<![CDATA[Superior bacterial isolates and optimum growth conditions for potassium-solubilizing bacteria (KSB) are essential for effective biofertilizer formulation. This study aimed to screen superior KSB isolates from feldspar mining areas, determine optimum inoculation dosage and pH levels, and evaluate their effects on maize growth. KSB were isolated via serial dilution of rhizosphere soil samples on Aleksandrov selective media. Isolates were selected using scoring and ranking methods based on their K-feldspar mineral solubilization capacity. Growth optimization employed a completely randomized design with seven inoculation doses (0.00–1.50% v/v) and nine pH levels (5.0–9.0), followed by quadratic polynomial regression analysis. A maize bioassay used a randomized block design with two treatments (with and without KSB inoculation), analyzed via independent T-tests and Pearson correlation. Three superior KSB isolates were isolated from feldspar mining areas, namely Kosakonia sacchari (KSB B1), Burkholderia sp. (KSB B4), and Kosakonia sacchari (KSB B3). An inoculation dose of 0.98% and pH 7.0 indicated the optimum growth conditions of KSB. Compared to the control, KSB inoculation increased KSB populations, root volume (26.06%), stomatal conductance (39.27%), chlorophyll index (62.44%), and potassium (K) uptake (43.28%). A strong positive correlation was found between K-uptake and root volume (r = 0.72). These optimum growth conditions enhance maize growth and K-uptake, demonstrating KSB's potential as a biofertilizer to improve crop productivity in K-deficient soils. Key words: K-feldspar, KSB, K-uptake, Optimization, Selection ABSTRAK Isolat bakteri unggul dan kondisi pertumbuhan optimum bakteri pelarut kalium (BPK) yang teridentifikasi diperlukan untuk formulasi pupuk hayati yang efektif. Penelitian bertujuan untuk menjaring isolat BPK unggul dari area pertambangan felspar, menentukan dosis inokulasi serta tingkat pH optimum, dan menguji pengaruhnya terhadap pertumbuhan tanaman jagung. Isolasi BPK melalui pengenceran berseri sampel tanah rizosfer pada media selektif Aleksandrov. Isolat BPK diseleksi menggunakan metode penskoran dan pemeringkatan berdasarkan kemampuan melarutkan mineral K-felspar. Optimasi pertumbuhan BPK menggunakan rancangan acak lengkap dengan tujuh dosis inokulasi (0,00–1,50% v/v) dan sembilan tingkat pH (5,0–9,0) serta analisis regresi polinomial kuadratik. Uji hayati tanaman jagung menggunakan rancangan acak kelompok dengan dua perlakuan (dengan dan tanpa inokulasi BPK) serta analisis uji t saling bebas dan korelasi Pearson. Tiga isolat unggul BPK dapat diisolasi dari area pertambangan felspar, yaitu Kosakonia sacchari (BPK B1), Burkholderia sp. (BPK B4), dan Kosakonia sacchari (BPK B3). Dosis inokulasi 0,98% dan pH 7,0 menunjukkan kondisi pertumbuhan optimum BPK. Inokulasi dapat meningkatkan populasi BPK, 26,06% volume akar, 39,27% konduktivitas stomata, 62,44% indeks kadar klorofil, dan 43,28% serapan kalium (K) tanaman jagung dibandingkan kontrol. Korelasi positif kuat ditemukan antara serapan K dan volume akar (r = 0,72). Kondisi pertumbuhan optimum BPK dapat meningkatkan pertumbuhan dan serapan K tanaman jagung yang menunjukkan potensi aplikasi BPK sebagai pupuk hayati dalam meningkatkan produktivitas tanaman pada tanah yang kekurangan K. Kata kunci: BPK, K-felspar, Optimasi, Seleksi, Serapan K]]>
