HNG DN S DNG PHN MM CROPWAT 8.0 KS. Thu Dng S dng phn mm CROPWAT tnh ton xc nh nhu cu nc, ch ti v k hoch thc hin ti cho cc loi cy trng ti mt rung trong cc iu kin khc nhau. y l chng trnh tnh ton ti cho cc loi cy trng c p dng ph bin trn ton th gii, c t chc Lng thc - Nng nghip ca Lin hip quc FAO cng nhn.1. TI LIU TNH NHU CU NC TI CHO CY TRNG

Ti liu v kh tng thu vn - Nhit trung bnh cc thng - m trung bnh khng kh trong khu vc - Lng bc hi trung bnh nhiu nm - Tc gi trung bnh thng nhiu nm - Lng ma bnh qun thng nhiu nm - S gi nng trung bnh thng nhiu nmTi liu v nng nghip

- Thi v gieo cy v din tch ca cc loi cy trng trong khu vc cn tnh nhu cu nc dung - Giai on sinh trng ca cc loi cy trng - Cc ch tiu c l ca t canh tc 2. NI DUNG TNH TON NGUYN L CN BNG NC tnh ton lng nc cn (IRR) cho cy trng ta da vo phng trnh cn bng nc. Phng trnh cn bng nc tng qut c dng nh sau: IRR = (ETc + LPrep + Prep) - Peff Trong : IRR: Lng nc cn ti cho cy trng trong (mm/ngy). thi on tnh ton (mm/ngy)

ETC: Lng bc hi mt rung trong thi on tnh ton (mm). Peff: lng ma hiu qu cy trng s dng c trong thi on tnh ton (mm)

Prep: lng nc ngm n nh trong t trong thi on tnh ton (mm/ngy) LPrep: lng nc lm t (mm) Xc nh lng bc hi mt rung (ETc): Lng bc hi mt rung c trnh theo cng thc: ETc= Kc x ET0 Trong cng thc (1): KC: H s cy trng, ph thuc vo vng canh tc, giai on sinh trng ca cy trng. ET0: lng bc hi mt nc t do tnh ton theo cng thc ca PenmanMonteith. ET0= C [W x Rn + (1-W) x f(u) x (ea-ed)] Trong cng thc (2): C: H s hiu chnh v s b tr i vi tc gi cng nh s thay i ca bc x mt tri. W: H s c quan h vi nhit v cao khu ti. Rn: Lng bc x thc t c xc nh t s gi chiu sng, nhit v m. f(u): Hm quan h vi tc gi : (ea-ed): chnh lch gia p sut hi bo ho nhit trung bnh ca khng kh v p sut hi thc t o c. Kc: ph thuc tng loi cy trng v thi on sinh trng ca cy . Vic xc nh Kc ca tng loi cy trng c trnh by phn trn. Tnh ton ma hiu qu (Peff): Tnh ma hiu qu theo phng php t l c nh: Peff = C x Pma. Trong cng thc (3): Peff : lng ma hiu qu trong thi on tnh ton (mm) Pma : lng ma thc t trong thi on tnh ton theo m hnh MTTK (mm) (mm) (3) (mm/ngy) (2) (mm/ngy) (1)

C: % lng ma s dng c trong thi thi on tnh ton Tnh ma hiu qu ph thuc theo cng ma: Peff = 0.6*Pma - 10 khi Pma < 70 mm Peff = 0.8*Pma - 24 khi Pma > 70 mm c. Lng nc ngm n nh (Prep) Prep= K x t Trong cng thc (4): K: h s ngm n nh ca t (mm/ngy). t: thi gian tnh ton (ngy). d. Lng nc lm t (LPrep) Lng nc lm bo ha tng t canh tc (S): S= (1-Sm/100)*d*P/100 (mm) Trong cng thc (5): d: su lp t bo ha nc (mm) Sm: su c sn u thi on tnh ton (%) P: rng t (% th tch t) Lng nc to thnh v duy tr lp nc trn mt rung trong thi gian lm t (L). L= (L/T + S + P + E) - Peff Trong cng thc (6): L: tng lng nc cn cung cp trong thi gian lm t (mm) T: thi gian lm t (ngy) P, S: lng nc thm ng v ngang (mm/ngy) E: lng bc hi mt rung (mm/ngy) Peff: lng ma hiu qu (mm) i vi cy trng cn phng trnh c dng: IRR = ETc - Peff Cc i lng trong phng trnh nh nu trn. (mm/ngy) (6) (5) (mm) (4)

3. CCH S DNG PHN MM CROWAT 8.0 TRONG TNH IRR Nhp d liu u vo thay i mc nh n v ca d liu u vo, phng php tnh ma hiu qu, thi biu ti, hiu qu phng php ti vo phn settings