Total aluminum reduced but aluminum hydroxide increased in red soil of southern China after long-term swine manure amendment

Abstract

Aims

Swine manure as an alternative amendment has proven to effectively alleviate red soil acidification, but the mechanisms are not fully understood.

Methods

A 32-year field experiment was selected to investigate the effectiveness of swine manure amendment on red soil aluminum species, and their contribution to acidification and maize yields. The treatments included no fertilization (control), chemical nitrogen, phosphorus and potassium (NPK), NPK with straw return (NPKS), NPK combined with swine manure (NPKM), and swine manure only (M).

Results

As compared to control, soil total aluminum (Al_t) decreased by 10.12 and 21.15 g kg⁻¹ under NPKM and M, respectively, while mineral aluminum (Al_min) and iron oxide-bound aluminum (Al_DCB) decreased by 5.36—20.12 g kg⁻¹ and 674.77—772.98 mg kg⁻¹ under NPKS, NPKM and M treatments. Aluminum hydroxide (Al_oh) increased by 158.02 and 330.16 mg kg⁻¹ under NPKM and M treatments, but decreased 101.00 mg kg⁻¹ under NPK treatment. Exchangeable aluminum (Al_ex) increased by 702.71 and 624.95 mg kg⁻¹ under NPK and NPKS treatments, respectively. The correlation analysis showed that maize yields were positively affected by soil pH and Al_oh, but negatively correlated with Al_ex (p < 0.01). Furthermore, Al_ex was negatively correlated with soil pH, exchangeable calcium (Ex.Ca²⁺) and Al_oh. The Al_oh was positively correlated with soil pH, Ex.Ca²⁺, soil organic matter fractions, dissolved organic matter component 1 and component 2.

Conclusions

This research indicates that long-term swine manure amendment reduced total aluminum but increased aluminum hydroxide in surface soil, which played an important role in preventing red soil acidification and sustaining maize yields.