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Nitrogen fertiliser replacement values for organic amendments appear to increase with N application rates
- Hijbeek, R., ten Berge, H.F. M., Whitmore, A.P., Barkusky, D., Schröder, J.J., van Ittersum, M.K.
- Nutrient cycling in agroecosystems 2018 v.110 no.1 pp. 105-115
- animal manures, crop residues, crop yield, crops, farmers, fertilizer rates, fertilizer requirements, long term experiments, nitrogen, nitrogen fertilizers, nutrient use efficiency, slurries, soil types, Europe
- Nitrogen (N) supply from organic amendments [such as farmyard manure (FYM), slurries or crop residues] to crops is commonly expressed in the amendment’s Nitrogen Fertiliser Replacement Value (NFRV). Values for NFRV can be determined by comparison of crop yield or N uptake in amended plots against mineral fertiliser-only plots. NFRV is then defined as the amount of mineral fertiliser N saved when using organic amendment-N (kg/kg), while attaining the same crop yield. Factors known to affect NFRV are crop type cultivated, soil type, manuring history and method or time of application. We investigated whether long-term NFRV depends on N application rates. Using data from eight long term experiments in Europe, values of NFRV at low total N supply were compared with values of NFRV at high total N supply. Our findings show that FYM has a significant higher NFRV value at high total N supply than at low total N supply (1.12 vs. 0.53, p = 0.04). For the other amendment types investigated, NFRV was also higher at high total N supply than at low total N supply, but sample sizes were too small or variations too large to detect significant differences. Farmers in Europe usually operate at high rates of total N applied. If fertiliser supplements are based on NFRV of the manure estimated at low total N supply, N fertiliser requirements might be overestimated. This might lead to overuse of N, lower N use efficiency and larger losses of N to the environment.