Root-and-shoot growth and yield of different grass-clover mixtures

The effect of different grass-clover mixtures on yield, root biomass, root length and the symbiotically fixed N quantity was investigated in a two-factorial field experiment at a location in Freising (Germany). Three grass-clover mixtures with different compositions were tested in two different management systems (various harvest and mulching): a standard mixture (SM) consisting of 40% legumes and 60% grass; a multi-species legume-grass mixture suitable for forage use (FM) and a mixture adapted for green manure (GM) with a high share of legumes (70%) and herbs (5%). The botanical composition shifted in favour of the amount of grass in mulching variants. Certain herbs managed to do well in the mixtures despite intensive management with four cuts. Grass-clover mixtures with herbs and legumes achieved high shoot yields (15.9-16.5 t ha-1). Due to its lower share of grass, GM showed the smallest root length (95 km m-2). FM and SM achieved a length of 130 km m-2 (depth: 0-30 cm). The measurement of root biomass gave high dry matter yields (FM 8.1 t ha-1, GM 6.5 t ha-1, SM 5.3 t ha-1). N uptake depended on the share of legumes and on the management system. The amount of symbiotically fixed nitrogen that accumulated in shoots and roots was about 90 kg N ha-1 (SM), 290 kg N ha-1 (FM) and 340 kg N ha-1 (GM). The C input was increased by mulching systems and a high root biomass. FM has shown possibilities for optimizing grass-clover mixtures with respect to the root parameters, effects on soil fertility and increasing C input without a decline in yield. The rooting patterns can be used to compose grass-clover mixtures with a higher root biomass and root penetration.