KHOA HOC CdNG NGHE
DIEN BIEN HOA HOC v A TINH BEN VLfNG CUA DAT LUA TRONG no HINH LUA - TOM TAI BAC LIEU
Lam Van Khanh', Ngo Ngoc Hiftig", Nguyin Bao Ve', Nguyin Thanh Ti/cfng'
TOM TAT
Mo hinh canh tac lua - torn la mpt mo hinh canh tac dac thii ciia viing bi nhiem man theo mua. Mac dii canh tac torn sti co the dtfa de'n IcJi nhuan cao, tuy nhien dan man de nuoi tom co the diTa de'n giam tong san liTcfng lua do lam cho da't liia thoai hoa. Nang sua't liia d Bac Lieu la khoang 3-4 tan ha' va trong mpt so nam thi dien tich trong liia trong mo hmh liia - tom bi thiet hai hang ngan hecta. Sau ddt khao sat da't va nirdc du'dc thUc hien tif thang 8/2007 de'n thang 6/2008 tai 4 vung sinh thai co mo hinh liia - tom d Bac Lieu. pH nifdc kenh, rach va niTdc rupng va pH da't tang mat 6 trong khoang thich hdp cho viec trong lua. Dp dan dien ciia dung dich chiet suat (ECe) cua da't liia thay ddi theo dp dan dien (EC) cua niTdc tirdi: O PhUdc Long ECe cua dat cao liic dau vu liia (12 mS/cm) va van cao de'n cuoi vu (8 mS/cm), cac gia tri ECe nay khong thich hdp cho sinh tnrdng liia, do do the hien tinh kem ben vCng cho trong liia. Viec dan man vao da't de nuoi torn sii sau nhieu nam 6 cac rupng ltia khao sat tai PhiTdc Long tao nen da't co gia tri phan tram natri trao ddi (ESP) va ty le natri tron^ phiic he hap phu (SAR) ra't cao va do dd da't diTdc xep vao nhdm "man-sodic". Can cd nhii'ng nghien ciJu ddng rupng ve cai thien tinh trang man-sodic cua da't trong mo hinh canh tac lua-tom.
TU khoa: Mo htnh lua-tom, do ddn dien cua dung dich chiet sudt (ECe), do ddn dien (EC) nUdc ruong, phdn trdm natri trao doi (ESP), ty le natri trong phdc he hdp phu (SAR), ddt man-sodic.
I. DAT VAN DE
Md hinh canh tac lua - tdm la mot md hinh canh tac dac thii cua viing bi nhiem man theo miia, nhieu ndng dan da biet thich Ung vdi dieu kien tU nhien bang each Uong lua Uong mua mUa va nudi tdm su (Penaneus monodon) Uong mua khd. O tinh Bac Lieu, md hinh canh tac lua-tom cung la mot Uong nhffng mo hinh canh tac rat dac sac vdi tinh kha thi cao, da thu hiit dUdc sU quan tam dac biet va cd sUc hap dan manh ddi vdi ngUdi dan Uong vung va cac dia phUdng lan can, ud thanh phUdng thUc san xua't ciia nhieu hp ndng dan.
Quang canh hoac ban tham canh tdm su dUdc phat trien thuan ldi Uen da't lua nUdc vao miia nhilm man d Bac Lieu. Tuy nhien, viec canh tac tdm su nay cd the dUa den nhffng tac ddng bat ldi cho Uong lua. Sau mpt thdi gian thUc hien md hinh lua-tom, mpt so van de ve mdi UUdng bat dau nay sinh va gay ra mdi quan ngai ve tinh ben vffng cua md hinh nay (Vd Tong Xuan, 1995). NUdc man do canh tac tdm xam nhap vao da't liia mang nguy cd lam suy Uioai da't (Le Xuan
' Sd Khoa hpc va Cong nghe tinh Bac Lieu - Tnrdng Dai hpc Can Thd
Thuyen, 1999). Tham canh va ban tham canh tdm su lam phat thai lUdng ldn chat hii\i cd, vd cd va ddc chat hoa hpc vao ngudn nUdc ma nd cd tiie dUa den sU phu dudng va ddc chat Uong da't cao (Beverage and Phillips, 1993; Deb, 1998; Haherty et al., 1999).
