Effect of vpd, K nutrition and root-zone temperature on leaf area development, accumulation of Ca and K and yield in tomato

Crop scale experiments were carried out in 1998/99 to investigate the indiv idual and interactive effects of vapour pressure deficit (vpd), root-zone t emperature (RZT) and potassium nutrient feed concentration on the accumulat ion of Ca and K in shoot tissues, vegetative growth, fruit yield and qualit y in tomato (Lycopersicon esculentum Mill). RZT and K nutrition had no dete ctable effect on growth but high K nutrition (10 mM) compared with the low (4 mM) increased the accumulation of K in the leaves and older fruits. In c ontrast, severe deficiencies of K were detected in young expanding leaflets (0.66-0.75%) near to the shoot apex under high (0.1 kPa vpd) compared with control humidity (1.50-2.03%; 0.5 kPa vpd). The accumulation of Ca was eit her unaffected or increased in leaf tissue at high humidity. Fruits develop ing on trusses in the top half of the shoot had markedly lower K concentrat ions under high humidity. In contrast the concentration of Ca was increased in fruit. The area of individual leaves was initially increased and then d ecreased by high humidity, but these responses did not appear to affect abo ve ground dry-matter accumulation within the 56 d exposure period but a lar ger proportion of assimilates was partitioned to the fruits. Reduced accumu lation of K detected under high humidity appeared to exhibit a close relati onship with reduced leaf expansion, lower yield and a decreased proportion of class I fruits. The relationship between vpd and K, Ca accumulation, lea f growth, assimilate partitioning and yield responses are discussed.