Potential of high- or low-solubility calcium to correct stem sinuosity in fast-growing Pinus radiata D. Don

Background: Pinus radiata D. Don is widely planted in Chile due to its fast growth and adaptability to various soil types and environmental conditions. However, the species is prone to stem sinuosity due to factors such as genetics, environmental stresses including nutrient availability, and management practices. This study assessed the efficacy of either low- or high-solubility calcium (Ca) additions in reducing stem sinuosity in young radiata pine plantations grown on Andisols. Methods: We compared growth and stem sinuosity of a 3-year-old pine plantation subject to two types of Ca sources: agricultural low-solubility crushed lime (ag-lime), and finely ground pelletised high-solubility lime (pell-lime), applied at three concentrations (300 kg Ca ha-1, 600 kg Ca ha-1, 1,200 kg Ca ha-1) alongside a control. Results: Our findings revealed that both calcium sources increased the soil Ca content post-application but was only significant for the highest concentration in each case (1,200 Kg Ca ha-1). The soil Ca availability rate was higher in pell-lime treatments. Agricultural lime had no effect on growth, whereas two of the pell-lime treatments increased the basal area, the lowest concentration increased the cumulative diameter at the root collar, and the highest concentration reduced tree height. Interestingly, while pell-lime did not mitigate stem sinuosity in 3-year-old pine trees, ag-lime reduced stem sinuosity severity although this result was not correlated with soil Ca content. Notably, the ag-lime treatment at 600 kg Ca ha-1 was most effective, decreasing the proportion of severely deformed trees from 32% to 14%. Conclusions: The application of both low-solubility calcium (ag-lime) or high-solubility calcium (pell-lime) calcium increased the soil Ca content. Ag-lime treatments showed no adverse impact on stand growth and led to a reduction in stem sinuosity being the most effective treatment applying 600 kg Ca ha-1. Pell-lime treatments had mixed effects on growth: diameter at root collar (DRC) and basal area increment (BAI) increased, and height decreased. Pell-lime treatments did not reduce stem sinuosity. Our results suggests that stem sinuosity might be more closely associated with deficiencies in trace metals like Cu and Mn rather than Ca content alone.