Dien tich canh tac lua - tdm toan vung d Bac Lieu tang nhanh tU nam 2000 - 2004 len gap 4,7 lan.
NhUng nang sua't lua chi tang tha'p va dao ddng Uong khoang tU 3-4 tan ha"' va tai mdt sd nam thi dien tich udng lua Uong md hinh lua - tdm bi tiiiet hai hang ngan hecta (Sd Ndng nghiep va Phat Uien Ndng tiidn Bac Lieu, 2008). De tai dUdc tiiUc hien nham muc dich (i) Khao sat diin tie'n cua tinh chat hoa hpc nUdc va da't Uen md hinh lua-tdm; (ii) Danh gia tinh ben vffng cUa canh tac lua Uong md hinh lua-tdm qua cac diin bien hoa hpc da't va nUdc.
II. PHUONG TIEN VA PHUCfNG PHAP 1. Dja diem nghien ciili
De tai dUdc thUc hien tai 4 vung sinh tiiai cd md hinh Ilia - tdm d Bac Lieu:
Hdng Dan la vUng cd ngudn nUdc ngpt ddi dao tU sdng Hau, it man.
Phudc Long la vung cd ngudn nUdc ngpt tU sdng Hau de canh tac liia, ddng thdi chiu
anh hudng bdi sU xam nhap man tU bien Ddng va bien Tay.
Gia Rai la viing cd ngudn nUdc ngpt chii ye'u tU nUdc Udi va mdt phan tU sdng Hau de canh tac liia, ddng thdi chiu anh hudng man kha manh tU bien Ddng.
Vinh Ldi cd ngudn nUdc ngpt chu yeu la tU nUdc Udi de canh tac lua, bi xam nhap man manh me tU Uieu bien Ddng.
2. Th&i diem nghien cufu
Miia vu canh tac liia - tdm toan vung'fifdng dd'i nhU nhau, vu udng ltia tU thang 8-12 va vu nudi tdm tU thang 1-7. Thdi diem ciia sau ddt khao sat da't va nUdc tUdng Ung vdi cac giai doan canh tac Ifia/tdm dUdc Uinh bay Uong bang 1.
Bang 1. Thdi diem khao sat da't va midc
Bang 2. PhUcfng phap phan ti H cac chi tieu dat
TT 1 2 3 4 6 7
Chi lieu CEC
Fe Al^^
Ca'*, Mg"* va Na*trao ddi
pH ECe
Ddn vi cmol/kg
% Fe203
cmol/kg cmol/kg
-
mS/cm
Phtfdng phSp phan tich
Trich bing BaCl- 0,1 M, chuan do vdi EDTA 0,01 M Trich d ty le 1:20 vdi dung dich oxalat - oxalic axit d pH = 3, do tren may hap thu nguyen tu'
Trich bing KCl 1 N, chuan do vdi NaOH 0,01 N, tao phiJc vdi NaF 4%, chuan dp vdi H2SO4 0,01 N Trich bing dung dich BaCl:, do tren may hap thu nguyen tii
Trich bao hoa bing niidc caft, do bing pH ke Trich bao hoa bing nifdc caft, do bing EC ke
Ddt khao sat
1 2 3 4 5 6
Th5i diem khao sat (thang/nam)
8/2007 9/2007 11/2007 12/2008 02/2008 6/2008
Giai doan lua/tom Khi cai tao dat lua Sau sa hoac cay 30 ngay Khi lua tro
Khi thu hoach lua Ltic tha torn su Cudi vu torn 3. PhUdng phap thu m i u va phan tich
Tai mdi viing chpn nglu nhien 09 diem thu mEu dat va nudc. Tai indi diem, da't dUdc lay d 05 vi Ui theo dUdng cheo gdc va trpn chung vdi nhau lai thanh mpt mlu. Da't dUdc lay d 2 dp sau tU 0 - 20 cm va 20 - 40 cm. Mdi mlu da't dUdc thu vdi khdi lUdng 2 kg va trff trong bpc nildng.
