Short-term Nitrogen Availability from Lupine Seed Meal as an Organic Fertilizer is Affected by Seed Quality at Low Temperatures

ABSTRACT

A high and short-term supply of nitrogen (N) is required in organic vegetable production, especially during early spring under temperate conditions. Lupine seed meal, which can be on-farm produced, has the potential to fulfill this requirement if used as an organic fertilizer. However, no detailed information is available regarding seed meal quality effects on N mineralization potential at low temperatures. Lupine seed meals from five blue lupines (Lupinus angustifolius L.), two yellow lupines (Lupinus luteus L.) and two white lupines (Lupinus albus L.) were tested in the incubation experiment at a lower (5°C) and an increased temperature (18°C) to evaluate the effect of seed meal composition on short-term N mineralization. The results showed that 50–70% of organic fertilizer N was released as mineral N after 7 days of incubation at 18°C. At 5°C, the same level of mineral N was detected in soils on day 28. N mineralization was strongly correlated with N content of the seed meal (R² = 0.85, p ≤ = 0.05) and negatively correlated with cellulose content (R2 = 0.54, p = 0.05) at 5°C. Lignin and polyphenols had no effect on N mineralization due to their low content in lupine seed meal. The results also indicated that soil-borne organic N was mobilized by microorganisms during the biological degradation of the fertilizers, but did not cause corresponding mineral N release from soil-borne organic matter.