PHOSPHORUS-NUTRITION OF LINSEED (LINUM-USITATISSIMUM L) AS AFFECTED BY NITROGEN SUPPLY - EFFECTS ON VEGETATIVE DEVELOPMENT AND YIELD COMPONENTS

The effects of phosphorus (P) and nitrogen (N) supplies on the growth and yield components of linseed cv. Glenelg were studied in a glasshouse experiment using controlled P and N supplies that ranged from deficient to more than adequate for maximum growth. The main effect of constant P stress on yield components was a reduction in the number of capsules per plant as a result of reduced numbers of tillers and fruiting branches per plant. Phosphorus-stressed plants required longer to reach seed maturity than plants which received high P. Phosphorus supply had little effect on either single-seed weight or seed oil concentration, and had no significant effect on the number of seeds per capsule. Nitrogen stress did not affect the timing of maturity or single-seed weight or the number of seeds per capsule; however, it reduced the number of capsules per plant and slightly increased seed oil concentration. The onset of P stress at the start of flowering reduced capsule number by 20%, and seed and oil yields by 16%. The onset of P stress at half-seed-fill of the main stem capsules had no effect on seed or oil yields. The relief of P stress at the start of flowering resulted in a recovery of seed and oil yields to about 80% of the values for unstressed plants. Seeds contained over 80% of the total shoot P at maturity. Seed and oil yields could be predicted with reasonable precision from the dry matter or P content of the whole shoot as early as flower buds visible, and this could provide the basis of an oil yield prediction model for linseed.