Mineralisation of soil organic phosphorus with different P sources: results from three long-term field experiments

Abstract

Phosphorus (P) is a major nutrient for crops, and its application to agricultural soils as inorganic or organic fertilizer is crucial for optimising P availability to plants to sustain and ensure 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. The rate was determined by applying to SOP the modelling approach developed by Hénin and Dupuis in 1945 for soil organic carbon. We used three French long-term field experiments (LTFEs) on P fertilisation combining different P rates (0–112 kg P ha-1yr-1), applied for decades 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 topsoil SOP and soil inorganic phosphorus (SIP) contents and annual crop measurements. For the three LTFEs, the initial SOP stocks were 446, 595, and 1145 kg P ha-1, the P amounts exported during harvest were 26.5, 26.6, and 25.3 kg P ha-1yr-1, and the P remaining in the topsoil as crop residues were 15.0, 14.4, and 11.5 kg P ha-1yr-1 with significant differences across yields, plant organs, and fertilisation treatments. During the post-harvest year, 2.5, 7.9, and 11.0 kg P ha-1yr-1 were incorporated into SOP by the decomposition of crop residues and OWPs. 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 did not change significantly with the years of cropping and fertilisation, irrespective of P fertilisation. The SIP stocks closely corresponded to the cumulative P budget (i.e., cumulative sum of applied P – exported P).