LAPORAN HASIL PENELITIAN DISERTASI DOKTOR TAHUN ANGGARAN 2011

Pemanfaatan biochar sebagai bahan amendemen tanah untuk meningkatkan efisiensi penggunaan air dan nitrogen tanaman

jagung (Zea mays) di lahan kering Lombok utara

Ir. Sukartono, M.Agr

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

BIDANG ILMU PERTANIAN

Pemanfaatan biochar sebagai bahan amendemen tanah untuk meningkatkan efisiensi penggunaan air dan nitrogen tanaman jagung (Zea mays)

di lahan kering Lombok Utara (Sukartono, 2011)

============================================================= RINGKASAN

Potensi pertanian lahan kering di Kabupaten Lombok Utara sekitar 38.000 hektar dan baru 30% yang dimanfaatkan untuk pengembangan tanaman pangan khususnya jagung (Zea mays L) dan ubi kayu (Manihot esculenta Crantz). Lahan kering ini didominasi oleh tipe tanah berpasir (sandy loam) dengan kualitas kesuburan tanah yang rendah yakni tanah porous, rendah bahan organik(<1.0%) dan juga miskin hara (N, P, K, Ca, Mg). Hal ini dianggap paling bertanggung jawab terhadap rendahnya efisiensi pemakaian air, hara dan produktivitas tanaman jagung. Penambahan biochar sebagai pasokan karbon ke dalam tanah diharapkan berpotensi membenahi sifat tanah tersebut. Biochar saat ini telah menjadi fokus perhatian ilmuan dalam menciptakan ”a sustainable technology” untuk memperbaiki kesuburan tanah di daerah tropik. Meskipun demikian informasi berkenaan dengan potensinya dalam membenahi tanah berpasir (sandy loam soils) pada sistem pertanaman jagung di daerah semi-arid tropis masih sangat terbatas. Dalam kaitan ini maka berbagai sumber limbah organik yang tersedia secara lokal di Lombok seperti: tempurung kelapa (56.180 ton per tahun) dan kotoran sapi (2.830. 256 ton per tahun) nampaknya potensial dijadikan bahan pembuatan biochar.

Penelitian ini bertujuan untuk mengkaji potensi biochar (bahan tempurung kelapa dan kotoran sapi) sebagai bahan amendemen untuk memperbaiki kesuburan tanah, efisiensi nitrogen dan penggunaan air tanaman jagung (Zea mays) di lahan kering Lombok Utara. Percobaan lapangan telah dilakukan di stasiun penelitian lahan kering UNRAM di Kecamatan Bayan, Lombok Utara (08o25‟LU, 116o23‟BT), 20.5 meter dari permukaan laut. Klasifikasi tipe tanah termasuk Ustipssamment (Soil Survey Staff, 1998), dengan bahan induk abu vulkan berbatu apung yang berasal dari hasil erupsi G. Rinjani. Curah hujan tahun 2010 di daerah penelitian sebesar 1234,2 mm, tersebar antara bulan Desember/Januari sampai April/Mei, suhu dan kelembaban relatif udara masing-masing 31o C dan 84%. Tanah lapisan atas bertekstur lempung berpasir (sandy loam) dengan kandungan pasir ≥ 55%, pH 5.97 dan C-organik tanah 0.89%, 0.13% N, 23.60 mg kg–1 extractable P dan 0.57 cmol kg–1 exch. K.

Biochar diproduksi dari bahan baku limbah kotoran sapi dan tempurung kelapa. Biochar tempurung kelapa dibuat dengan pembakaran dalam lubang tanah berukuran panjang 1,5 m, lebar dan dalam 1,0 m. Biochar kotoran sapi dibuat dengan memanaskan kotoran sapi (kadar air 15%) dalam drum berukuran diameter 56 cm dan tinggi 42 cm, dipanaskan pada tungku kontruksi batu bata berukuran panjang 120 cm, lebar 70 cm dan tinggi 40 cm. Hasil biochar diayak untuk mendapatkan ukuran partikel 1,0 mm.

