Legacy effects of diversity in space and time driven by winter cover crop biomass and nitrogen concentration

Plant diversity can increase nitrogen cycling and decrease soil‐borne pests, which are feedback mechanisms influencing subsequent plant growth. The relative strength of these mechanisms is unclear, as is the influence of preceding plant quantity and quality. Here, we studied how plant diversity in space and time influences subsequent crop growth. During 2 years, we rotated two main crops (Avena sativa,Cichorium endivia) with four winter cover crop (WCC) species in monocultures and mixtures. We hypothesized that, relative to monocultures,WCCmixtures promoteWCCbiomass (quantity) and nitrogen concentration (quality), soil mineral nitrogen, soil organic matter, and reduce plant‐feeding nematode abundance. Additionally, we predicted that preceding crops modifiedWCClegacies. By structural equation modelling (SEM), we tested the relative importance ofWCCshoot biomass and nitrogen concentration on succeeding crop productivity directly and indirectly via nitrogen cycling and root‐feeding nematode abundance. WCCshoot biomass, soil properties and succeedingAvenaproductivity were affected by first‐season cropping, whereas subsequentCichoriumonly responded to theWCCtreatments.WCCmixtures’ productivity and nitrogen concentration showed over‐ and under‐yielding, depending on mixture composition. Soil nitrogen and nematode abundance did not displayWCCmixture effects. Soil organic matter was lower than expected afterRaphanus sativus+Vicia sativamixture. SubsequentAvenaproductivity depended upon mixture composition, whereas finalCichoriumproductivity was unresponsive toWCCmixtures.SEMindicated thatWCClegacy effects on subsequentAvena(R2 = 0.52) andCichorium(R2 = 0.59) productivity were driven byWCCbiomass and nitrogen concentration,although not by the quantified soil properties. Synthesis and applications. Through understanding plant–soil feedback, legacy effects of plant species and species mixtures can be employed for sustainable management of agro‐ecosystems. Biomass and nitrogen concentration of plants returned to the soil stimulate subsequent plant productivity. Winter cover crop quantity and quality are both manipulable with mixtures. The specificity of spatial and temporal diversity effects warrants consideration of plant species choice in mixtures and rotations for optimal employment of beneficial legacy effects.