Soil Use Manage. 2019;35:323–333. wileyonlinelibrary.com/journal/sum | 323 © 2018 British Society of Soil Science 1 | INTRODUCTION Silage maize is an important forage crop on NW European farms with intensive dairy cattle production. On these farms, cattle manure is most often returned to the field at rates to meet the nitrogen (N) needs of the maize crop, leading to ac- cumulation of phosphorus (P) in the soil (Rubæk, Kristensen, Olesen, Østergaard, & Heckrath, 2013). Availability of P during the early growth of maize has a major impact on final yields (Gavito & Miller, 1998; Plénet, Etchebest, Mollier, & Pellerin, 2000). Therefore, to ensure an efficient P supply in the period after germination, placement of mineral fertilizer-P at maize planting has become routine even on soils receiving generous inputs of P in animal manure. In the year of applica- tion, however, the crop recovers only 15%–30% of P applied with mineral fertilizers (Johnston, Poulton, Fixen, & Curtin, 2014) confirming that the release of plant available P from the pool of soil P, accumulated from previous applications of manure and mineral fertilizers, is essential to sustain subse- quent maize growth and achieve optimum crop yields. Animal manures differ not only in their concentration of total-P but also in their contents of different P compounds (Sharpley & Moyer, 2000; Toor, Hunger, Peak, Sims, & Sparks, 2006). Water extractable manure-P, considered a Received: 6 September 2018 | Revised: 3 December 2018 | Accepted: 5 December 2018 DOI: 10.1111/sum.12477 RESEARCH PAPER Long-term effects of animal manure and mineral fertilizers on phosphorus availability and silage maize growth Jingying Jing | Julie T. Christensen | Peter Sørensen | Bent T. Christensen | Gitte H. Rubæk Department of Agroecology, Aarhus University, AU-Foulum, Tjele, Denmark Correspondence Gitte H. Rubæk, Department of Agroecology, Aarhus University, AU-Foulum, Tjele, Denmark. Email: gitte.rubaek@agro.au.dk Funding information Ministry of Environment and Food of Denmark–Green Development and Demonstration Program Abstract A better appraisal of the plant availability of soil phosphorus (P) added with animal manure is crucial to alleviate environmental impacts from over-application of P. This study compares the availability of P to maize in the Askov long-term experiments using unmanured plots and plots receiving corresponding rates of nitrogen (N), P and potassium (K) in mineral fertilizers or manure. Total-P and water extractable P (Pw) in soil, and plant height, dry weight, P concentration and P uptake were determined in early August. Final yields were determined in late October. Soil Pw was similar for plots receiving corresponding rates of P in mineral fertilizer or manure form. With a strong relationship between Pw, and maize growth and final yields, Pw was a reliable indicator of P availability to maize. Plant dry weight, P concentration and P uptake in early August were 23%, 8% and 31% higher, respectively, for maize grown on soil receiving manure compared with mineral fertilizer, while final maize yield in late October was 13% higher. Plant height and dry weight determined in early August sug- gested that maize development at this growth stage defined final maize yield. We conclude that the availability of P was similar after long-term application of corre- sponding rates of P in animal manure and mineral fertilizers, and that animal manure improves the growth of maize compared to mineral fertilizers. This is ascribed to mi- cronutrients and residual N effects from previous additions of manure. KEYWORDS cattle slurry, long-term experiment, maize, mineral fertilizer, water extractable P