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Uptake of Fertilizer and Soil Nitrogen by Ryegrass, as Affected by Carbonaceous Residue¹

ABSTRACT

Annual ryegrass (Lolium multiflorum) was grown on limed Hartsells fine sandy loam and Decatur silty clay loam fertilized with 0, 120, 300, 600, and 900 mg of N as ¹⁵N-labeled (NH₄)₂SO₄ per pot (3 kg of soil). Half of the pots also received 15 g of corn (Zea mays) forage residue (1.05% N) mixed with the soil and half received none. Six clippings of forage and roots were harvested after the final clipping.

Total yield of dry forage and uptake of N were linear for all rates of applied N without residue and for the 300-, 600-, and 900-mg rates with applied residue. As estimated by linear regression from total N uptake, apparent recovery by six clippings of ryegrass plus roots, grown without residue, was 78% from Hartsells soil and 76% from Decatur. The corresponding slightly lower recoveries of 75 and 72% of the fertilizer N applied reflect uptake of soil N. Recoveries of fertilizer N were 90% from the Hartsells and 85% from the Decatur soil-plant systems. As estimated by difference, recoveries of fertilizer N by ryegrass increased, and recoveries from the plant-soil systems decreased with increase in amount of applied N.

Crop uptake of soil N increased as fertilizer N was depleted from the soils.

Addition of the carbonaceous residue caused apparent immobilization of 141 mg of fertilizer N in Hartsells and 164 mg in Decatur soil. Percentages of fertilizer N immobilized in the soils decreased, but actual amounts increased with increasing amount applied. A portion of the fertilizer N, independent of amount applied, was immobilized in each soil.

¹ Contribution from the Soils and Fertilizer Research Branch, National Fertilizer Development Center, TVA, Muscle Shoals, Alabama.

² Agronomist and former Soil Chemist, now with Turf-Grass Specialties, Inc., Fort Lauderdale, Florida.

Received for publication June 16, 1967. Accepted for publication October 4, 1967.