Electronic Theses and Dissertation

RINGKASAN

MUHAMMAD NASIR. Optimasi Produktivitas Tanah Melalui Model Teknik Konservasi pada Lahan Kebun Serai Wangi Rakyat di Dataran Tinggi Gayo, Dibawah Bimbingan Abubakar sebagai Promotor, Hairul Basri sebagai Ko-Promotor I dan Ichwana sebagai Ko-Promotor II.

Sentral Serai wangi (Cymbopogon nardus L) Provinsi Aceh terdapat di Dataran Tinggi Gayo (Kabupaten Gayo Lues, Aceh Tengah dan Bener Meriah). Di Dataran Tinggi Gayo (DTG) Serai wangi dibudidayakan di wilayah perbukitan bahkan bertumpang sari dengan tegakan Pinus. Namun demikian di wilayah perbukitan yang ditanami Serai wangi ini produktivitas lahan mulai menurun sebagi akibat dari erosi dan degradasi lahan. Sebagai komoditas unggulan bernilai ekonomi tinggi, keberlanjutan budidaya Serai wangi perlu didukung oleh strategi konservasi tanah yang efektif dalam menekan kehilangan tanah sekaligus menjaga kesuburan tanah dan efisiensi pemanfaatan lahan.
Tujuan penelitian untuk (1) mengkaji kondisi eksisting dan pola pengembangan kebun Serai wangi, (2) mengevaluasi kesesuaian lahan, kualitas tanah, dan tingkat bahaya erosi, dan (3) menyusun model optimasi produktivitas tanah melalui penerapan teknik konservasi tanah dan air yang berkelanjutan.
Penelitian I menunjukkan bahwa kebun Serai wangi rakyat di Dataran Tinggi Gayo berkembang pada lingkungan biofisik yang sangat heterogen, mencakup 33 Satuan Peta Lahan (SPL) dengan ketinggian 400 hingga >1.200 m dpl dan kelas lereng 0 hingga >40%. Total luasan kebun mencapai 4.191,39 ha, dengan kontribusi terbesar berasal dari Kabupaten Gayo Lues (46,9%), diikuti Bener Meriah (28,2%) dan Aceh Tengah (24,9%). Sebagian besar kebun berada pada lereng 15–40%, bahkan >40%, yang mengindikasikan bahwa pengembangan Serai wangi masih bersifat empiris dan belum sepenuhnya berbasis evaluasi kesesuaian lahan, sehingga berpotensi meningkatkan risiko degradasi tanah.
Penelitian II membuktikan bahwa secara iklim, wilayah penelitian tergolong sangat sesuai (S1) bagi Serai wangi, dengan curah hujan rata-rata 2.109 mm/tahun, ketinggian 1.010 m dpl, dan periode bulan kering 2–3 bulan. Namun demikian, kesesuaian lahan aktual didominasi oleh kelas cukup sesuai (S2) akibat pembatas utama berupa kemiringan lereng, kedalaman efektif tanah, drainase, dan ketersediaan fosfor. Nilai Indeks Kualitas Tanah (IKT) sebesar 0,84 menunjukkan bahwa kualitas tanah masih berada pada kategori tinggi. Prediksi erosi menggunakan model USLE menghasilkan kisaran erosi 0,06 hingga 1.220,88 ton/ha/tahun, yang menegaskan bahwa variasi pengelolaan lahan (faktor C dan P) lebih menentukan besarnya erosi dibandingkan faktor alami. Analisis kesesuaian lahan potensial menunjukkan bahwa sebagian besar faktor pembatas bersifat dapat diperbaiki, sehingga peningkatan kelas kesesuaian dari S2 menjadi S1 sangat memungkinkan melalui intervensi konservasi dan pengelolaan hara.
Penelitian III menunjukkan bahwa penerapan teknik konservasi tanah dan air secara terpadu mampu menurunkan aliran permukaan sebesar 75,0% dan erosi tanah sebesar 58,7% dibandingkan tanpa konservasi. Secara parsial, terasering merupakan teknik paling efektif dengan penurunan erosi 44,4%, diikuti jarak tanam rapat (17,2%) dan mulsa (9,5%). Model optimasi produktivitas tanah menunjukkan bahwa sistem konservasi terpadu mampu mempertahankan 84% produktivitas tanah potensial, jauh lebih tinggi dibandingkan kondisi tanpa konservasi yang hanya mencapai 61%. Penerapan konservasi terbaik juga mampu mempertahankan kapasitas hara tanah sekitar 2,3% lebih tinggi dibandingkan kontrol.
Secara keseluruhan, penelitian ini menegaskan bahwa pengembangan kebun Serai wangi di Dataran Tinggi Gayo harus diarahkan berbasis kesesuaian lahan dan SPL, serta diintegrasikan dengan penerapan konservasi tanah dan air sebagai prasyarat utama. Model optimasi produktivitas tanah yang dihasilkan memberikan kontribusi ilmiah dan praktis sebagai dasar perencanaan pengelolaan kebun Serai wangi rakyat yang produktif, adaptif, dan berkelanjutan.

