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thurnhat Oja ly Tho nhirdng o n e TfNH VfiT LV CUR DflT THAN BUN i n i KHU BHO TON THI€N NHICN v 6 DOI - U MINH Hfl - Cn MHU I r a n Ba Linh* Nguyen M/ Hoa* V6 Thi Gi/cfng* Huynh Thanh Ghi* LGIUITHIEU Trong nhang nam qua ben canh su suy thoai dat rung do tac dong cua con nguai, dien tich dat than bun cung dang bi sut giam nghiem trong. Tong dien tich than bun nhiet ddi la khoang 38.295.000ha, trong do Dong Nam A chiem khoang 26.000.000ha (69%), dien tich dat than bun tai Viet Nam khoang 35.000ha (Dat Viet Nam, 1996). Nam 1995-1999 khi du an Mega Rice Projects duoc phat tnen a Indonexia thi dat than bun a Kalimantan da dirac sir dung vao mue dich nong nghiep nhirng khong thanh cong, hau qua la lam ton that mot dien tich kha Ian. 6 Viet Nam, Rung dac dung V6 Dai dagc cdng nhan la vuon bao ton qudc gia nham muc dich bao ton nguon than bun quy hiem nay. Do do, viec khao sat cac tinh chat cua dat than bun phuc vu cho cong tac bao ton nay la rat can thiet. De tai "Dac tinh vat ly cua dat than bun tai Khu bao ton thien nhien Vo Ddl • U Minh Ha • Ca Mau"6ugc thuc hien vol muc tieu la xac dinh cac tinh chat vat ly cua dat than bun de phuc vu viec nghien ciru cac dac tinh hoa hoc va sinh hoc, quan ly nude phuc vu cdng tac bao ve rung, bao ton da dang sinh hoe va phdng chdng chay ri/ng mot each cd hieu qua. 2. PHl/OTNG PHAP NGHIEN CUU De tai tien hanh lay m i u tai Khu bao ton thien nhien ri/ng dac dung Vd Dai thudc Vi/dn Qudc gia U Minh Ha - ap Vo Dai - xa Tran Hai - huyen Tran Van Thdi - tinh Ca Mau. M l u than bun duac lay tai 3 vi tri: T3, T5, Vd (hinh 1). Mau duac lay 4 Ian lap lai cho moi tang 0-10cm, 10-20cm va 30-40cm tai vi tri T3 va a cac tang 0-10cm, 20-30em va 60-70em cho hai vi tri T5, Vd. Cac chi tieu phan tich bao gdm thanh phan ca gidi, dung trong, am dd, he so tham bao hoa Ksat, kha nang truang eo eua vat lieu than bun. Thanh phan ca giai duac phan tich bang phuang phap dng hiit Rhobinson. Bo mon Khoa hoc dat va QLDO - Oai hoc Can Tho. Ty trong duac phan tich theo phL/ong phap pycnometer. Do xop duac linh toan di/a vao ty trong the r^n va dung trong cua than uun. He sotham bao hoa (Ksat) dirac xac dinh theo cot ap c6 dinh. Lt/ong ni/oc can de bao hoa 100cm^ vat lieu than bun I<h6 duac xac dinh bang each bao hoa mau, luong nude nay sau do duac tinh toan dua tren su chenh lech ve trong luong sau khi say khd. am dp dat khoi luong duoc xac dinh dua vao khoi lucng dat kho kiet sau khi say a 105°C. am do the tich xac dinh tren mau dat khong xao tron duoc lay bang cac ong ring CO the tich 98,125cm-, Am do thuy dung dong ruong, am do diem heo trong dat duac xac dinh bang he thong do pF vdi ap luc 0,1 bar (pF = 2,0) va 15bar (pF = 4,2) tuang ung. Luang nuac hCru dung duoc tinh toan thong qua gia tri chenh lech giCra luang nude thuy dung dong ruong va luang nuac tai diem heo. Kha nang truang - eo duoc tinh toan dua vao the tich con lai cua vat lieu nguyen thuy sau khi say kho a 105°C. 3. KET QUA VA THAO LUAN 3.1. Dac diem chung cua cac phau dien dat than bun Than bun tai Vo Dai la san pham phan buy cua xac ba hufu ea dudi su tac dong cua vi sinh vat trong dieu kien ngap nude, Tuy vao dieu kien va muc dd phan buy ma than bun cd thanh phan va dac tinh khae nhau. Tang than bun a vi tri T3 cd dd day 40cm, ben dudi tang than bun la tang dat khoang day 40-50cm, ke den la tang sulfunc a dd sau 50-85em, tang pyrit d dd sau > 85em; dd sau muc nude ngam la 5em, Tang than bun d vi tri T5 dd day la 90em, ke den la tang dat khoang 90cm -110cm, tang sulfuric va tang chua vat lieu pyrit d dd sau >110cm, dd sau muc nude ngam la 25cm, Dd day tang than bun tai Vd la 90cm, ke den la tang dat khoang 90em -110cm, tang sulfuric va tang ehua vat lieu piritic d dd sau >110cm, dd sau mue nude ngam la 30em,. 