Classification and assessment models of first year byproducts nitrogen plant-availability from literature data

- Data from 37 studies were collected to assess byproducts N plant-availability.
- Three models of byproducts N plant-availability based on C/N were developed.
- Byproducts were classified into six categories of N efficiency.

Byproducts can provide an important amount of nutrients for crops and improve soils properties. According to their C/N, nitrogen (N) mineralization or immobilization may be observed after their application onto agricultural land. Therefore, an indicator is needed to assess byproducts N availability for crops. Thirty-seven studies from the scientific literature on N mineralization or immobilization after application to agricultural land under a wide range of climatic and experimental conditions were collected in order to elaborate models assessing non-composted byproducts N availability during the first growing season according to the C/N ratio. Four methods were used to evaluate N availability: incubation, apparent N recovery (ANR), relative N effectiveness (RNE) and fertilizer equivalence (FE). Since ANR was the model most related to C/N (R2 = 0.77), this model was used to define six categories of C/N. Results expressed in terms of FE were converted into RNE values. Although RNE is less precise than ANR, efficiencies of byproducts were expressed in terms of average RNE because it is the most appropriate for fertilization grids. Therefore, depending on C/N of non-composted byproducts, six categories were defined. i) high mineralization: + 66% RNE and 5 ≤ C/N, ii) moderate mineralization: + 33% RNE and 5 < C/N ≤ 16, iii) low mineralization: + 9% RNE and 16 < C/N ≤ 38, iv) low immobilization: − 9% RNE and 38 < C/N ≤ 90, v) moderate immobilization: − 27% RNE and 90 < C/N ≤ 140, and vi) high immobilization: − 55% RNE and C/N > 140.

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