Micronutrients in temperate forage crops grown in Sweden : species differences and effects of phenological development and soil

Abstract: Forage crops are the most important feed for ruminants and provide energy, fibre and protein as well as essential micronutrients such as cobalt (Co), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo) and zinc (Zn). In this thesis, different aspects of the micronutrient concentrations of forage crops were investigated in temporary grasslands in Sweden. Common and novel forage grasses (cocksfoot, meadow fescue, perennial ryegrass, tall fescue, timothy), legumes (birdsfoot trefoil, red clover, white clover) and forbs (caraway, chicory, ribwort plantain, salad burnet) were grown on contrasting soils in a pot experiment (two soils) and a field experiment (timothy, meadow fescue, red clover, white clover, chicory in mixtures, three sites, two soils in common with the pot experiment). The soils were micronutrient-poor/low pH (granitic, till), micronutrient-rich/high pH (alum shale, till) and the third field site had a low soil pH but average soil micronutrient concentrations granitic/sandstone, postglacial) compared to Swedish arable soils. It was found that micronutrient concentrations differ between forage species, but that varietal differences are few and small. Legumes and forbs generally had higher Co, Cu, Fe and Zn concentrations compared to grasses. There were few species differences in Mn concentrations whereas plant Mo concentrations was strongly affected by soil pH. Overall, the plant micronutrient concentrations appeared to be more dependent on the soil pH than on the soil micronutrient concentration (as extracted by EDTA and 7 M nitric acid). The micronutrient concentrations of the grass-legume mixture were affected by the differences in micronutrient concentrations between legumes and grasses, as well as by the botanical composition of the grasses and legumes in the mixture. An increased proportion of red clover was positively correlated to increased concentrations of several micronutrients in grass-legumes mixtures. The changes in micronutrient concentrations with phenological development at five defined stages were studied in three species. The decline of micronutrient concentrations was largest in timothy, less in perennial ryegrass and least in red clover. The generally low concentrations found in timothy were largely due to the high DM proportion of micronutrient-poor stems. It is concluded that of the forage crops, clover-rich swards harvested at an early development stage have higher micronutrient concentrations, although the soil characteristics also have a large impact.