3.2 Dac tinh vay ly dat than biin. Ket qua trinh bay a bang 1 cho thay thanh phan ca gidi cua Idp dat khoang chu yeu la set va thit, cat chiem ti le rat thap. Theo phan loai cua USDA thanh phan eo gidi cua Idp dat khoang la set.. 3.2.1. Thanh phan cdgldl cua Idp dat khoang. Bang 1. Thanh phan ca giai lap dat khoang dudi Idp than bun Vi tri. Do sau (cm). %cat (2-0,053 mm). ' '. %thit (0,053-0,002mm). % set (<0,002mm). Phan loai (USDA,). T3 T5 Vo. 40 -50 90-110 90-110. 0,4 1,9 0,5. :. 49,0 46.0 47,5. 50,6 52,1 52,0. Set Set Set. j. 3.2.2 Dung trong, ty trong, dp xop Dung trong, ty trong va dd xd'p cua dat than bun phu thudc vao dd nen de. ngudn gde thue vat tao thanh. vat lieu than bun va mue dd phan buy ctia vat lieu. Ket qua dung trong. ty trong va dd xop eua than bun duac thnh bay d bang 2.. Bang 2, Dune trong, ty trong va do xop cac tang dat than bun Vilri. Tang (cm). Dung trong (g cm3). T3. 0-10 10-20 30-40. 0,26 ns 0.21ns 0,21ns. T5. 0-10 20-30 60-70. Vo. 0-10 20-30 60-70. Ty trong (g.cm3). Do xop(%). 1.50b 1,55a 142c. 83,0 ns 86,5 ns 85,3 ns. 0,19b 0,18 b 0,27 a. 1,41ns 1,40 ns 1,45 ns. 87,0a 87,2a 81,4b. 0,23 ns 0,20 ns 0,23 ns. 1,45a 1,43b 142b. 84,1 ns 86,0 ns 83,8 ns. , '. Ghi chu Cac so (rung binh trong cung mot cot a tung vi tn theo sau cung mot chCf thi khac biet khong c6 y nghia, ns bieu thi su khac biet khong co nghia thong ke 5%. Ket qua cho thay gia tn dung trong cua than bun tai Vd Dai thap, bien ddng trong khoang 0,18-0,27g/cm-, ty trong 1,4-1,55 g/em-, dd xop 81,4-87,2g/em', Gia tn dung trong, ty trong than bun thap han va dd xop eao ban rat nhieu so vdi nhieu loai dat khoang thdng Ihuang 0 Dong bang sdng Cuu Long (DBSCL), Dung trong va ty trong giura cac tang d cac vi tri nhin chung khdng cd su khac biet dang ke {hang 2). Rieng vi tri T5 tang 60-70cm CO dung trong eao han, dd xop thap ban cho thay vat lieu huu ca d tang nay co su khac biet so vdi eac tang d cac vi tri khae, Quan sat ngoai dong cho thay tang nay cd vat lieu huu ca ket ciing rat chat. So vdi dat than bun d Sarawak, Malaixia cd dung trong 0,12-0,09g/cm^ (Andnesen, 1974) va dat than bun fibric d Indonexia cd dung trong < 0,1g/em^ (Dnesen va Rochimah, 1976), thi dat than bun dVd Dai cd dac tinh vat ly trung gian giCra vat lieu than bun fibnc va sapne (Rieley and Page, 2005), 3.2.3. LWcfng nWcfc bao hoa va trong IWcfng kho kiet cua than biin Ket qua trinh bay a bang 3 cho thay luang nude bao hoa dat 60,3-81,6g/100cm^ vat lieu than bun, eao gap 2,78-4.22 Ian khoi luang than bun khd kiet, khdng cd. khac biet ve luang nude bao hoa 100em^ dat than bun giCra cac tang trong cung vi tri duac khao sat d T3 va Vd. Luang nude bao hoa eua than bun d vi tri T5 cd su khac biet a 3 tang; gia tn nay dat eao d tang 0-10cm (72,4g), thap nhat d tang 20-30cm (60,3g). Su khae biet nay cd the do vat lieu tao than bun d tang 0-1 Oem la Idp vat lieu huu CO phan buy va ban phan buy Iham nude nhieu ban vat lieu trong tang 20-30cm cd nhieu re eay tuai. Bang 3, Luong nude bao hoa 100cm than bun kho va khoi luong sau khi say. tn T3 1. T5. Vo. ^. ^"9 "^"^' 0-10 10-20 30-40 0-10 20-30 60-70 0-10 20-30 60-70. Luong nude bao 1 hoa lOOem-vat lieu J than bun kho (g). j. Khoi luong lOOcm^ dat than bun sau khisayd1050C(q). 