Micrometeorological test of microsprinklers for frost protection of fruit orchards in Northern Italy Stefano Anconelli a , Osvaldo Facini b , Vittorio Marletto c , Andrea Pitacco d , Federica Rossi b, * , Franco Zinoni c a CER, Bologna, Italy b CNR––Inst Ecofisiologia Piante Arboree da Frutto, via P Gobetti 101, Bologna 40129, Italy c ARPA-SMR, Bologna, Italy d Universit  a di Padova, Italy Received 10 December 2001; received in revised form 31 May 2002; accepted 17 July 2002 Abstract Microclimate modification induced by intermittent water sprinkling at ground level has proven to be suitable to enhance pro- tection against spring hoarfrosts in orchards. This research investigates about the efficiency of different sprinkler types and water volumes in enhancing air temperature in the canopy layer and to optimise the amount and the cycling of the water applied. Tests have been done over three consecutive years in purpose-built boxes delimited by polyethylene film where different sprinklers and sprayers tested were positioned along two pipes. Microsprinklers and microsprayers with different characteristics and outflow ca- pacitywerecomparedtoevaluatewhetherthesizeofthedropscaninducemodificationofenergybalanceatthesurface.Theimpact of below-tree water sprinkling on the temperature profile appeared to be evident independently on the irrigation device and of the outflow tested. While no substantial differences between sprinklers and sprayers did not arise when the temperatures kept above 3 °C, when temperatures fell below 3 °C (even down to 7/)8 °C), a better performance of the microsprinklers with respect to mi- crosprayerswasobserved.Differencestendtofadeoutwithheight.Inthesametemperatureconditions,abetterperformanceofthe microsprinklers with higher outflow (65 l/h) with respect to the same model characterised by a lower outflow (45 l/h) clearly emerged. Ó 2002 Elsevier Science Ltd. All rights reserved. 1. Introduction Increasing, alarming economic losses and serious in- juriestofruittreeshavebeenrecordedinNorthernltaly orchards in the last years due to late spring frosts. Several protection methodologies, more or less effec- tive according to the geographic area, the local micro- climate and the type of culture are known and utilized so far (Aa. Vv., 1998; Bagdonas et al., 1978; Rieger and Myers, 1990). Above-canopy water sprinkling is a widespread defence method against frosts that is mainlyeffectiveforwinteradvectionfreezing,duetothe movement of cold air masses with temperature largely below zero. The large amount of water needed and the consequent water logging are concrete limitation to this protection method, although the heating power of freezing water is a recognized powerful way of defence againstthisclimatichazard.InEmiliaRomagnaregion, some interesting indication arise from preliminary ex- perimentscarriedoutonbelow-canopywatersprinkling (Zinoni and Anconelli, 1997; Anconelli and Zinoni, 1998). Microclimate modification induced by intermit- tent water sprinkling at ground level make such kind of irrigation a good method an interesting and sustainable alternative for the protection against spring hoarfrosts, mainly of radiation type, also because the irrigation plants already present in the many of the fruit tree or- chards can be used and the water amount reduced. Intermittent irrigation proved to be very good both for plant protection and for better water use (greater irrigatedarea,lowerriskofoxygendeficiencyintheroot zone). The goal of this research is to investigate about the efficiency of different sprinkler types and water vol- umes in enhancing air temperature in the canopy layer andtooptimisetheamountandthecyclingofthewater applied. Physics and Chemistry of the Earth 27 (2002) 1103–1107 www.elsevier.com/locate/pce * Corresponding author. Fax: +39-51-6399024. E-mail address: rossi@istea.bo.cnr.it (F. Rossi). 1474-7065/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII:S1474-7065(02)00146-8