Effect of Freeze–Thaw Cycles on Phosphorus Fractions and Their Availability in Biochar-Amended Mollisols of Northeast China (Laboratory Experiment)

Abstract

Freeze–thaw cycles stimulate the release of available soil phosphorus (P) in winter, and biochar as a soil amendment could improve P availability. Nevertheless, it is unclear how freeze–thaw cycles and biochar amendment interact to affect the soil P fractions and their availability in winter, particularly under different soil water conditions. We simulateda freeze–thaw cycle experimentto assess the effects of three factors on soil P fractions: soil moisture content (22%, 31%, and 45%), frequencies of freeze–thaw cycles (0, 1, 3, 6, and 12 times) and biochar amendment (soil and biochar-amended soil). Modified Hedley sequential P fractionation was conducted to measure the soil P fractions. Increasing the number of freeze–thaw cycles increased soil labile P fractions in the soil with the lowest moisture content (22%). After biochar amendment, the content of labile P decreased as the number of freeze–thaw cycles increased. Biochar amendment enhanced P availability in Mollisols owing to the direct effect of NaOH-Po, which has a large direct path coefficient. Principal components analysis showed that moisture content was a major factor influencing the variation in the P fractions. The P fractions were separated by the interactive effects of biochar amendment and freeze–thaw cycles in soils with a higher moisture content (45%), indicating that the effects of freeze–thaw cycles on P availability appear to be more pronounced in biochar-amended Mollisols of higher water contents.

The application of biochar mitigated the negative effects of freeze-thaw on soil and nutrient loss in the restored soil of the alpine mining area

“…Similar to inorganic N, freezing and thawing caused an increase in TP and DP concentrations in the initial runoff, which was mainly related to the damage of soil aggregates and the rapid release of adsorptive P from soil particles under FTCs (Han et al, 2019). Although DP in biochar may enhance soil P availability, increasing the risk of P loss (Li et al, 2019;Han et al, 2019), the application of biochar in this study effectively reduced the TP and DP loss in FT soil. In addition, the increase in the BARs promoted the inhibitory effect of biochar on P loss.…”