Non-leguminous forbs in productive temporary grasslands
Plant diversity is often low in European grasslands with a major dominance of grass-clover mixtures. Recently there has been growing interest in multi-species grasslands for the purpose of increasing plant productivity and sustainability of grass-arable cropping system.
Chicory (Cichorium intybus L.), ribwort plantain (Plantago lanceolata L.) and caraway (Carum carvi L.) are three promising non-leguminous dicot forage herbs (hereafter forbs) that we have started to include in grassland mixtures.
Forbs have different physiological and morphological features than grass and clover species, with deep and dense root system and the ability to utilize nutrients from deeper soil layer. The forbs have shown potential to be an important component of grassland agriculture due to their high competitive strength, and ability to grow in adverse weather conditions and in low fertility soils.
In addition, the forbs may increase forage quality in terms of mineral nutrition and effect on palatability, meat quality and animal health. However, the forbs are not yet commonly grown grassland species. There have been very few studies including forbs in grassland mixture and sparse investigations in the dynamics of N processes in multi-species grasslands including forbs. Danish farmers still grow forbs in grasslands based on non-scientific local information.
Effect on N2-fixation, N transfer between legumes and non-legumes and soil N fertility
Our project MultiPlant conducted field and semi-field studies to determine how inclusion of forbs in the grassland mixture influences the dynamics of legume N2-fixation, N transfer between legumes and non-legumes and soil N fertility.
Overall, addition of forbs to perennial ryegrass-red clover mixtures (grass-clover-forb mixture) increased plant diversity and substituted the grass component without affecting herbage production, clover N2-fixation and N transfer. Furthermore, similar level of short-term residual soil N fertility was obtained.
Mixtures of grass-clover and forbs had yield comparable to red clover in pure stand and traditional grassland mixture of perennial ryegrass and red clover. Chicory and plantain showed strong competitive strength in the mixtures reflecting higher ability to utilize available above- and below-ground resources than caraway.
Including forbs in the grass-clover mixture did not change percentage of legume N derived from atmosphere (%Ndfa). The forbs affected the input of N from N2-fixation by affecting clover content in the harvested biomass. However, only the grass-clover mixtures containing high proportions of chicory had significantly decreased N2-fixation compared to clover pure stand and grass-clover mixture. The forbs relied very little on N transferred from the red clover and did not influence the N transferred to the grass in the mixture. The three forbs had similar ability to assimilate N transferred. Similarly, replacing the grass with the forbs did not change the residual soil N fertility to the subsequent cereal crop in rotation when the grasslands were cultivated.
Hence, our study encourages to design and implement diversified leys including forbs combining the valuable N inputs from legumes N2-fixation, efficient N uptake in grasses transferred from companion legume species and deep-soil nutrient acquisition by forb to produce herbage and quality forage without affecting short-term residual soil N fertility to subsequent crops in the rotation.
This study was supported financially by the Green Development and Demonstration Program (GUDP project MultiPlant) as part of the Organic RDD-2 programme, coordinated by the International Centre for Research in Organic Food Systems (ICROFS).
PhD student Nawa Raj Dhamala
Department of Agroecology
Professor Jørgen Eriksen
Department of Agroecology