MU SC T1. KHI NIM V MU SC T Mu sc t phn nh c im pht sinh pht trin ca t lin quan ti cc thnh phn ho l hc trong t. Mu sc t cn th hin tnh trng dinh dng v s thay i cht lng t trong qu trnh canh tc. Nhiu nh nghin cu s dng mu sc t nh gi tnh trng dinh dng v mt s tnh cht t ai. Mi loi t thng c mu sc c trng khc nhau. Ngi ta thng cn c vo mu sc t t tn cho cc loi t. V d: t , t vng, t nu, t en. Trong cng mt loi t, mu sc t c th thay i ph thuc vo cc thnh phn ho hc t thay i trong qu trnh pht trin ca t. V d, cng loi t xm nhng khi cn l t rng th thng c mu xm en hn so vi khi chuyn sang t trng trt do trong t rng hm lng cht hu c (mn) cao hn. Mu sc t thay i theo chiu su. Trong phu din t, tng mt t thng c mu xm hoc en. Theo chiu su ca t mu en xm gim dn, thay vo cc mu vng, vng tng ln. 2. NH HNG CA NGUYN T HA HC TRONG T TI MU SC T Trong s cc nguyn t ca quyn t cn tch ra phn nhm cc nguyn t c bit m hp cht ca chng c nh hng n mu sc ca t, l cc nguyn t C, Fe, Mn, Ca. Silic c th c xp vo nhm ny v hp cht silic chim mt khi lng ln trong t v b sung thm vo mu trng ban u ca t. Nhng cht to nn mu sc ca t v cc tng t c gi l nhng cht mu ca t. Sau y l mt s cht mu ch yu ca t: . Mangan thng lm cho t c mu ti, nn en l do trong t c pirohazit MnO2 nhng bn thn mu ny cng khc nhau. . Trong nhng iu kin kh, vic to thnh cc sunfua kim loi cng lm cho t c mu ti, hu ht l mu en. . Cc hp cht ca st cho mu sc r rng v a dng nht trong cc phu din t. Ph mu do cc hp cht ca st gy nn rt rng. l mu vng, mu vng rm, mu , mu nu, mu ong (vng ln xanh), mu xanh lam, mu en. Hu nh tt c cc to thnh t ti b u c cha cc hp cht ca st mt mc no . Nn mu ph bin trong phu din t l mu vng rm hoc mu nu, nhng do c s phn b li st trong phu din t nn mu ny c th nht i hoc m ln v trong nhiu t mu sc tr nn khng ng nht do vic hnh thnh oscotein (ct tm st) cha st. Mu sc c bit khng ng nht do st gy nn xut hin trong cc t c cc qu trnh xy ho kh. i vi nhng hp cht ca cacbon c nh hng 2 mt n mu sc ca t. l cc hp cht cacbon v c thng c mu sng, cn cc hp cht cacbon hu c thng to mu sm cho t.

Cc hp cht v c ca cc cacbon c bit l nhm cacbonat (cacbonat ma gie v cacbonat can xi) lm cho t c mu trng. Nhng cacbonat ca cc kim loi kim th phn tn rng trong t, hoc l do cc qu trnh bin i ho hc to thnh cc hp cht mi nh th si gi, mt trng,... c trng chung ca cc cht ny l c mu sng, nhng khi tp trung nhng cacbonat ph tn li, mu ca chng khng ng nht, c cc vt m c trng. Ngc li vi cc hp cht cacbon v c, cc hp cht hu c ca cacbon lm cho t c mu sm, nu v hu ht lm cho t c mu en, mu ny biu hin r nht l trong cc t checnozem (t en). Nhn chung mu sc ca t rt phc tp, nhng c bn l s pha trn hoc kt hp ca 3 mu sc c bn: Mu en (ch yu l mn hoc MnO2), mu (Ch yu l Fe2O3). V mu trng (ch yu l khong st kaolinit, SiO2 hoc CaCo3), S.A.Zakharop xy dng mt tam gic mu th hin s pha trn phi hp gia cc mu sc c bn ca t.

