Applications of mineral nitrogen increase the yield and content of crude protein in narrow-leaf lupin seeds

Abstract

In a plant pot experiment with non-inoculated seed stock of narrow-leaf lupin (Lupinus angustifolius, L.) of the variety ‘Prima’ we explored the effects of nitrogen compounds applied in the form of NH₄NO₃ on different dates (before sowing, after emergence and during flowering) and at various levels (0–0.5–2–3 g N per pot) on changes in the number of pods per plant, the 1000-seed weight, seed yields and the content of crude protein in seeds. The experiment included four treatments; the first was a control treatment not fertilized with nitrogen. In the other treatments we applied nitrogen either as a single application before sowing or in three split applications. In all the nitrogen-fertilized variants the number of pods per plant, total seed yields per plant and the concentration of crude protein all increased compared to the unfertilized control variant. The highest levels of nitrogen (3 g N per pot) reduced the 1000-seed weight compared to the unfertilized control variant. The total application of 2 g N per pot split into application before sowing (0.5 g N), after emergence (0.5 g N) and during flowering (1 g N) resulted in a highly significant increase in the number of pods per plant (+78%), the 1000-seed weight (+20.1%) and therefore higher seed yields per plant (+139.8%) compared to the control treatment not fertilized with nitrogen. Increasing levels of nitrogen linearly increased the content of crude protein in seeds during harvest from 24.2% to 40.6%, thus increasing the nutritional quality of the seeds.