Soil organic phosphorus mineralisation rate in cropped fields receiving various P sources

International audience

English. Phosphorus (P) is a major nutrient for crops, and its application to agricultural soils as inorganic or organic fertiliser is crucial for optimising P availability to plants to sustain food production. The mineralisation of soil organic phosphorus (SOP) may play a significant role in supplying plant-available P. This study aimed to determine the SOP mineralisation rate in soils cropped under contrasting agropedoclimatic conditions. By applying the modelling approach developed by H & eacute;nin and Dupuis in 1945 for soil organic carbon, to SOP, we were able to determine the rate of SOP mineralisation. We used three French long-term field experiments (LTFEs) on P fertilisation, which combine different P doses (0-112 kg P ha(-1) yr(-1)), applied for decades (14-18 years) as superphosphate or various organic waste products (OWPs), on different soil types, and different annual crop successions. These databases include long time-series data of SOP and soil inorganic phosphorus (SIP) stocks and annual crop measurements. For the three LTFEs, the initial SOP stocks were 446, 595, and 1145 kg P ha(-1). During the post-harvest year, 2.5, 7.9, and 11.0 kg P ha(-1) yr(-1) were incorporated into SOP by the decomposition of crop residues and OWPs. Conversely, 12.5, 27, and 46 kg P ha(-1) yr(-1) were released as phosphate ions and contributed significantly to the plant-available soil P. The rates of SOP mineralisation, 2.1, 5.4, and 11.2 kg P ha(-1) yr(-1), differed significantly across the LTFEs. The SOP stocks remained stable across time, and during repeated crop production and fertilisation, irrespective of P treatments. The SIP stocks closely corresponded to the cumulative P budget. Overall, the average SOP mineralisation rate is low and appears to play a minor role in the plant-available soil P and its uptake.