalimantan

Kata Kunci: Padi sawah, status hara, spesifik lokasi, rekomendasi pupuk The recommendations of Phosphorus (P) and Potassium (K) fertilization for rice are still not site-specific yet due to a lack of required soil data information. The P and K status of the paddy fields that provide information on the low, medium, and high P and K nutrient status are very useful for determining recommended the site-specific fertilizer in the the district area. The purpose of the research was to determine the site-specific fertilizer recommendation for paddy field based on their P and K status. This research was based on the field survey and the soil analysis in the laboratory. The soil samples were taken using a grid system, and the P and K levels were assessed by using a 25% HCl extraction. Soil samples were taken in a composite manner on all paddy fields in which their status have been identified. The composite soil samples were determined from 10 15 individual samples (sub-samples) with a sampling distance of each sub-sample of 25-50 m in the field. The soil samples were taken in the overlay with a depth of 0-20 cm. Taking sub-samples were done by a diagonal or a zigzag method according to the conditions of paddy fields. The results of the study presented that the nutrient status of P and K and the fertilizer recommendations in paddy fields for rice plants located in 9 sub-districts in Mempawah Dsitrict had shown that nutrient status of P, on average, were from moderate to high levels, meanwhile, the nutrient status of K was from low to high levels. Recommendations for fertilizing rice fields in several sub-districts in Mempawah Regency are mostly 150 kg NPK (15:15:15) ha, 200 kg Urea ha and 25 kg KCl ha.


