Efficient utilization of various phosphorus (P) sources for producing optimum yields in P-deficient conditions requires knowledge of best management under changing weather conditions. In this study, barley (Hordeum vulgare) was grown in an extremely P-deficient soil with variable moisture conditions. During a wet growing period, utilization of P from dairy cow manure (DCM), fox manure (FM) and meat and bone meal (MBM) was compared with the utilization of P from superphosphate (SP) with concomitant effects on grain yield and quality. High P application rates were necessary to compensate for severe yield losses due to waterlogging. Only 7 kg P/ha was required for optimum yield in less waterlogged conditions, while 43 kg P/ha was needed in waterlogged conditions. In both moisture conditions, broadcast DCM-P increased grain yield similar to banded SP-P, although P acquisition was lower in early growth stages. FM-P and MBM-P were less efficiently utilized.Waterlogging also depressed yield quality when P was applied. Extreme rainfall events are predicted to become more frequent at northern latitudes. As an alternative to higher P fertilizer rates, improving soil drainage could be a favourable, longterm measure for better utilization of applied P and soil P resources, even at very low soil P status.nutrient uptake, root growth, soil test P, yield quality 1 | INTRODUCTION Phosphorus (P), an essential plant nutrient, is supplied to crops from soil P reserves, mineral fertilizers or P-rich by-products, for example manures. The need for P application on a certain field depends on its soil test P (STP) value, and above a soil type-dependent critical STP, P fertilization gives negligible, if any, yield response (Valkama, Uusitalo, & Turtola, 2011;Valkama, Uusitalo, Ylivainio, Virkaj€ arvi, & Turtola, 2009;Valkama, Virkaj€ arvi, Uusitalo, Ylivainio, & Turtola, 2016). Below the critical STP, however, yield fluctuates strongly and is obviously affected by factors other than STP only. Due to the strong adsorption of P in mineral soils, P availability is diffusion-controlled (Barber, 1961), and especially in low STP soils, continuous root growth is essential for P uptake (Sheppard & Racz, 1984).Extreme weather conditions, such as periods of drought or heavy rain, are predicted to occur more frequently in the boreal zone due to future climate change, causing both water stress and waterlogging. In waterlogged conditions, root growth of barley has been shown to cease, depressing grain yield (Trought & Drew, 1980). Decreased uptake of P, nitrogen (N), potassium (K), magnesium (Mg) and calcium (Ca) due to waterlogging has been observed in pot experiments (Drew & Sisworo, 1979;Leyshon & Sheard, 1974;Trought & Drew, 1980) and when using nutrient solution (Wiengweera & Greenway, 2004).In Finland, the annual P output in manure of cattle, pig, fur animals and poultry is about 17.5 million kg, corresponding to manure P requires knowledge of its plant availability, which may depend on the animal species and the diet (Ylivainio,...