Effects of Planting Density on Soil Bulk Density, pH and Nutrients of Unthinned Chinese Fir Mature Stands in South Subtropical Region of China

Abstract

Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) is a fast-growing evergreen conifer with high-quality timber and is an important reforestation and commercial tree species in southern China. Planting density affects the productivity of Chinese fir plantations. To study the effect of five different planting densities and soil depth on soil nutrient contents of a mature C. lanceolata plantation, the soil nutrient contents (soil depths 0–100 cm) of 36-year-old mature Chinese fir plantations under five different planting densities denoted A (1667 trees·ha−1), B (3333 trees·ha−1), C (5000 trees·ha−1), D (6667 trees·ha−1), and E (10,000 trees·ha−1) were measured in Pingxiang county, Guangxi province, China. Samples were collected from the soil surface down to a one meter depth from each of 45 soil profiles, and soil samples were obtained at 10 different soil depths of 0–10, 10–20, 20–30, 30–40, 40–50, 50–60, 60–70, 70–80, 80–90, and 90–100 cm. Twelve soil physical and chemical indicators were analyzed. The results showed that: (1) as planting density increased, the organic matter, organic carbon, total N and P, available N, effective Fe, and bulk density decreased. Soil pH, total K, and effective K increased with increasing planting density. Planting density did not significantly influence the exchangeable Ca and Mg. (2) Soil organic matter; organic carbon; total N and P; effective N, P, and K; exchangeable Ca and Mg; effective Fe content; and bulk density decreased with increasing soil depth. This pattern was particularly evident in the top 30 cm of the soil. (3) Excessively high planting density is not beneficial to the long-term maintenance of soil fertility in Chinese fir plantations, and the planting density of Chinese fir plantations should be maintained below 3333 stems·ha−1 (density A or B) to maintain soil fertility while ensuring high yields.

Soil fertility indices of tropical loamy sand as influenced by bambara groundnut variety, plant spacing and fertilizer type

“…Ikenganyia et al (2017) similarly reported that lower density of bambara groundnut plants led to higher available P at crop harvest. Gil (2009) and Duan et al (2019) found that higher plant densities decreased soil contents of plant nutrients including P. Considering that Ikenganyia et al (2017) and the present study share similar climate, and that the effect of plant density on soil fertility could be climate dependent (Duan et al, 2019), we deduce that wider spacing is a more sustainable option than narrower spacing for bambara groundnut in the study location.…”

Formation of Soil Chemical Environment in Coastal Pinus thunbergii Parlatore Forest in Southwestern Japan

“…The pure Pinus stand showed lower soil pH as well as throughfall compared to the Pinus stand with broadleaf trees in the understory. Soil acidification is a common process in coniferous forests [20]; however, acidification appears in the surface horizon of the mineral soil [13,21]. Thus, the soil of the pure Pinus stand would be kept acidic by the acidic throughfall after canopy leaching and proton exchange by base cation in sea salt.…”

Comparison of Topsoil Organic Carbon Stocks on Slopes under Soil-Protecting Forests in Relation to the Adjacent Agricultural Slopes

“…Our research also confirms this characteristic (Tables 1 and 2). In addition, the research of Duan et al [49] showed that soil bulk density in the 0-10 cm soil layer is influenced by stand planting density. The thickness of the humus horizon along the studied slopes used for agricultural purposes depends mainly on the plowing depth, that normally ranges from to 31 cm, on average reaching to a depth of 26 cm.…”