Tgp chi Khoa hgc Tnrdng Dgi hgc Cdn Tho Phan B • Ndng nghiep. Thuy san vd Cong ngh? Sinh hgc. 2612013/: 262-268
Tap chl Khoa hoc Triidng Oai hpc Can Thd website: sj. ctu. edu. vn
MO PHONG DONG THAI DAM H C U DUNG TRONG D A T LUA B A N G PHAN M E M STELLA
Nguyin Van Qui, Le Tan Lgi va Ngd Nggc Hung'
Klioa Mdi trudng & Tdi ngu^'in Thiin nhiin, Trudng Dgi hgc Cdn Tha Thong tin chung:
Ngdy nhdn: 03/04/2013 Ngdy chdp nhdn: 20/06/2013 Title:
Simulation of dynamics of available soil nitrogen in the lowland rice systems using Stella software TO- khda:
Md phdng. N huu dung, Stella, chu trinh N, N khodng hda, N bdt dgng Keywords:
Simulation, available N.
Stella, N cycle, N mineralized, N immobilization
ABSTRACT
Nitrogen management in loM'land rice systems is characterized by high N rates, low nitrogen use efficiency (NUE) and high losses. Simulation models are important tools for better predicting optimal N rates on a specific field that would help avoid excessive N input or deficiency. This study has been conducted with using Stella software for modeling soil N cycle. Basic data for constructing N cycle model have been collected from field research in Giong Rieng soil. There is good agreement in the simulation for the release mineral N by paddy soils corresponded with the .V requirements of the rice crop at various stages. The importani factor that affected N mineralization simulated was plant residues input from last crop biomass. Simulated results also showed that, in no nitrogen applied, amount of mineralized N was only 25 kg ha' while N uptake of rice plant was 45 kg ha'' In N application treatment, simulation for N uptake in rice was 80 kg ha', this amount was a result of balance in soil with different processes of N volatilization, mineralization and denitrification. The simulated of soil N dynamic and plant N need is a basic step to help adding N fertilizer for plant need reasonably
TOM T A T
Ddc tinh cua ddt lua ngdp nudc Id bdn dgm (N) cao, sir mat N cao vd hieu qud sir dung thap. Mo hinh mo phdng Id cdng cu hd trg manh cho uac dodn lugng N ldi hdo cho cdnh ddng chuyin biit vd giup trdnh bon thita hoac bdn ihiiu .V Di tdi dirac thuc hiin vdi su dung phdn mem Stella di thiit ki chu trinh N Du lieu ca sd sit difng cho thiit ke md hinh duac thu thdp lir kil qud nghiin cuu thuc li trin ddt lua Giong Rieng- Kiin Giang. Kit qud cho ihdy yiu td quan trong dnh hirdng din chu trinh N khodng hda mo phong trong ddt Id luang ihdi thuc vdt cd duac tir sinh khoi cdy tidng dirac tgo nen a vu tritdc. Kit qud md phong cung cho thd}' lugng dam dugc khodng hoa Irong mot vu Id 25 kg ha'', irong klu lugng dam hiit thu trong cdy liia Id 45 kg hd'. KJii bdn dgm. luang .V hiit Ihu md phong cua cdy liia Id 80 kg ha'', ddy la luang N dugc cdn bang vdi cdc tiin trinh bdc hai N. khodng hda vd miin hda xa)' ra trong ddt MS phong dugc diin biin ciia N trong ddt vd nhu cdu N cua cdy se la ca sd giup ta bS sung pbdn dgm ddp icng nhu cdu cdy trong mgt cdch hgp ly.
Tgp chi Khoa hgc Tnrdng Dai hoc Can Tha Phdn B .Sdng nghiep. Thuy san vd Cdng nghe Smh bgc 26 (2013)- 262-26 1 .MODAU
Sir dung N tten ddt Ida ngap nudc dugc dac tnmg bdi viec bdn N d lieu lugng cao nhung hieu qua sit dung thdp. Nghien cuu chien luge quan tri N cho limg loai dat va he thdng canh ldc cu the la van de cap thiet. Xac dinh lugng N bdn tdi hao va n ^ e n cuu cac tien trinh cua N cho dat Ilia dang Id mdt thu thach Idn.
