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Nitrogen Fertilization of Semiarid Grasslands: Plant Growth and Soil Mineral N Levels 1
Author(s) -
Power J. F.,
Alessi J.
Publication year - 1971
Publication title -
agronomy journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 131
eISSN - 1435-0645
pISSN - 0002-1962
DOI - 10.2134/agronj1971.00021962006300020024x
Subject(s) - agronomy , fertilizer , mineralization (soil science) , soil water , human fertilization , grassland , nitrogen , ecosystem , environmental science , zoology , chemistry , biology , ecology , soil science , organic chemistry
To evaluate the fate of mineral N in a grassland ecosystem, fertilizer N was applied to native grassland in North Dakota at rates up to 540 kg N/ha either (a) all in 1 year, (b) one‐third in each of 3 years, or (c) one‐sixth each of 6 years. Cumulative production of grass tops for the 6 years increased with increased amounts of total N applied, but was not affected by timing of fertilizer application. With continued annual fertilization, responses were measureda at progressively lower rates. At 270‐kg N or more, residual effects were still significant 6 years later. Dry weights of three oats crops grown on these soils in the growth chamber indicated that greater N availability in fertilized soils contributed appreciably to these residual effects. Soil NH 4 + ‐ and NO 3 ‐ ‐N levels for many treatments exhibiting residual effects were no higher than for unfertilized plots, indicating residual N was present in other than mineral forms. Fertilizer N is probably immobilized by all components of the soil‐grass ecosystem (especially grass roots) and the mineralization of this immobilized N may contribute to residual effects. Fertilizer N applied in excess of the immobilizing capacity of the ecosystem remains in mineral form until required by the grass. Consequently, the presence of a mineral N pool indicates that N has been eliminated as a growthlimiting factor and maximum production from the available water is being achieved.