Percobaan dilakukan dalam tiga musim tanam jagung secara beruntun yakni jagung-1 (MT1) berlangsung musim hujan 2010/2011 (November 2010 - Maretl 2011), jagung- 2 (MT-2) dan jagung-3 (MT3) berlangsung musim kemarau dengan rentang

waktu masing-masing Maret – Juli 2011 dan Juli - Oktober 2011. Bahan pembenah organik yang diuji pada percobaan ini ialah biochar tempurung kelapa (BTK), biochar kotoran sapi (BKS) dan pupuk kandang (PK) dan tanpa pembenah tanah sebagai kontrol (K). Pada MT-1 perlakuan meliputi: BTK, BKS, PK dan kontrol, sedangkan pada pertanaman jagung berikutnya (MT-2 dan MT-3), perlakuan PK terdiri dari pukan aplikasi hanya sekali pada MT1 (PkA) dan pukan diaplikasi setiap musim tanam (PkB). Percobaan dirancang menurut Rancangan Acak Kelompok dengan empat ulangan pada petak berukuran 3.5 m x 4.0 m. Bahan pembenah organik dicampurkan secara merata dengan tanah pada kedalaman 10 cm, diinkubasikan selama 7 hari pada kondisi lengas tanah 80% kapasitas lapang. Benih jagung (var. BC-2) ditanam seminggu setelah inkubasi dengan jarak tanam 20 x 70 cm (100 tanaman per petak).

Pupuk Urea, superphosphate, dan KCl diberikan dengan takaran masing-masing 135 kg N ha–1, 75 kg P2 O5 ha–1 dan 75 kg K2 O ha–1 . Pupuk P dan K diberikan sebagai pupuk dasar, sedangkan N diberikan dalam dua kali:: 40% (54 kg N ha–1 ) pada umur 21 hari sesudah tanam (21 HST) dan 60% (81 kg N ha–1 ) pada umur 45 HST untuk jagung MT-2. Sedangkan untuk jagung MT-3, pupuk N diberikan tiga kali yakni 40% (54 kg N ha–1 ) diberikan umur 20 HST dan sisanya masing-masing 30% (40,5 kg N ha-1) pada umur 30 HST dan 45 HST.

Sebelum tanam dan sesudah panen dari masing-masing jagung MT1, MT, 2 dan MT3, dilakukan pengambilan 4 sampel tanah pada setiap petak perlakuan pada kedalaman 20 cm dengan pola zig-zag untuk analisis sifat tanah. Sifat tanah yang dievaluasi meliputi: pH, total N, P-tersedia, KTK, K, Ca, Mg tertukar. Sedangkan untuk mempelajari dinamika C-organik tanah, pengambilan sampel tanah dilakukan pada dua kedalaman (0–10 dan 10–20 cm) secara periodik pada hari ke 1, 2, 4, 7, 14, 28, 56, 105, 155, dan 210 hari sesudah inkubasi. Pengukuran variabel agronomis meliputi berat kering tanaman dan hasil biji jagung, serapan hara juga diukur pada setiap musim tanam.

Hasil penelitian menunjukkan bahwa aplikasi biochar meningkatkan kandungan C-organik tanah (COT) khususnya pada kedalaman tanah 0-10 cm. Kandungan COT yang tinggi pada petak biochar bertahan sampai musim tanam jagung kedua bahkan sampai jagung ketiga. Sebaliknya, COT pada petak perlakuan pupuk kandang tidak berbeda nyata terhadap petak tanpa pembenah sesudah panen jagung 1 dan jagung 2. Hal ini mengimplikasikan bahwa pengaruh pupuk kandang terhadap C-organik tanah tidak dapat bertahan lama lebih dari satu musim tanam. Dengan demikian untuk mempertahankan kandungan COT yang tinggi maka seharusnya pupuk kandang diberikan pada setiap musim tanam. Penelitian sebelumnya telah membuktikan bahwa pada kondisi tropis, C-organik dari sumber pupuk kandang (cattle manure) mengalami dekomposis hampir secara sempurna dalam satu musim tanam (Diels et al., 2004). Berbeda dengan C-organik dari biochar dengan struktur C-aromatik bersifat lebih tahan terhadap dekomposisi (Lehman et al., 2006).

