Soil characteristics and tillage can predict the effect of ‘structure lime’ on soil aggregate stability

Abstract

Context. In Sweden, mixtures of 80-85% ground limestone and 15-20% slaked lime (hereafter, 'structure lime') are used in subsidised environmental schemes to improve aggregate stability and mitigate phosphorus losses on clay soils. Aims. This study investigated different rates of structure lime application and soil variables on aggregate stability on clay soils, and whether soil properties can predict aggregate stability following structure liming. Methods. Increasing application rates of 0-16 t ha −1 of structure lime (SL0, SL4, SL8 and SL16) were tested in 30 field trials in Sweden. Soil aggregates (2-5 mm) were collected 1 year after liming and subjected to two rainfall events in a rain simulator. Key results. Leachate turbidity after the second simulated rainfall event decreased significantly (13% and 20%, respectively, in SL8 and SL16) compared with SL0, indicating improved aggregate stability. There was a near-significant interaction (P = 0.056) between treatment and trial. Grouping by initial pH ðH 2 OÞ (range 6.2-8.3), clay content (10-61%), soil organic matter content (SOM, 2.2-7.1) and clay mineralogy (SmV index, 0.2-3.8) revealed different effects on turbidity. Discriminant analysis of soil characteristics and four tillage variables correctly classified the outcome for 27 of the 30 trial sites. Conclusions. Results show that structure liming can improve aggregate stability 1 year after liming, and can thereby prevent particulate P losses from soils with high clay and SOM content, low SmV index and low initial pH. The discriminant analysis also showed the importance of tillage for the outcome of structure liming. Implications. Clay soil characteristics such as SOM and pH significantly affected aggregrate stability after structure liming.

Site characteristics determine the duration of structure liming effects on clay soil

“…In a previous study examining the effect on turbidity approximately one year after structure liming at the eight trials used in the present study together with another 22 field sites, we found that structure liming had the most pronounced short-term effect on soils with high clay content and low initial pH (Blomquist et al 2022). Therefore, Rel.…”

“…In fact, the variation seen indicates a need for a site-specific application strategy and for soil characteristics to be taken into consideration. In a previous study, we observed this type of interaction between liming treatment and trial in the short term (Blomquist et al 2022) and suggested that the interaction derives from soil properties such as clay content and soil organic matter, clay mineralogy, initial pH and management factors such as tillage before and after structure liming.…”

“…The initial pH was lower and soil organic matter content was higher in the LC group than in the HC group. Based on suggestions by Blomquist et al (2022) that structure liming may be more effective in stabilising aggregates on soils with low pH and high SOM, stronger responses could have been expected for the LC group, which was not the case (Table 4). Thus, it appears that clay content, rather than pH and organic matter, was the conclusive soil property for the differences between the LC and HC groups in this study.…”

“…Positive short-term effects on aggregate stability and a reduced risk of phosphorus (P) losses as a result of increasing application rates of structure liming products have been reported. For example, Blomquist et al (2022) observed increased aggregate stability and an associated reduced risk of P losses about one year after structure liming, while Blomquist et al (2018) detected effects of the same magnitude 2.5 years after structure liming. In contrast, Norberg et al (2021) found no significant effect on aggregate stability one and two years after structure liming on a clay soil where effects could be expected.…”

Mitigating phosphorus leaching from a clay loam through structure liming

“…Aggregate stability testing, as described in Blomquist et al (2022), was performed on soil samples from the top layer (0−5 cm), which were sieved to obtain samples of the 2−5 mm aggregate fraction. The samples were airdried and then subjected to simulated rainfall in two events, with 24 h between events.…”