Su khdc nhau ve sd luong va chdt Iugng cua chat hiru co ttong ddt, yeu td thdi tiet; bien phap canh t a c . . . dan den dam khoang hda tten ddng rudng thay ddi theo thdi gian va khdng gian. Dam khoang hda do dugc qua thuc nghiem hodc du doan qua su dung md hinh.
Du doan dam khoang hda tren ddng rudng Id van de nghien cuu quan frgng trong tham canh (Campbell and ZenUier. 1993).
Nhieu nghien cuu tten the gidi cho thdy md hinh mo phong cd the dugc su dung ttong nghien cuu chuyen hod ciia N frong ddt va nudc, nghien cuu cac lien trinh sinh trudng va phdt trien cdy trdng; \ a tten su can bang nudc ttong ddt. Dieu nay cd the gdp phdn to ldn trong viec hieu biet ve ddng thai N va cdy trdng. Cdc chuang trinh mo hinh hoa cd the chi ra dugc nhirng mang kien thiic cdn thieu
sdt cdn thilt cho cdc khao cuu sap ldi va giup hiiu rd van d l cho viec cai thien quan tri phan N tten ddt iiia.
Do dd. d l tai dugc thuc hien vdi muc dich:
(i) Danh gid kit qua md phdng chu k>- dam thilt k l bang Stella tten ddt liia Gidng Rieng - Kien Giang; (ii) Md phdng su bien dgng lugng N huu dung frong ddt lua.
2 PHU'ONG P H A P NGHIEN C U t l 2.1 P h u o n g tien
Md hinh mau "'Chu trinh N"' (N cycle) cua phdn mim Stella (Isee systems, 2008) dugc su dung ttong phat trien md hinh loan cua de tai.
Cac du lieu dau vao (input data) cua md hinh dugc thu thap t u thi nghiem ddng rudng tai Gidng Rieng, Kien Giang nam 2011 thudc du an '"Quan ly dinh dudng tdng hgp tren ddt liia*' Id chuong trinh bgp tac Dai hpc Cdn Tho - Dan Mach (Danida, chu nhiem de tai: Ngd Nggc Hung).
2.1.1 Ddt
Du lieu dac tinh ddi dugc trinh bay d Bang I.
Bang 1: Dac diem cua dat tdng mat (0-20 cm)
„ EC N long so Carbon P (mS/cm) (%N) (%C) 3.8 2.3 0.18 2.08
1 d dia diem Giong Rieng - P de tieu Bray 2 (mg k g ' ) 1.17
- Kiln Giang, thdng 1 nam 2011 Sa cau dat
%Cat %Thit %Set 0,4 41,5 58.1 2.1.2 Giong cdy trong
Gidng Ilia dugc sir dung cho thi nghiem la OM4498.
2.2 Phircmg phap ngbien ciru 2.2.1 Su dung va chuyen doi dir lieu
N trong chdt miin: Theo ket qua phdn tich dat d Gidng Rieng - Kien Giang. ham Iugng Carbon (%C) bdiTg 2,08%. Tu dd lugng carbon (tdn/ha) dugc tinh nhu sau:
C = ((2,08x2.10^100)
Theo Brady vd Weil, (2001) trong thdnh phan chat miin chua khoang 50 - 60% carbon va 5% nittosen. cd ti le C:N tCr 10 hoac 12.
N frong chdt mun = ham Iugng Carbon/lO.
— Trgng lugng re liia: qua viec dao va xac dinh trgng Iugng re cua cac thi nghiem trudc, ngudi ta cd the udc lugng dugc frgng lugng re chiem 10 — 15 % sinh khdi fren mat dat luc chin (Bergersen i d ctv, 1989; Unkovich va ct\:
1994).
— Trong lugng ram. ram Iua cua cac giong Ida cao san chiem khoang 40 - 50% sinh khdi phdn tten mat dat. Ti sd rom so vdi sinh khdi ciia cac ^ d n g cd thdi gian sinh trudng ddi se cao ban gidng cd thdi gian sinh trudng ng^n (Akita, 1989). Ham lugng N frong ram Iua dien hinh nam frong khoang 0.5 d i n 1,0 %.
Tgp chi Khoa hgc Trudng Dgi hgc Cdn Tho Phdn B: Ni Theo Dobermann va Fairhurst, (2000) ham Iugng N trong rom va r l trung binh la 0.65 %.
Toe do phdn hiy re lua: Tdc do phan huy cua r l Ida trong giai doan 15 ngay sau khi sa la 1.80% va giai doan tu ngay 16 den ngay 90 la 0.4% (Nguyin Thdnh H6i, 2008).
