Estimating soil available nitrogen with a hot H2O2/KCl extraction

Appropriate and simple analysis methods for an accurate estimation of soil N mineralization potential are required to optimize N fertilizer recommendations. We used soils from non-cultivated and cultivated plots in central Côte d’Ivoire to investigate the quantum of ammonium (NH4 ) that could potentially be mineralized. The soil was first treated with H2O2 at 60°C for 2, 4, 6 or 8 h (and referred to as hot extraction) or at room temperature (25°C and referred to as 0 h). The NH4 -N extracted increased with the heating time but decline slightly after 6 h. More NH4 -N was extracted in non-cultivated plots with the hot extraction, and the difference was significant at 6 h. The NH4 -N measured with the hot extraction correlated significantly with the CEC. We obtained the strongest correlation in non-cultivated plots (r = 0.88, p < 0.0001) at 6 h, and the weakest also at 6 h but in cultivated plots (r = 0.64, p < 0.0001). Similarly, we observed a significant correlation between the NH4 -N extracted and the amount of N taken up by rice seedlings grown in pots, and the best correlation was again at 6 h. The study illustrated that N mineralization with H2O2 at 60°C for 6 h is an appropriate procedure for extracting potentially mineralizable NH4 -N in soils.