71.0 ns 70,5 ns 69,2 ns. 25,81a 20,42b 17,70b. 724a 60.3c 68,81b. 18,55b 18,04b 26,33a. 81,6 ns 80,8 ns 81,0 ns. 23,03a 1948b 22,57ab. Ghi chu Cac so trung binh trong cung mot cot d tung vl tri theo sau cung mot chu thi khac biet khong c6 y nghia, ns bieu thi su khac biet khong c6 nghia thong ke 5%,. 100. b. 75. T5. DTB. f-^. • VO. 50. 25. Lu9n{> nuo'c hao hoa lOOcmi than hiin kho. Khui luong I 0 0 c m 3 than bun sau khi say kho kiet. Hinh 1. Luang nude bao hoa va trong luong kho kiet eua than bun tang 0-10cm So sanh ham luang nude bao hoa tang mat d cac vi tri (hinh 1) cho thay luang nude can de bao hoa lOOem^ than bun khd d Vd eao ban T3 va T5, Su khae biet nay la do mue nude ngam tai Vd ludn thap hon va do dd tang mat tai Vd cd vat lieu huu ca mm va muc dd phan buy eao ban nen giu nude nhieu han.. 3.2.4. Am dp thuy dung dong ruong, am dp diem heo, am dp hCru dung Kha nang giu nude la mot dac tinh quan trong cua dat than bun trong viec bao ton ngudn tai nguyen quy nay, bao ve he sinh thai rung, du tru ngudn nude ngot cho vung, rat can thief de' bd tri che dd nude hop ly.. 100. D i; h. 75. •i. I. 15. a \ (). i. h. so. 25. .\ni d(i thiiy dune. .'\ni do hfi 11 diiny. Hinh 2. Am dd thuy dung va am do huu dung Ket qua trinh bay trong hinh 2 cho thay a'm dd thuy dung ddng ruong trung binh glCra cac tang tai T3 (72%), T5 (73%) thap han so vdi vi tri Vd (82%), la do cd su khac biet ve trang thai vat lieu giCra cac vi tri, va muc nude ngam tai Vd ludn thap ban T3 va T5. Vat lieu d tang mat tai Vd cd mire dd phan buy manh hon nen kha nang giu nude eao hon. Luang nude huu dung trung binh giua cac tang tai T3, T5 va Vd kha eao, dao ddng tu 55%-67%, khac biet cd y nghia thdng ke giua cac vi tri nghien ct;u, eao nhat d vi tri Vd va thap d vi tri T3. Nghien ei;u gan day duoc thuc hien d Kalampanga, Central Kalimantan cung cap cac gia tn ve am dd thijy dung ddng rudng bien ddng trong khoang 42%-52% (Kurnain et al, 2001). Nhu vay kha nang giu nude Idn. nhat eua dat than bun d Vd Dai Idn hon nhieu so vdi dat than bun d Kalimantan, Indonexia. 3.2.5 He sotham (Ksat) Tinh tham nude eua dat cd lien quan chat che den mdt so van de ve giu nude va tieu thoat nude cua rung, td'c dd nay chiu su kiem seat eua mdt so yeu to nhu loai than bun va mue do phan buy. Ket qua bang 4 cho thay su khac biet cd y nghia thdng ke ve he so tham giua cac tang than bun d tren mat va tang than bun sau hon tai T3, T5 va Vd. Toe dd tham manh nhat d nhung tang tren mat (108-134 cm/h), toe dd tham thap d tang sau (12-22em/h),. Dieu nay chLmg to rang cd su khac biet ve trang thai vat lieu giura cac tang, tang tren vat lieu toi xop han trong khi tang dudi vat lieu min nen da lam giam tinh tham nude. Rieng d T5 tang ben dudi ket chat nen toe do tham nude dat thap nhat. Td'c do tham cua dat than bun d Vo Doi nhanh han nhieu so vdi mot so dat than biJn Ontario State d My khi gia tri Ksat tai day dao dong tij 22-4cm/h cho dp day tang tu 0-45cm hoae gia tri Ksat d mot so dat than biJn d bang Florida la 67-29cm/h khi add sau tang 12-21 cm. Bang 4. He so tham cua dat than bun tai 3 vi tri T3, T5, Vo Vitri. T3. T5. Tang (em). He so tham (Ksat, cm/h). 0-10 10-20 3040 0-10 20-30 60-70. 