Effect of nitrogen supply on the response of Majestic potato to gibberellic acid

SUMMARY Potato plants sprayed with gibberellic acid (GA) were given extra nitrogen either through the soil (as ammonium nitrate) or through the leaves (as urea). GA increased the initial production of dry matter but the effect did not persist, even with additional N. The number of leaves on lateral branches was decreased by GA partly because leaf production on laterals at lower nodes was inhibited. N increased the rate leaves were produced on lateral branches; the soil application doubled the leaf number and the urea increased it by 50%. GA, but not N, increased the area of a main‐stem or lateral‐stem leaf; however, nitrogen produced the largest total leaf area because it produced more leaves. There was no evidence for any interaction between GA and N either in the effect on leaf number or total leaf area. The fall in total N content per unit area caused by GA found in an earlier experiment was confirmed and additional N did not arrest this decline. Loss of efficiency of GA‐sprayed plants is unlikely to result from indirect deficiency caused by rapid leaf expansion.