INTRODUCTION
One of the many efforts in stabilizing a national food self-sufficiency is to optimize paddy fields for rice farming by increasing the rice production and productivity. Increased production and productivity of rice in paddy fields, among others, are by increasing the soil productivity and soil fertility. Increased productivity and soil fertility are concerning to the nutrient input given to the soil in the form of fertilizer. Up to present, the farmers have not been rationally used fertilizers according to crop needs and the ability of the soil to provide nutrients, the soil properties, the water quality, and the management by farmers. The disadvantages of fertilization aside from being a waste of resources, it also will disrupt the balance of nutrients in the soil and cause the environmental pollution Moersidi et al. 1989), Nagumo et al. (2013) reported that excess phosphorus (P) has accumulated in Japanese paddy soils due to continuing used of P fertilizer. Moreover, the diminishing marginal utility of soil Olsen-P was also found, indicating that high-level P application in the present condition could not increase soil Olsen-P contents anymore (Shi 2015). While, giving a small amount of fertilizer can not provide optimal production levels. If a sufficient fertilization is not carried out, the plant will lake the nutrients from the soil. If the soil is fertile, in the short term, rice crops will not show a decrease in production, but in the long term, there will be a decrease in soil and plant productivity. If the soil is not fertile, rice plants will show productivity far lower than the actual productivity potential (Sukarman et al. 2012).
A simpler approach for establishing fertilizer recommendations for major crops is urgently required to improve the application efficiency of commercial fertilizers in China. To address this need, a method was developed based on field data drawn from the China Program of the International Plant Nutrition Institute (IPNI) rice experiments and the investigations were carried out in the southeastern China from 2001 to 2012. The results showed that using the agronomic efficiencies and a sustainable yield index (SYI), this new method for establishing fertilizer recommendations robustly estimated the mean rice yield (7.6 Mg ha -1 ) (Jin 2012; Chuan et al. 2019;Liu et al. 2017).
The nutrient depletion, imbalanced use of fertilizer nutrients, inappropriate tillage, and rainwater management practices often result in the land degradation. Declining soil health contributes to climate change through loss in soil productivity, biodiversity, soil carbon, and moisture and ecosystem services (Raj et al. 2019). Xu et al. (2014) reported that compared to the current farmers' fertilizer practices (FP), nutrient efficiency (NE) maintained grain yield and profitability, but it decreased 30.4% of nitrogen (N) fertilizer (68 kg N ha -1 ) and 11.3% of phosphorus (P) fertilizer (7 kg P 2 O 5 ha -1 ), while potassium (K) fertilizer rate increased by 38.8% (19 kg K 2 O ha -1 ). NE increased agronomic efficiency of applied N (AEN) by 47.0%, N recovery efficiency (REN) by 51.0%, and partial factor productivity of applied N (PFPN) by 35.5%. More importantly, NE decreased by 21.5 and 49.7 kg ha -1 of apparent N loss for summer maize and spring maize as compared to FP, respectively.
The recommendations for the amount of P and K fertilizer applied for rice are still general, not site-specific due to the lack of information/data needed. In other words, the recommendations for fertilizing paddy rice in each region are still uniform, not based on the soil nutrient content. The P and K nutrient status of paddy fields that provide information about P and K in the low, medium, and high nutrient status are very useful for determining site-specific fertilizer recommendations.
Up to the present, the P and K fertilization for lowland rice is around 100-150 kg TSP per hectare per season and 100 kg KCl per hectare per season. Determination of these recommendations is carried out without considering the nutrient content of P and K in the soil and nutrient requirements for rice plants, making it less efficient (Jamil et al. 2012). Therefore, it is necessary to know the nutrient content of P and K in wetland so that the determination of fertilizer dosage will be more rational. Triharto et al. (2014) reported that rainfed lowland in Durian Village, Labu Sub-district, Deli Serdang Regency had a low to moderate N-total status, P status was very low and K status was very high. Manurung (2017) reported that the total Nsoil content in peatlands in Sungai Purun Village Mempawah Regency is almost entirely including the medium category covering 97.49% of the area of the study. Status P varies from very low, low, medium and very high, very high status has the largest area (87.6%). Very high K status has the largest area (38.1%). The diversity of nutrient status in several locations and soil types indicates that fertilizer recommendations in several areas should be different. This can be caused by the differences in the parent materials, the intensity to broken down, the erosion effect, the biological influence, the hydrological differences, and the errors in the analysis (Yudichandra et al. 2016).
Nutrient status in soil is strongly influenced by the level of land management carried out by farmers. Rice fields that are managed intensively and continuously fostered are thought to have increased levels of soil nutrients, especially levels of P and K, and experienced nutrient imbalances. On the other hand, in paddy fields that are not managed intensively or rarely being fertilized, there will be a decrease in nutrient levels, especially K nutrients that are easily leached out. For this reason, we need the information on soil nutrient status, especially P and K, to support the accuracy of sitespecific fertilizer recommendations. According to Nandor et al. (2013) who testing various fertilizer recommendation systems in Hungary, the fertilizer recommendation system that is cost-effective and environmentally friendly and the correctness of the method is very important in the recommendation of an appropriate fertilizer. Indonesia adopts a balanced fertilization, a framework that is founded on the site-specific nutrient management. The fertilizer is added to the soil to achieve balanced and optimum nutrient availability (Sulaiman et al. 2012).
The status of P and K nutrients of paddy fields is useful for compiling recommendations for fertilizing location-specific lowland rice and the direction of fertilizer needs at the district and subdistrict level. Mempawah Regency is the largest food crop producing center, especially rice in West Kalimantan. A reliable nutrient status information in Mempawah Regency can be obtained by extracting a large amount of soil characteristics data that spreads in the area of Mempawah Regency. To obtain fertilizer recommendations, it is necessary to have comprehensive data so that fertilizer recommendations can be applied appropriately, which one of the soil nutrient status data.
The purpose of this study was to determine fertilizer recommendations for lowland rice-based on P and K nutrient status in several sub-districts in Mempawah District, West Kalimantan Province. In determining fertilizer recommendations in the area of Mempawah Regency, data on the characteristics of paddy soils will be carried out, such as pH, C-organic, Cation Exchange Capacity (CEC), bbases saturation and other soil properties.

Survey Preparation
The research was carried out in July -December 2017 on paddy fields in Mempawah Regency, West Kalimantan Province. This research was based on a field survey and the soil analysis in the laboratory and making nutrient status maps, especially P and K. Materials and tools used included soil survey equipment, chemicals for soil analysis, and other materials and tools as well as supporting maps such as administrative maps, land maps, topographic maps, land use maps, and others. The operational map was made on a scale of 1: 25,000 which was made from topographical maps as a guide when conducting the survey.

Soil Sampling
The soil samples were taken using a grid system, and P and K levels were assesed by using 25% HCl extraction. Sampling of composite soil was carried out according to the method of Soepartini et al. (1994). Soil samples were taken in a composite manner on all paddy fields in which their status have been identified.
Sampling was done on "signs" that have been made in the field map. At each retrieval mark that has been made, one composite soil sample was taken. Composite soil samples were determined from 10-15 individual samples (subsamples) with a sampling distance of each subsample of 25-50 m in the field. The tool used for soil sampling was a Belgian drill or rice field drill. Soil samples were taken in the overlay with a depth of 0 -20 cm.
Taking sub-samples was done by a diagonal or zigzag method according to the conditions of paddy fields in several places. After all of the composite samples had been collected, the composite soil samples were then being analyzed in the laboratory to examine the nutrient content, especially P and K.
The nutrient status criteria is refer to the criteria for assessing the status of chemical properties and soil fertility of the Bogor Soil Research Institute (Table 1).
The recommendation regarding fertilizer refers to the Minister of Agriculture Regulation Number 40 /Permentan /0 T .140 /04 /2007 concerning, P, and K Fertilization Recommendation on Site Specific Rice Fields .This recommendation is based on criteria between 3 nutrient status of P (low , medium , high) and 3 nutrient status of K (low, medium , and high). This recommendation is preferred for compound fertilizer due to its widely availability in the market.

