Usulan sistem pengendalian persediaan continuous review dan periodic review yang mempertimbangkan back order dan lost sales untuk produk pupuk urea di PT Pusri Palembang
P emasaran Pusri Daerah Sumsel (PPD Sumsel) berperan untuk memasarkan pupuk urea di daerah Sumsel. Pemasaran pupuk urea yang sudah di kantong (in bag) mencakup pupuk subsidi untuk petani dan pupuk non subsidi untuk perkebunan. Tujuan PPD Sumsel adalah memasarkan pupuk urea untuk memenuhi permintaan distributor di Sumsel. Permasalahan di PPD Sumsel terjadi karena permintaan distributor yang bersifat probabilistik, sehingga menyulitkan PPD Sumsel dalam permintaan pupuk urea di Sumsel Tujuan dari penelitian ini adalah menentukan peramalan permintaan pupuk urea subsidi dan non subsidi selama 6 bulan mendatang antara bulan Januari 2011 hingga Juni 2011. Disamping itu juga, mengusulkan sistem pengendalian persediaan pupuk subsidi dan non subsidi agar mencapai tingkat persediaan optimal dengan total biaya persediaan minimum. Model yang diterapkan sebagai kebijakan pengendalian persediaan pada pupuk urea adalah Continuous Review dan Periodic Review. Sebelum melakukan perhitungan, terlebih dahulu dilakukan plot data permintaan, peramalan untuk 6 periode ke depan menggunakan metode Double Moving Average (DMA) N-2, Double Exponential Smoothing (DES) 4 parameter (a = 0,1; 0,2; 0,4; 0,7), Weighted Moving Average (WMA) (N= 2), Simple Moving Average(SMA) N=2, Simple Exponential Smoothing (SES) 4 parameter (a = 0,1; 0,2; 0,4; 0,7), dan Siklis. Berdasarkan perhitungan nilai error peramalan, metode siklis untuk pupuk urea subsidi dan non subsidi terpilih sebagai metode peramalan karena memiliki mean squared error (MSE) terkecil. Selanjutnya, hasil pengujian Kolmogorov-Smirnov untuk pupuk urea subsidi dan non subsidi terbukti berdistribusi normal. Oleh karena itu, model Continuous Review dan Periodic Review dapat digunakan untuk pengendalian persediaan pupuk urea subsidi dan non subsidi. Persediaan pupuk urea subsidi lebih sedikit dari permintaan adalah backorder, sedangkan persediaan pupuk urea non subsidi lebih sedikit dari permintaan adalah lost sales. Continuous Review untuk kondisi backorder pada pupuk urea subsidi lebih hemat dibandingkan dengan Periodic Review untuk kondisi backorder pada pupuk urea subsidi karena selisih total biaya persediaan per 6 bulan sebesar Rp. 8.567.567,68. Continuous Review untuk kondisi lost sales pada pupuk urea non subsidi lebih hemat dibandingkan dengan Periodic Review untuk kondisi lost sales pada pupuk urea non subsidi karena selisih total biaya persediaan per 6 bulan sebesar Rp. 606.119,46. Model persediaan Continuous Review untuk kondisi backorder pada pupuk urea subsidi lebih hemat dibandingkan dengan model persediaan saat ini sebesar 9,25%. Model persediaan Continuous Review untuk kondisi lost sales pada pupuk urea non subsidi lebih hemat dibandingkan dengan model persediaan saat ini sebesar 54,98 %. Analisa sensitivitas dilakukan terhadap biaya simpan dan biaya pesan pada pupuk urea non subsidi. Apabila biaya simpan dinaikkan hingga 10% adalah total biaya persediaan semakin besar dan ukuran lot pemesanan optimal (Q) semakin rendah. Apabila biaya pesan diturunkan antara 20% sampai 25%, maka total biaya persediaan semakin rendah dan tidak mempengaruhi ukuran lot pemesanan.
P emasaran Pusri Daerah in South Sumatra (PPD South Sumatra) which takes the role on marketing the urea fertilizer in the area of South Sumatra. Marketing of urea fertilizer which is already in the bag include fertilizer subsidies to farmers and non-subsidized fertilizer for plantations. PPD's goal is to market urea fertilizer to fulfill demand of distributor in South Sumatra. The problems in South Sumatra PPD is due to distributor demand which is probabilistic, making it difficult for PPD Sumatra to fulfill demand for urea fertilizer in South Sumatra. The purpose of this research is to determine forecasts in terms of demand for the subsidized fertilizer and non-subsidized fertilizer for the next six months starting from the month of January 2011 to June 2011 as well as purposing inventory control system in the subsidized fertilizer and non-subsidized fertilizer in order to achieve optimal inventory level's with the minimum total inventory cost. The Models made in inventory control on urea fertilizer are Continuous Review and Periodic Review. Demand's data plotting is the first step, followed by demand forecasting for the next six periods using the method of Double Moving Average (DMA) N = 2, Double Exponential Smoothing (DES) 4 parameter (a = 0.1: 0.2: 0.4: 0.7), Weighted Moving Average (WMA) (N = 2), the Simple Moving Average (SMA) N = 2, Simple Exponential Smoothing (SES) 4 parameter (a = 0.1: 0.2: 0.4: 0.7), and Cycle. Based on the error measurement of each forcasting method, the Cycle method on subsidized fertilizer and non-subsidized fertilizer, has been chosen as the forecast method, due to the calculation of the mean squared error (MSE) that resulted the least error. Next, Kolmogorov-Smirnov test results for subsidized urea fertilizer and non-subsidized urea fertilizer was normally distributed. Continuous Review and Periodic Review can be used for control inventory model in term of subsidized urea fertilizer and non-subsidized urea fertilizer. Lesser demand for subsidized urea fertilizer is backorder condition and Lesser demand non-subsidized urea fertilizer is lost sales condition. As compared to Periodic Review, Continuous Review is more cost efficient under the backorder condition of subsidized urea fertilizer and non-subsidized urea fertilizer because the difference in cost per 6 months amounts to Rp.8.567.567,68. In terms of lost sales condition of non-subsidized urea fertilizer, Continuous Review is more cost efficient as compared to Periodic Review because the difference in cost per 6 months amounts to Rp.606.119,46. As compared to the current inventory model, Continuous Review is more cost efficient under the backorder condition of subsidized urea fertilizer because the difference in percentages amounts to 9,25%. As compared to the current inventory model, Continuous Review is more cost efficient under the lost sales condition of non-subsidized urea fertilizer because the difference in percentages amounts to 54,98 %. Sensitivity analysis was done toward the cost of holding and ordering. If the cost of holding is increased by 10%, the total cost of inventory will increase , the number of order will reduce. If the cost are reduced between 20%-25% so the total cost of in inventory will reduce and will not impact of the number of orders.