Abstract
Dangerously high nitrate concentrations in groundwater used for domestic purposes prompted field and lysimeter studies which highlighted the importance of minimising drainage and N-fertilizer applications in intensively irrigated areas. 76 g N (field) and 60 g N (lysimeter) ha-1 were leached mm-1 of drainage on plots receiving 120 kg fertilizer-N ha-1 as sulphate of ammonia. Within the range of 0-120 kg fertilizer-N ha-1 the total N ha-1 leached was 2-10 kg (field) and 2-28 kg (lysimeter) with 110 and 465 mm drainage over 81 and 56 days. Three times (field) and ten times (lysimeter) more N was leached as nitrate than as ammonium; total N losses were similar from sulphate of ammonia and urea. The amount of N leached increased by 160% from a three-fold increase in N-fertilizer rate. A crop of chillies 1 removed the equivalent of 47 and 67% of the fertilizer N; yields of dry chillies increased from 300 to 700 kg ha-1 in response to 0-120 kg fertilizer-N. There was no yield response to farmyard manure (FYM) at 12.5 t ha-1 (= 100 kg N ha-1), even in the absence of fertilizer. N leached from FYM plots was much less than from plots receiving 40-120 kg fertilizer-N ha-1.