108,25a 118,50a 22,25b 125,00a 134,00a 12,00b. 0-10 20-30 60-70. 117,25a 133,75a 18,00b. 3.2.6 Kha nang trifdng • co Hau het cac dat than bun deu co lai khi khd va trudng ra khi udt, kha nang truang co la mot dac tinh dac biet cua dat than bun. Ket qua bang 5 cho thay kha nang truang co cija dat than biJn tai n:fng dae dung Vo Dai the hien rat ro. Tang truang co manh nhat la tang dudi cung d cac vi tri T3, T5 va Vd. Dieu nay cho thay than biJn cac tang nay cd miJc do phan huy eao nhat. Phan tram co d eac tang ben dudi la eao nhat cho thay kha nang giu' nude cua cac vat lieu ben dudi eao hon. Do dac tinh truang eo d cac tang ben dudi eao cho thay kha nang than biJn bi mat di va mire dp lun xijp eao neu vat lieu than bun b| de khd va oxy hoa. Ket qua nay phij hap vdi nghien ciru cija Andneses (1988) da chi ra hau het nhung tang than biJn d ben dudi cung la cd kha nang truang co nliieu nhat.. Ket qua nghien ciJu d Kereng Bangkirai, Sebangau, Central Kalimantan cho thay phan tram truang co bien ddng \\s 34,7%-22,0% (Hans et al, 1998). Ket qua nay tucmg tu vdi phan tram trudng co cua dat than bun Vo Ghi chii: Cac so taing binh trong ciing mot cot d tung vi tri theo Dai d eac tann mat. sau cung mot chU khac biet khdng y nghia. Vo. Bang 5. The tich dat than bun sau khi say khd d 105°C Vi tri. Tang (cm). The tich to/dc khi say (cm3). The tich sau khi say (cm3). The tich dat than bun bi co. T3. 0-10 10-20 30-40. 98 125 98 125 98 125. 73,11a 66,87b 56,18c. 25,50c 31,85b 42,75a. T5. 0-10 20-30 60-70. 98 125 98 125 98 125. 72,07a 52,83b 46,71b. 26,56b 46,16a 52,39a. Vd. 0-10 20-30 60-70. 98 125 98 125 98 125. 75,63a 66,73b 60,87b. 22,92b 32,00a 37,97a. (%). Ghi chii; Cac so trung binh trong cung mot cot cr tUng vi tri theo sau cung mdt chu thi khac biet khong cd y nghia 3.2.7. Am do cua vat lieu than biin d cac miTc ni/dc ngam khac nhau Am dd eija vat lieu than bun d eac muc nude ngam khae nhau dudc xac dinh bang each xac dinh am dp tang mat eua than bun d thdi diem 5 ngay sau khi mt/c thuy cap trong phSu dien ha thap dan den dp sau khao sat. Ket qua dupe trinh bay trong bang 6 cho thay, mue thiJy cap 0 dd sau 15cm thi am dp tang mat la 76,65%, tuang duang am dp thuy dung ddng ruong, khi mue thuy cap ha thap d dp sau 20em thi am dp tang mat giam manh chi edn 62,8(3%, vat lieu than bun be mat tuang ddl khd. Vi vay de phdng chdng chay riing va bao ton da dang sinh hoc, nen duy tri muc thuy cap it nhat tu 15em trd len.. Bang 6. Am dp the tich tang mat tuong ung vdi do sau muc thuy cap Dp sau muc thuy cap tinh tu tang .Tiat (cm). am dd the tich tang mat. 00 05 10 15 20. (%) 87,92 81,95 79,01 76,65 62,80. ±1,0 ±1,2 ±1,3 ±1,9 ± 2,7. 4. tET LUAN Dat than bun d Vd Dai la loai dat than bun tre, mLrc dp phan buy thap. Dp day tang than bun tai eac diem khao sat Idn nhat la 90cm, muc nude ngam thap nhat la 30cm tinh tu be mat. Vi tri T3 cd Idp than bun mdng, do. sau muc nude ngam eao, vat lieu than bun kem phan huy hon cac vi tri cd Idp than bun day, muc nude ngam sau (VI tri T5 va Vd). Tang than biJn duoc hinh thanh tren nen dat khoang cd sa eau set, ke den la tang sulfunc va tang pint, Dat than bun d Vd Dai cd dac tinh vat ly trung gian giua vat lieu than bun fibric va saphe, Cung vi tri, vat lieu than bun d cac tang khac nhau ve muc dd thd mm. muc dd phan huy do dd cd cac dac tinh vat ly khac nhau. Tang mat thudng cd vat lieu re, la cay min; nhin chung vat lieu than