A field experiment was carried out over three cropping seasons with 1 year old strawberry plants (Fragaria x ananassa Duch. 'Elsanta' and 'Honeoye'), where irrigation was scheduled based upon tensiometer measurements and a climatic water balance model. Both irrigation schedules were compared to the non-irrigated one. The influence on fruiting response, the impact on soil moisture tension, mineral nitrogen content in the soil and nitrogen content in the leaves were investigated. In all the years, irrigated plants had significantly higher yields than the non-irrigated ones. The mean fruit weight was also increased by irrigation. Optimisation of irrigation was best achieved in both varieties when the climatic water balance model was used to schedule irrigation. During dry periods, soil moisture tension under non-irrigated strawberries increased to values above 300 hPa at 20 cm soil depth. In a year, with dry conditions and high evapotranspiration, maximum values above 700 hPa were reached. Differences in soil moisture were observed between the two irrigation schedules within and over the years of the experiment. The hydraulic gradients calculated from tensiometer measurements showed that in the periods with irrigation, percolation did not occur below 40 cm soil depth. Therefore, leaching of mineral nitrogen out of the rooted area of strawberries could be excluded for both irrigation schedules. The nitrogen level in dry leaf matter was not influenced by irrigation, except in one year when irrigation followed the climatic water balance model. The present study shows the potential to optimise the irrigation of strawberries using the climatic water balance model, which is less labour intensive and time consuming than tensiometer measurements. Besides the economical aspects, the results from the analysis of different soil parameters indicate that scheduling irrigation based upon this model was also environmentally safe. (C) 1999 Elsevier Science B.V. All rights reserved.
