Apparent recovery of fertilizer n by vegetable crops

Abstract

Apparent recoveries of fertilizer N by crops were studied as their treatment in simulation models is a serious problem. Multi-level N fertilizer experiments in which fertilizer was broadcast and incorporated in soil immediately before drilling were carried out on a range of vegetable crops on adjacent sites of the same field. At final harvest, apparent recovery always declined approximately linearly with the increase in fertilizer N even when less was applied than was needed for maximum uptake; this contrasts with the well-known constancy of apparent recovery of Gramineae (winter wheat and grass) over widely different rates. At the seedling stage (of vegetables), when N-uptakes were very small, N-uptake and invariably dry weight, unexpectedly increased with the increase in fertilizer N until very high levels were reached. A single simulation model, with species differences accounted for by variations in the value of only one coefficient, defined, at least qualitatively, all the various phenomena. It is argued that substantial quantities of nitrate may always remain in soil at harvest of some vegetable crops if a sufficient amount of N-fertilizer is applied by the conventional broadcast method to obtain high yields.

Key Words:

• efficiency of fertilizer-use
• nitrate pollution
• N-uptake and response
• simulation models