Tuber growth and biomass partitioning of two potato cultivars grown under different N fertilization rates with and without irrigation

Nitrogen and water deficiencies are known to affect potato yield, but much less is known of their effect on tuber growth and biomass partitioning. The objective of this on-farm study conducted at two sites in each of three ye ars, 1995 to 1997, was to determine the effects of supplemental irrigation and N fertilization rates on tuber growth and biomass partitioning of the c ultivars Shepody and Russet Burbank. The N fertilization rates were 0, 100, and 250 kg N ha(-1) in 1995, and 0, 50, 100, and 250 kg N ha(-1) in 1996 a nd 1997, The highest bulking rate observed in our study (7.3 g fresh tubers m(-2) degreesC(-1)) can be considered near the potential bulking rate in N ew Brunswick. The water deficit in the absence of supplemental irrigation r educed this potential bulking rate by as much as 40%, but this reduction wa s much less at five of six sites and negligible at two of six sites. Nitrog en deficiency reduced the bulking rate at two of six sites. This negative e ffect of N deficiency on bulking rate was greater with irrigation than with out irrigation at two of six sites; the tuber bulking rate with irrigation was reduced by as much as 50% with no N applied at one site. Shepody had a greater bulking rate than Russet Burbank, The tuber bulking of Russet Burba nk, however, started earlier and lasted longer than that of Shepody, Water and N deficiencies increased biomass partitioning to tubers and large roots . Shepody partitioned a greater proportion of its biomass to large roots an d had a greater root biomass than Russet Burbank. Our results demonstrate t he ability of potatoes to modify biomass partitioning when grown under wate r and/or N stresses. As a result of this compensation, the reduction in tub er yield due to limited N and water stresses is minimized.