bun cd dung trong thap (0,18-0,27g/cm^), ty trong thap (1,40-1,55g/cm'),. dd xop eao. Luang nude bao hoa cua than bun tudng ddi thap (60,3-81,6g/100cm'), he so tham eao cho thay vat lieu than bun giu nude kem va thoat nude nhanh, mire dd mao dan thap, vi vay trong cdng tac quan ly nude phdng chdng chay rUng can chii y gii; muc nude eao phu hop, duy tri muc thuy cap tif 15cm trd len la tot nhat. Dac tinh truang co eao cho thay kha nang bi giam dd day tang than bun neu vat lieu than bun bi de kho. Do dd, viec bao ton dat than bun va bao ton da dang sinh hoc can chii y eac dac tinh tren eiia dat than bun VdDot.. TAI LIEU THAM KHAO 1 Andnesse. J.P. 1988, Nature and management of tropical peat soil, FAO soils Bulletin 59, FAO, Rome, 2 Boeller. D.H. 1964. Water storage characteristic of several peats in situ, soil science soc. Am, Proc, 28 3 Kurnai. A.. J. Notohadihusum. B. Rajagukguii, Sn Hastuti. 2001. Peat soil properties related to degree of decomposion under different land use system. International Peat Journal 11 4, Malay. C.D.A.. R.F. Alibmok. K.ThompsonA%2. Effect of development and cutivation on physical properties of peat soils in New Zealand. Geoderma 54,. 5 Radjajagulfguk. B. 2001 Subtainable agriculture on tropical peatlands International Journal for Management of Tropical Peatlands 1(1). 6. Umon. M.. T.Yamaguchi. 1997 The water absortion ability of peat. International Peat Journal 7. International Peat Society, Jyvaskyla 7 Rieley. J.O. and Page. S.£. Eds (2005) Wise Use of Tropical Peatlands Focus on Southeast Asia ALTERRA Wageningen University and Research Centre and the EU INCO - STRAPEAT and RESTORPEAT Partnerships, Wageningen, 265 pp.. Summary. PHVsicni pnopeRTi€s. OF PCRT LRND RT VO DOI NRTURRL. R€S€nve - u MINH. HR. - cn. MRU. Tran Ba Linh Nguyen My Hoa Vo Thi Guong Huynh Thanh Ghi The study was carried out to characterize physical properties of peat soils at Vo Doi natural reserve • U Minh Ha - Ca Mau for a good water management to prevent fire risk in the area. Soil samples were collected triplicates in profile T3. T5 and Vo in the protected core zone The results showed that the peal soil at Vo Doi had low bulk density (0,180,27g/cm-), low particle density (1,40-1,55g/cm'). high total pore space (81,4%-87.2%), low water holding capacity, about 60-82g of water was required to saturate 100 cm' of dry peat material, which was about 3-4 times higher than dry peat weight (17,7-26,3g/100cm-), high shrinking and swelling. (22,92-52,39%), high hydraulic conductivity (Ksat =12-134 cm/h) Peat soil at Vo Doi had physical characters that are intermediate between fibric and sapric peat and degree of peat decomposition was dependent on water table depth. Because of quick drainage properties, low water holding and low capillary capacity, water should be kept at high level of about 15 cm below soil surface to prevent fire risk Shrinking and swelling of peat soil was high, therefore soil subsidence will be high when it was dried out Physical properties of peat soil should be considered in water management for preventing fire nsk and biodiversity conservation.. Rat mong cac t^c gia xem ky va thuc hien T h d L$ VI^T VA GLfl BAI cho TAP CHi KHOA HQC D A T : kdm theo b^i b^o phiil c6 tSn b^l bSo bling tieng Anh, ph^l c6 torn tat (Summary) bSng tieng Anh. Phai gUl dTa CD ho^c E.mail. Luxi y c^c yeu cSu ve quy cdch bai b^o, c^ch viet va dcinh miiy..