Effect of Soil Thickness on Nitrogen Distribution and Use by Crested Wheatgrass1
- J. F. Power,
- S. D. Merrill and
- S. J. Smith2
Soil thickness can affect nitrogen (N) cycling and use in several ways, particularly if the solum contains materials restrictive to root growth. Microplots of 0.093 m2 were established on a reconstructed mine soil composed of 0.2 m A horizon (Haploborolls) over 0.05, 0.30, 0.55, or 0.80 m of B and C horizon material spread over sodic (SAR 29.5) minespoil, giving soil thicknesses of 0.25, 0.50, 0.75, and 1.00 m, respectively. The area had previously been seeded to crested wheatgrass (Agropyron desertorum var. Mandan) and fertilized annually with 55 kg N ha−1. In spring 1978, the grass on eight microplots received enriched (27.5%) K15NO3 at 48.6 kg N ha−1. Grass on 16 other microplots harvested in 1979 and 1980 also received enriched 15N fertilizer in late November 1978 and commercial ammonium nitrate (NH4NO3) (50 kg N ha−1) in November 1979. After harvest in each of the 3 yr, soil in the eight microplots was excavated, and 15N enrichment in forage, roots, and soil organic N was determined. Increased soil thickness greatly increased forage and root growth, but had much less effect on N concentration in plant material. Uptake of labeled N in neither forage nor roots was greatly influenced by soil thickness, either in the year of application or the following year. Uptake of labeled N in forage the 2nd yr was only 5 to 10% of that found the 1st yr. However, uptake of soil N in both forage and roots generally increased two- to threefold as soil thickness increased from 0.25 to 1.00 m. Soil inorganic N and forage N concentrations suggested that available N supply was not limiting. Thus, the increase in soil N uptake probably resulted from deeper and more effective root functioning with increased soil thickness. Approximately 35% of the labeled N applied was removed in harvested forage and 12% remained in roots, regardless of soil thickness. However, the quantity of labeled N immobilized as soil organic N varied from over 40% of that applied with 0.25-m soil thickness to about 30% for 1.00-m thickness. Because there was no runoff or leaching, this difference was probably due to gaseous losses, possibly by ammonia volatilization from plant material.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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