Kecenderungan dinamika dekomposisi dapat dilihat dari besarnya nilai koefisien t pada persamaan hubungan C dan waktu, dimana pada petak perlakuan pupuk kandang nilai t lebih tinggi dari pada perlakuan lain. Hal ini merupakan petunjuk bahwa laju dekomposisi dari pupuk kandang lebih cepat dari sumber pembenah lannya. Lebih lanjut dapat diungkap bahwa dalam waktu relatif singkat yakni 14 hari ternyata COT pada petak perlakuan pupuk kandang turun mencapai 18%, lebih tinggi dari penurunan

yang ditunjukan pada petak BTK dan BKS. Penurunan COT dalam tanah sebagian juga berpeluang disebabkan oleh gerakan kebawah (downward movement) partikel biochar bersama perkolasi, akan tetapi data C-org pada kedalaman 15-20 cm menunjukkan bahwa selama musim pertanaman jagung tidak dipengaruhi secara nyata oleh penambahan pembenah organik. Hal ini menunjukkan belum ada kontribusi yang nyata dari gerakan kebawah partikel biochar selama percobaan, sehingga penurunan COT yang diamati mungkin hanya disebabkan oleh dekomposisi (Cheng et al., 2006).

Selain meningkatkan COT, aplikasi biochar dan pukan juga memperbaiki sifat tanah. Konsentrasi hara yang lebih tinggi pada petak perlakuan biochar dan dan pukan dibandingkan petak kontrol menyarankan adanya kontribusi positif pembenah organik dalam memperbaiki ketersediaan hara. Namun demikian untuk melanggengkan pengaruh positif ini maka pukan seharusnya diaplikasikan setiap musim tanam, sementara aplikasi tunggal biochar dapat mempertahankan pengaruh tersebut dalam waktu relatif lebih lama. Lebih dari itu, meningkatnya KTK dengan penambahan biochar juga dapat mengurangi resiko pencucian hara bermuatan positif seperti potassium dan amonium-N. Meningkatnya ketersediaan hara dan KTK dari hasil penelitian ini selaras dengan hasil peneliti sebelumnya (Novak et al., 2009; Yamato et al., 2006). Tingginya muatan negatif permukaan (surface negative charge) hasil oksidasi gugus fungsional, utamanya gugus karboksil dan phenolik yang terjadi pada permukaan luar partikel biochar dan besarnya luas permukaan partikel biochar merupakan alasan utama yang menyebabkan tingginya kemampuan adsorpsi partikel biochar (Cheng et al., 2006). Sifat ini pada pada gilirannya berdampak positif menurunkan pencucian hara khususnya yang bernuatan positif seperti NH4+, K, Ca, dan Mg .

Adanya perbaikan terhadap kualitas kesuburan tanah dengan aplikasi biochar juga dicerminkan oleh: meningkatnya hasil tanaman, serapan hara, dan juga efisiensi penggunaan N dan air. Efisiensi penggunaan N tanaman jagung petak biochar sebanding dengan pukan yang diaplikasi setiap musim tanam dengan nilai masing-masing 42% dan 47%, Nilai ini mencapai 2 kali lipat dibandingkan efisiensi penggunaan N tanaman jagung pada petak tanpa pembenah tanah (23%).

Respon positif tanaman jagung terhadap aplikasi biochar pada penelitian ini juga seiring dengan hasil penelitian sebelumnya di daerah tropik yang lebih basah (Yamato et al., 2006). Untuk mempertahankan hasil jagung yang tinggi, tampaknya pupuk kandang seharusnya juga diaplikasikan setiap musim tanam. Sifat rekalsitran dari biochar telah dilaporkan secara meluas oleh banyak peneliti (Lehmann et al., 2006; Islami et al., 2011), dan tidak memberikan efek negatif terhadap serapan hara tanaman jagung. Serapan hara tanaman jagung pada petak biochar secara umum sebanding dengan serapan hara tanaman jagung yang diberi pupuk kandang.

Secara keseluruhan, penelitian ini mengkonfirmasikan bahwa biochar dan pupuk kandang merupakan pembenah organik yang sangat bermakna (valuable amendments) dalam memperbaiki kesuburan tanah, efisiensi penggunaan nitrogen dan air, sehingga pada giliranya diharapkan berkontribusi menciptakan sustainabilitas produksi jagung di lahan kering berpasir Lombok. Pupuk kandang yang diaplikasikan setiap musim tanam berkecenderungan memberikan hasil jagung yang lebih tinggi, akan tetapi dari aspek mempertahankan stabilitas karbon dalam jangka waktu yang lama dalam tanah, aplikasi biochar dalam sistem pertanaman tampaknya lebih menjanjikan. Menyadari keterbatasan capaian penelitian ini maka penelitian jangka panjang (long-term study)

dalam beberapa tahun sistem pertanaman dengan memodifikasi aplikasi biochar dan pupuk kandang di daerah semi-arid tropis sangat diperlukan untuk mengkonfirmasi kecenderungan ini.

