Phosphorus Uptake in Six Selected Scandinavian Wheat and Barley Cultivars at Low Soil Phosphorus Availability as Related to Root Hair Length

Lower soil phosphorus (P) levels are to be expected if more sustainable agriculture practices (organic farming, low-input farming) are adopted. Crop plants can be adapted to lower soil P levels by selecting and breeding for higher P efficiency. Longer root hairs are found to enhance the P efficiency of cereals by increasing the P uptake. In this study, three pairs of Swedish and Norwegian cereal cultivars (wheat cvs. NK0058 and Diamant; 6-row barley cvs. NK94682 and Herse; 2-row barley cvs. Tyra and Herta), with respectively short and long root hairs within each pair as measured in solution culture were grown. The cultivars were grown at four soil P levels (P0: 35 mg P-AL kg-1 soil; P16: 49 mg; P32: 87 mg; P48: 130 mg) in a long-term PK fertilisation field trial. The choice of cultivars was based on root hair lengths measured in a previous solution culture experiment. The aim of this study was to investigate the effect of cultivar and soil P level on P concentration (P utilisation efficiency), P uptake efficiency, grain chemical composition, root hair length, dry matter production, grain yield, root growth, 1000-grain weight, hectolitre-weight and phenological development. The results showed higher dry matter production and grain yield at low soil P levels in Diamant, Herse and Herta than in NK0058, NK94682 and Tyra, respectively, indicating a higher P efficiency in these cultivars. Total P uptake at low soil P levels was also higher, and the P concentration (mg P g-1 shoot dry matter, P utilisation efficiency) tended to be lower, suggesting higher P uptake and P utilisation efficiencies in these three cultivars. Probably the P uptake efficiency accounted for most of the variation between the cultivars, whereas variation in the P utilisation efficiency was of less importance. Dry matter production, grain yield and P uptake generally increased with increasing soil P level. However for most cultivars, except for the modern cultivar Tyra, dry matter and grain yield decreased at the highest soil P level. As soil P level increased, the differences in yield and P uptake within the three pairs of cultivars diminished, suggesting that the factors increasing the P uptake at low soil P are less important at high soil P level. Recordings of phenological development and grain moisture content confirmed that increasing soil P level increases the rate of development in cereals. 1000-litre weight and hectolitre-weight were generally found to increase with increasing soil P level. Root growth in the topsoil was found to increase as the soil P level increased. The root hairs grew longer in field soil than in the previous solution culture experiment. The ranking of cultivars with regard to root hair was only in part similar to that found in solution culture, and the differences in root hair length was much smaller or insignificant in this study as compared to the solution culture experiment. Hence, ranking of cultivars in terms of root hair length might prove difficult. A previous study reported longer root hairs in barley as a response to lower soil P level. In contrast, these results suggested the opposite. The higher P uptake in Diamant, Herse and Herta might be due to longer root hairs. However, it is suggested that variations in other factors such as root exudation of organic acids and phosphatase and lowering of rhizosphere pH were as important factors for the higher P uptake. Grain concentrations of N, P, K, Ca and Mg were consistent with former findings. There were no effects of cultivar or P level on the grain concentrations of N, Ca and Mg in this study. In conclusion, this study suggested that there is great variation in P efficiency between cereal genotypes. This may only in part be explained by different root hair lengths. Adapting crops to lower soil P levels, by selection and breeding, is thus a possible means of increasing the sustainability of the agroecosystem.