Cd ta't ca 432 mlu da't dUdc thu thap (4 vung x 9 diem/vung x 6 ddt khao sat x 2 dp sau). ECe va pH ciia cac mlu da't dUdc xac dinh Uong dieu kien trich bao hoa.
Rieng 3 mdng dai dien cho toan vung dUdc lay m l u da't tai Phudc Long, ky hieu m l u va ten hd ndng dan nhu sau: PLl: Nguyin Van Tai; PL2: Sdn Ngpc Sang; PL3: Sdn Ngpc Budi. M l u se dUdc phan tich cac tinh cha't danh gia cua nhiem man, phen nhuham lUdng Fe^Oj, A l ^ Ca-^ Mg^\ Na^ CEC, phan Uam naUi Uao ddi (ESP) va ty le naUi Uong phUc he ha'p phu (SAR) (Bang 2).
-t- Tinh tri sd ESP (Exchangeable sodium percentage):
phan Uam Na trao ddi.
ESP{%)--Na*
CEC -xlOO
-I- Tinh SAR dUdc dUa vao phUdng trinh:
ESP
100-ESP = ^-^'^
Trong dd Kg la he sd Gapon cd gia tri la 0,015 (mmolL-')-0,5 (U.S Salinity Laboatry Staff, 1954).
4. PhUdhg phap {dian nhom dat theo tinh nhilm man Su phan nhdm da't theo tinh nhilm man dUa vao cac gia Ui dp d i n dien (EC), SAR va ESP dUdc trtnh bay d bang 3.
Bang 3. Phan nhom theo tinh nhilm man hoac sodic cua dat (Brady va Wei, 2001).
Nhom daft Man Man-sodic Sodic
EC (mS/cm)
>4
>4
<4
SAR
<13
>13
>13
ESP (%)
<15
>15
>15 III. K E T QUA THAO LUAN
1. Diin bien pH nUSc va dat cua vimg lua-tom Dp chua ctia da't dUdc xac dinh qua do pH ciia dung dich da't trich bao hda, pH nUdc Uong kenh (7-8) va Uong rupng (7-9) (Hinh la va lb) tU Uung tinh de'n kiem nhe phu hdp cho nudi Uong Uiuy san, cu die nudi tdm sii Uong md hinh lua - tdm. pH nUdc kenh rach cua tUng vung nghien cfiU Uia'p hdn pH nUdc Uong rupng liia - tdm, dieu nay cd the do tac ddng cua ngUdi ndng dan Uen mdng canh tac lua - tdm qua cac bien phap bdn voi, bdn phan.
Nhin chung, qua cac giai doan san xua't cua md hinh Ilia - tdm, d i i n bien pH nUdc kenh, rach va pH nUdc rudng trong toan vCing nghien CLH, cd gia Ui thich hdp cho viec Uong ltia va nudi tor .
KHOA HOC CONG N G H E
a)
pH nifdc
7 - 6 - 5 -
c)
X
5 -
b)
-•— Hong Dan -n— PhiJdc Long -#— Gia Rai -©— Vinh Ldi
4 i 1 1 1 1 1 1
1 2 3 4 5 6
1 1 1 1 1
1 2 3 4 5 6
d)
1 2 3 4 5 6 1 2 3 4 5 6 D^t lay m l u
Hmh 1. D i i n bie'n pH cua: (a) midc kenh, (b) nUdc ruong, (c) da't of do sau 0 -20 cm va (d) da't d do sau 20-40 cm theo cac giai doan trong mo hinh liia - torn.
Chii thich: Dc/t 1 - Khi cdi tqo dcit liia; deft 2 - Sau sa hodc cdy 30 ngdy; deft 3 - Khi liia trd; deft 4 - Khi thu hoach lua; dat 5 - Lite thd torn su; deft 6 - Cudi vu torn.
pH da't toan vung khao sat bie'n ddng tU axit den trung tinh, da't d tang 0 - 2 0 cm cd pH dao ddng tU 5,2- 7,2 va d tang 20-40 cm cd pH dao ddng tU 4,7 - 6,8.
Cd the do viec rai vdi cua ndng dan (Uung binh la 60 kg/ 1.000 m") da giup cho sU dn dinh pH da't d tang 0 - 20 cm.