3. CH TH V MU SC T LIN QUAN VI TNH CHT V VIC S DNG T Theo Edward Plaster (1997), mu sc t l mt trong nhng ch tiu quan trng nh gi tnh trng ca t. C th cn c vo mu sc t quyt nh vic s dng t. Mu sc t c coi nh l bin ph thuc ca hm s pht trin t, trong cc bin c lp bao gm cc iu kin kh hu, th nhng, canh tc. t c mu trng hoc mu sng thng c ph thp bi v c th t b ra tri mnh hoc t c cha nhiu mui. Vic iu chnh bng cc bin php thu li, bn phn cn i hoc kh mn trong t s gp phn lm tng ph ca nhng loi t ny. t c mu en cha nhiu mn th hin ph ca t cao. Tuy nhin i vi t ly tht thng c thnh phn hu c cao nhng cha chc tt v mc giy hoc mc ym kh ca loi t ny rt cao. t c mu nu, vng v thng th hin s c mt ca oxit st trong t Mu l ch th ca s thot nc tt. t c s thong kh tt (y xy) gp phn to nhiu oxit st trong t.

Mu xm xanh trong t thng th hin trng thi kh. l ch s t thiu xy. S thiu xy c th do ngp nc. y cng l ch s th hin t c s thot nc km, thng km theo hin tng giy mnh nhng ni ngp nc. Bng 1 : Bng hng dn s dng mu sc t ca M nh gi mc thot nc t nhin trong t (ngun USDA - Edward -1997) Mc thot nc Rt km Km Trung bnh Tt Rt tt M t nhng vng thp, hay ni ngp nc, tng mt c mu en v mu xm di tng A, AB. Mc nc ngm gn tng mt v lin tc quanh nm. Mc nc ngm cao nhng khng thng xuyn quanh nm, c mu xm v mu en tng mt, mu xm tng B. Tng B c cha nhiu ht kt von mu nu (brownish mottles) Mu xm v nu tng A, c th c mt s ht kt von mu xm tng B (giy mottles) Nhiu kt von (mottles), c th c mtss ht kt von di tng B t ct c thot nc tt, t trn sn dc

4. PH MU SC V S PHN X NH SNG CA T nh gi vai tr ca cc nguyn t ring bit v cc hp cht ca chng trong vic hnh thnh mu sc ca t v m nht ca cc mu trong t, chng ta c th da trn h thng quc t v s i mu sc, trong mu c xc nh bi cc phn ca cc mu iu kin (xanh lam, xanh lc, ) trong cc mu nghin c Trong nhiu trng hp thun li hn v c nhiu thng tin hn ngi ta s dng kh nng phn x ca ng cong ph. i vi mu sc ca t thng ch ch ti vng nh sng kh kin (nh sng c bc sng t 400 n 750 mm). Mt loi t bt k u c b mt g gh v vy khi c nh sng p vo th nh sng s c phn x theo tt c cc hng. S phn x nh vy c gi l s khuch tn. c trng nh lng cho s phn x khuch tn ngi ta s dng hai i lng: H s phn x v h s chi ( sng) -H s phn x: L t l gia cng ca bc x phn x theo tt c cc hng(1) vi cng ca dng bc x p vo b mt t(0) v c k hin bng ch.

-H sng chi: L t l gia dng bc x (cng bc x) c phn x bi b mt t theo mt hng vo vi dng bc x p vo b mt t.

