PRACTICAL MEANS OF ENHANCING TUBER CALCIUM CONTENT AND REDUCING INCIDENCES OF SOFT ROT AND INTERNAL BROWN SPOT BY APPLICATION OF SOLUBLE FORM OF CALCIUM DURING BULKING

Abstract

We have shown that tuber calcium can be enhanced by supplying soluble forms of calcium near the tuber stolon region during bulking. In the present study we applied calcium nitrate or N-HIB during bulking (hilling, 3 and 6 wks after hilling) by injecting these Ca sources into sprinkler irrigation line. Field plots were established with cv `Russet Burbank' in sandy loam soil containing about 1200 Kg Ca ha -1 . All plots received equal amounts of nitrogen. Plots receiving only nitrogen (as NH 4 NO 3 ) at the same time served as split N controls and the plots receiving complete nitrogen by the time of hilling (non-split N) served as the grower control. In 1990 compared to non-split-N control a consistently higher tuber yield was obtained with split-N, N-HIB (113 Kg.Ca ha -1 ) calcium nitrate (113 Kg Ca ha -1 ). However, these differences were not significant. Tuber calcium contents were increased with N-HIB and calcium nitrate. After 5 months of storage the incidence of soft rot and of internal brown spot was significantly reduced. In 1991 N-HIB (113 Kg ha -1 ) gave significantly higher tuber yield than other treatments. Tuber calcium contents were increased with both calcium nitrate and N-HIB treatments. After four months of storage incidence of internal brown spot was reduced by calcium nitrate and N-HIB although calcium nitrate was most effective. These results demonstrate that it is possible to improve tuber calcium contents by application of 113-226 Kg Ca ha -1 during bulking even in a soil containing sufficient calcium for plant growth.