Effects of phosphorus fertiliser levels on phosphorus accumulation, growth and yield of hybrid squash in the field

Abstract

The effects of four levels of phosphorus fertiliser on the tissue phosphorus concentration and growth of hybrid squash ( Cucurbita maxima L. cultivar ‘Delica’) sown in the field in early spring and summer were examined at Pukekohe, New Zealand. Plants were sampled regularly from emergence until harvest, and dry weight and phosphorus concentration of aerial components were measured. Crop growth was related to the integral of temperature (growing degree days). Leaf area expansion and dry matter accumulation (on logarithmic scales) were described using quadratic regressions. Phosphorus deficiency affected the relative rates of leaf area expansion and crop growth during early stages, and the effects were greater in the early-sown crop. Tissue phosphorus concentrations and relative growth rates declined concomitantly during growth. The rates of decline increased with increasing levels of applied phosphorus, so that tissue phosphorus concentrations and relative growth rates eventually were not significantly affected by the level of applied phosphorus. The transient effects of phosphorus supply on relative growth rate caused sustained effects on the absolute growth rate and yield. Fruit yields at harvest were increased 109 and 67% by applied phosphorus in the early- and late-sown crops, respectively. These increases resulted from significant effects on fruit number per plant and average fruit weight. The implications of these results for fertiliser management in hybrid squash are discussed.