Greenhouse Cooling for Production of Peppers Under Hot Summer Conditions in a High-Roof

Greenhouse Cooling for Production of Peppers Under Hot Summer Conditions in a High-Roof Passively-Ventilated Greenhouse

D.J. Cantliffe, S.K. Saha, N.L. Shaw Horticultural Sciences Department University of Florida Gainesville, FL USA

N. Gruda Humboldt University of Berlin Berlin, Germany

Keywords: hydroponics, soilless culture, protected agriculture, shade, mist

Abstract

In order to insure good fruit yields of greenhouse pepper crops in Florida in late fall (November) and winter, when prices are high, planting is dictated to be in late July to early August when greenhouse day temperatures can be in excess of 40°C. In order to reduce daytime temperatures during summer, two cooling methods were examined and compared to no cooling: 1) Aluminized shade system (Aluminet, Polysack, Israel), and 2) mist cooling (Netafim USA). ‘Shamrock’ peppers were transplanted on 18 August, 2004 and 13 July, 2005, in to 11 L plastic pots containing pine bark in a Top Greenhouse, Ltd., high-roof plastic greenhouse in Citra, Florida. Plant densities were 1.9, 3.0, and 3.8 plt.m-2. At transplanting the cooling systems were ‘activated’ when greenhouse temperatures reached 28°C. The mist system was timed to apply mist for 15 sec. every 15 min. PAR (μmol.s-1.m-2) was reduced in excess of 50% compared to outside during mid- day and up to 66% in morning and late afternoon by the shade system. The mist system gave readings which were one-third higher PAR than the shade system in mid-day. Temperatures at the plant canopy were reduced by both cooling methods compared to the control. Plant height was increased and stem diameter reduced in shade, compared to the mist system. Fruits could not be harvested in 2004 due to damage from two hurricanes. In 2005, early fruit yields (6 October) were greater from the mist system, compared to shade or the control. More fruits were harvested from the highest plant density compared to the lowest density. Both cooling system treatments were terminated in 2005 on 1 September. When the yields from all three harvests (6, 27 October, 18 November) were combined, there was no significant difference between cooling method and plant density for marketable yield per hectare.