Nitrogen fertilizer requirements of irrigated potatoes on the Atherton Tableland, North Queensland

Abstract

Seven field experiments were carried out during 1980 and 1981 to determine the nitrogen fertilizer requirements of potatoes grown in basaltic krasnozem soils in North Queensland. Rates of 0, 40, 80, 160 and 320 kg nitrogen/ha were compared in all experiments. Comparisons of urea and ammonium nitrate as fertilizer forms and basal and split application methods were also carried out in four of the experiments. Total yields of fresh tubers from nil-nitrogen plots varied from 18.1 to 29.7 t/ha and nitrogen applications increased these yields at all sites to levels varying from 136 to 325% of the control plots. Ninety-eight per cent of maximum yields calculated from quadratic functions were produced by rates of basally applied urea nitrogen varying from 108 to 205 kg/ha. These rates were poorly correlated with relative yields and topsoil (0-20 cm depth) nitrate nitrogen but were well correlated with nitrogen in 20-50 cm depth. Nitrogen application increased the average tuber weights from 135 to 179 g but reduced the specific gravity of tubers. Splitting nitrogen applications reduced average tuber weights.