Toe do phdn huy ram: Tdc do phan huy cua rom Iua frong giai do£m 15 ngay sau khi sa Id 1.47% va giai doan tu ngay 16 din ngay 90 la 0.56% (Nguyin Thanh Hdi, 2008).
Phdn bon: Lugng NPK bon cho cac Ida vy Dong Xuan, Xuan He va He Thu: Thu thdp so lieu thuc le tai Gidng Riing - Kien Giang.
Bang 2: L i l u l u g n g va thdi ky bon N P K cho cay lua
Lo^i phdn 10 2 0 4 5
NSKS N S K S NSKS D ? n i ( k g N / h a ) 33.3 33,3 33.3 Lan (kg PjOj/ha) 60 0 0 Kali (kg KjO/ha) 15 0 15 Hieu qud sir dung N = 40% (Tnnh Quang Khuong va crv , 2010).
Ti 14 CO dinh N tu do trong rugng lua:
xac dinh bang phuong phap khu acetylene (ARA Acethylene Reduction Assay). Kit qud thi nghiem moi vu Ida (90 ngay) udc tinh trung binh cd dinh dam tu do d rupng ngdp nudc lien luc khoang 22.8 kg N/ha va rugng kho ngdp xen ke khoang 17,8 kg N/ha.
Ti le miin hod: Su phdn huy cua xac ba hiiu CO sau mdt nam viii vao trong ddt. Hon 2/3 cua chat nay bi oxid hoa thdnh COi va it ban 1/3 cdn Iai frong dat ma phdn Idn Id chat mun (Brady va Weil, 2001).
Theo Brady vd Weil (2001), chat hiru co trong ddt bao gdm nhilu nhdm khac nhau nhu:
nhdm de phdn huy, nhdm chdm phan huy \ a nhdm khd phan buy. Trong do nhom de bi phan huy chiem li Ie nhd khoang 10 - 20 % cua tone chdt hdu co vd co thdi gian phdn hiiy la tir I den 2 nam. Cdn cac nhdm cdn lai chiem ti le Idn nhtmg thdi gian phdn buy cd the la tir hang chuc den hang fram nam.
Ti le khodng hod: Theo Brady \ a W eil (2001), N hiiu co trong dat dugc khoang hda hang nam vdi ti le 2 - 3,5 %.
ng nghiep. Thiiy san vd Cdng nghe Sinh hgc: 26120I3): 262-26S Nhu cdu hdp thu N cua cay lua dua theo sd lieu nghien cuu cua Akita vd ctv. (1989).
Dugc bilu diln theo mo hinh loan Gauss bdc I
"General model Gaussl": f(x)-a/EXP(-((x- b)/c)-) vdi: a - 0.025; b = 38.17: c = 12.12 va R- = 0,94.
Md hinli phat triln sinh khdi Iua vu He Thu 2011 tai Gidng Riing:
y=8.3207Ln(x)-^ 0.0188
- Chj sd thu hoach lua vu He Thu 2011 tai Giing Riing: HI = 0.378.
2 2.2 Thiet ke vd vdn hdnh mo hinh Phan mem Stella dugc su dung dl thilt kl cac mo hinh loan sau:
Mo hinh miin hoa \ a khoang hda frong ddt.
Mo hinh N hihi dung frong ddt lua.
3 KET QUA VA T H A O LUAN 3.1 Mo phong tien trinh miin hda va
khoang hoa trong dat
Luu dd md phdng lien trinh miin hda va khoang boa trong ddt, vu He Thu 2011 tai Giong Riing Kien Giang (Hinh 1) ngudn hiiu ca du nhap vao dat tu cac thai thuc vat nhu rl cay, la cay de lai ttong ddt sau khi thu hoach.
Cac thai thuc vdt nay se bi cdc vi sinh vdt su dung va chuyen hda de trd thanh chdt mun. Su cd dinh dam tu do ciia cdc vi sinh vat, su c6 dinh nay tang len theo su phat ttien cua cdy Ilia. Cudi cung cua tien trinh Id su khoang hda chdt mun de phdng thich vao ddt mdt Iugng dam hiru dung doi vdi cdy trong.
