Author:
Cookson W. R.,Rowarth J. S.,Cameron K. C.
Abstract
Large amounts of the nitrogen (N) fertiliser applied to ryegrass seed crops
remain within the soil at seed harvest and can potentially affect subsequent
pasture production and environmental contamination. The fate of residual
urea-15N-labelled fertiliser and the effect of previous
fertiliser application on subsequent leaching losses and pasture production
was assessed during a 9-month period after seed harvest using monolith
lysimeters (diameter, 180 mm; length, 300 mm) in Canterbury, New Zealand.
Results indicated that leaching losses and pasture uptake of residual
15N-labelled fertiliser were largely restricted by the
immobilisation of 15N-labelled fertiliser into soil
organic pools and the expanding root mass. Most of the
15N-labelled fertiliser remaining in the soil 9 months
after the seed harvest was present within the humified organic matter
(50%) and microbial biomass (40%) pools; the majority
(62%) was anaerobically mineralisable. The
15N-labelled fertiliser that became available was
largely recovered in rapidly expanding ryegrass roots, which increased
3–4-fold between seed harvest (December 1997) and pasture harvest
(September 1998). Root mass, soil mineral N, and soil microbial biomass N were
significantly (P < 0.05) greater in fertilised
treatments than in controls at pasture harvest; clay-fixed N, anaerobically
mineralisable N, and total N were not affected. The results indicated that, in
the short term, N mineralisation rates were increased by previous fertiliser
application but there was little evidence of a longer term effect on N
mineralisation rates.
Subject
General Agricultural and Biological Sciences
Cited by
8 articles.
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