ngheo, den ngheo va trung binh den kha (hinh 6), dao ddng tir 0.23 den 3.64%. Ham lugng nita tdng sd d miic rat ngheo den trung binh kha, dao dong tir 0.022 den 0.196%. Ham lugng photpho tdng sd d miic rat ngheo, dao dong tir 0.02 den 0.09%. Ham lugng kali tdng sd cung d miic rat ngheo, dao dong tir 0.14 den 0.33%.
Ham lugng chat hiru ca va N, P, K tdng sd thap nhat d mSu NS-01 la dat trdng sdn, tang dan d mSu NS-02 la dat trdng xoai va NS-03 la dat trdng xoai, trdng sdn, tang dan d mSu NS-02 la dat trdng xoai va NS-03 la dat trdng xoai, sau rieng, cao nhat d mau NS-13 la dat trdng chom, mit va sau rieng, den miu NS-09 la dat trdng liia va NS-11 la da't trdng chom ch6m va mit.
Ham lugng chat hiru ca trong cac da't d Quang San d miic ngheo den rat ngheo (hinh 7), dao dong tir 0.23 - 1.99%, cao nhat d mau NS-24 la dat trdng ngheo (hinh 7), dao dong tir 0.23 - 1.99%, cao nhat d mau NS-24 la dat trdng
liia va NS-26 la da't trdng mia, thap nhat d miu NS-28 va NS-29 la dat chua sir dung va dat trdng mia..
2.50 2.00 2.00 1.50 1.00 0.50 0.00 0 M % N% P205% K20% 0.400 0,300 0.200 0.100 0.000 OM % N% P205% K20% M^u
Hinh 7. Ham lirgng chat hiru co, N, P, K tdng sd trong dat xam nau viing ban kho han Quang Son, Ninh Son, Ninh Thuan
Ham lugng nita tdng sd deu d miic ngheo den rat ngheo (hinh 7), dao dong tir 0.022 - 0.128%, cao nhat d mau NS-24 do cd tuang quan thuan vdi ham lugng chat hiru ca trong dat. Ham lugng photpho tdng sd deu d miic ngheo, dao dong tir 0.014 - 0.057%, cao nhat d mau NS-24, NS-26 la dat trdng liia va mia duac bdn them lan. Ham lugng kali tdng sd cung d mire rat ngheo, dao dong tir 0.09 - 0.26%, eao nhat d mSu da't trdng liia (0.26%) va trdng mia (0.16%) do dugc bd sung them N, P, K vao da't.
Cac dat d xa Nhi Ha, Phude Vinh, Phude San, huyen Ninh Phude cd ham lugng chat hiiu ca d miic ngheo (hinh 8), dao dong tir 0.496 - 1.876%, thap nhat d mau NP-05 la dat ddng cd, tai mau NP-01, NP-04, NP-06, NP-10, NP-12 la dat trdng xoai, ngo, tao ed ham lugng chat hiru ca eao han. Ham lugng nita d miic rat ngheo, ngheo va tiem can trung binh (hinh 9), dao dong tir 0.039 - 0.123%, thap nhat d mau NP-05 (0.039%) la da't ddng cd, cao nhat d mau NP-04 (0.123%) la dat trdng ngo. Ham lugng photpho tdng sd d miic ngheo den giau (hinh 9), dao dong tir 0.012 - 0.27%, thap nhat d mau NP-07 trdng liia 1 vu, cao nhat d mau NP-06 la dat trdng tao, tiep den cac mSu dat trdng xoai, ngo va tao.
NP-01 NP-03 NP-04 NP-05 NP-06 NP-07 NP-08 NP-t) NP-12 • 0 M % 1.876 0.94 1.759 0.496 1.524 1.407 0.938 1642 1.524 3 N% 0.1t7 0.072 0.123 0.039 O.W 0.112 0089 0.106 0.X)1 P205% 0.15 0.012 0.10 0.02 0.27 0.03 009 0.16 0.24 K20% 0.75 Oil 0.46 0.17 0.38 023 0.46 0.42 0.43 Miu I OM % ] N % P205% K20%
Hinh 8. Ham lirgng chat hiiru co, N, P, K tdng sd trong dat xam nau vung ban kho han Ninh Phude, Ninh Thuan
Ham lugng kali tdng sd (hinh 8) d miic rat ngheo, dao dong tir 0.11 - 0.75%, cao nhat d mau dat trdng xoai NP-01, tiep den cac mSu NP-04, NP-06, NP-08, NP-10, NP-12 la cac dat trdng ngo, tao, thude la, nho.
