In Scandinavia high losses of soil and particulate‐bound phosphorus (PP) have been shown to occur from tine‐cultivated and mouldboard‐ploughed soils in clay soil areas, especially in relatively warm, wet winters. The omission in the autumn of primary tillage (not ploughing) and the maintenance of a continuous crop cover are generally used to control soil erosion. In Norway, ploughing and shallow cultivation of sloping fields in spring instead of ploughing in autumn have been shown to reduce particle transport by up to 89% on highly erodible soils. Particle erosion from clay soils can be reduced by 79% by direct drilling in spring compared with autumn ploughing. Field experiments in Scandinavia with ploughless tillage of clay loams and clay soils compared to conventional autumn ploughing usually show reductions in total P losses of 10–80% by both surface and subsurface runoff (lateral movements to drains). However, the effects of not ploughing during the autumn on losses of dissolved reactive P (DRP) are frequently negative, since the DRP losses without ploughing compared to conventional ploughing have increased up to fourfold in field experiments. In addition, a comprehensive Norwegian field experiment at a site with high erosion risk has shown that the proportion of DRP compared to total P was twice as high in runoff water after direct drilling compared to ploughing. Therefore, erosion control measures should be further evaluated for fields with an erosion risk since reduction in PP losses may be low and DRP losses still high. Ploughless tillage systems have potential side‐effects, including an increased need for pesticides to control weeds [e.g. Elytrigia repens (L.) Desv. ex Nevski] and plant diseases (e.g. Fusarium spp.) harboured by crop residues on the soil surface. Overall, soil tillage systems should be appraised for their positive and negative environmental effects before they are widely used for all types of soil, management practice, climate and landscape.

Available phosphorus (P) is one of the most important factors affecting crop production worldwide. Study on improving plant P uptake is hence of global importance. We have investigated the responses of root morphology and root-exuded organic acids to low P availability in three important food crops (barley, canola and potato) with divergent root traits using a hydroponic culture system. Results showed that plants evolved divergent adaptations of root morphology and exudation as a response to low P availability. These results could underpin future efforts to improve P uptake of the three crops which are important for future sustainable crop production.

Purpose The main purposes of the study were to assess the NPK fertilizer value of biogas digestates in different soils and to evaluate the risk of unwanted nutrient leaching. Methods The fertilizer value of digestates from anaerobic digesters was investigated in a greenhouse pot experiment with wheat in three different soils; silt, loam and sand. The digestates were based on different feedstock and had a low, dry matter content. The fertilizing effect of digestates was compared to mineral fertilizer and manure. To investigate the fate of excess nutrients in soil after the growing season, the pots were leached after harvest. A complementary soil column leaching experiment without plants was carried out in the laboratory. Results The concentration of ammonium in digestates provided a good indicator of the nitrogen fertilizer value of the digestates. In the silt and loam, the ammonium N fraction in digestates had a fertilizer replacement value equal to that of mineral fertilizer N, whereas the replacement value was higher in the nutrient poor sandy soil. Digestates often have a ratio between nitrogen, phosphorus and potassium which is not favourable for plant growth. However, the suboptimal balance did not result in reduced plant growth or unwanted leaching from soil. Conclusions The results show that digestates from biogas production based on fundamentally different feedstock are promising as NPK fertilizers. The N fertilization can simply be based on the digestate NH 4 + concentration and, at least for wheat production, considerable variation in the concentrations of K and P can be tolerated.

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Constructed wetlands consist of soil filled beds with aquatic plants. Wastewater is treated when flowing through these beds. It has been questioned if constructed wetlands will be able to operate when subjected to cold conditions in sub arctic regions. Experience from Norway indicates that significant biological activity occurs at temperatures between 0 and 5°C, and that high removal rates of nutrients and organic matter are achieved in ponds and soil amended with wastewater at these temperatures. Results from using constructed wetlands in Denmark, Sweden and North America show that winter performance is not significantly reduced as compared to other seasons, but in order to obtain high removal of organic matter and nitrogen in cold climates aerobic pretreatment is probably a prerequisite. Cold climates may also require careful installation of larger and deeper systems with a longer detention time. Results of 15 months operation of a Norwegian multi-stage constructed wetland pilot plant optimised for nutrient removal, show 55% nitrogen and 98% phosphorus removal. The large phosphorus removal is obtained by using sand with a high content of iron oxides and a fabricated porous medium that has a high phosphorus adsorption capacity. It remains to be seen if long term cost efficient phosphorus removal can be obtained in constructed wetlands. The results indicate that properly designed constructed wetlands can operate satisfactorily in a cold climate. When adequate design criteria are developed several possible applications exist for these simple low maintenance systems as main treatment system, or in conjunction with other treatment methods.