The potential use of biochar as an amendment for improving crop water use efficiency and nitrogen under maize cropping system (Zea mays) in sandy loam of Northern Lombok, eastern Indonesia

(Sukartono, 2011) ========================================================

Summary

Sandy soils cover about 38,000 ha in the semiarid tropics of North Lombok, Indonesia and almost 30% of these have low fertility status. Major crops grown on these soils are maize (Zea mays L.) and cassava (Manihot esculenta Crantz). Low nutrient content (N, P, K, Ca, Mg), organic C (<1.0%), and low CEC (12 cmol) are, however, major production constraints of these soils. Althoug biochar recently has attracted considerable interest asa sustainable technology to improve soil fertility in the tropics, information on their potential to amend infertile sandy loam soils under maize cropping system in the semiarid tropics is rather limited. Furthermore, many local organic resources such as coconut shell and cattle dung available in Lombok (approximately 56,180 and 2, 830, 256 Mg per year, respectively in this area), which by and large remain under-exploited, are suitable for biochar production. Use of such residues for improving soil quality as well as crop productivity in the dry land farming systems of Lombok might be ecologically promising also. The present study was aimed to address the potential of biochar (produced from cattle dung and coconut shell) for improving fertility of sandy loam soils, nitrogen and crop water use under maize cropping system in Northern Lombok.

The experiments were carried out at the dry land experimental station of Mataram University at Bayan District in northern Lombok, Indonesia (08o25’S, 116o23’E; altitude 20.5 m above mean sea level). Annual rainfall of northern Lombok in 2010 was 1234.2 mm, distributed between December/January to April/May;mean air temperature was 31o C and atmospheric humidity about 84%. Soils of the experimental sites were Ustipssamment (Soil Survey Staff, 1998) derived from volcanic ash containing pumice stone materials erupted from Mount Rinjani. The surface soil has a sandy loam texture (55% sand and 9% clay) with pH of 5.97 and had low soil organic carbon (0.89%) with poor nutrient status (0.13% N, 23.60 mg kg–1 extractable P, and 0.57 cmol kg–1 exchangeable K).

Biochars used in the study were produced from cattle dung and coconut shell. Coconut shell biochar (CSB) was prepared through auto thermal combusting of the shells in pits (1.0 m deep, 1.0 m wide, and 1.5 m long. Cattle dung biochar (CDB) was prepared from sun dried cattle dung (15% water content), filled into two drums (56 cm diameter and 42 cm high) and heated on a stove constructed with brick (70 cm wide, 120 cm long, and 40 cm high). The biochars were crushed and sieved (1.0 mm).

Field trials were conducted in the wet season of 2010– 11 (November 2010 to March 2011) and the first dry season of 2011 (April to July 2011) and subsequently followed by the second dry season of 2011 (July to October 2011) The experimental tratments included of three organic amendments applied at the rate of 15 Mg ha–1 : CSB, CDB, cattle manure (CM), and no organic amendment control (C). In the wet season of 2010–2011, the treatments were CSB, CDB, CM, and C. In both dry season of 2011, the CM treatment consisted of CM applied once for the first maize, and CM