2. Dien bie'n EC cua nUdc va da't cua vung lua - torn EC cua nUdc kenh va nUdc rudng cua bdn viing cd khuynh hUdng cao vao dau vu lua (4-7 mS/cm), giam xudng thai'p vao giai doan giffa vu Ilia ( 2 - 3 mS/cm) va tang cao vao cudi vu ltia sang de'n dau vu nudi tdm (7- 20 mS/cm) va cao nha't vao cudi vu tdm (25-50 mS/cm) (Hinh 2a va 2b). Nhin chung, EC U-ong mua vu nudi tdm ciia tUng viing thich hdp cho nudi tdm, tuy nhien cd bat ldi cho sinh trUdng liia vi EC ciia nUdc rupng cao, gay bat ldi de'n tinh ben vffng cho trdng lua.
EC cua nUdc kenh va nUdc rudng Uong ddt lay mau 4, 5 va 6 ciia Phudc Long va Gia Rai cao hdn so Hdng Dan va VTnh Ldi (Hinh 2a va 2b), dieu nay do vting Hdng Dan chi chiu anh hUdng bdi ngudn nUdc trong ndi ddng va tU sdng Hau nen cd dp dan dien tUdng dd'i tiiap, cdn vting trieu hdn hdp d PhUdc Long va Gia Rai chiu anh hudng nhieu ngudn nUdc tU ndi ddng, tU phia bien Tay va Ddng ke't hdp vdi dieu kien thdi tiet da lam cho dp dan dien d 2 vung nay cao;
vung VTnh Ldi thi khac ban so vdi 3 vtmg khac ve dieu kien sinh tiiai va dia hinh, vi vung nay gan vdi bien Ddng nen kha nang Uao ddi nUdc d l dang hdn, ddng thdi do chu Upng nhieu Uong nudi tdm nen nUdc Uong rudng tiiUdng xuyen dUdc giff d mUc cao, nen dp din dien khdng tang cao Uong mua nang.
Dp man cd the dUdc tinh dUa tren he sd chuyen ddi cua EC: Ndng dp mudi (g/l)= mS/cm x 0,64. Ket
qua cho tha'y Uong vu canh tac Iiia dp man nUdc kenh dao ddng tU 0,91 - 15,8%o va dp man nUdc rudng dao ddng tU 1,08 - 12,5%c. Tuy nhien, theo khuyen cao, khi nUdc cd pH >8,4 va EC >2 dS m' da la khdng thich hdp tUdi cho liia (Dobermann and Fairhurst, 2000). Trong mua vu canh tac tdm dp man nUdc kenh dao ddng tU 8,69 - 31,l%c va dp man nUdc rupng dao ddng tU 8,83 - 34,l%o, dp man ciia nUdc trong rupng liia cd xu hudng cao hdn dp man nUdc kenh, cd the do kha nang bd'c thoat hdi nUdc Uen rupng Ilia nhieu. Tdm su cd ngUdng dp man tU 0- 40%c (Pham Van Trang va ctv., 2004), dp man td't nha't de tdm sti tang UUdng nhanh tU 15-30%c (Kungvangkiji etal., 1986).
ECe cua da't tang mat (0 - 20 cm) d Gia Rai va Phudc Long cao vao dau vu Ma (>10 mS cm') va giam dan de'n gan cudi vu lua, khi chuyen sang vu tdm
thi ECe Uong da't bat dau tang tU ddu vu tdm va cao nha't vao cudi vu nudi tdm (Hinh 2c). ECe ciia tang da't 20-40 cm d Gia Rai va Phudc Long dat gia Ui 8- 10 mS cm' ludn cao hdn Hdng Dan va Vinh Ldi qua cac thdi diem Uong nam.
SUngap man keo dai Uen mdng lam thtic day tien Uinh rUa udi cac cation kiem va gia tang dp man va dp chua ciia da't (Douglas, 1994; Flaherty et al., 1999; Landon, 1991).
Cay liia khdng tiie chd'ng chiu dp man cao (ECe > 7 dS/m) va dp chua cao (pH < 4) va nhU the sinh trUdng va nang sua't lua se bi giam (Mass and Hoffrnan, 1977; Kyuma, 2004; Ponnampemma et al, 1973).
