SUMMARY
Abstract This paper discusses the cooling effect of the root zone (the root zone cooling) at a floating hydroponic for the shallot production in tropical lowland by cooling the nutrient bath. The study was conducted at three different temperatures, i.e. low temperatures (8-10OC), medium temperature (13-15OC), and control (23-26OC) with variable responses that include wet weight, dry weight, number of bulbs and weight per bulb. Plant growth responses were analyzed using statistical methods Fisher's least significant difference (LSD), while the temperature distribution on a floating hydroponic was analyzed by computational fluid dynamics (CFD) simulation approach. CFD simulation approach was able to describe the temperature distribution on a floating hydroponic well, where the coefficients of determination (R2) for each treatment of low temperature, medium and controls are 0.983, 0.980 and 0.862 respectively. The results showed that the number of bulbs was the most responsive variable, where the induction of bulb formation at low temperature is more than 200% of the control temperature and more than 60% of the medium temperature.Abstrak Makalah ini membahas tentang efek pendinginan daerah perakaran (root zone cooling) pada hidroponik rakit apung untuk produksi bawang merah di dataran rendah tropika dengan pendinginan pada bak nutrient.Penelitian dilakukan dengan 3 suhu berbeda, yaitu pada suhu rendah (8-10OC), suhu sedang (13-15OC), dan kontrol (23-26OC) dengan variabel respon pertumbuhan tanaman bawang merah meliputi bobot basah, bobot kering, jumlah umbi dan bobot per umbi. Respon pertumbuhan tanaman dianalisis menggunakan metoda statistik Fisher's least significant difference (LSD), sedangkan distribusi suhu pada hidroponik rakit apung dianalisis melalui pendekatan simulasi computational fluid dynamics (CFD). Pendekatan simulasi CFD mampu menggambarkan sebaran suhu pada hidroponik rakit apung dengan baik dimana koefisien determinasi (R2) untuk masing-masing perlakuan dari suhu rendah, sedang dan kontrol berturut-turut sebesar 0.983, 0.980 dan 0.862. Hasil penelitian menunjukkan bahwa jumlah umbi merupakan variable yang paling responsif, dimana pada suhu rendah induksi pembentukan umbi bawang merah mencapai 200% lebih banyak dari pada suhu kontrol dan 60% lebih banyak dari suhu sedang.