Advantages of grass-legume mixture for improvement of crop growth and reducing potential nitrogen loss in a boreal climate
A three-year field experiment was established to assess intercropping for sustainable forage production in Finland. In split-plot design, fertilizer treatment with unfertilized control, organic fertilizer, and synthetic fertilizer was the main plot factor, and crop treatment with fallow, red clover (Trifolium pratense), timothy (Phleum pratense), and a mixture of red clover and timothy was the sub-plot factor. Dry matter, carbon and nitrogen yields in mixture plots were highest with relatively high N% and the optimum C:N ratio (p < 0.05). Fertilization increased annual yields of mixture and timothy but not that of red clover. Soil NO3-N changed over time (p < 0.05) and was highest in fallow, followed by red clover, mixture, and timothy (p < 0.05), and the decrease during late growing season was smaller in the mixture and timothy plots. At the end of the experiment, soil C/NO3-N ratio was higher in timothy and mixture while lower in red clover and fallow plots (p < 0.05), and the relationship between soil DNA and NO3-N content may indicate that the potential nitrogen loss was lower in mixture and timothy than that in fallow and red clover plots.