3. Danh gia dien bie'n hoa hpc da't tren tinh ben vifng cua mo hinh lua-tom tai Phufdc Long
Phudc Long dUdc chpn de khao sat tinh cha't va sU thay ddi hda hpc da't, ke't qua phan tich cua 3 mdng dai dien dUdc trinh bay d bang 4.
U U 3U
20
10
G e
- ^ ' ' ' ' ' 1 2 3 4 5 6 ' 2 3 4 5 6 n ^ . , - «
DgTt lay mlu
Hinh 2. Diin bie'n EC cua: (a) nUoTc k&nh, (b) nUoTc rupng, (c) da't & dp s§u 0 - 20 cm va (d) da't d dp sau 20 - 40 cm theo cac gjai doan trong m6 hinh lua - torn.
Chu thich: Deft 1 - Khi cdi tao ddt lua; deft 2 - Sau sg hoac cdy 30 ngdy; deft 3 - Khi Ida trd; deft 4 - Khi thu hoach Ilia; deft 5 - Liic tha torn sii; deft 6 - Cudi vu torn.
KHOA HOC CONG N G H E
Al trao ddi va Fe boat ddng cua da't dUdc khao sat de danh gia mUc dp dpc chat phen Uong da't. Ham lUdng Al Uao ddi chi xua't hien d tang 20-40 cm cua mdng PL2 va PL3 va cd sU bie'n ddng khdng dang ke giffa cac tiidi ky lay mlu, ham lu'dng trong Al khoang 0,7 - 2,75 cmol/kg. Ham lUdng Fe boat dpng xua't hien d ca 2 tang, it cd khac biet giffa cac mdng va cac tiidi ky lafy mau, bien ddng trong khoang 0,73 - 1,74 % FeiO-i.
Bang 4. Anh hUcfng cua cac thdi ky nhiem man deh sU thay ddi hoa hpc cua dat tai PhUdc Long, tinh Bac Lieu - Nam 2007 - 2008
Ba\ay niau
1
4
5
6 hieu
PLl
PL2
PL3
H,l
PU.
F U
PLl
PL2
P U
PLl
PL2
P U E>6sau
(cm) 0-20 2040 0-20 2040 0-20 2040 O20 2O40
O20 2O40
O20 2040 O20 2O40
O20 2O40
O20 2040 O20 2040 O20 2040 O20 2040
Al trao d6i (cniolkg-')
0 0 0 233
0 1,4
0 0 0 235
0 2,75
0 0 0 1,51
0 0,7 0 0 0 U 5
0 1,23
F e , 0 j
(%)
1,34 1,74 0,97 1,71 0.96 1,44 1,23 12 1 1,66 1,07 1,43 1,39 1.65 0,73 1,16 0,98 1,37 0,97 1,54 1,13 1,41 1,16 0,97
CEC (cniol kg"')
32,2 33,6 31,2 31,7 30,9 31,8 33,6 33,7 32,1 32,1 33 31,7 33,8 33,5 30,8 31,5 32,7 32,7 34,1 33,8 31,7 31,7 31,8 32,1
Cation trao doi (cniol Na*
733 6,75 731 5,97 7,16 5,98 637 6,02 5,75 5,84 5,84 5 3 6 7,86 6,71 7,86 6,75 834 621 9,72 7,1 9,75 6,64 10,0»
6,45 Ca-*
4,1 5,53 3,34 3,96 3,67 2,8 4,69 329 3,79 4,03 4,62 3,1 2,95 5,03 4,96 3,98 3,77 2,97 5,15 526 5 2 431 5,38 523
Mg=*
538 537 5,39 5,03 5,42 4,98 534 5 3 525 5,03 534 4,92 5,6 532 539 538 537 522 5,61 534 5,63 5 2 5,62 5,16
ESP
(%)
234 20,1 24,1 18,8 232 18,8 18,9 17,9 17,9 182 17,7 16,9 23,3 20,1 25,5 213 253 19 283 21 30,7 20,9 31,6 20,1
SAR
204 16,8 21,1 15,4 20,1 15,4 15,6 143 143 14,8 143 13,6 202 16,7 22,8 182 22,8 15,6 26,6 17,7 29,6 17,7 30,7 16,8
ECe (mS cm"')
11,8 112 133 112 13,6 9,59 824 8.95 7,63 7,89 6,36 8,00 143 9,48 14,7 123 153 9,4 27,4 132 30,9 132 33,0 11,7
* Ky hieu mdu duac lay tii ruong cua 3 ho nong ddn tgi Phudc Long: PLl: Nguyen Vdn Tdi; PL2: San Ngoc Sang; PL3: San Ngoc Buoi
Ddt 1 - Khi cai tao da't liia; ddt 2 - Sau sa hoac cay 30 ngay; ddt 3 - Khi lua ti6; ddt 4 - Khi tiiu hoach lua;
ddt 5 - Luc tha tdm su; ddt 6 - Cudi vu tdm.
