Plant and Soil 256: 403–411, 2003. © 2003 Kluwer Academic Publishers. Printed in the Netherlands. 403 Effect of high boron application on boron content and growth of melons

Management options for reducing drainage water volumes on the west side of the San Joaquin Valley of California, such as reuse of saline drainage water and water table control, have the potential to adversely impact crop yields due to a build up in soil solution boron concentration. An earlier experiment had shown that extrapolation of B soil tests to field conditions provided poor predictability of B content of melons despite statistically significant relationships. Consequently, three tests for extractable soil B were evaluated for their ability to predict conditions of potential B toxicity in melons grown under controlled conditions. Melons were grown for 95 days in two consecutive years in containers of Lillis soil (very-fine, smectitic, thermic Halic Haploxerert) that had been pretreated with solutions containing B concentrations as great as 5.3 mmol L−1. Extractable soil B was determined using ammonium acetate, DTPA-sorbitol, and a 1:1 aqueous soil extract at the beginning and end of the experiment. The B treatments caused various deleterious effects on melon growth and development. Fresh and dry plant matter decreased significantly with increasing B concentrations, while B concentration of plant leaves, stems, and fruits increased significantly with increasing B. The number of days to first flowering was significantly delayed from 35 days at B treatments < 2 mmol L−1 to 51 days at B treatments> 3 mmol L−1. Fruit set was completely inhibited at the highest B treatment of 5.3 mmol L−1. Plant analysis revealed a highly significant relationship between soil extract B obtained with al