Due to the reduction of cattle farming, the Finnish agricultural sector currently needs solutions to replace animal manure with new sustainable alternatives. This problem is especially acute for organic farms, which need livestock manure to improve soil fertility and soil organic carbon (SOC) to sustain yield. On the other side, plywood manufacturers aim to find ways to reuse waste fractions such as sandy, wet spruce bark waste. To address both issues, a new soil conditioner was developed from crushed bark (CB) and approved for organic farming by the Finnish Food Authority. To test the advantages of CB in organic wheat production, we conducted a two-year field experiment on a farmer’s field in Mikkeli (Finland) on loamy sand with moderate soil fertility (C 3.5%, C/N ratio 17, pH 6.2). CB (organic matter 80%, C/N ratio 78, pH 5.7-6.0) at 40 t ha–1 was applied either in the first year of the experiment or in both years. In addition to CB, half the plots received base ash (4 t ha–1) obtained from a power plant using wood to maintain the optimal soil pH. All plots were fertilised annually with commercial organic fertilisers. The control plots received no CB or base ash. A one-year application of CB with base ash statistically significantly increased the grain yield by 800 kg ha–1 and grain N uptake by about 10 kg ha–1 in the following growing season compared with the control. In terms of grain yield quality, a one-year application of CB with or without base ash already showed an improvement of 1000 seed weight by 2 g in the first year, and the effect was even more pronounced in the second year of the experiment. Hectolitre weight was increased in the following year after application of CB with base ash. In contrast, a two-year application of CB either alone or with base ash caused no changes in grain yield, N uptake, or yield quality compared with the control. The results indicate that the use of spruce CB with a high C/N ratio as soil conditioner in a large amount may be beneficial in terms of yield and quality when it is applied only once, but not twice in successive years. Future studies need to focus on the long-term residual effects of CB on productivity, as well as soil parameters such as SOC, cation exchange capacity, and soil microbial activity. Highlights - Crushed bark (C/N ratio 78) - a side stream of plywood manufacture - was tested in a two-year organic field experiment. - A one-year (40 t ha–1) application of crushed bark with base ash increased yield and the quality of organic wheat. - Residual effects of a one-year application were pronounced. - Crushed bark application in two successive years provided no benefits for organic wheat production.

<p>Adding organic matter in the soil is especially important for organic agriculture, which relies on good soil health for plant production. Crushed bark (CB) of Picea abies (L.) Karsten is a forestry by-product, which has been developed into a new soil conditioner for organic farming. It contains up to 80 % organic matter with C/N ratio of 78 and pH 5.7-6.0, but is rather nutrient poor.</p><p>Organic field experiments on loamy sand with moderate soil fertility took place in Mikkeli, Finland in 2017-2018 in order to test the substance. The fertilization was based on commercial organic fertilizers: chicken manure and blood meal fertilizer in the first year and meat and bone meal fertilizer in the second one. The treatments were control (only fertilization) and one- or two-year applications of CB (40 t ha<sup>-1</sup>) with or without base ash (4 t ha<sup>-1</sup>). Other half of plots were left without substances in 2018.</p><p>No differences between treatments were observed without the base ash in any of years. A one-year application of crushed bark with base ash increased both spring wheat yield quantity and quality. The statistically significant effects were found for yield, N uptake, grain protein content, 1000-seed weight and hectolitre weight compared to control in 2018, a year after application. Despite the severe drought during that growing season, the wheat yields for CB with base ash and control were 3100 kg ha<sup>-1</sup> and 2250 kg ha<sup>-1</sup>, respectively. The positive effects of soil amendments were not as clear in the first year as in the following. No benefits were visible after two-year successive application of CB either alone or with base ash. Spruce CB in addition with base ash may be beneficial in terms of yield and quality when it is applied only once in large amounts. In our study the effects were overall greater in the following year after the application.</p>