Monday, 1 February 2021

Wood-based biochars reduced N leaching, N2O emissions, enhanced plant uptake of NO3- but reduced the uptake of NH4+

As part of our PhD student Subin Kalu's doctoral study, we have just published a in Biology and Fertility of Soils a greenhouse pot experiment to test the effectiveness of two types of wood-based biochars in reducing N leaching, N2O emissions, and plant N uptake. Using 15N tracing technique, we studied the effects of biochars on the fate of added ammonium (15NH4+) and nitrate (15NO3-) fertilizer.  

 

 The two types of biochars used were a regular biochar and a Kon-Tiki produced nutrient-enriched biochar at two application rates: 1% and 5%. Kon-Tiki is a conical kiln for producing home-made biochar that follows the principle of flame curtain pyrolysis i.e. even though the feedstock seems to be burnt in an open fire, the flame itself acts as a barrier between feedstock and atmosphere maintaining oxygen-free condition. Right after pyrolysis, the hot Kon-Tiki produced biochar was enriched with a cattle-slurry mixture.  

Both the biochars significantly increased plant aboveground biomass by 22–23% at the higher biochar application rate. The biochars significantly reduced NH4+ and NO3- leaching by 21–53% and 47–68%, respectively. Similarly, the biochars significantly suppressed N2O emission by 57–81%. At the higher application rate, the biochars significantly increased plant N uptake by 24%. Interestingly, we found that the biochars increased the plant uptake and soil recovery of added 15NO3- fertilizer. 


These results suggest that the biochars were able to retain highly mobile 15NO3- ions in soil by preventing them from leaching and denitrification. Such retained 15NO3- ions were accessible for plants. On the other hand, biochars decreased the plant uptake and soil recovery of added 15NH4+ fertilizer although biochar helped to reduce 15NH4+ leaching. We suspect that added 15NH4+ fertilizer was lost due to biochar induced ammonia volatilization (conversion of NH4+ to NH3). Increased soil pH with biochar justifies our reasoning because high soil pH favors ammonia volatilization. 

We also noticed that the significant increase in the plant biomass due to the addition of the biochars was because of the enhanced uptake of N derived from the soil. This suggests that the interactions between biochar and native soil organic N may be important determinants of the availability of soil N to plant growth.  Read more at

Kalu, S., Oyekoya, G. N., Ambus, P., Tammeorg, P., Simojoki, A., Pihlatie, M., & Karhu, K. (2021). Effects of two wood-based biochars on the fate of added fertilizer nitrogen—a 15 N tracing study. Biology and Fertility of Soils, 1-14.

Wednesday, 9 September 2020

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.