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METHODS TO DETERMINE CROP WATER REQUIREMENT

METHODS TO DETERMINE CROP WATER REQUIREMENT. Agricultural Water Management. METHODS. Blaney - Criddle Radiation Penman Evaporation Pan. Eto = c. Eto *. Required Measure Data . C value (CORRECTION NUMBER). 1. Application of Blaney-Criddle Formula. Eto = c [p ( 0.46 T + 8)] mm/ day.

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METHODS TO DETERMINE CROP WATER REQUIREMENT

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  1. METHODS TO DETERMINE CROP WATER REQUIREMENT Agricultural Water Management

  2. METHODS • Blaney- Criddle • Radiation • Penman • Evaporation Pan Eto = c. Eto*

  3. Required Measure Data

  4. C value (CORRECTION NUMBER)

  5. 1. Application of Blaney-Criddle Formula Eto = c [p ( 0.46 T + 8)] mm/ day

  6. Tabel 1. p Value

  7. Tabel 2. c value

  8. Procedure for BlaneyCriddle Formula • Determine latitude • Determine p from Table 1 • Determine mean monthly temperature • Determine c value from Table 2 • Calculate Eto using the formula

  9. Example • Using the Blaney-Criddle formula, calculate the Eto on February at Porong, West Java if:: • Mean monthly temperature on February is 25,7oC • Latitude is 7.5oS

  10. Task • Calculate the Eto of Solo city (Latitude: 7.5o S) , if it is known that mean monthly air temperature for ten years are:

  11. Required Measure Data

  12. 2. Radiation Method Eto = c (W . Rs) W= factor of temperature and elevation effects Rs= radiasigelombangpendek yang diterimabumi Dimana Rs = (0,25 + 0,54 n/N ) Ra n/N = kecerahanmatahari Ra = radiasigelombangpendek yang meemnuhibatasluaratmosfer, besarnyatergantungletaklintang

  13. ProsedurRumusRadiasi • Carisuhu rata2 bulanan • Tentukannilai W dariTabel R.1 • CariLetaklintang • Tentukannilai Ra dariTabel B.01 • Cari data kecerahanmatahari (n/N) • Hitung Rs ataugunakanTabel B.02 • Cariangkakoreksi (c) dariTabel 5 • HitungnilaiETo

  14. Kebutuhan Data Terukur

  15. 2. PenggunaanRumus Penman Eto= cW(0,75 Rs-Rnl)+(1-W).f(u).(ea-ed) W= faktorpengaruhsuhudanelevasi Rs= radiasigelombangpendek yang diterimabumi Dimana Rs = (0,25 + 0,54 n/N ) Ra Ra = radiasigelombangpendek yang meemnuhibatasluaratmosfer, besarnyatergantungletaklintang Rnl= Radiasibersihgelombangpanjang (mm/day) Rnl = f(t) . f(ed) . f(n/N) (ea-ed)= perbedaantekananuapjenuhdengantekananuap yang sebenarnya ed = ea . RH c = angkakoreksi

  16. ProsedurRumus Penman • Carisuhu rata2 bulanan • Tentukannilai ea, W (1-W) dan f (t) dariTabel PN.1 • Cari data RH • TentukannilaieddariTabel PN.4 • Tentukannilai f (ed) dariTabel PN.5 • CariLetaklintang • Tentukannilai Ra dariTabel B.01 • Cari data kecerahanmatahari (n/N) • Hitung Rs ataugunakanTabel B.02 • Tentukannilai f(n/N) dariTabel PN.6 • Cari data kecepatanangin (u) • Tentukannilai f(u) dariTabel PN.7 • HitungbesarnyaRnldenganrumus • Cariangkakoreksi (c) dariTabel PN.8 • HitungnilaiEtodenganrumus

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