SALING TINDAK TANAH GAMBUT DAN SUBSTRATUM BAHAN SULFIDIK SERTA PENGARUHNYA TERHADAP SIFAT KIMIA TANAH

Arifin fahmi, Prof. Dr. Bostang Radjagukguk M.Agr.Sc.

2012 | Disertasi | S3 Ilmu Tanah

Penelitian bertujuan mempelajari perubahan sifat tanah gambut dengan substratum bahan sulfidik akibat perbedaan ketebalan gambut dan fluktuasi muka air tanah, dan faktor-faktor yang mempengaruhi perubahan tersebut. Mempelajari peranan lapisan gambut dan bahan sulfidik terhadap sifat-sifat tanah gambut dengan substratum bahan sulfidik. Mempelajari pengaruh ketebalan gambut terhadap derajat dekomposisi gambut, kandungan bahan humus dan sifat spektroskopinya serta kandungan gugus fungsionalnya. Mempelajari perubahan sifat tanah yang terjadi akibat hilangnya atau menipisnya lapisan gambut. Serangkaian penelitian dilaksanakan di lapangan dan di laboratorium. Penelitian lapangan dilaksanakan pada tanah gambut tipis, sedang, tebal serta pada tanah sulfat masam potensial dan tanah sulfat masam potensial bergambut. Titik contoh tanah ditentukan berdasarkan keberadaan lapisan interlayer dan kondisi horizon tanah. Pengamatan dilaksanakan pada musim hujan, transisi dan musim kemarau. Penelitian laboratorium dilaksanakan untuk mengkarakterisasi tanah gambut yang berasal dari tapak penelitian di lapangan. Hasil penelitian menunjukkan bahwa perubahan sifat–sifat tanah yang diamati dapat dipengaruhi oleh beberapa faktor yang sama atau berbeda-beda. Konsentrasi, laju pelepasan dan agihan hara dalam tanah dipengaruhi oleh fluktuasi muka air tanah, ketebalan gambut dan sifat setiap unsur hara itu sendiri. pH, Eh, KPK, konsentrasi Fe dan SO4 lebih dipengaruhi oleh fluktuasi muka air tanah. Kadar abu, DHL, konsentrasi Al dan H lebih dipengaruhi oleh ketebalan gambut; selain itu kadar abu, konsentrasi Al dan Fe juga dipengaruhi oleh derajat dekomposisi gambut. Lapisan gambut menjadi sumber unsur hara utama bagi tanah gambut dengan substratum bahan sulfidik, sedangkan unsur Al, H dan Fe pada tanah gambut bersumber dari bahan sulfidik. Penipisan atau hilangnya lapisan gambut dapat menurunkan ketersediaan unsur hara, meningkatkan kelarutan Al dan Fe, serta meningkatkan kemasaman tanah gambut. Proses kelasi bahan humus terhadap ion logam lebih dipengaruhi derajat dekomposisi gambut daripada ketebalan gambut. Ketebalan gambut juga mempengaruhi derajat dekomposisi, kandungan kemasaman total, karboksilat, fenolat, asam humat dan gugus fungsional gambut.

The objectives of this research are to study the change of peat soil characteristics with sulphidic material substratum due to the difference in peat thickness and water table fluctuations, and factors that influence the change; to study the role of peat layer and sulphidic material on peat soil characteristics with sulphidic material substratum; to study the effect of peat thickness on its decomposition stage, humic substances content, spectroscopic characteristics, and functional moieties content; to study the change of soil characteristics as a result of the depletion or loss of peat layer. A series of studies were conducted on the field and laboratory. Field studies were conducted on shallow, moderate and deep peat, potential acid sulphate soil and peaty acid sulphate soil. Soil samples were collected according to the interlayer and the condition of soil horizons. Observation was carried out on wet season, transition from wet to dry season, and dry season. Laboratory studies were conducted for characterizing peat material originating from the field study sites. The results show that the change of soil characteristics may be influenced by the same or different factors. Concentration, dissolution rate, and distribution of soil nutrients were influenced by water table fluctuations, peat thickness and characteristics of each nutrients. Soil pH, Eh, CEC, Fe and SO4 concentrations were more influenced by water table fluctuations. Ash content, DHL, Al and Fe concentrations were more influenced by peat thickness; apart from that, ash content, Al and Fe concentrations were also influenced by peat decomposition stage. The peat layer was the source of soil nutrients for peat soil with sulphidic material substratum, whereas Al, H and Fe in peat soil were originated from the sulphidic material. The depletion or loss of peat layer may decrease soil nutrients availability, increase Al and Fe concentrations and peat soil acidity. Chelatization process of metal ion by humic substances was more determined by peat decomposition stage than peat thickness. Peat thickness also influenced the peat decomposition stage, total acidity content, phenolic content, carboxylic content, humic fulvic acid content and functional moiety content.

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