PENGARUH MEDIA TANAM DAN FREKUENSI PEMBERIAN AIR TERHADAP SIFAT FISIK, KIMIA DAN BIOLOGI TANAH SERTA PERTUMBUHAN JARAK PAGAR
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Pusat Penelitian dan Pengembangan Perkebunan
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ABSTRAKLahan pertanian yang didominasi oleh partikel pasir di daerah lahankering iklim kering mempunyai kapasitas yang rendah dalam menyimpanair dan unsur hara, serta rentan terhadap erosi. Penambahan tanah liat,zeolit, dan bahan organik diharapkan dapat meningkatkan kadar unsur haratanah, kadar air tanah, dan pertumbuhan tanaman. Penelitian yangdilakukan dari bulan Mei sampai Desember 2008 ini bertujuan untukmengetahui pengaruh penambahan tanah liat, zeolit dan interaksinyadengan bahan organik terhadap stabilitas makroagregat, kadar unsur haraC, N, P, dan K, daya pegang air tanah berpasir, populasi mikroorganismetanah serta pertumbuhan jarak pagar. Media tanam yang diuji sebanyak 5jenis, yaitu (1) 100% tanah pasir, (2) 95% tanah pasir + 5% tanah liat, (3)95% tanah pasir + 5% zeolit, (4) 94,2% tanah pasir + 5% tanah liat + 0,8%bahan organik, dan (5) 94,2% tanah pasir + 5% zeolit + 0,8% bahanorganik. Untuk mengetahui kemampuan daya pegang air tanah, makaperlakuan jenis media tersebut dikombinasikan dengan perlakuanfrekuensi pemberian air, yaitu dengan interval 7 dan 21 hari sekali.Perlakuan disusun dalam rancangan acak kelompok faktorial denganempat kali ulangan. Hasil penelitian menunjukkan bahwa penambahan 5%tanah liat + 0,8% bahan organik pada tanah berpasir dapat meningkatkanproporsi makroagregat, kadar unsur hara C, N, P, dan K, serta kapasitasdaya pegang air tanah. Penambahan sebanyak 5% zeolit pada tanah pasirmeningkatkan populasi bakteri. Peningkatan populasi jamur lebih dipacudengan frekuensi pemberian air 7 hari sekali. Pertumbuhan tinggi tanamanjarak pagar juga lebih dipercepat oleh pemberian air dengan frekuensi 7hari sekali.Kata kunci: Jatropha curcas, pasir, liat, zeolit, bahan organik, kesuburantanah, pengairanABSTRACTThe role of clay, zeolit, and organic matter in increasingsoil fertility of sandy soil as growth media for JatrophacurcasAgricultural sandy soils have low capability to retain water andnutrients. Addition of clay, zeolit and organic matter to these soils wasexpected to increase macro-aggregate stability, soil nutrients and waterholding capacity. The research had been conducted from May up toDecember 2008 to find out the effect of addition of clay, zeolit, and theirinteractions with organic matter in increasing sandy soil fertility as growthmedia for Jatropha curcas. The study had an objective to quantify theeffect of plant media and frequency of watering on soil macro-aggregatestability, soil nutrients, water holding capacity, soil microorganismspopulation, and growth of J. curcas. Plant growth media tested in thisstudy consisted of 5 types, i.e. (1) 100% sand soil, (2) 95% sand soil + 5%clay soil, (3) 95% sand soil + 5% zeolit, (4) 94.2% sand soil + 5% clay +0.8% organic matter, and (5) 94.2% sand soil + 5% zeolit + 0.8% organicmatter. Watering of plant was divided into two time intervals, i.e. each of 7days and each of 21 days. Results showed that plant media which was amixture of 94.2% sand soil + 5% clay + 0.8% organic matter increasedproportion of maco-aggregate, plant nutrients (C, N, P, K) and soil waterholding capacity. Plant media consisted of mixture of 95% sand soil + 5%zeolit was suitable for development of bacteria population. Acceleratingof growth of J curcas was induced by watering with interval of 7 days.Key words: Jatropha curcas, sand, clay, zeolit, organic matter, watering,soil fertility