Simulation of soil phosphorus dynamics and crop yield for organic and mineral fertilization treatments at two long-term field sites

The efficacy of phosphorus (P) based fertilizers is frequently compromised by soil dynamics that render much of the applied P unavailable for crops. This study aimed to: (i) validate a new P model's prediction of plant-available P; (ii) analyze the effects of organic versus mineral fertilization on P availability and crop yield; and (iii) examine temporal changes in P pools under various fertilization regimes. Data were collected from two long-term field trials, Dikopshof and Bad Lauchstädt, in Germany, using organic (FYM), mineral (MIN), a combination of organic and mineral (MIX) fertilizers, and unfertilized treatments. The AgroC model, incorporating a new P module, accurately predicted P dynamics in cropped plots. At both sites, MIX presented the highest yield, P removal, total P and available soil P. After 120 years of repeated P fertilization, simulations at Dikopshof revealed a positive P balance in MIN (11.1 % with observed 13 %) and in MIX (15 % with observed 15 %), but negative in FYM (-4.9 % with observed -5 %). However, at Bad Lauchstädt, the P balance was negative in all treatments except in MIN (+1.04 %), indicating P depletion. Among crops, cereals showed the most variated yields, with P-use efficiency ranging from 50 % to 99 %, while sugar beet presented the highest P-use efficiency (up to 122 %). The lowest P application rates exhibited, FYM treatment, the highest P-use efficiency for all crops. Model pools were successfully linked to field-measured soil P fractions using CAL and DGT methods, providing initial predictions of various soil P fractions across different fertilization strategies.