Kata kunci: produktivitas tanah, konservasi lahan, serai wangi, erosi, Dataran Tinggi Gayo, USLE, optimasi.

SUMMARY MUHAMMAD NASIR. Optimization of Soil Productivity through a Conservation Technique Model on Smallholder Citronella (Cymbopogon nardus L.) Plantations in the Gayo Highlands, supervised by Abubakar as Promoter, Hairul Basri as Co-Promoter I, and Ichwana as Co-Promoter II. The main citronella (Cymbopogon nardus L.) production centers in Aceh Province are located in the Gayo Highlands, encompassing Gayo Lues, Aceh Tengah, and Bener Meriah Regencies. In this region, citronella is predominantly cultivated on hilly and mountainous terrain, in some cases intercropped under pine stands. However, land productivity in these upland citronella plantations has shown a declining trend due to soil erosion and land degradation. As a high-value economic commodity, the sustainability of citronella cultivation requires effective soil conservation strategies capable of reducing soil loss while maintaining soil fertility and improving land-use efficiency. This study aimed to (1) assess the existing conditions and development patterns of smallholder citronella plantations, (2) evaluate land suitability, soil quality, and erosion hazard levels, and (3) develop a soil productivity optimization model through the application of sustainable soil and water conservation techniques. Research I revealed that smallholder citronella plantations in the Gayo Highlands are distributed across highly heterogeneous biophysical environments, represented by 33 Land Mapping Units (LMUs), with elevations ranging from 400 to >1,200 m above sea level and slope classes from 0 to >40%. The total plantation area reached approximately 4,191.39 ha, with the largest contribution from Gayo Lues Regency (46.9%), followed by Bener Meriah (28.2%) and Aceh Tengah (24.9%). Most plantations were located on slopes of 15–40%, and even >40% in several LMUs, indicating that citronella development has largely been empirical and not fully based on land suitability evaluation, thereby increasing the potential risk of soil degradation. Research II demonstrated that, from a climatic perspective, the study area is classified as highly suitable (S1) for citronella cultivation, with an average annual rainfall of approximately 2,109 mm, a mean elevation of 1,010 m above sea level, and a relatively short dry period of 2–3 months. Nevertheless, actual land suitability was dominated by the moderately suitable class (S2), mainly constrained by slope gradient, effective soil depth, drainage conditions, and phosphorus availability. The Soil Quality Index (SQI) value of 0.84 indicated that soil quality remained in the high category. Soil erosion prediction using the Universal Soil Loss Equation (USLE) showed a very wide erosion range, from 0.06 to 1,220.88 t ha⁻¹ yr⁻¹, confirming that land management factors (C and P factors) exert a stronger influence on erosion magnitude than natural factors. Potential land suitability analysis further indicated that most limiting factors are improvable, allowing for the upgrading of land suitability from S2 to S1 through appropriate conservation measures and nutrient management. Research III confirmed that the integrated application of soil and water conservation techniques significantly reduced surface runoff by approximately 75.0% and soil erosion by 58.7% compared to non-conservation practices. Partial analysis showed that terracing was the most effective technique, reducing erosion by 44.4%, followed by dense planting (17.2%) and mulching (9.5%). The soil productivity optimization model indicated that integrated conservation systems were able to maintain approximately 84% of potential soil productivity, substantially higher than non-conservation conditions, which maintained only 61%. The best conservation treatments also preserved soil nutrient capacity by approximately 2.3% more than the control. Overall, this study emphasizes that the development of citronella plantations in the Gayo Highlands must be directed based on land suitability and LMUs, and integrated with soil and water conservation as a fundamental prerequisite. The resulting soil productivity optimization model provides both scientific and practical contributions as a basis for planning productive, adaptive, and sustainable smallholder citronella plantation management. Keywords: soil productivity, land conservation, citronella, erosion, Gayo Highlands, USLE, optimization.