Effect of irrigation method on the recovery of 15N fertilizer in a slowly permeable clay soil cropped with maize

A study using 15N~labelled fertilizer was initiated in a lysimeter facility to quantify the amount of N assimilated by maize plants and that which remained in the soil at the end of a cropping season. Maize was planted in 0.43 m2 by 1.35 m deep intact Marah clay loam soil cores removed from an improved pasture in mid-October 1983. Two irrigation treatments, flood-impounding water on the soil for up to 72 h, and control-applying enough water to prevent plant stress without ponding, were employed. The crop was harvested in early April 1984 and the amount of fertilizer- and soil-derived N in the plant and remaining in the soil was determined. Grain yields were reduced about 33% by flood irrigation. Although about 30 kg N ha-1 more fertilizer N was lost from the flood-irrigated system, the difference in N recovery between the flood- and control-irrigated soils was not sufficient to account for the reduced grain yield. Flood-irrigated plants were less efficient in transporting fertilizer N to the seed than were control irrigation plants. The data suggest that the reduced seed yield and total N content of maize plants grown under flood irrigation was metabolically controlled rather than being derived from a difference in soil mineral N content compared with control-irrigated soils.