Judul: Bowen Ratio and Evapotranspiration Dynamics: The Influence of Season and Diurnal Micrometeorological Variables
Abstrak: Tanaman membutuhkan air untuk mengoptimalkan proses biofisik dimana kebutuhan air dapat dikuantifikasi sebagai evapotranspirasi (ET). Rasio Bowen merupakan salah satu metode yang umum digunakan untuk praktik pertanian. Metode rasio Bowen digunakan untuk mengestimasi ET pada PTPN VI di Provinsi Jambi periode 2014-2015 menggunakan data observasi mikrometeorologi dan melihat pengaruh komponen mikrometeorologi seperti radiasi neto (Rnetto), fluks bahang (laten LE dan terasa H), tekanan uap aktual (ea), kelembaban tanah (SM), kecepatan angin (WS), suhu udara (Ta), fluks bahang tanah (G), dan LE-H terhadap pola harian dan diurnal. Hasil penelitian menunjukan bahwa pola harian rasio Bowen dipengaruhi secara kuat oleh LE-H, LE, H, SM ditunjukan dengan koefisien korelasi sebesar -0.85, -0.75, 0.84, -0.58. Pola diurnal rasio Bowen dipengaruhi oleh ea dengan koefisien korelasi sebesar -0.52 sedangankan pola harian ET dipengaruhi secara kuat oleh Rnetto, LE-H, H, rasio Bowen dengan koefisien korelasi sebesar 0.85, 0.95, -0.63, -0.75. WS, Ta, Rnetto, G, ea, RH dan LE-H mempengaruhi pola diurnal ET dengan korelasi sebesar 0.72, 0.72, 0.96, 0.89, 0.51, -0.64 dan 0.9. Nilai rasio Bowen yang konstan tidak akan akurat untuk menentukan ET karena perbedaan nilai maksimum rasio Bowen sebesar 10 kali lipat dari nilai minimum. Periode Desember 2014 – November 2015 menunjukan bahwa terdapat 7 bulan dimana curah hujan > ET (musim basah Desember 2014-April 2015, November 2015) dan 5 bulan dimana curah hujan < ET (musim kering May 2015-Oktober 2015). Kelapa sawit sangat rentan selama periode kering panjang ini yang disebabkan oleh fenomena El Nino kuat., Plant requires water to optimize its biophysical processes and this requirement can be quantified as evapotranspiration (ET). Bowen ratio is one method commonly used for agricultural practices. Bowen ratio method used to estimate ET from PTPN VI in Jambi province for the period 2014-2015 using observed micrometeorology data and looked at the strength of micrometeorological components in influencing the daily and diurnal patterns, which include net radiation (Rnetto), heat fluxes (latent LE and sensible H heat), actual vapour pressure (ea), soil moisture (SM), wind speed (WS), air temperature (Ta), ground heat fluxes (G), and LE-H. We found that the daily pattern of Bowen ratio was strongly influenced by LE-H, LE, H, SM shown by correlation coefficient of -0.85, - 0.75, 0.84, -0.58 respectively. Diurnal pattern of Bowen ratio was affected by ea with correlation coefficient of -0.52 while daily ET were strongly influence by Rnetto, LE-H, H, Bowen ratio with correlation coefficient of 0.85, 0.95, -0.63, - 0.75 respectively. WS, Ta, Rnetto, G, ea, RH and LE-H affected diurnal ET with correlation coefficient of 0.72, 0.72, 0.96, 0.89, 0.51, -0.64 and 0.9 respectively. Constant Bowen ratio value will not accurately estimate ET because maximum value is 10 times greater than minimum value. Within this period of 2014-2015 there were 7 months where rainfall > ET (wet period December 2014-April 2015, November 2015) and 5 months where rainfall < ET (dry period May 2015 - October 2015). During this long dry period of 2015, caused by strong El Nino events, oil palm become vulnerable to drought.
Keyword: Latent heat fluxes, Net radiation, Sensible heat fluxes, Temporal analysis  ET, Water requirement