Using the 15 N natural abundance for a quantitative approach to N recovery from organic fertilizers

ABSTRACT The influence of organic inputs, such as manure and compost, on the 15 N values of growing plants suggests it may be possible to use of 15 N natural abundance (NA) as a nitrogen (N) tracer. This study aimed to verify the feasibility of using the TM15 N values to estimate compost-N recovery by plants. A field experiment was carried out by growing head lettuce, carrots and broccoli in sequence under increasing levels of compost (randomized complete blocks, six doses, four replicates). The compost was produced on-farm using horse bedding manure and vegetable waste. We found a positive and significant correlation between vegetables yield × TM15 N-plant as well as between N-harvested × TM15 N-plant, alongside the response to the increasing levels of compost. Positive and significant (α = 0.05) correlations were found for carrots (R = 0.91 and 0.95) meanwhile, no significant correlations were found for broccoli (R = 0.60 and 0.66). Lettuce did not respond to compost levels. We applied an equation to estimate compost-N recovery by carrots based on the variation pattern that was found in TM15 N-plant. A positive and significant correlation between TM15 N-plant and plant yield (or N harvested) is the first condition to obtain valid estimates. The estimated compost-N recovery for carrots was from 4.7 to 9.1 %, respectively, at 0.5 and 2.0 kg m -2 of compost (dry basis). Sources of uncertainty are also discussed, and include intra-plant 15 N fractionation, which might require further studies of sampling strategies. This study shows the theoretical and experimental basis of using compost (dry basis). Sources of uncertainty are also discussed, and include intra-plantN to estimate organic fertilizer-N recovery by crops.