EFFECTS OF NITROGEN ON THE DEVELOPMENT AND GROWTH OF THE POTATO PLANT .2. THE PARTITIONING OF DRY-MATTER, NITROGEN AND NITRATE

Potatoes (Solatium tuberosum L) were planted in pots in a temperature-controlled glasshouse The treatments consisted of three levels of mtrogen supply, 1 e 2 5, 8 and 16 g N per pot (treatments called Nl, N2 and N3) The accumulation rates of dry matter and nitrogen showed an upper limit of response to nitrogen supply, N3 plants continued to accumulate dry matter and N at a constant rate for a longer period of time than N2 and Nl plants The uptake of nitrogen slowed earlier m time than the rate of dry matter accumulation in all treatments The proportion of the dry matter in tubers of mature plants was not affected by nitrogen treatment, but the start of tuber bulking was delayed in the N3 plants The final proportion of total plant nitrogen in the tubers was similar for all treatments The concentration of nitrogen in the dry matter of mature plants increased with the level of N supply Maximum haulm weight increased with the level of N supply Apical lateral branches of the first and second order made up larger proportions of the total haulm dry weight and total leaf area as more nitrogen was supplied Yet, the distribution of dry matter over stems and leaves was not different between nitrogen treatments Stems were the most responsive to N treatment in terms of N concentrations.In each of the component organs (stems, leaves, tubers) the concentration of nitrogen declined with time Fairly strong associations were observed between the concentrations of N in component organs The oncentration of nitrate in leaves usually increased initially with leaf age, peaked and declined A substantial part of the differences between treatments in the concentrations of N in leaf dry matter were attributable to differences in nitrate concentration Nitrate in stems and tubers fell virtually below the limit of detection at total nitrogen concentrations of less than 1%, but increased in proportion to total N above that threshold, especially in stems. © 1992 Annals of Botany Company.