BIDANG ILMU PERTANIAN
LAPORAN HASIL PENELITIAN DISERTASI DOKTOR TAHUN ANGGARAN 2011
Pengaruh Residual Biochar terhadap Hasil Tanaman Pada Sistem Tumpangsari Berbasis Tanaman Ubikayu
Ir. Titiek Islami, MS
Dibiayai Oleh Direktorat Jenderal Pendidikan Tinggi, Kementerian Pendidikan Nasional, melalui DIPA Universitas Brawijaya REV.1 Nomor: 0636/023-04.2.16/15/2011 R, tanggal 30 Maret 2011 dan berdasarkan Surat Keputusan Rektor Nomor: 214/SK/2011 tanggal 2 Mei 2011
UNIVERSITAS BRAWIJAYA NOVEMBER 2011
RINGKASAN Tanaman ubikayu (Manihot esculenta crantz) merupakan tanaman yang mempunyai berbagai macam pemanfaatan, dapat tumbuh pada berbagai kondisi agroekologi, bahkan pada kondisi agroekologi yang marginal, dan mudah dibudidayakan. Oleh karena itu sangat tepat kesimpulan utama Simposium tiga tahunan ke 14 Internasional Society for Tuber and Root Crops (ISTRC) yang diselenggarakan di Trivandurm, India, pada bulan Nopember 2006 menyatakan bahwa tanaman ubi-ubian, terutama ubikayu, adalah tanaman masa depan. Pemerintah Indonesia telah memilih tanaman ubikayu sebagai salah satu tanaman utama yang perlu dikembangkan dalam rangka diversivikasi pangan untuk meningkatkan ketahanan pangan. Disamping itu dengan peraturan pemerintah No.5/2006, telah menetapkan tanaman ubikayu sebagai tanaman penghsil energi untuk menggantikan bahan bakar minyak. Untuk itu pemerintah Indonesia mentargetkan bahwa pada tahun 2025 Indonesia akan menghasilkan 60 juta ton, dari produksi saat ini 20-25 juta ton. Salah satu kendala dalam budidaya tanaman ubikayu karena sebagian besar tanaman ubikayu tumbuh pada lahan marjinal dan bahkan telah terdegradasi. Kedalaman efektif tanah sangat dangkal, kandungan bahan organik tanah rendah dan mengakibatkan rendahnya kesuburan tanah, baik kesuburan fisik, kimiawi maupun biologis. Dengan demikian strategi untuk mendapatkan produktivitas tinggi dan berkelelanjutan pada tanah terdegradasi adalah peningkatan kandungan bahan organik. Permasalahan utama dalam pengelolaan bahan organik tanah adalah dosis yang diberikan harus tinggi, dan di dalam tanah, pelapukan bahan organik berjalan sangat cepat. Dengan demikian pemberian bahan organik harus diberikan secara berulang setiap musim. Pada fihak lain, ketersediaan dan akses petani ubikayu terhadap bahan organik sangat terbatas. Dengan demikian, adanya bahan organik tahan dekomposisi semacam ”biochar” akan sangat berharga sebagai sumber bahan organik untuk pertanian. Hasil penelitian tahun pertama menunjukkan bahwa penggunaan biochar dalam sistim tumpangsari berbasis tanaman ubikayu memberikan hasil yang positif. Jika biochar memang tahan dekomposisi, maka pada masa tanam kedua dan selanjutnya pengaruh positif biochar diharapkan masih dapat dipertahankan. Dengan demikian penelitian yang dibahas dalam laporan ini bertujuan untuk: (1) Mempelajari pengaruh susulan (residual) biochar terhadap pertumbuhan dan tanaman pada sistim tumpangsari berbasis tanaman ubikayu, (2) mempelajari kecepatan perombakan bahan organik tanah, khususnya biochar dan pengaruhnya terhadap kesuburan tanah. Dengan dicapainya tujuan tersebut, maka diharapkan hasil penelitian dapat digunakan untuk membantu petani dalam penyusunan teknologi budidaya tanaman ubikayu yang mampu memberi hasil tinggi secara berkelanjutan. Teknologi yang dikembangkan didasarkan pada pengelolaan bahan organik tanah, dengan masukan bahan organik yang tahan dekomposisi. Untuk keperluan tersebut dilakukan penelitian di kebun percobaan Universitas Brawijaya di Jatikerto. Tanah percobaan mempunyai kedalam efektif tanah kurang dari 30 cm, kandungan bahan organik dan kandungan unsur N dan P rendah. Percobaan ini merupakan kelanjutan percobaan tahun pertama (2009/2010), tanaman ubikayu
