Scarcity of P-fertilisers: humic-complexed phosphate as an adaptive solution for wheat and maize under rainfed conditions

The current context of food security and global geopolitical crises calls for proactive efforts to seek adaptive strategies for limited resources in agriculture. The production of phosphatic-based fertilisers has caused a substantial depletion of natural phosphorus (P) reserves, raising concerns about price increases due to the growing demand for P. The aim of the study is to assess whether the use of liquid organo-mineral P-complexes can be an adaptive strategy to address the issue of the limited P-fertiliser resource. A complete randomised block design was implemented with three replicates, spanning two contrasting cropping seasons under a Mediterranean climate with reduced tillage and rainfed conditions. The study aimed to assess the response of a durum wheat–maize rotation to various rates of liquid organo-mineral P-complexes (humic-complexed phosphate; HCP) in comparison to granular triple superphosphate (TSP). The evaluation focused on several parameters, including P availability, plant architecture, dry matter accumulation, grain yield and yield components and P use efficiency (PUE) for both durum wheat and maize. The results revealed that applying HCP at a rate of 4 or 8 kg/ha increased soil P availability on average by 66% and 144%, respectively, compared to the control (no P-fertilisation), although a significant interaction with the monitoring year emerged. For wheat, applying HCP at a rate of 8 kg/ha of P resulted in higher grain yield (+15%), protein content (+0.9%) and P uptake (+48%) than the control on average considering both monitoring years. In the season characterised by favourable rainfall patterns, the application of HCP at 5 or 10 kg/ha of P for maize showed similar effects in terms of soil P availability, dry matter accumulation, grain yields and PUE. Conversely, in the season marked by a deficiency in summer precipitation, low PUE for maize was observed for HCP fertilisers, although they remained positive, unlike the case of TSP. Using HCP in conservation agriculture appears promising as an adaptive solution to address P-fertiliser scarcity, especially amid food security challenges and global crises. However, further studies are required to validate these findings in diverse pedo-climatic contexts and cropping systems.