In the land of plenty

Catch crops (CC) reduce nitrate leaching, and may resolve a major concern in nitrogen (N) intensive agriculture. CC efficiency depends on N uptake ability, which is related to root development, biomass partitioning, and competition with soil microbes. We investigated the effect of N addition on this with three CC species.Three CC species were grown in pots with three N concentrations. Shoot and root biomass, C:N content, and specific root length were determined, whereas residual N, dissolved organic N (DON) and C, and microbial biomass N and C were measured.Addition of N did not consistently effect plant biomass nor its partitioning, probably because of overall high N. However, CC did reduce residual N, and so did soil microorganisms, likely facilitated by C-release from roots. Moreover, plant presence reduced DON, likely through uptake by soil microorganisms, partly followed by plant uptake.CC not only take up residual N themselves, but also trigger considerable N uptake by soil microorganisms that thrive on C-release from roots. This plant-microbe-nitrogen interaction has to be considered when evaluating CC systems. It remains unclear to which extent soil microorganisms immobilise inorganic N and mineralise or take up DON.