NITROGEN UPTAKE AND UTILIZATION BY BELL PEPPER IN SUBTROPICAL AUSTRALIA

Concern over the pollution potential of nitrogen (N) fertilisers has p rompted studies of the utilisation efficiency of applied N by crops. T his study was conducted to determine the efficiency of N usage by bell pepper (Capsicum annuum L.) grown with plastic mulch and trickle irri gation, and to define a rate of applied N which is equal to uptake by the crop. The relationships between applied N (0, 70, 140, 210, and 28 0 kg/ha), nutrient uptake, and yield for spring and autumn bell pepper crops grown on a major soil type (Tropeptic Eutrustox) in the Bundabe rg region of subtropical Australia were investigated. Maximum dry weig ht yield of fruit, leaves, roots, and stems corresponded with N210 to N280 for both spring and autumn crops. In addition, maximum fresh weig ht of marketable fruit corresponded with N210 to N280 for both seasons . Nitrogen uptake was equal to the applied rate at N140. Plant uptake of elements increased with applied N and, at N280, were ranked as foll ows: K> N> Ca> Mg> S> P. Fruit accumulated the greatest proportion of K, N, and P (40 to 64%, 40 to 64%, 49. to 76%, respectively), and only a comparatively small amount of Ca (6 to 7%). The efficiency of fruit production from absorbed applied N declined with increasing N rate. D istrict standard rates of P, N, K, and S application exceeded uptake b y plants grown at an equivalent N rate (differences of 68 and 65 kg P, 57 and 52 kg N, 32 and 24 kg K, and 19 and 24 kg S for spring and aut umn, respectively). Because of the importance of pepper yield as a det erminant in economic outcome and the relatively low cost of fertiliser N, application rates in excess of N140 are likely to continue by dist rict growers in an attempt to maximise yield.