Project code: 22014107
Contract period: 01.01.2008
Budget: 325,212 Euro
Purpose of research: Applied research
Under current economic conditions only a few crops are grown on dry sandy soils in northern Germany. Known issues of crop rotations with high proportion of maize increase because of the low yield level in this regions and the absence of crops with positive effects for the soil fertility.
White and yellow sweet clover (Melilotus albus and M. officinalis) are deep-rooted overwintering legumes with high biomass yields on sandy soils with low precipitation. The cultivation of sweet clover promotes humus formation, improves soil structure, reduces the need of nitrogen-fertilizer and increases biodiversity. The biomass can be used as energy plant for biogas-fermentation. It is not suitable for modern animal nutrition.
The objective of literature review and field experiments was the description of the growth of sweet clover and cultivation methods. Origin tests, trials for sowing time, liming, weed control, nitrogen-fertilization and the follow crop maize were the basis for cultivation recommendations. The occurrence of sweet clover weevils was observed for two years. Also experiments for ensiling and biogas fermentation were carried out with sweet clover biomass.
This work assesses the yield potential of biennial sweet clover of 25 – 80 dt DM ha-1 in the first year and 100 – 150 dt DM ha-1 in the second year. This corresponds to methane yields of 1200 - 2850 m3 CH4 ha-1 and about 3000 m3 CH4 ha-1.
Essential ingredients depend on the development of the plants. Known data listed in feed tables were validated. Data for the stages „before winter“, „before bud“, „bud“ and „after flowering“ were added.
Because of its short life cycle sweet clover is ideal for arable crop rotations. It grows well if it is sown between March and May. Sowing on dates later than the beginning of July has low yields in first and second year. Cover crops, mixed seed and sowing dates between mid-May and beginning of July were not tested.
Sweet clover can be terminated at variable dates. The subsequent crop can sow between spring and autumn. Sweet clover has its maximum growth at full bloom stage in the second year. Later harvests give lower biomass yield. Early termination dates give more N-yield for the following crop but lower sweet clover biomass. Sweet clover has a good preceding crop effect for subsequent maize crop.