H s chi tm c cc c ly o ca kh nng- phn x ca t, khi nghin cu tng khu vc ca b mt t quan st c mt gc xc nh no . tm c h s phn x cn phi o cc bc x, phn x theo tt c cc hng, c th dng khi cu hoc qu cu Taylor (Hnh 7.2). y l mt qu cu rng bn trong c ph mt cht chun c kh nng phn x gn nh 100%. Cht c th l MgO, BaSO4 hay thy tinh c bit. Mu t chun b c t vo mt cuvet, sau t cuvet ny vo khe h ca qu cu sao cho b mt t tip xc vi b mt bn trong ca qu cu. Dng sng phn x 1 t b mt t hon ton bn trong ca qu cu khi b mt ca n phn x nhiu ln. Nh vy khi chiu vo bn trong qu cu s thu nhn c nhng bc x t l vi cng bc x ca t. Kh nng phn x ph v kh nng phn x ton phn c s khc bit. H s phn x ton phn c trng cho dng bc x trong khong tng i rng ca bc sng nh sng, thng c k hiu l x v thng o trong khong 400 - 750nm. H s phn x ph c xc nh i vi tng tia bc x n sc v c k hiu l trong l bc sng ca tia bc x. V d o h s phn x ph bc sng 620 mm th h s ny c k hiu l 62.

1 B mt bn trong qu cu . 2: Cuvet, 3. Lp t, 4. Lng knh, 5. Dng bc x p vo t bo quang in, 6. T bo quanh in 0: Dng bc x chiu vo 1: Dng bc x phn x t phn x khng ng u, cc bc x c cc bc sng khc nhau v gi tr lin tc thay i trong khong 400 - 750 mm ph thuc vo bc sng. th biu th s ph thuc ca pa vo bc sng c gi l ph phn x, ph ny cho cc thng tin y nht v kh nng phn x ph ca t. Mu sc ca cc tng tch t mn l do trong tng c cht mn. Trong t checnozem c mu xm hoc xm ti. Trong nhng t t mn, trong phn phn x c s tng ln tng i ca cc phn bc x sng di, ngha l phn nh sng , mu ca nhng t ny thng l mu nu xm hoc thm ch l mu xm nu. nh hng mnh nht ca cht hu c n kh nng phn x l bc sng 700 750 mm. S ph thuc gia h s ph phn x750 v hm lng cht hu c (H) c ch ra hnh 7.3a v biu th bng phng trnh thc nghim

750 = o + nekH hay ln (750 -o) = ln- KH y o l h s phn x cc tiu khi hm lng cht hu c c th l ln nht, n v k l cc hng s ca phng trnh, cc thng s n v k ca phng trnh c tnh l hng s ch i vi nhng t c cng loi mn (chung v tnh cht ho hc v hnh thi hc).

Hnh 7.3a: S ph thuc ca kh nng phn x ca t vo hm lng cht hu c 1. Gi tr trung bnh; 2. Gii hn dao ng

Hnh 7.3b: nh hng ca hp cht st n kh nng phn x 1 . Kaolinit; 2. Kaolinit + Fe(OH)3 3. Kaolinit + Fe2O3

Cc ng cong ph dng th ba thng lin quan n s tch ly cc oxit st v cc hydroxit st trong t. Kaolinit tinh khit c c trng bi s tng dn dn ca h s phn x ph t 400 n 550 nm v sau gi tr hu nh khng thay i n 750 nm (Hnh 7.3b). S c mt ca hydroxit st trong kaolinit lm gim r rt kh nng phn x ti 400 nm v sau tng nhanh t bc sng 480 nm n 600 nm lm cho ng cong c khc ln. Nu ly kaolinit trn vi Fe(OH)3 nung 3000C th hydroxit st s chuyn thnh Fe2O3, Trong ph ca kaolinit vi oxit st cng c khc ln nhng chuyn dch sang vng c bc sng ln hn.

