Plant and Soil (2005) 270: 135–146 © Springer 2005 DOI 10.1007/s11104-004-1311-3 High fertigation frequency and phosphorus level: Effects on summer-grown bell pepper growth and blossom-end rot incidence A. Silber 1,5 , M. Bruner 2 , E. Kenig 2 , G. Reshef 2 , H. Zohar 2 , I. Posalski 2 , H. Yehezkel 3 , D. Shmuel 3 , S. Cohen 3 , M. Dinar 3 , E. Matan 3 , I. Dinkin 1 , Y. Cohen 1 , L. Karni 4 , B. Aloni 4 & S. Assouline 1 1 Institute of Soils, Water and Environmental Sciences, Agricultural Research Organization, the Volcani Center, Bet Dagan, 50250, Israel. 2 Shaham, Extension Service, Ministry of Agriculture, Israel. 3 Besor Experimental Station, Israel. 4 Institute of Field and Garden Crops, Agricultural Research Organization, the Volcani Center, Bet Dagan, 50250, Israel. 5 Corresponding author ∗ Received 4 June 2004. Accepted in revised form 12 July 2004 Key words: heat pulse, irrigation, leaf conductance, Mn deficiency, root/shoot ratio, tensiometer Abstract The objective was to examine the effects of fertigation frequency and P application rate on bell pepper growth and blossom-end rot (BER) incidence, under hot conditions. The experiment comprised six treatments: two concen- trations of phosphorus (3 and 30 mg L -1 ) combined with three fertigation frequencies (two and eight events per day, and for 1.5 min every 25 min throughout the day). Increasing the fertigation frequency significantly increased the plants’ acquisition of nutrients, especially phosphorus and manganese. A significant linear regression was obtained between aboveground biomass, and leaf P concentration in the early vegetative stage. Based on the linear regression, 96% of the dry weight variations could be explained by differences in leaf P concentration, indicating that the main effect of fertigation frequency was related to improved P mobilization and uptake. Increasing the daily fertigation frequency from two to eight and to 30 applications reduced the number of BER fruits from 7 to 3 and to 2 per plant, respectively, and accordingly, increased the yield of export-quality fruits from 6.5 to 10 and to 10.5 per plant, respectively. The Mn concentration in plants exposed to low fertigation frequency were low, probably in the deficiency range, but they increased with increasing fertigation frequency. A negative correlation was found between the accumulated number of BER-affected fruits throughout the experiment and fruit-Mn concentrations. In light of recent findings that BER effects in the fruit tissue include the production of oxygen free-radicals and diminution of anti-oxidative compounds and enzymatic activities, and the known crucial role of manganese in enzyme activities and in detoxification of oxygen free-radicals, the relationships between BER incidence and fruit- Mn concentration may indicate that BER is related to Mn deficiency. Future researches are needed to validate this hypothesis. Introduction In modern irrigated agricultural systems, especially under arid or semi-arid conditions or in greenhouses using soilless culture techniques, water and nutri- ents are supplied simultaneously (fertigation), mainly by drip irrigation devices (Bar-Yosef, 1999; Hagin et al., 2002). Frequent application of water and nu- ∗ E-mail: avnsil@volcani.agri.gov.il. trients ensures that the root surface and its vicinity are well supplied with fresh nutrient solution during the fertigation events and the subsequent redistributions. These frequent replenishments prevent the formation of a depletion zone in the vicinity of the root surface by uptake of nutrients between successive fertigation events, decrease the concentration gradient between the medium solution and the root-medium interface, and diminish the role of diffusion in transporting nu- trients toward the roots (Silber et al., 2003). Previous