Ket qua md phong tien frinh miin hda va khoang hda dugc the hien d Hinh 2. Dudng bieu dien ham Iugng dam tir thai thuc vat tang len frong giai doan 25 ngdy sau khi sa va sau dd dn dinh dan ve cudi vu. Do giai doan ddu cac Ihanh phan de phdn huy ciia xac ba thuc vdt (re cdy ttong vu trudc) dugc trd Iai frong dat dugc phan hiiy trudc. Sau do chi cdn Iai cac thanh phan khd phan buy nen ham lugng dam tu thai thuc vdt dugc bd sung it di. Tien trinh khoang hda xdy ra ddng ihdi vdi tiln trinh miin hda nen khi lugng dam tir thai thuc
Tgp chi Kboa bgc Trudng Dai hgc CAn Tha Phdn B: .Ndng nghiep. Thuy san va Cong nghe Sinh hgc: 26 (2013): 262-268
vat khdng cdn dugc bd sung thi tien trinh khoang hda Iam cho ham Iugng dam nay dn dinh ddn d cudi vu. Trong khi dd ham Iugng dam trong chdt mijn thi gan nhu thay ddi it tir ddu vu (416! kg ha'') den cudi \v (4150 l^ ha"'). Dilu nay phu hgp vdi nghien cuu cua Pampolino vd ctv. (2007) sudt 15 nam trong Ilia lien tuc. Carbon trong Idp ddt mat (0 - 20 cm) dugc duy tri hoac gia tang. Carbon
trong Idp ddt mat tang len 10% trong thi n ^ e m ttdng lua 3 vu ttong nam vdi phdn rom tten mat sau moi vu dugc lay di. Do do, su keo dai ddt ngap nudc cd thi duy tri hoac gia tang chdt hihi CO trong ddt (Cassman vd en.. 1995;
Bronsoo va ctv., 1997; Witt vd cA.. 2000).
Lugng dam huu dung dugc tao ra tii Idioang hda trong ddt tang ddn va sau mgt vu lua la khoang 25 kg ha"' (Hinh 2).
O^r-^^-^i
o
>ileUNianghoa
Hinh 1: Luu do mo phong tien trinh mun hoa va klioang hoa trong dat
if^ Untitled fi 1 Ntuthaithucv
I .= 11B IkaJ
1' N-tfT>ng chat mun
Hinb 2: Ket qoa mo phong dien bien tien trinh miiD hoa khoang boa trong dat
Tgp chi Khoa hgc Tneang Dai hgc Cdn Tha Phan B: Ndng nghiep. Thuy san vd Cong ngh? Sinh hoc. 26(2013) 262-268
3.2 Mo phdng chu trinh dgm trong dat liia Mdi quan he giiJa dam huit dung va sinh khdi Iiia frong vu He Thu dugc xdy dung dua vao lugng dam hihi dyng frong ddt va dac diem sinh ly cua cdy liia (hinh 3 va Hinh 4).
Lugng N huu dung frong ddt dugc tang them
tir cac ngudn chu yeu nhu: su khoang hoa chdt hihi CO, N trong nudc mua, nudc tudi va phdn bdn. Trong khi do lugng N hun dung bi mdt di la do bat ddng dam bdi vi sinh vat su dung dam va lugng N him dung bi mdt phdn ldn la do cay ttdng Idy di dl tao thanh sinh khdi.
Hinh 3: Luu dl mo ta chu trinh d^m trong ddt lua
i_hoa)*Q 1 5 C I ] N_huu_dunga> = N_huu_aunQa- at) -• rToc_do_khDang_hoa * tang_N - mat_ao * dt
INIT N_huu_auno = 40 INFLOWS.
^5fr Toc_dO_khoang_hoa = N_trong_chat_mun*ty_le_khoang_hoa OUTFLOWS; ~ _ _ _ _
^ e - mat_dl = N_cay_lua_hut_trong_1_ngay*Tham_lau
d l N_lrong_chat_mijnCD = N_tronQ_chat_munC! - dl) * a"oc_do_mun_hoa - Toc_elo_khoi [NIT N_trong_chat_mijn = 41 60
INFLOWS
•OE' T o c _ d a _ m u n _ h o a = cN_1u_thai_thijc_varTyJe_fr OUTFLOWS:
^ c Toc_do_khoana_hoa = N_trong_ctiat_mtjn-t¥_lB_
C H N_tu_thaUhuc_vatCO = N_tu_thai_inuc_vai(i- at) - (thai_l rNiT N_tu_mai_thijc_vat = i
INFLOWS
- 5 * lhai_thuc_val= Cre_phar_huyo 6S)+(rom_phan_mjv~0 B5*0)*co OUTFLOWS.
