Fate of nitrogen applied to maize on conventional and minimum tilled Nitisols in Western Ethiopia

Abstract

Maize production in western Ethiopia is practiced mainly on Nitisols inherently low in N. Neither conventional nor minimum tilled maize reaches its full yield potential without fertilization. A large amount of applied N usually escapes from the soil-crop system and this may exert harmful effects on the environment in addition to yield losses. Hence, the objective was to quantify the fate of labelled urea applied to conventional and minimum tilled maize. The study was conducted in 2004 on selected plots of experiments started in 2000 at three sites. At each site, the experiment was laid out in a randomized complete block design with three replications. Three tillage systems (MTRR = minimum tillage with residue retention, MTRV = minimum tillage with residue removal and CT = conventional tillage) and three N fertilization levels (recommended rate of 92 kg N ha⁻¹ and 25% less and 25% more than this rate) were combined in complete factorial arrangement. Only the CT and MTRR plots fertilized at the recommended rate were used for this study. A micro plot of 2.4 m² was demarcated in the center of every selected 24 m² macro plot where labelled ¹⁵N @ 5 atom % urea was applied instead of unlabelled urea. The grain, stover and total biomass N derived from fertilizer was consistently higher for CT than MTRR. Conversely, the grain, stover and total biomass N derived from soil was consistently higher with MTRR than CT. Therefore, the fertilizer N recorded in the MTRR soils was higher than in the CT soils and mainly confined to the upper 450 mm. The fate of fertilizer N was in MTRR: 47% recovered by maize, 17% remained in the soil and 36% unaccounted for and in CT: 54% recovered by maize, 12% remained in the soil and 34% unaccounted for.