Abstract:
The effect of phosphorus banded at planting, at rates up to 240 kg/ha, on the specific gravity of tubers of cvv. Kennebec (10 sites) and Coliban (5 sites) was investigated using field experiments conducted during 1984-85, 1985-86 and 1986-87. The relationship between specific gravity and phosphorus concentration in petioles of youngest fully expanded leaves (P-YFEL) was also determined. As the rate of applied phosphorus increased there were significant positive and negative trends in specific gravity. However, the size of the effect varied between sites; for example, the maximum and minimum ranges in specific gravity (based on treatment means) due to phosphorus application were 1.0762-1.0869 (site 13) and 1.0753-1.0772 (site 24), respectively for the cv. Kennebec and 1.0598-1.0683 (site 22) and 1.0715-1.0753 (site 17), respectively for the cv. Coliban. Rates of applied phosphorus, which resulted in maximum specific gravity, also varied between sites. Maximum specific gravities occurred at phosphorus rates in the ranges 0-100 and 40-240 kg/ha for cvv. Kennebec and Coliban, respectively. There were significant relationships (5 quadratic and 1 negative linear) between phosphorus concentration in P-YFEL and specific gravity for cv. Kennebec at all 6 responsive sites. Phosphorus concentrations in P-YFEL associated with maximum specific gravities were in the range 0.29-0.51%. For cv. Coliban, over similar tissue phosphorus concentration ranges, there were significant (P<0.05) positive linear relationships for 1 responsive and 2 non-responsive sites. When data for cv. Kennebec were pooled for all sites, there was a significant (P<0.05) quadratic relationship between specific gravity and tissue phosphorus concentration (range 0.22-0.77%). For the cv. Coliban the trend was not significant (P>0.05). We have concluded that the rate of phosphorus banded at planting can affect specific gravity and that the cvv. Kennebec and Coliban differ in their sensitivity to this effect.