Foliar absorption of nitrogen and phosphorus by cashew

Abstract

An investigation was undertaken at the College of Horticulture, Kerala Agricultural University, Vellanikkara during 1993-'94 to study the foliar absorption of nitrogen and phosphorus by cashew. The main objectives of the study were to develop a method to study the foilar absorption of 14c-urea and 32p and to identify the factors affecting foliar absorption of nitrogen and phosphorus by cashew. It was also aimed to compare the root absorption with foliar absorption and to study the leaf anatomy of cashew in relation to foliar absorption. The experiment was done using three month old cashew seedlings and six year old cashew trees (var.Anakkayam-l). The salient findings are abstracted below.

A leaf washing technique was developed to quantify the foliar absorption of 14c-urea and 32p• Accordingly a sequential washing programme involving four washings each with 50 ml of 2 per cent teepol was found to be reasonable to quantify the foliar absorption of 14C-urea and 32P in cashew. Factors affecting foliar absorption of urea and phosphorus by cashew have been identified. Leaf age, leaf surface, duration allowed for absorption, time of application in a day, month of application in an year and presence of a surfactant in the spray solution are certain important factors that are found to decide the extent of absorption of foliar applied 14C-urea and 32P in cashew. Greater absorption of foliar applied urea was obtained when nutrient solution was sprayed in 0.05 per cent teepol between 11 00 hours and 14 00 hours, directing the spray to the lower surface of terminal leaves of latest flush during March and by giving a minimum absorption period of seven days. The efficiency of foliar applied phosphorus was increased by spraying around 11 00 hours to the lower surface of basal leaves of latest flush during December and by giving a minimum absorption period of six days. Root absorption from solution culture was more compared to foliar absorption in the case of 14C-urea and 32P .The absorption efficiency of 32P both through root and leaf was low compared to 14C-urea. The cashew leaves contain thicker cuticle. on the upper surface with no stomata and thinner cuticle on the lower surface with large number of stomata. The latest flushes of a six year old cashew tree (var. Anakkayam-1) during flushing account for 80 per cent of total leaf area in the crown.