Low-Fe lake sediments recycled to agriculture improved grass growth- and hardwood biochar reduced leaching of N and P

 

In AgriChar research group, we are trying to find ways to best close the phosphorus (P) cycles in the environment by recycling nutrients in sediments back to the agriculture and restoring eutrophic lakes.

The nutrients including Phosphorus (P) in upstream agricultural soils are washed out by erosion and reach the bottom of the lake sediment. Excessive load of (P) causes eutrophication problems in many lakes. One of the effective restoration methods especially for small shallow lakes is removal of sediments enriched with nutrients. We examined the factors behind P release from sediment to lake water after removal of sediments from a 1-ha shallow eutrophic lake during two-year follow up period. Removing 7 500 m3 of nutrient-rich sediment removed 6 400 kg of P, including the potential source of P for algae. 

 

However, high pool of releasable P was rebuilt soon after the removal of sediment due to high external P loading, resulting in high internal P loading which sustained eutrophication of the lake. So ways that help to control nutrient losses from fields upstream are of great importance! Our study documented clear strong linkage between sediment P and iron dynamics after the restoration. We also found that the Fe-P and labile P fractions were the most important sources of P release evidenced by their considerable seasonal and interannual changes after the sediment removal. 

Our story did not stop at this point. In the next step, during a nine-month lysimeter experiment, we examined the potential solutions for the disposal of large amounts of excavated lake materials after restoration procedures, and sustaining agricultural crops yields without increasing the nutrients leaching from soil. We also tried self-made biochar with Kon-Tiki kiln in reducing the leaching of nutrients- and were surprised to see that indeed EBC premium-grade biochar can be made fully DIY:

 

From this study we learned that reusing excavated nutrient-rich sediment from a eutrophic lake, with a low iron (Fe) to P ratio, improved properties of a nutrient-deficient sandy loam surrounding the lake by increasing the availability of P and other nutrients in soil. Although the soil chemical fertility enhancement of the depleted soils alone would suffice to make this application advisable, the substantial increase in plant growth and P uptake in treatments with sediment-amendments adds further interest. 

 Of all components of soil P, the Fe-P fraction was the most important contributor to plant P uptake. Considering the environmental impact, applying a relatively thick layer of sediment on a 25-cm topsoil layer did not increase the risk of phosphate and mineral nitrogen leaching. Also, a biochar layer was  a promising addition for reducing P and N leaching from sediment.

Please check the following recently published articles for more interesting information:

Kiani, M., Tammeorg, P., Niemistö, J., Simojoki, A. and Tammeorg, O., 2020. Internal phosphorus loading in a small shallow Lake: Response after sediment removal. Science of The Total Environment, p.138279.

Kiani, M., Raave, H., Simojoki, A., Tammeorg, O. and Tammeorg, P., 2021. Recycling lake sediment to agriculture: Effects on plant growth, nutrient availability, and leaching. Science of The Total Environment, p.141984.

Harvesting ongoing and drainage experiment started in August

 In these days our HYKERRYS team has been busy with harvesting rye and barley. The growing season has been more rainy here in Helsinki than in 2018 and 2019 and the bags seem heavier 😊 We also shot videos with key project partners to share the progress of the project, these will soon be uploaded to HYKERRYS website: https://blogs.helsinki.fi/hykerrys-hanke/

 

Harvesting HYKERRYS 2 barley yield, Aug 2020

HYKERRYS 2 coordinator Mari Unnbom at harvest 2020

 In the end of August 2020, AgriChar research group together with partners Carbofex Oy and Nivoo Oü started also our first biochar field experiment that focuses on long-term carbon sequestration via application of biochar to subsoil. The great majority of biochar field experiments worldwide study the effects when biochar is applied to topsoil (typically up to 20 cm depth), while technological challenges have hindered the application of it to deeper soil layers. In our fresh experiment in Estonia we study the effects of 5+ cm layer of EBC premium-grade spruce biochar on plant growth and nutrient leaching via drainage- as well as naturally the potential of sequestering C in this way. The experimental setup allows us to compare the effects of biochar to the control treatment with sand only. Looking forward for the results of this pioneering study funded by Tiina and Antti Herlin Foundation!

AgriChar 2020 drainage experiment started in August 2020

 

Growing season 2020 started in our field experiments, including urban biochar park in Helsinki

Since March 2020 the University of Helsinki has been working under emergency situation rules due to #COVID19, this has posed several challenges also to establishing field experiments. The AgriChar team has however managed to start all three field experiments we have here in Finland and hope to collect data from our Estonian sites during the summer.

Seeds of red clover being sown to biochar experiments

Our long-term biochar field experiments have now entered the 11th growing season! The timothy and ryegrass were growing fine (sown in spring 2019) but the clovers did not survive over winter. For this reason additional sowing of red clover was completed in May to all the plots. Keeping now fingers crossed for rain :)

Fertilizing HYKERRYS 2 fields in May 2020

 In our recycling #fertilizer experiment in Haltiala Helsinki, the fertilization and sowing tasks were arranged for the first time without helping hands of student trainees. Thus the tasks took all a bit more time (and the sowing was postponed) but thanks to great teamwork led by Mari Unnbom we managed to complete the tasks! Also this year we had the challenge with bird damage in Haltiala on canola, thus it was decided to replace canola with barley. 

  And lastly, our newest experimental site is urban biochar park in Jätkäsaari, Helsinki. In order to achieve the ambitious goals of carbon (C) neutrality within next 15–20 year, cities worldwide need to increasingly apply negative emission technologies. Biochars, thanks to their stability against microbial degradation, suit well for application to both agricultural and urban soils as a C- fixing technology providing multiple co-benefits. While providing support for the city planners and policymakers to develop tools for more sustainable management practices of urban green areas, high visibility and impact can be gained in the densely populated urban areas. Our project focuses on general principles of urban demonstration areas for carbon sequestration as well as following up a pilot park in Helsinki. The project includes Carbon Lane project funded by EIT Climate-KIC as well as #Hiilipuisto project funded by Rikala puutarhasäätiö.

Baseline tree measurements of biochar urban park-experiment in 2020

Last November the growing media were applied to Hyväntoivonpuisto in Helsinki and we sampled them for physicochemical analyses. In April-May 2020, 80 trees were planted to the park in different biochar media. Last week our team kicked off the #Hiilipuisto #CarbonPark project by recording the starting condition of all individual trees. This data will be used to establish a baseline on which biochar-containing growing media perform best in long-term considering carbon sequestration.

By the way, the list of all peer-reviewed studies regarding to biochars and lake sediments conducted in Finland is updated recently with more than 10 fresh papers, check them out: http://biochar-hy.blogspot.com/p/biochar-studies.html