Theo gi tr ng un cong trn ng cong kh nng phn x ph trong mt s trng hp c th suy on v hm lng tng s ca st trong cc t (theo cc ph ca cc mu nung ca t) hay suy on v s phn b tng i ca cc oxit v hydroxit st trong phn din t, m cc hp cht ca st ny sp xp trn b mt ca cc nguyn t c hc. Khi s dng kh nng phn x ph ca t nu cc c im v thnh phn ha hc ca t chun on v khong cch ca bn cn lu rng gi tr ( v ph thuc vo m ca t v thnh phn cp ht. 5. PHNG PHP NH GI MU SC T DA VO H THNG MU MUNSELL 5.1. c im ca h thng mu Munsell Mu sc t c th c xc nh thng qua vic so snh vi h thng mu chun. Hin nay h thng mu chun c s dng rng ri nht l h thng mu Munsell. H thng mu Munsell rt tin li trong vic xc nh mu v th hin kt qu. Cu to ca h thng mu (thang mu) Munsell gm 9, bng thang mu vi 322 mu th hin s thay i cc kiu mu sc ca t. Trong mi mu tiu chun gn vi nhng tiu ch phn cp nht nh. c im ca thang mu chun Munsell c da trn 3 thng s (i lng) chnh m t tt c cc loi mu sc ca t. l cc thng s nh: Hu, Value v Chroma. -Thng s hue l ch s mu lin quan ti cc gam mu nh mu , vng, xanh v chm tm. . Thng s value l ch s sng (lightness) ca cc gam mu. . Thng s chroma th hin sc mu (strength) trong cng mc sng. Mu sc th hin trn cng mt bng mu l c cng gi tr hue. C 9 bng mu trong thang mu Mullsell th hin 9 gi tr hue c k hiu theo th t: Gleyl; Gley2; 10R; 5R; 2,5YR; 7,5YR;10YR; 2,5Y v 5Y. Trong mi bng mu, theo chiu t di ln trn th hin mc sng tng dn. Tc l cc thng s ca value ( sng) trong cng bng mu s tng dn t di ln trn theo cc mc: 2,5; 3; 4; 5; 6; 7 v 8. Gi tr chroma trong mi bng mu c th hin theo chiu ngang vi mc m s tng dn t tri qua phi. Trong 2 bng mu hue u tin ca thang mu Munsell (Gley 1 v Gley 2), gi tr chroma t tri qua phi th hin theo 6 ct vi cc gi tr chroma tng ng l N, 10Y 5GY, 5G v 5G. Cn trong 7 bng mu hue tip theo (10R; 2,5YR; 5R; 7,5YR; 10YR; 2,5Y v 5Y), gi tr chroma t tri qua phi th hin theo 6 ct vi cc gi tr chroma tng ng l 1, 2, 3, 4, 6, 8. Trong bng mu Munsell, gi tr ca hue th hin qua ch vit tt ca cc mu sc. V d: R - reo l mu , YR - yellow reo l mu vng, Y- yellow l mu vng. Pha trc cc ch vit tt cn c thm phn s vi cc s t 0-10. Trong cng mt k hiu ch, v d vi YR, nu phn s cng ln th gi tr hue mu vng tng v mu gim. Gi tr gia ca mi gam mu s l 5, gi trim 0 ca gam mu s tng ng vi

gi tr im 10 ca mu hn tip theo ca hue. V d: 5YR l im gia ca ph mu vng (yellow-red) t 0YR (tng ng vi 10R) ti 10YR (tng ng vi 0Y).

Hnh 7.4: V d cu to ca bng mu Hue 10R vi cc thng s chroma t 1-8 (theo chiu ngang),cc thng s Value 2,5 -8 (theo chiu dc) Gi tr ca value nu bng 0 th hin mu en, sng mu gim dn n s 10 tc ln hon ton mu trng.Nu gi tr vallte bng 5 l mu nm trong khong gia trng v en. Cc gi tr ca chroma bao gm cc con s bt u t 0 biu hin mu xm tro trung tnh (neutral grays), tng dn u theo cc khong cch nht nh n s 20. Tuy nhin rt t khi t c gi tr chroma bng 20. 5.2. Cch s dng h thng mu Munsell xc nh mu ca t Xc nh mu ca t theo h thng mu Munsell khc nhau i vi t kh v t -Phng php xc nh mu kh: Mu t c phi kh v nghin nh. Sau ly mt t t nghin tri ln trn nn giy trng v so snh vi cc bng mu hue trong h thng mu Mullsell xc nh c bng mu hue ph hp nht. Sau tip tc so snh mu t vi cc mu ca bng mu hue la chn bng cch t li cc mu ln trn t giy trng c cha t. Mu t c xc nh l mu ca mu no ging nht, i chiu vi gi tr thch hp ghi trong bng gi tr mu Mullsell trang bn bit cc gi tr hue, value, chroma tng ng.