^x> T o c _ d o _ m u n _ h o a = (N_tu_thai_thuc_varTv_la_mijn_hoa)*C-15
^ & Co2 = (N_1u_thai_thuc_varTv_1e_mun_hoa)'0 6 CD Slnh_khol_LuacO = SlnM_krtoi_Luaa - dt) - aai-ig_sinh_khol) - dt
INIT Sinh_khoi_Lua = 0 INFLOWS-
^ p tanB_sinh_khol = kha_nang_tao_slnh_khoi I—I Trong_luong_re(t) = T r o n g _ l u o n g _ r e ( l - dl) * (- re_phan_huy) - dt
i N i T T r o n g _ l u o n g _ r B = 1 ooo OUTFLOWS;
^C" rB_phan_hijy = Trong_luong_re'Toc_do_phan_hiiy_re I—I Trong_luong_rQmCD = TronB_liJDno_fom(t- dt) + t- rom_phan_huv5''iat
INIT T r o n g _ l u o n g _ r o m = 3000
= Trong_luorig_rom*toc.
ll 4: Phinnig trinh toan mo ta chu trinh d^m trong dat lua vu He Thu 2011 tai Giong Rieng - Kien Giang
Tgp chi Khoa hgc Trucmg Dgi hgc Cdn Tbo Phdn B: Nong nghiep. Thuy san vd Cong n^f Sinh lute: 26(2013/: 262- Nhu cdu hiit thu N cua cdy udng dugc
md ta dac tnmg d 3 nguong: tdi da, tdi thieu va tdi ban. Trong md hinh nhu cau hdp thu N ciia cay Iiia dugc bieu dien theo phuang trinh y= a/EXP(-((x-b)/c)-) (Akita va ctv 1989). Nd cung phil hgp vdi nghien ciiu ciia Dobermann va Fairhurst (2000) la cay liia can N frong sudt qua trinh sinh trudng va phdt Uien nhung nhu cau N Idn nhdt la giai doan tir giua thdi ky de nhdnh den ddn ddng. Su bien ddng ciia mdt bien sd frong chu trinh la su ket gan vdi cdc mdi lien ket khac, thi du: (i) Lugng dam hdu dung bang Iugng dam huu dung lai thdi diem t cdng them Iugng dam tii khoang hda, phan bdn, nudc mua va nudc tudi. Tru di Iugng
dam bi cay ttdng hdp thu, lugng dam bi thdm lau va lugng dam hi bit ddng theo thdi gian;
(ii) Sinh khdi lua bing sinh khoi nang suat Ida tai thdi diem t cdng vdi kha nang tao s i i ^ khdi theo thdi gian. Kha nang tao sinh khdi Iai bdng nhu cdu dam cua cay Iua nhdn vdi lugng dam huTj dung.
Nhu cdu ve N cua cay Ida tang cao frong giai doan tu khoang 20 d i n 45 ngdy sau khi sa (Hinh 5). Trong khi dd lugng N hiJu dung frong dat ciing giam manh trong giai doan nay va sau 45 ngay thi lugng N huu dung trong ddt ddn dn dinh, ddng thdi sinh khdi ciia cay Ida ciing bat ddu tang manh tii ngay 23 va den ngay 45 sau khi xa.
Jr UntrtJed
1: p
P39=1
cacaylua
?
2. N hiKi *ai9 3: Ssii idicpilus
/^\
i /v / \ !
^^^^'
23.15 45JiD 87:75 SOJM^'—^ ;
Days 9.42 f«d Sm. Hon 07.2010
IkiMed ^
Hinh 5: Dien bien sinh khoi lua va Bdng 3 trinh bay so lieu thuc t l v l diln bien ham Iugng NH4 frong ddt liia d Giing Rieng. He Thu 201. Ket qua md phdng tuong ddi tuong thich vdi thuc t l (Hinh 6).
