Quantifying biological nitrogen fixation of different catch crops, and residual effects of roots and tops on nitrogen uptake in barley using in-situ 15N labelling

Abstract

Background and aims Contributions of legume-based catch crops (LBCCs) to succeeding cereals may be significant. We quantified biological N fixation (BNF) and residual N effects of contrasting CC tops and roots. Methods BNF of three LBCCs (red clover, winter vetch, perennial ryegrass-red clover mixture) was quantified in microplots by 15 N labelling. Their residual effects on spring barley were tested against two non-LBCCs (perennial ryegrass, fodder radish) after spring incorporation of CC tops or roots in monoliths. Results Total N accumulated in LBCCs was 153-226 kg N ha −1 , of which 62-66 % was derived from BNF in tops and 31-46 % in macro-roots (0-18 cm soil). Macro-roots represented 31-50 % of total plant N.LBCCs showed similar capacity for soil N extraction as non-LBCCs. After incorporation of LBCC residues, the dry matter and N yields of spring barley were comparable to the effect of 50 kg N fertilisation ha −1 , whereas no extra N uptake was derived from non-LBCCs. The 15 Nbased N fertiliser values of LBCC tops were 34-47 % against 26-29 % for non-LBCCs. Conclusions LBCC roots contributed substantial amounts of N to the system, a source that is usually underestimated. N immobilisation after incorporation of non-LBCCs may hamper the growth of following main crops especially after removing tops.Keywords Legume-based catch crop . Biological N fixation . Soil N uptake . Residual N effect . 15 N isotope dilution . Spring barley Abbreviations N N i t r o g e n DM Dry matter CC Catch crop (Non-)LBCC (Non-)legume-based catch crop BNF Biological N fixation CL Red clover GC Perennial ryegrass-red clover mixture WV Winter vetch FR Fodder radish GR Perennial ryegrass CO Control without catch crops in large plots Plant Soil

Reviews and syntheses: Review of causes and sources of N<sub>2</sub>O emissions and NO<sub>3</sub> leaching from organic arable crop rotations

“…Bhogal et al (2016) showed that for pig slurry and poultry layer manure with a C : N org of 9-12 : 1, up to 70 % of the organic N was mineralised after five growing seasons, whereas in cattle slurry and straw-based farmyard manure with a C : N org of 10-21 : 1, only 10 %-30 % of N was mineralised (net). For crop residues with a high C : N content there will be initial immobilisation and the net mineralisation may only start very late or after the growing season of the main crop (Li et al, 2015b). The mineralisation process of the more stable N can continue over years to decades.…”

“…5.3). CCs containing legumes have a lower C : N ratio than CCs without legumes, which enhances the N fertiliser value for the following crop (Li et al, 2015b).…”

Traditional agriculture: a climate-smart approach for sustainable food production

“…They add nitrogen to the agroecosystem either by fixation or by improving the N-mineralization, consequently declining synthetic fertilisers inputs and their resultant GHG emissions (Dabney et al 2001;Thorup-Kristensen et al 2003;Fageria et al 2005;Schipanski et al 2014;Li et al 2015;Alvarez et al 2017). Legume cover crops provide sufficient nitrogen to crops grown in rotation and consequently reducing external inputs of the synthetic fertilisers (Magdoff and Weil 2004;Gselman and Kramberger 2008;Robacer et al 2016).…”

Contributions from carbon and nitrogen in roots to closing the yield gap between conventional and organic cropping systems

“…In the current study, the effect of catch crops and the application of manure were evaluated for both organic and conventional rotations. The legume‐based catch crops in the organic cropping systems contributed N to the cropping systems through both biological N fixation (Li et al ., 2015b) and through retaining N by recycling this in above‐ and belowground plant residues.…”