applied for first, second, and third maize crops (i.e., CM applied at each planting time, CMT). Thus the complete treatments of the dry season were CSB, CDB, CM applied once during the wet season (first maize crop), CMT, and C. The treatments were laid out in a randomized block design with four replications in plots of size 3.5 x 4.0 m. The organic amendments were thoroughly incorporated in the soil to a depth of 10 cm and incubated for seven days by watering (± 80% field capacity). A week after biochar incubation, maize (Hybrid BC-2) was sown (one per hill) at 5 cm depth with a row spacing of 20 x 70 cm (100 plants per plot). Urea, superphosphate, and KCl were applied at the rate of 135 kg N ha–1, 75 kg P2 O5 ha–1 , and 75 kg K2 O ha–1 respectively. While all P and K were applied basally, N was applied in two splits: 40% (54 kg N ha–1 ) at 21 days after planting, and 60% (81 kg N ha–1 ) at 45 days (second crop), and three splits in the third crop : 40 % (54 kg N ha-1) at 20 days after planting and 30 % (40,5 kg N ha-1) each applied at 30 days and 45 days after planting. Before planting and after harvesting, four soil samples were taken from each plot to a depth of 20 cm following a zigzag pattern. Soil properties evaluated includes pH, total N, available P,CEC, and exch.K. To study the soil organic C dynamics, soil samples (0–10 and 10–20 cm depth) were periodically collected (1, 2, 4, 7, 14, 28, 56, 105, 155, and 210 days after incubation) by driving a stainless steel ring cylinder of about 7.5 diameter.

The results of field trial showed that biochar application increased soil organic carbon content, especially in the 0 to 10 cm soil layer. The high organic C contents of soils treated with biochars also persisted even after the harvest of the second as well as at the third crop. Conversely, soil organic C in the CM treated plots were not significantly different from that without organic amendments after the harvest of the first and the second maize crops, implying that the effect of CM on soil organic C do not last beyond one crop season. To maintain high soil organic matter levels, therefore, CM should be applied every year. Previous studies also confirm that under the wet conditions of tropics, organic C from cattle manure decomposed almost completely within one season (Diels et al., 2004). Organic C of biochars with an aromatic structure, however, is more resistant to decomposition (Lehman et al., 2006).

In fact, SOC of CM treated plots dropped by 18% within 14 days, which is much higher than the corresponding values for CSB and CDB. Although a decrease in soil organic C, partly due to downward movement by percolation was expected, the data of C-org at depth of 10-20 cm show that throughout the cropping season soil organic C was not significantly influenced by the organic amendments. Implicit in this is that there was no significant downward movement of organic C from biochar. The drop in soil organic C observed is presumably due to decomposition (Cheng et al., 2006).

A part from enriching soil organic C, application of biochar and CM improved other soil properties too. Higher nutrient concentrations of biochar and CM treated plots compared to control is suggestive of the positive contribution of organic amendments to improve soil nutrient availability. However, to sustain these positive effects, CM should be applied every planting season, whereas a single application of biochar can maintain these positive attributes for a longer period of time. In addition, the increase of CEC with addition of biochars will also minimize nutrient leaching, especially potassium and ammonium N. The increase nutrient availability and higher CEC observed in this study is consistent with the results of previous authors (Novak et al., 2009; Yamato et al.,

2006). High surface negative charge resulting from oxidation of functional groups, mainly carboxylic and phenolic, on the outer surface of biochar particles and the high surface area of biochar will probably explain this higher cation adsorption (Cheng et al., 2006). This would in turn decrease the leaching of positively charged nutrient such as K, Ca, and Mg of soil treated with biochar.

Improvements in soil fertility status with biochar application also were reflected increased maize yields, nutrient uptake of N, P and K as well as nitrogen use eficiency (NUE) and water use efficiency (WUE). The value of NUE of maize grown on biochar treated soil (43%) was relatively comparable to the corresponding value of maize at CM-treated soil (applied every planting time). These value was double to the NUE of maize at without ammended-soil (23%).

The positive response to biochar found in this study seems to be in concordance with the previous results reported in other tropical regions (Yamato et al., 2006). To maintain higher maize yields also, CM should be applied every planting season. The recalcitrant nature of biochar has been reported by many workers (Lehmann et al., 2006; Islami et al., 2011). However, this has not adversely affected the nutrient uptake by the maize crop. It shows that nutrient uptake of maize grown on biochars treated soils was generally comparable to that of the CM. The N,P, and K uptake of the second maize for biochar treated soil was also similar to that of the first crop. Overall, this study confirms that biochar and cattle manure are valuable amendments

for improving soil fertility, nitrogen and water use efficiency and to sustain maize

production in the sandy loam soils of semiarid North Lombok, eastern Indonesia.

Although cattle manure applied every planting time tend to produce higher maize yields,

in term of maintaining stability of soil organic C on a long term basis, application of

biochar would be more promising. However, confirmation based on a long term study

for many years of the cropping sequence, particularly in the semiarid tropical regions,

may be necessary to confirm these trends.

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