Qua cac ket qua nghien cuu d tren cho thay ham lugng chat hiru ca, N, P, K tdng sd d xam nau vimg ban khd ban deu d miic rat ngheo, ngheo den trung binh thap. Dieu nay phan anh eong tac dau tu vdn, khoa hoc ky thuat vao qua trinh canh tac chua cao. Ben canh dd, cac dat nay lai phan bd tren nhung bac dia hinh eao, da sd nhap nho, go ghe, trong dieu kien khi hau ban kho ban, cd nhiet do eao, nen cac qua trinh khoang hda cac hgp chat hiru ca trong dat di^n ra manh me ban so vdi dat viing nhiet ddi am, lam cho da't bi thieu hut cac hgp chat miin gdp phan ban che boat dong cua cac loai sinh vat dat, lam ban che qua
trinh cung cap cac chat dinh dudng dt tieu cho cay trdng. Van de khan hiem
ngudn nude da gay nhi6u khd khan trong viec cung cap ngudn nude tudi cho cay trdng va viec thuc hien cac bien phap canh tac ndi chung.
Hien nay phan Idn dien tich dat xam nau viing ban khd ban la dat cay liim bui xen ed dai, dugc ddng bao dia phuang sir dung chan tha gia siic, khoang 15 - 20% dien tich la dat ndng nghiep, chu yeu la khai thae nuang ray vao miia mua. Nhirng ban che ve ham lugng chat dinh dudng trong dat cung nhu ve dieu kien dia hinh va nude tudi cd the dugc khac phuc bang nhirng giai phap cu the nhu:
dSu tu phan bdn, cai tao da't, san iii mat bang, thiet ke ddi rugng va thuc hien cac bien phap khoa hoc ky thuat giir do ^m da't nham gdp phan nang eao hieu qua sir dung loai da't nay.
3.1.3. Nhdm dat man
Nhdm dat man d Ninh Thuan cd dien tich 3.666 ha, chiem 1.09% dien tich tu nhien, phan bd chu yeu d cac huyen Ninh Hai (2.638 ha), Ninh Phude (835 ha) va Phan Rang - Thap Cham (148 ha). Do dieu kien hinh thanh trong viing khi hau ban khd ban nen d Ninh Thuan cd ca dat man ndi dia va dat man ven bien.
Nhdm dat man kiem dugc lay tai thon Phii Thi, xa My San, huyen Ninh Son va phudng Dd Vinh, Thi xa Phan Rang Tinh Ninh Thuan la dat thit pha cat vdi ham lugng cat la 78.27%, limon 11.56%, set 10.17% va cat la 65.24%, limon 11.66%, set 23.10%, theo thii tu. Dat cd phan ling chua nhe (pH^a = 5.6)
d My San va kiem vira (pH^ci - 8.41) d Phan Rang. Ham lugng chat hiJu ca
ngheo d My San (1.524%) va rat ngheo d Phan Rang (0.469%). N, P, K tdng sd tai cac mSu dat nghien cuu deu d miic rat ngheo.
Hien tai nhdm dat man kiem d My San mdi chi trdng liia dugc 1 vu nhd vao dieu kien nude trdi, cdn d phudng Dd Vinh, Thi xa Phan Rang ehii yeu cd suong rdng phat trien. Nhin chung ham lugng cac chat dinh dudng ciia loai dat nay d miic thap. Dat thudng phan bd d nhiJng khu vue khd khan ve ngudn nude tudi nen de gia tang he sd ciing nhu hieu qua sir dung dat, can phai dau tu thiiy Igi, giai quyet nude tudi de bd tri tang vu cay trdng hoac cung cap nude man de nuoi trdng thuy san nude man.
3.2. Dac diem phan bd vi sinh vat
Vi sinh vat dat ddng vai trd quan trgng trong cac qua trinh ehuyen hda vat chat de cung cap cac chat dinh dudng d6 tieu cho cay trdng, tao thanh cac hgp chat miin hinh thanh ket eau dat. Su phong phU va da dang ve thanh phan loai, sd lugng cac quan thd sinh vat trong dat phan kha rd net do phi cua dat.
Cho den nay chua cd nhirng ket qua nghien ciiu cu the ve dac diem phan bd vi sinh vat trong cac nhdm dat viing ban khd ban Ninh Thuan. Do vay day la nhirng ket qua ban dau tai cac dia diem nghien cuu.
Ket qua ve sd lugng vi sinh vat tdng sd (vi khuan, xa khuan, nam mdc, nam men) trong cac nhdm dat dd, dat xam nau, da't man ki6m viing ban kho ban tinh Ninh Thuan dugc the hien tren hinh 9, 10, 11 va 12 nhu sau:
3.2.7. Suphdn bdcua quan thevi khuan
D B A - l a B B A - l b DBA-2a DBA-2b B F R - l a D FR - lb • NP - 3a D NP - 3b • NP - 4a • NP - 4b nNP-6a DNS-11 BNS-SOa • NS - 30b • NS - 7a