Pemetaan Potensi Erosi dan Kehilangan Hara Makro di Kawasan Transmigrasi Mahalona

Abstract

Erosi akibat alih fungsi lahan merupakan ancaman serius terhadap keberlanjutan lahan seperti yang umum terjadi di Kawasan Transmigrasi. Di Kawasan Transmigrasi Mahalona, lahan pertanian tersebar di kemiringan landai hingga curam dengan lahan tanpa tutupan hingga hutan alam. Pemetaan sebaran erosi dalam penelitian ini menggunakan metode Universal Soil Loss Equation (USLE) yang diintegrasikan dengan Sistem Informasi Geografis (SIG). Estimasi besarnya kehilangan nitrogen (N), fosfor (P), dan kalium (K) akibat erosi dihitung berdasarkan konsentrasi hasil uji laboratorium. Erosivitas hujan (R), erodibilitas tanah (K), panjang dan kemiringan lereng (LS), serta tutupan dan tindakan konservasi tanah (CP) ditentukan masing-masing dari data curah hujan bulanan selama 5 tahun, sifat fisika-kimia contoh tanah, data DEMNAS, dan referensi CP. Hasil analisis menunjukkan bahwa 71,14% kawasan (10.581 ha) termasuk kelas TBE sangat ringan (<15 ton ha?¹ tahun?¹), 2,89% (429 ha) kelas ringan (15-60 ton ha?¹ tahun?¹), 13,39% (1.991 ha) kelas sedang (60-180 ton ha?¹ tahun?¹), 9,30% (1.383 ha) kelas berat (180-480 ton ha?¹ tahun?¹), dan 3,29% (489 ha) kelas sangat berat (>480 ton ha?¹ tahun?¹), dengan erosi tertinggi mencapai 2.801,39 ton ha?¹ tahun?¹ pada lereng curam yang aktif mengalami pembukaan lahan. Kelas sedang hingga sangat berat muncul sebagai bercak-bercak terpisah yang terkonsentrasi di lereng perbukitan bagian utara kawasan. Rentang kehilangan hara N, P, dan K berturut-turut sebesar 0,033-12.112, 0,001-11.286, dan 0,019-22.471 kg ha?¹ tahun?¹, dengan kehilangan tertinggi di zona lereng perbukitan yang telah mengalami konversi hutan untuk kebun lada. Diperlukan upaya konservasi tanah dan air seperti pembangunan teras, penanaman cover crop, dan pengembangan sistem agroforestri guna mengurangi erosi dan kehilangan unsur hara di Kawasan Transmigrasi seperti di Mahalona.

Erosion due to land use conversion is a serious threat to land sustainability, as commonly occurs in transmigration areas. In the Mahalona Transmigration Area, agricultural land is spread across gentle to steep slopes with land cover ranging from bare soil to natural forest. Erosion distribution mapping in this study used the Universal Soil Loss Equation (USLE) method integrated with a Geographic Information System (GIS). Estimates of nitrogen (N), phosphorus (P), and potassium (K) losses due to erosion were calculated based on laboratory analysis concentrations. Rainfall erosivity (R), soil erodibility (K), slope length and steepness (LS), and land cover and conservation practices (CP) were determined from five-year monthly rainfall data, soil physicochemical properties, DEMNAS data, and CP references, respectively. The analysis results show that 71.14% of the area (10,581 ha) falls under the very slight EHL class (<15 ton ha?¹ yr?¹), 2.89% (429 ha) under the slight class (15–60 ton ha?¹ yr?¹), 13.39% (1,991 ha) under the moderate class (60–180 ton ha?¹ yr?¹), 9.30% (1,383 ha) under the severe class (180–480 ton ha?¹ yr?¹), and 3.29% (489 ha) under the very severe class (>480 ton ha?¹ yr?¹), with the highest erosion rate reaching 2,801.39 ton ha?¹ yr?¹ on steep slopes undergoing active land clearing. The moderate to very severe classes appear as discrete patches concentrated on the hill slopes in the northern part of the area. The ranges of N, P, and K losses are 0.033-12,112, 0.001-11,286, and 0.019-22,471 kg ha?¹ yr?¹, respectively, with the highest loss in hillslope zones that have undergone forest conversion for pepper plantations. Soil and water conservation measures such as terrace construction, cover crop planting, and agroforestry system development are needed to reduce erosion and nutrient loss in transmigration areas such as Mahalona.