Reaction of potatoes to calcium and phosphate levels as affected by wind
In am attempt to increase the number of mini tubers produced per potato plant, the effect of calcium and phosphorus nutrition was investigated. It is believed that high phosphorus (P) and low calcium (Ca) levels stimulate tuberization. Three nutrient solution treatments were used in this study; a well-balanced control, a Ca-poor solution and a nutrient solution with a relatively high level of P. These were applied at pH levels of 6.0 and 4.6, growing 'Van der plank' potatoes under greenhouse conditions. Air from the ventilation system entered the greenhouse from a basement, moving upwards at the sides. Two pots were used as a split plot experimental unit, one pot at the windy side and the other next to it at the wind-protected inside. Three replications were used. Single buds, removed from seed tuber tissue were used to produce homogeneous plants, raised in seedling trays, filled with a vermiculite/pine-bark mix as medium. After two weeks, the single stemmed plants were transplanted into Mitcherlich pots, filled with five litres of sterilised river sand. Standard disease and pest control measures were applied and the potatoes were harvested 54 days after transplanting. The low Ca treatment did not significantly affect total tuber mass, tuber numbers or tuber dry matter percentage, not even at the low pH level. The lack of Ca reaction may be due to the fact that the pH in the root zone increased since an ammonium-free nutrient solution was used or due to the mild growing conditions. In contrast to the reported increased number of tubers when P was applied to soil at extremely high levels, addition of P beyond the optimum level reduced the number of tubers per plant but significantly increased tuber size. Of interest was the fact that foliage and tuber yields were significantly reduced by wind at the high P nutrient levels with no effect at the low Ca level.