RESULTS AND DISCUSSION
Paddy fields in this study are paddy fields that are patched and limited by a dike rice field, a channel to channel water that is usually planted with rice. Land in the area of Mempawah Regency according to its utility is divided into three types of land, namely paddy fields, non-rice fields, and non-agricultural land. In 2017, paddy fields in the area of Mempawah Regency decreased by around 2.49%, which initially was 18,400 hectares became 17,943 hectares (CBS 2017). The sub-district rice fields in Mempawah Regency are as shown in Table 2.
The P nutrient status in paddy fields in Mempawah District is generally classified as moderate to very high, as in Sungai Kunyit Subdistrict, most of the paddy fields have low P status, while in Sungai Pinyuh, Anjongan, Segedong, and Siantan Sub-districts most of the status P nutrients are high. The nutrient status of K is classified as low to very high, such as in the Districts of Siantan, Segedong, Toho, East Mempawah, Mempawah Hilir, Anjongan, Sungai Kunyit, and Sadaniang classified as high K status. As has been done by Muhammad et al. (2018) that the P and K nutrient status classes of paddy fields in Pandeglang district Banten Province varied from low to high.

Siantan Sub District
The area of paddy fields in Siantan Sub-district is 3,762 ha which is spread in several villages such as Wajok Hilir, Wajok Hulu, Jungkat, and Sungai Nipah. The nutrient status of P 2 O 5 in paddy fields in the Siantan sub-district is high, with an average  (Figure 1).

Segedong Sub District
The area of paddy fields in Segedong Sub District is 4,265 hectares. The nutrient status of P 2 O 5 in the paddy fields of the Segedong Sub-district is high, that is, on average P 2 O 5 of 56.13 mg (100g) -1 , as well as the nutrient status of K 2 O is also relatively high,

Sungai Pinyuh Sub District
The area of paddy fields in Sungai Pinyuh Sub District is 1,525 hectares. The nutrient status of P 2 O 5 in paddy fields in Sungai Pinyuh Sub-district is classified as moderate to high, which is between 29.37 mg (100g) -1 and 56.56 mg (100g) -1 , while for K 2 O nutrient status is high at 67.50 mg (100g) (Figure 3).

Anjongan Sub District
The area of paddy fields in the Sub District of Anjongan is 1,550 hectares. The nutrient status of P 2 O 5 in the wetland area of the Anjongan Sub-district is high, with an average of 56.89 mg (100g) -1 , and some are very high as in Anjongan Melancar   Village, which is 120.82 mg (100g) (Figure 4).

Sungai Kunyit Sub District
The area of paddy fields in Sungai Kunyit Sub District is 1,184 hectare. The nutrient status of P 2 O 5 in paddy fields in Sungai Kunyit Sub-district is high, with an average of 53.32 mg (100g) (Figure 7).

Toho Sub District
The area of paddy fields in Toho Sub District is 2,498 hectares. The nutrient status of P 2 O 5 in the paddy fields of the Toho Sub-district is high, with an average of 55.38 mg (100g) -1 . K 2 O nutrient status is high to very high, namely from 30.87 mg (100g) -1 to 43.12 mg (100g) (Figure 8).

Sadaniang Sub District
The area of paddy fields in Sadaniang Subdistrict is 1,743 hectares. The nutrient status of P 2 O 5  (Figure 9).

CONCLUSIONS
Based on the P and K nutrients status in Mempawah District, it can be concluded that paddy fields with high P nutrient status are spread in 46 villages in 9 Sub-districts and medium P status of paddy fields is spread in 8 villages in 3 Sub-districts, meanwhile, there are no paddy fields that have low P nutrient status. Paddy fields with high K nutrient status are spread in 24 villages in 8 sub-districts, with medium K nutrient status are spread in 21 villages in 6 sub-districts, and with low K nutrient status are spread in 2 villages in 2 sub-districts.

ACKNOWLEDGEMENTS
Our deeply acknowledgment is being delivered to Head of Indonesian Agency for Agricultural Research and Development for supporting this