Daft cd gia tri ECe > 10 mS cm' se lam lua tiiudc gid'ng min cam man giam nang sua't de'n 50%
(Dobermann and Fairhurst, 2000). Cac rudng khao sat d Phudc Long cd gia tri ECe cao d dau vu (12 mS
cm') va cudi vu (8 mS cm') dieu nay cd tiie lam giam manh sinh UUdng va nang sua't ltia, do dd ECe dat Uong tinh Uang nay tiie hien tinh kem ben vffng cho u-dng ltia.
6 giai doan cai tao da't lua, cac rudng khao sat d Phudc Long cd ESP > 20 mS cm"', ESP giam dan va khi thu hoach lua vin dat > 15 mS cm"'. Theo sUphan nhdm tinh nhilm man hoac sodic cua da't (bang 3), da't ciia 3 diem khao sat dai dien d PhUdc Long tiiudc nhdm man - sodic. NhU vay da't lua Uong tinh Uang nay can cd bien phap cai tao man tich cUc hdn.
Quang canh tdm su cd the nhanh chdng lam giam ham lUdng chat hiili cd Uong da't (Shang va ctv., 1998). Da't va nUdc cd dp man va dp chua cao cung se anh hUdng xa'u den cac loai thuy sinh sdng Uong mdng lua (Flaherty et al., 1999;
Greenland, 1997; Khatun and Flowers, 1995; Welfare et al., 1996). Mac du canh tac tdm su dUa den Idi nhuan cao hdn udng liia, tuy nhien canh tac tdm su dUa den giam tdng san lUdng Ma do lam cho dat thoai hoa, nang sua't lua bi giam va de doa den tinli ben vffng cua he sinh thai da't lua, va vi tiie nhieu hp ndng dan tiieo nghe nudi tdm d Bangladesh ud nen thie'u lUdng thUc va ngheo khd (Abu Muhammad, 2006).
IV. KET LUAN VA DE NGHI Dien bie'n cua mdi trUdng tU nhien anh hUdng den tinh cha't da't, nUdc va tinh ben vffng cua md hinh canh tac Iiia Uong he thd'ng lua-tdm nhU sau:
pH nUdc kenh va nUdc rupng mang tinh kiem nhe vao dau vu lua va giam de'n trung tinh Uong tiidi gian lua sinh tmdng; pH da't tang mat (5-7) d Uong khoang thich hdp cho viec udng lua.
Dp din dien cua nUdc kenh va nUdc rudng ciia 4 vung cd khuynh hUdng cao vao dau vu lua (4-7 mS cm'), giam xud'ng tha'p vao giai doan giffa vu lua (2- 3 mS cm') va tang cao vao cudi vu lua sang de'n dau vu nudi tdm (7-20 mS cm'). ECe cua da't diin bie'n
song hanh vdi viec din nUdc tUdi cho rudng ltia, ECe 3. Dobermann A. and Fairhurst T., 2000. Rice:
cua da't Uong vu lua d PhUdc Long cao luc dau vu (12 Nutrient disorders & nutrient management. Handbook mS cm"') va vin cao de'n cudi vu (8 mS cm'), cac gia series. Pomsh & Phosphate InstiUite (PPl), PoUish &
tri ECe nay khdng tiiich hdp cho sinh UUdng lua, do phosphate InstiUite of Canada (PPIC) and Intemational dd tiie hien tinh kem ben vffng cho Uong lua. ^dce: Research Institute. 191 p.
