Main content area

Nitrogen Fertilization of Semiarid Grasslands: Plant Growth and Soil Mineral N Levels

Power, J. F., Alessi, J.
Agronomy journal 1971 v.63 no.2 pp. 277
nitrogen fertilizers, fertilizer application, arid lands, grasslands, soil nutrient balance, plant growth, dry matter accumulation, nitrogen
To evaluate the fate of mineral N in a grassland ecosystem, fertifizer N was applied to native grassland in NorthD akotaa t rates upt o 540 kg N/ha either (a) all in year, (b) one-third in each of 3 years, or (c) one-sixth each of 6 years. Cumulativep roductiono f 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 t 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- and NO-N levels for many treatments exhibiting residual effects were no higher than for unfertilized plots, indicating residual N was present in other than mh~eral forms. Fertilizer N is probablyi mmobilizedb y all componentos f the soil-grass ecosystem (especially grass roots) and the mineralization of this immobilizedN mayc ontribute 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 maximumpr oduction from the available water is being achieved.