ditanam bersama tanaman jagung dan tanaman kacang tanah pada bulan September 2010. Tanaman jagung dan kacang tanah ditanam pada bulan Januari 2011 dan tanaman ubikayu dipanen pada bulan Juli 2011. Perlakuan yang diuji dalam percobaan ini adalah: 1. Tumpangsari ubikayu + jagung tanpa pemberian bahan organik (UJ) 2. Tumpangsari ubikayu + jagung diberi pupuk kandang 10 t/ha, diberikan sekali pada tahun pertama (UJPk) 3. Tumpangsari ubikayu + jagung diberi pupuk kandang 10 t/ha, diberikan setiap tahun tanam (UJPk1) 4. Tumpangsari ubikayu+jagung diberi biochar pupuk kandang 7,5 t/ha (UJBpk) 5. Tumpangsari ubikayu+jagung diberi biochar batang ubikayu 7,5 t/ha (UJBuk) 6. Tumpangsari ubikayu+Kctanah tanpa pemberian bahan organik 10 t/ha (UK) 7. Tumpangsari ubikayu+kacang tanah diberi pupuk kandang 10 t/ha, diberikan sekali pada tahun pertama (UKPk) 8. Tumpangsari ubikayu+kacang tanah diberi pupuk kandang 10 t/ha, diberikan setiap tahun (UKPk1) 9. Tumpangsari ubikayu+kacang tanah diberi biochar pupuk kandang 7,5 t/ha (UKBpk) 10. Tumpangsari ubikayu+kacang tanah diberibiochar batang ubikayu 7,5 t/ha (UKBuk) Kesepuluh perlakuan tersebut diatur dalam Rancangan Acak Kelompok dengan 3 ulangan. Petak percobaan yang digunakan berukuran 6,25 X6,0 m dan tanaman ubikayu ditanam pada jarak 1,25 X 1,0 m. Hasil penelitian menunjukkan bahwa sampai panen tahun kedua, perbaikan pertumbuhan dan kenaikkan hasil tanaman pada pola tanam tumpang sari ubikayu + jagung dan ubikayu + kacang tanah, karena pemberian biochar masih bertahan. Baik tanaman sela jagung dan kacang tanah maupun tanaman ubikayu, pada tanah yang diberi biochar pada tahun sebelumnya, mempunyai pertumbuhan yang lebih baik dengan hasil yang lebih tinggi bila dibandingkan dengan tanaman pada perlakuan tanpa bahan organic maupun perlakuan pupuk kandang diberikan sekali pada tanaman sebelumnya. Hasil ubi pada perlakuan biochar bervariasi dari 21 Mg ha-1 sampai 23 Mg ha-1, sedang pada perlakuan tanpa pupuk kandang hanya 14 Mg ha-1 pada pola tanam ubikayu + jagung. Jika menggunakan tanaman kacang tanah sebagai tanaman sela, hasil ubi yang diperoleh 19 Mg ha-1. Pada perlakuan pupuk kandang yang diberikan sekali pada tanaman sebelumnya, pertumbuhan dan hasil tanaman tahun kedua tidak berbeda nyata dengan pertumbuhan dan hasil pada perlakuan tanpa pupuk kandang. Agar pengaruh positifnya masih bertahan, pupuk kandang harus diberikan setiap musim tanam. Jika hal ini dilakukan hasil ubikayu yang diperoleh tidak berbeda nyata dengan perlakuan biochar, bahkan pada pola tanam ubikayu + kacang tanah dapat memberi hasil lebih tinggi ( 24,80 Mg ha-1). Ditinjau dari efisiensi penggunaan lahan dan pendapatan petani, sampai tahun kedua biochar masih mampu meningkatkan efisiensi penggunaan lahan (yang ditandai dengan NPL lebih tinggi) serta pendapatan kotor petani. NPL tertinggi (1,75) diperoleh perlakuan biochar dari ppuk kandang pada pola tanam ubikayu + jagung dengan
pendapatan kotor Rp. 24,24 juta. Perlakuan tanpa bahan organic pada pola tanam ubikyu + jagung mempunyai NPL dengan pendapatan kotor Rp. 15,46 juta. Pemberian biochar telah terbukti dapat meningkatkan hasil tanaman sela, tanaman ubikayu, efisiensi penggunaan lahan dan pendapatan kotor. Pengaruh positif biochar masih bertahan sampai tanaman tahun kedua. Walaupun demikian, sebelum memberikan anjuran perlu dilakukan analisis ekonomi. Mengingat biocahar diharapkan dapat memberi pengaruh positif dalam waktu yang lama, untuk dapat melakukan analisis dengan benar percobaan perlu diteruskan untuk jangka waktu yang lebih lama, sampai pengaruh positif biochar hilang.
