Estimating the contribution of nitrogen from legume cover crops to the nitrogen nutrition of grapevines using a 15N dilution technique

The aim of this controlled environment experiment was to quantify the distribution of leaf-fed-¹⁵N and canopy fed-¹³C within nodulating, non-nodulating or N fertilized non-nodulating Cicer arietinum L. and in their surrounding rhizosphere soil, excluding soil?+?root respiration. Nodulating chickpea partitioned 32% of its total N and 27% of its total recoverable C below-ground, of which only 50% of N and 36% of C were in the clean root fraction. Non-nodulating chickpea allocated equal recoverable C but slightly less N (28%) below-ground but lost less C from plant induced below-ground respiration. The importance of this below-ground partitioning for crop systems C and N balances is highlighted by their large (45% and 33%, for N and C, respectively) contribution to the total plant derived residue (recyclable) fraction. Recovered ¹⁵N and ¹³C were greater (P?15N and 3.2 mg ¹³C core^?1) than in the inner-rhizosphere soil (detached from roots during freeze-drying; 18?µg ¹⁵N and 67?µg ¹³C core^?1) in relation with the relative size of these compartments. This highlights the significance of the outer-rhizosphere soil when estimating C and N budgets and quantifying rhizodeposition, and the benefit of a double (¹⁵N, ¹³C) isotope approach to determine this flow against large background soil C and N pools.