Viec din man vao da't de nudi tdm su sau nhieu 4 Le Xuan Thuyen, 1999. Ke't qua nghien c\hi nam d cac rupng lua khao sat tai PhUdc Long tao nen ^^^^^ ^-^^ ^y ^^^ ^da da't vung Ban dao Ca Mau. Ky dat cd gia ui ESP va SAR rat cao va do dd da't dUdc ^^^ ^^^ ^^^ ^^^^ ^^^^ ^^^^g ^gj^g ^^ ^ g j tnrdng khu xdp vao nhdm "man-sodic", thupc nhdm khd khan ^^^ ^.^^ ^.^^ ^.^^ ^ ^ ^ ^ong td chUc tai Cin Thd, uong qua Uinh rUa man. ^ j . ^ ^^^ j ^ ^ ^^ ^^^ ^^^^ ^^^^ ^g^g ^^ ^ o i UUdng
Can nghien cUu them ve dinh dUdng tU nhien (-^^iThd, 250 Uang, U 1 - 13.
trong dat va nUdc. Dong thdi, can cd nhffng nghien , .,,
° . „ . . ' . - , • - / u - A - 5. Sd Ndng nghiep va Phat Uien Nong tiion Bac cUu ddng rudng de cai thien Unh Uang man-sodic cua <= ^ f , , . . , - ' . v.v.^
; i? . u . ' i ' .- Lieu, 2008. Bao cao ket qua thUc hien ke hoach hang dat Uong mo hinh canh tac lua-tom. ^ ^ ' ^^ • • , .
nam (2000 - 2007) va ke hoach phat Uien nong nghiep ndng thdn hang nam (2001 - 2008).
6. Vd Tong Xuan, 1995. Danh gia tinh ben vffng cac he thd'ng canh tac vung nUdc Id ddng bang sdng TAI LIEU THAM KHAO
1. Abu Muhammad, 2006. Rice to shrimp: Land use/land
cover changes and soil degradation in Southwestem ^ Bangladesh Land Use Policy 23. PP42M35. ?^".^°"f 1. ^ 1 ° '^^^ "^^*^" ''^" ^ " " ^ ° ' ' ^"""^
2. Brady, N. C , and R. R., Weil. 2001. The nature and properties of soils. 13th ed. Prentice Hall, N. J.
Dai hoc Can Thd.
CHEMICAL PROPERTIES AND SUSTAINABILITY OF RICE SOIL IN RICE-SHRIMP FARMING IN BACLIEU
Lam Van Khanh, Ngo Ngoc Hung, Nguyen Bao Ve, Nguyen Thanh Tuong
Summary
Rice-shrimp farming is a special cultural system in seasonally saline areas. Rice-shrimp farming may give highly profitable land use practice, in tum, soil and water environment may become degraded. Rice grain yield in Bac Lieu only reached about 3-4 t ha' and at some years, a thousand ha of the rice area which belongs to rice-shrimp system were unharvested. The surveys on soil and water have been conducted in Bac Lieu during August 2007 to June 2008 at four agro-ecosystems with existence of rice-shrimp farming. pH of canals, fields and soil surfaces were at suitable range for rice cultivation. ECe of rice fields varied with irri- gated EC.At Phuoc Long, soil ECe was high at beginning of the rice crop (12 mS cm"') and remained high at harvest (8 mS cm"'). These ECe values were not suitable for rice growth and therefore less suitability for rice production. The use of saline water to rise shrimp at Phuoc Long after many years has caused high soil ESP and SAR and the soil could be grouped as saline-sodic soil. There is the need to have field research related to mitigate saline-sodic situatiion in rice-shrimp farming.
Keywords: Rice-shrimp farming, electrical conductivity of extract, field-water electrical conductivity, exchangeable sodium percentage, sodium adsorption ratio, saline-sodic soil.
NgUdi phan bien: TS. Biii Huy Hien