Hinh 6: Ham lirgng NH^ troug dat d 20 cm tdng dat mat mo phong va thuc do
ham lirgng N hOn dung trong d i t
Bang 3: Diln bien ham lifOTig NH4 (ppm) thgc te trong ddt ir nghiem thuc khdug bon N. Gidng Riing, He Thu 2010 Ngay sau khi sa (ngay) 1 10 20 45 Ham lugng NHj Uong dat (ppm) 36.6 42.0 38.5 9.8
Mt4m..|<|>,i|4; ,
Tgp cbi Khoa bgc Trudng Dgi hgc Cdn Tho 4 KET LUAN V A D E X U A T
Kit qua md phdng cho thdy y l u td quan trpng anh hudng din khoang hda N frorig dat la lugng thai thuc vdt cd dugc tir sinh khdi cay frdng dugc tao nen d vu trudc.
Lugng dam khoang hda md phdng tren ddt Ilia d Gidng Rieng Kien Giang trong mgt vu Id 25 kg ha"'. Khi bdn dam, Iugng N hiit thu md phong ciia cdy Ida la 80 kg ha'', day la lugng N dugc can bang vdi cac tiln trinh bdc hoi N , khoang hda va mun hda xay ra frong ddt.
Ket qua md phdng ham Iugng NH4 trong dat kha tuong thich vdi sd lieu do thuc t l d nghiem thiic khdng bdn N.
Md phdng dugc diln biln cua N trong ddt va nhu cau N cua cay se la c o sd giup ta bd sung phdn dam dap ung nhu cau cay udng mdt each hgp ly.
T A I L I E U THAM K H A O 1. Akita, S., 1989. Physiological bases of
heterosis in rice. Hybrid Rice, International Rice Research Institute, Los Banos.
Philippines, pp. 67-77.
2. Brady, N. and R. Weil. 2001. The Nature and Properties of Soils, 13th Edition, Prentice Hall.
Upper Saddle River. New Jersey. 960p.
3. Bronson, K.F., K.G. Cassman, R. Wassmann, D.C. Oik, M. van Noordwijk, and D.F. Canity.
1997. Soil carbon dynamics in different cropping systems in principal ecoregions of Asia. p. 35-57. In R. Lai el al. (ed.) Management of carbon sequesfration in soil.
CRC Press. Boca Raton, FL.
4. Campbell, C.A., Zentner, R.P., 1993. Soil organic matter as influenced by crop rotations and fertilization. Soil Science Society of America Joumal 57, 1034-1040.
I: Ndng nghiep. Thuy san vd Cong ngh? Sinh hgc. 26(2013). 262-268 5. Cassman, K.G., S.K. De Data, D.C. Oik. J.
Alcantara., M. Samson. J. Descalsota. and M.
Dizon. 1995. Yield decline and the niuogen economy of long-temi experiments on continuous, irrigated rice system in the tropics.
In: Soil management: Experimental basis for sustainability and environmental qualit>' (eds.
R. Lai. & B.A. Stewart), pp. 11-225-2.' CRC/Lewis Publisher, Boca Raton, Florida 6. Dobermann, A. and Fairhurst, T.R 2000. Rice:
Nutrient Disorders and Nutrient Management.
Potash and Phosphate Institute, International Rice Research Institute, Singapore. Makati City. 254. pp.
7. Isee systems. 2008. The world leader in System Thinking Software, http://www.isee- systems.coni/index.aspx
8. Nguyen Thanh Hoi. 2008. Anh hudng su chon vui ram ra tuai trong dat ngap nudc den sinh Uudng cua liia (oryza sativa 1.) d dong bang song Cdu Long. Luan an Tien sT Nong nghiep.
Tnrdng Dai hpc Can Tha.
9. Pampolino. M.F., Laureles, E.V.. Gines, H.C., Buresh. R.J., 2007. Soil carbon and niUogen changes as affected by fertilization in long- term continuous lowland rice cropping. Soil Sci. Soc. Am. J.
10. Trinh Quang Khuong, Ngo Ngoc Hung, Pham Sy Tan, Tran Quang Giau va Lam Van Tan.
2010. LTng dung quan ly duang chdt theo dja diim chuyen biet (SSNM) va s? hang uong canh tac liia Uen dat phu sa va ddt phen nhe d dong bang song Cuu Long. Tap chi Khoa hpc ddt. S6 33, u 115-118.
11. Witt, C , Cassman, K.G., 01k, D.C, Biker, U., Liboon, S.P., Samson. M.!., Oitow, J.C.G..
2000. Crop rotation and residue management effects on carbon sequesfration. nifrogen cycling and productivity of irrigated rice systems. Plant and Soil 225. 263-278
