YIELD AND CHEMICAL COMPOSITION OF RAPE IN RESPONSE TO NITROGEN, PHOSPHORUS AND POTASSIUM

Abstract

A field trial was conducted for 3 yr to monitor the response of seed rape (Brassica napus L.) to several fertilizer treatments at two seeding dates. The fertilizer treatments consisted of 0–200 kg N/ha, 0–100 kg P/ha and 0–180 kg K/ha broadcast with or without 4.2–7–0 kg N-P-K/ha banded below the seed. Total yield, seed yield, plant height, lodging index, seed contents of oil and N, and leaf contents of N, P, K, Ca, Mg, Mn, Cu, Zn and B were measured. Rape responded to broadcast N with maximum seed yields at 100 kg N/ha independent of seeding date or banded fertilizer. Leaf concentrations of N, P and K were influenced by nitrogen supply but the critical leaf N concentration varied considerably. Response to 7 kg P/ha banded or 25 kg P/ha broadcast occurred when the soil P was less than 10 μg/cc. The critical leaf P concentration was less than 0.2%. Very little response to broadcast K was observed with a soil test of approximately 60 μg K/cc. The early seeding date (late April to early May) increased seed yields an average of 225 kg/ha over the late seeding date (late May) and the band placement of fertilizer increased seed yields an average of 55 kg/ha over comparable treatments without banded fertilizer. Seed yield and leaf elemental composition are presented as functions of broadcast nitrogen, phosphorus and potassium.