Selenium accumulation and growth of perennial ryegrass (Lolium perenne L.) as affected by pig manure composting

At trace concentrations, selenium (Se) has been shown to exert positive effects on plant growth, but Se essentiality to higher plants remains in doubt. Plants can absorb Se from the soil in inorganic or organic forms, but the cycling and bioavailability of organic Se in the manure-soil-plant system remain to be fully understood. This study investigated the effects of pig manure composting on the growth and Se accumulation in Lolium perenne L. (cv. Riikka) at different growth stages. A pot experiment with silica sand amended with Se-enriched mineral fertilizer (NPK-Se), dried, ground pig manure (PM) and pig manure compost (PMC) at 200 mg N kg-1 soil was carried out under controlled greenhouse conditions. Addition of NPK-Se, PM and PMC significantly (p ≤ 0.05) increased dry matter content in the stems and roots, on average, by 28 and 19% respectively. Inorganic (NPK-Se) and organic (PM and PMC) treatments slightly increased net photosynthesis, stomatal conductance, transpiration and leaf area in plants. Inorganic Se (NPK-Se) markedly increased Se content in the shoots, on average, by 35% at all growth stages. Even though Se concentration in the roots was 3-fold higher in pig manure (PM and PMC) fertilized-plants, translocation to the shoots was reduced. Interestingly, Se concentration in the shoots was higher in PMC-plants compared to PM-plants at all growth stages. However, the effect of composting on Se concentration was not significant. Overall, the results indicate that composting improves the fertilizer value of pig manure with possible stimulatory effects on organic-Se mineralization.