A ' / I A' A ' 1 '
Neu xet ehi so am nhu la ty sd phan tram giiia lupng. mua va lupng bde hoi kha nang trong mot thoi ki xac dinh nao
do thi chi sd am nam nhin chung Idn hdn 150%, tile la dieu kien am cua Tay Nguyen kha phong phii. Tuy vay, do mua theo miia nen chi sd am hai miia khac biet nhau ro ret. Neu coi chi sd am thang nho hdn 25% la thdi ki khd thi d nhieu ndi thdi ki khd keo dai til 3 -^ 4 thang. Neu coi chi sd am miia dudi 50% la thdi ki thieu am thi d cac cao nguyen phia bac nhU Play Cu, Budn Me Thudt deu thieu am trong thdi ki gid miia miia ddng.
Nhu vay, qua phan tich che dp cac yeu td khi hau cd ban ta thay: d Tay Nguyen cd hai miia ro ret la mua mua va miia khd. Nhipt dp thich hpp, dp am phong phii trong miia mua la nhiing dieu kien het silo thuan loi ddi vdi san xuat ndng nghiep, dac biet la ddi vdi cay trdng ngan ngay. Ngupe lai, dieu kien thieu am, nhiet dd ban ngay cao, tdc dp gid Idn trong miia khd lai han che sy phat trien cua cay trong. Vi vay can cd nhung nghien eiiu chi tiet hdn anh hudng cua cac dieu kien khi tupng den san xuat ndng nghiep trong thdi ki nay.
Thdi tiet trong mua khd vdi cac dac trUng: it mUa, nhieu nang, gid manh rat thuan Ipi cho viec nghien eiiu cac hien tuong xay ra trong ldp khi quyen sat dat ndi chung va nghien cilu loan luu trong dd ndi rieng. Do dd nhiing nghien
- 50 -
cilu cua chiing tdi dupe tap trung chu yeu vao thdi ki khd trong nam.
Ill.2. Profil cac veu tn khi tuong:
Nhu tren da ndi, viec xac dinh dang profil cac yeu to khi tuong ed y nghla thyc te quan trong. Qua dd cd the tinh toan duoc cac dae trUng cd ban cua loan luu trong ldp KQSD.
Trong dieu kien phan tang nhiet d trang thai can bang (nhiet dp khdng ddi theo chieu c a o ) , phan Idn cac tac gia deu thdng nhat coi profil tdc dd gid cd dang loga:
u* z
u ~ — — In (3.1)
^ Zo trong dd Zo la dp cao go ghe.
ThUc ra cdng thilc (3.1) chinh la dang khac cua (1.11). Hdn niia nd cdn cd the dupc riit ra dya tren ly thuyet ban kinh nghiem. That vay, tu nhan xet ve sy tang tuyen tinh theo dp cao cua quang dudng dieh chuyen 1, ma giUa 1 va z lai cd ciing thu nguyen nen trong dieu kien can bang cd the gia thiet:
1 = 3f z (3.2) trong dd ^ la hang sd van nang. Ket hpp ( 1 . 6 ) , (2.19) va trong dd ^ la hang sd van nang. Ket hpp ( 1 . 6 ) , (2.19) va
(3.2) ta ed:
du u* u* u* dz
•*- du = (3.3 )