Nitrogen transfer from a legume tree to the associated grass estimated by the isotopic signature of tree root exudates: A comparison of the 15N leaf feeding and natural 15N abundance methods

Characteristics of Nitrogen Uptake, Use and Transfer in a Wheat-Maize-Soybean Relay Intercropping System

“…The effect of N transfer among crops on N uptake and use N transfer was detected from legumes to cereals (Xiao et al, 2004;Ofosu-Budu et al, 1993;Johansen et al, 1996), e. g. from white clover to grass (Rasmussen et al, 2013), from legume tree to the associated grass (Sierra, et al, 2007) in some intercropping systems. In addition, there was bidirectional N transfer in rice-peanut intercropping system, the N transferred from peanut to rice reached 22.6 mg N plant-1, accounting for 10.9% of the total N accumulated in rice plants, which improved the yield of rice; the amount of transferred N from rice to peanut was much less than that from peanut to rice .…”

“…The increasing economic and environmental pressures of the excess N inputs have led researchers to focus on N transfer between crops (Elgersma et al, 2000;Chu et al, 2004;Sierra et al, 2007;Rasmussen et al, 2013). Previous studies revealed that N use efficiency was improved in faba bean-maize and wheat-faba bean intercropping systems thourgh interspecific N transfer from legume to the companion cereal crops Xiao et al, 2004).…”

“…N dilution and 15 N-leaf-labeling are the universal techniques used to estimate N transfer in the intercropping system (Xiao et al, 2004;Sierra et al, 2007;Høgh-Jensen, 2006).…”

Temporal Variation of N Isotopic Composition of Decomposing Legume Roots and Its Implications to N Cycling Estimates inN15Tracer Studies in Agroforestry Systems

“…After shoot harvest or pruning of the N donor plant, isotopic ratio of the N recipient plants peaks rapidly within a few days and then decreases slowly over time. Such patterns were observed in different experimental setups and N donor species: in studies applying both 15 N natural abundance and 15 N enrichment methods for the legume tree Gliricidia sepium under field conditions [4,5] and in pot culture [6], and in a study applying the 15 N natural abundance method for the herbaceous legume Canavalia ensiformis in pot culture [7]. The similarity of the results from different setups suggests that the unexpected isotopic patterns of the N recipient plants represent a general phenomenon independent of N donor species and the 15 N tracing technique applied.…”

“…Together these two factors may result in considerable temporal variation in the isotopic patterns of N released from organic inputs (e.g., roots decomposing after pruning), which is subsequently reflected in isotopic composition of the N recipient pools such as soil compartments, soil microbial biomass, or associated N recipient crops. Studies applying modelling approaches suggest that isotopic composition of N released from decomposing roots of a legume tree differs from that of living roots just before pruning, both with 15 N natural abundance and 15 N enrichment methods [6] and that N uptake from 15 N-enriched, surface-applied residues is best explained when decomposition rate constants are estimated separately for labile and stable residue fractions [14]. However, because isotopic heterogeneity is considered difficult to evaluate over time, N uptake or N transfer studies often assume that isotopic composition of an organic N source remains constant over the length of an experiment.…”