SUMMARY Cassava is an incredible crop, it can grow in any agroecology condition and the crop can be utilized for many purposes; from human food, animal feeding, to be raw materials for many kinds of industry, and lately as fuel. Potentially, increasing world cassava production is still high. Therefore, International Society for Tuber and Root Crops, in their 2006 congress had proclaimed cassava as the future crops. Indonesian government, through their decree no. 5/2006, decided that as the third food crops and raw material for bio energy, Indonesia should produce 60 millions tone tubers by the year of 2025. The main limitation to achieve this goal is that cassava is mostly planted in marginal or degraded land with very low productivity. The soil usually has a very low soil organic matter with consequence of low plant nutrient and un-favorable condition for crop growth. Since the main limitation of these soils are its low soil organic matter content, therefore the easiest way to increase their fertility and productivity is by adding organic materials. However, under wet tropical condition such as Indonesia, these organic materials decompose rapidly, and hence the practice of applying organic materials should be done at every planting time. Application rate of organic material is usually very high, therefore it is becoming uneconomic, and hence, farmers reluctant to do this work. Therefore, the invention of recalcitrant organic materials such as “biochar” give a bright prospect. The result of the first experiment had shown that application of biochar produced from farm yard manure and unused cassava stem into cassava based cropping system improved soil fertility status, and increase the yield of the intercrops (maize and peanuts, as well as the yield of cassava. If it is true that biochar is resistant to decomposition, then its positive effect would still occurs in the next crops. To test this hypothesis, an experiment on the residual effect of biochar on crop yield in cassava based cropping was carried out in Jatikerto field experimental station of Brawijaya University from September 2010 to July 2011. The experiment was a continuation of the previous (2009/2010) experiment, and the treatments were two intercropping systems: cassava + maize and cassava + peanuts with 5 treatments of organic amendment application, i.e. (1) farm yard manure (FYM) applied once at the start of the experiment, (2) FYM applied every year, (3) biochar from FYM, and (4) biochar from cassava stem (CS), and (5) without FYM as the control. Then, the treatment combinations were: (1) cassava + maize with
FYM applied once at the start of the experiment, (2) cassava + maize with FYM applied every year (3) cassava + maize with FYM biochar, (4) cassava + maize with CS biochar (5) cassava + maize without organic amendment, (6) cassava + peanuts with FYM applied once at the start of the experiment, (7) cassava + peanuts with FYM applied every year , (8) cassava + peanuts with FYM biochar, (9) cassava + peanuts with CS biochar, and (10) cassava + peanuts without organic amendment. These treatments were arranged in a randomized block design with three replications in plots of size 6.25 x 6.0 m. The results of the experiment show that application of inorganic fertilizer alone could not maintain the crop yield planted in cassava based cropping system in a marginal or degraded soil of Jatikerto, Malang, Indonesia. It is absolutely important to apply organic amendments both for improving soil fertility status, increasing and stabilising crop yields. However, similar to inorganic fertilizer, application of farm yard manure (FYM) fail to stabilized the crop yield. In order to maintain the high yield, FYM should be applied every planting season. The stability of organic-C from FYM can be increased by processing FYM to be biochar. Cassava stem is also potential feedstuff for biochar. Biochar application also increase and stabilized land use eficiensy, and increasing gross farmers income.
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