Forage grasses and nutrient cycling

Sustainable agricultural production aims at maximum cycling of e.g. energy and nutrients in food production systems. Term sustainable intensification of agricultural production is used to describe all attempts to decrease the use of unrenewable resources in food production. One important aspect of sustainable intensification is efficient nutrient cycling. This results in changes in management practices such as increased use of organic fertilizers (for example slurry) where nutrients are mainly bound in organic molecules influencing the bioavailability of nutrients.

Our interest has been on selenium cycle in agroecosystem. This is due to the fact that soils in Finland are deficient in Se causing health problems to animals and humans that are consuming locally produced food and feed. Selenium is recognized as an essential microelement for humans and animals, mainly due to its antioxidative properties and health benefits such as improved immune system and reduced cancer risk. For plants, Se is not recognized as an essential micronutrient, but there is increasing evidence that Se has beneficial effects on plant growth. Selenium is mainly circulated to the food chain via crop plants and feed, the Se concentrations of which are dependent on the Se level of the soil. In Finland the agricultural soils are low in Se and thus, the daily intake of Se by humans is naturally low. To ensure the well-being of humans and animals, Se has been added to fertilizers for over 20 years in Finland, and this has successfully increased the daily Se intake of Finns to an adequate level. The bioavailability of applied Se decreases rapidly, so annual Se application is required. Selenium balance, that is, the ratio between plant Se uptake and rate of application, is low and therefore we have studied the fate of fertilizer selenium in the fields. We have compared crop species (Brassica, wheat, forage grasses and legumes) in their Se uptake and translocation efficiency of leaf Se into seeds and found out that forage grasses are superior in selenium uptake and circulation of Se in food chain. Majority of fertilizer Se is returned to field ecosystems via plant residue or manure. Our results show, however, that Se in these sources is not bioavailable to crops and thus annual inorganic Se addition is required also in the future. Selenium can have also some beneficial effects on plant growth. We observed enhanced activity of enzyme on carbon metabolism (fru 1,6 bis-phosphatase) in Se treated alfalfa plants resulting in higher soluble sugar and starch accumulation in these plants.

Ebrahimi N., Hartikainen H., Simojoki A., Hajiboland R. and Seppänen M.M. 2015. Dynamics of dry matter and selenium accumulation in oilseed rape (Brassica napus L.) in response to organic and inorganic selenium treatments.  Agricultural and Food Science 24:104-117.

Owusu-Sekyere, A. , Hajiboland, R. ,Konturi, J. Ebrahimi, N.,Hartikainen, H., Seppänen, M.M 2013. Influence of selenium (Se) on carbohydrate metabolism, nodulation and growth in alfalfa (Medicago sativa L.). Plant and Soil 373 (1):541-552.

Seppänen, M.M., Kontturi, J., Lopez Heras I, Madrid Y, Camara C, Hartikainen H. 2010. Agronomic biofortification of Brassica with Selenium – enrichment of SeMet and its identification in Brassica seeds and meal. Plant and Soil 337:273–283. DOI 10.1007/s11104-010-0523-y.

Seppänen 2015. Selenium cycle in field ecosystem. Report for the Ministry of Agriculture and Forestry19 p.

Holopainen, E. 2015. The impact of livestock protein feed in intake of trace elements. MSc thesis, 70 p.