Level and timing of nitrogen fertilizer application to early and semi-early potatoes (Solanum tuberosum L.) grown with irrigation on light soils in Norway

摘要

Trials were performed with early and semi-early potatoes to test the effects of nitrogen (N) fertilizer level (0-160 kg N ha~(-1)) and timing (all at planting versus half then and half either soon after emergence or 3 weeks later). All seven trialswith earlies were irrigated as required, whilst different irrigation regimes (moderate versus intensive) were compared in two trials with semi-earlies. No benefit was derived from splitting the N application. Haulm growth and N uptake increased in all cases almost linearly up to the highest N level, but tuber yield did not respond in the same way. The optimum N level was 86 kg N ha~(-1) for a yield of 15 Mg ha~(-1), rising to 120 kg N ha~(-1) for a yield of 40 Mg ha~(-1). Tuber quality was lowered by the use of excess N fertilizer, particularly in the case of earlies. The quantity of mineralised N present in the soil after harvest rose sharply with above optimum fertilizer use, and the amount of N present in crop residues also increased. The likely leaching after early potatoes was estimated to be up to 80 kg N ha~(-1). The proportion of fertilizer N which was not accounted for in either tuber yield, crop residues or mineral N in soil was 26 percent in earlies and 38 percent in semi-earlies.