Abstract
Addition of biochar to soil has been shown to reduce nitrogen (N) leaching in pot experiments, but direct field measurements are scarce, and data is lacking especially from colder, boreal conditions. We studied the effect of soil organic amendments on nitrate (NO3-) and ammonium (NH4+) leaching using the resin bag method, by placing the bags containing ion-exchange resins under the plough layer. We compared N leaching under five different treatments at the Päästösäästö project site (Soilfood Oy) in Parainen, south-western Finland: non-fertilized control, fertilized control, and three different organic amendments: spruce biochar, willow biochar and nutrient fiber. During the 2017 growing season, resin bags were changed monthly between the end of May and beginning of September, extracted with 1 M NaCl, and analyzed for inorganic N. The daily leaching rate of NO3- was greatest at the beginning of the growing season, right after fertilization. Ammonium leaching was generally lower, and independent of the time since fertilization. The spruce biochar reduced cumulative NO3- leaching by 68% compared to the fertilized control. The NH4+ leaching in the organic amendment treatments did not statistically significantly differ from the fertilized control in pairwise comparisons. In October 2017, after harvesting, the resin bags were placed under soil columns again, and left in the soil over winter to accumulate N leached during the plant-free period. Cumulative NO3- leaching during winter was consistent with the corresponding summer results, and average leaching decreased in the order: willow biochar > fertilized control > nutrient fiber > non-fertilized control > spruce biochar. Thus, we show here, for the first time in a field study from boreal conditions that spruce biochar soil application decreased nitrate leaching, while increasing its retention in the surface layer of the biochar-amended soil.
Highlights
Leaching of nitrogen (N) from agricultural fields is harmful, because it can cause eutrophication of waterways, and become transformed into a potent greenhouse gas N2O in the denitrification process (Galloway et al, 2008)
We studied the effect of soil organic amendments on nitrate (NO3- ) and ammonium (NH4+) leaching using the resin bag method, by placing the bags containing ion-exchange resins under the plough layer
Cumulative NO3- leaching during winter was consistent with the corre sponding summer results, and average leaching decreased in the order: willow biochar > fertilized control > nutrient fiber > non-fertilized control > spruce biochar
Summary
Leaching of nitrogen (N) from agricultural fields is harmful, because it can cause eutrophication of waterways, and become transformed into a potent greenhouse gas N2O in the denitrification process (Galloway et al, 2008). Reduced N leaching from biochar amended soils has been documented only in field experiments from warmer climates (Angst et al, 2014; Borchard et al, 2019; Güerena et al, 2013; Haider et al, 2017; Mia et al, 2017). Whether such an environmental benefit of biochar soil amendments is available in cool boreal climates remains unknown. Biochars can reduce NH4+ leaching by increasing the cation exchange capacity of soils (Liang et al, 2006; Gai et al, 2014). There is a pressing need for field studies on the effects on biochar and other soil amendments on N leaching in boreal conditions
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