Cch c v ghi kt qu mu sc t nh sau: + Nu mu t ph hp vi bng hue 5YR, c gi tr value l 5 v chroma l 6 th mu t c ghi l 5YR 516 ( vng nht - yellowish-red). + Nu mu t nm gia 5YR 5/6 v 5YR 6/6 th mu xc nh l 5YR 5,5/6. + Nu mu t nm gia 2,5YR 5/6 v 5YR 618 th mu xc nh l 5YR -Phng php xc nh mu t: Mu t t c nho k c m va phi (khng qu kh hoc qu t) Sau t c bi ln t giy trng sao cho th hin r mu t c trng nht. Cc bc tip theo thc hin nh m t i vi phng php xc nh mu kh. iu ch l trong phn kt qu cn ghi r l mu kh hay t. V d: 5YR 5/6 (t) hoc 5YR 5/6 (kh). Sau y l mt s v d cc bng mu trong thang mu Munsell:

5.3. S dng h thng mu Munsell m t phu din t Hin nay khi m t cc phu din t, s dng thang mu chun Munsell m t mu ca t c p dng rng ri. Kt hp vi mt s ch tiu hnh thi khc nh quan st thnh phn c gii v kt cu t, mu sc t l ch tiu quan trng phn bit cc tng t khc nhau trong cng phu din. Mu sc t thng c m t u tin, sau mi m t cc tnh cht khc. Sau y l v d m t mu sc t trong phu din t c s dng thang mu Munsell.

Bng 7.2: M t hnh thi phu din t rng Haplic Acrisols ti huyn ng H, tnh Thi Nguyn Tng su Cc c im m t (cm) Mu nu en (10YR 7.5/5 kh)- Dark brown (10YR 7.5/5 dry);tng LFH c lp thm mc mng b mt, tip theo l lp LFH v Ah 0- 12 hu c ang phn hu to thnh mn; tip theo l lp t tht nh c m kh cao; t c kt cu ht; nhiu hang ng vt t; nhiu r cy nh, ranh gii tng t r rng. Mu vng nu (10YR 7/5 kh) - Brownish yellow (10YR 7/5 tuy); nhiu st v li mon; kt cu ht v khi, nhiu r cy nh A v AB 12-22 v trung bnh, nhiu ng mao qun nh v trung bnh, m trung bnh,ranh gii tng khng r rng. Mu nu vng (7.5YR 6/8 kh) - Yellowish brown (7.5YR 6/8 tuy); nhiu st v li mon; kt cu ht v khi, nhiu cui nh c bao bc bi lp st, t m, nhiu r cy trung bnh v 22-42 ln, nhiu mao qun c trung bnh, ranh gii tng khng r rng. Mu vng (7.5YR 6/6 kh) - Reddish yellow (7.5YR 6/6 42-62 tuy);thnh phn c gii ch yu l st; m kh cao; kt cu ht mn; s lng r cy gim dn, cc mao qun nh; phn tng r. Bt Mu vng (7.5 YR 5/6 kh) - Yellowish reo (7.5 YR 5/6 tuy);nhiu st; nhiu sn phm phong ho ca phin thch st c 62-82 mu ta, c mt s ht kt von nh mu v sm; t cng khi kh, nhiu st bm trn cc ht cui kt v mnh vi nhiu mu sc v dnh khc nhau. (Ngun: ng Vn Minh, D.W. Anderson and R.E. Farrelt. 2002) Thang mu chun Munsell cn c s dng rng ri trong vic phn loi t v nghin cu cc qu trnh hnh thnh v pht trin ca t.