Chinese fir (Cunninghamia lanceolata (Lamb) Hook) is a commercially valuable timber species that is widely planted in southern China and accounts for 6.1% of the global plantation forests. However, appropriate planting density that ensures high plantation productivity is largely unexplored in this species. The aim of the study was to examine tree growth, biomass production, and its allocation among different organs in relation to initial planting density, and to examine whether planting density has an impact on root development. Mortality, diameter at breast height and tree-height of all trees were determined and measured in wider (2.36 × 2.36 m), intermediate (1.83 × 1.83 m) and narrow (1.44 × 1.44 m) spacing with stand density of 1450 trees ha−1, 2460 trees ha−1 and 3950 trees ha−1, respectively. In each stand, three plots of 20 × 20 m at a distance of 500 m were delineated as the sampling unit. Biomass was determined by destructive sampling of trees in each stand and developing allometric equations. Root morphological traits and their spatial distribution were also determined by carefully excavating the root systems. The results showed an increase in diameter of trees with decreasing stand density while tree height was independent of stand density. Biomass production of individual trees was significantly (p < 0.05) less in high-density stand (32.35 ± 2.98 kg tree−1) compared to low-density stand (44.72 ± 4.96 kg tree−1) and intermediate-density stand (61.35 ± 4.78 kg tree−1) while stand biomass production differed significantly in the order of intermediate (67.63 ± 5.14 t ha−1) > high (57.08 ± 3.13 t ha−1) > low (27.39 ± 3.42 t ha−1) stand density. Both average root length and root volume were significantly (p < 0.05) lower in the high-density stand than stands with low and intermediate density. Analysis of spatial distribution of root systems revealed no overlap between roots of neighboring trees in the competition zone in low-density stand, a subtle overlap in the intermediate density stand and larger overlap in the high-density stand. It can be concluded that better growth and biomass production in intermediate density stand could be explained by better root structural development coupled with minimal competition with understory vegetation and between trees; thus intermediate stand density can be optimal for sustaining long-term productivity and may reduce the management cost in the early phase of the plantation.

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It is known that forest management practices and land use affect soil quality worldwide. This study was conducted to assess the potential effects of stand density on soil quality in Chinese fir plantations. Low-(1,450 trees/ha with 2.36 × 2.36 m spacing), intermediate-(2,460 trees/ha with 1.83 × 1.83 m spacing), and high-density (3,950 trees/ha with 1.44 × 1.44 m spacing) stands in a 10-year-old Chinese fir monoculture plantation were examined, and different soil quality indicators were measured. The results indicated that stand density affected nitrogen (N), phosphorous (P), and magnesium (Mg) content, whereas potassium (K) and calcium (Ca) were not affected. Total N and total P contents were higher in the low-density stands, whereas total Mg was higher in the intermediate-density stands. Available N was higher in the low-density stands, whereas available P was higher in the intermediatedensity stands. No significant difference was observed in the contents of available K, total K, and total Ca among all densities. Soil organic matter was significantly higher in the intermediate-density stand than in the high-and low-density stands. Soil bulk density increased from the surface layer to the 40-60 cm soil layer. Soil pH was lowest in the surface layer of soils of all three densities and increased from the 0-20 cm layer to the 20-40 cm layer; however, it decreased from the 20-40 cm layer to the 40-60 cm layer. Soil pH differed significantly between soils of different densities but remained within an optimum range (4.1-4.5) for Chinese fir plantations. Soil moisture content was significantly higher in the high-density stand than the other stands. The observed effects of stand density on soil quality may be useful for policy makers and forest managers to implement improved forest conservation practices for preserving soil quality and stand production.

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Intercropping is one of the most widely used agroforestry techniques, reducing the harmful impacts of external inputs such as fertilizers. It also controls soil erosion, increases soil nutrients availability, and reduces weed growth. In this study, the intercropping of peanut (Arachishypogaea L.) was done with tea plants (Camellia oleifera), and it was compared with the mono-cropping of tea and peanut. Soil health and fertility were examined by analyzing the variability in soil enzymatic activity and soil nutrients availability at different soil depths (0–10 cm, 10–20 cm, 20–30 cm, and 30–40 cm). Results showed that the peanut–tea intercropping considerably impacted the soil organic carbon (SOC), soil nutrient availability, and soil enzymatic responses at different soil depths. The activity of protease, sucrase, and acid phosphatase was higher in intercropping, while the activity of urease and catalase was higher in peanut monoculture. In intercropping, total phosphorus (TP) was 14.2%, 34.2%, 77.7%, 61.9%; total potassium (TK) was 13.4%, 20%, 27.4%, 20%; available phosphorus (AP) was 52.9%, 26.56%, 61.1%; 146.15% and available potassium (AK) was 11.1%, 43.06%, 46.79% higher than the mono-cropping of tea in respective soil layers. Additionally, available nitrogen (AN) was 51.78%, 5.92%, and 15.32% lower in the 10–20 cm, 20–30 cm, and 30–40 cm layers of the intercropping system than in the mono-cropping system of peanut. Moreover, the soil enzymatic activity was significantly correlated with SOC and total nitrogen (TN) content across all soil depths and cropping systems. The depth and path analysis effect revealed that SOC directly affected sucrase, protease, urease, and catalase enzymes in an intercropping system. It was concluded that an increase in the soil enzymatic activity in the intercropping pattern improved the reaction rate at which organic matter decomposed and released nutrients into the soil environment. Enzyme activity in the decomposition process plays a vital role in forest soil morphology and function. For efficient land use in the cropping system, it is necessary to develop coherent agroforestry practices. The results in this study revealed that intercropping certainly enhance soil nutrients status and positively impacts soil conservation.

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Acacia nilotica is an important agroforestry specie, which is used in both compact and linear forms. The objective of the current study was to evaluate the effect of compost on the growth performance and biomass production of A. nilotica. Completely randomized design (CRD) was used to analyze the variations among several growth morphological traits. Two parallel trials, pot trial (seedlings), field trial (saplings) were conducted simultaneously. Compost and litter mixture were applied in mentioned trials. Following treatments were used: T0 – control; T1 - 25% of compost and 75% of nursery soil; T2 - mixture of 50% nursery soil and 50% compost; T3 - mixture of 75% compost and 25% of nursery soil; T4 - where 100% compost was applied. Increase in plant growth was observed with the increases in the amount of compost mixture. In field trial maximum plant height, shoot length, root length, rootshoot ratio and biomass production was observed when 100% compost level was applied, while minimum was observed without any compost appli-cation. In pot trials, the maximum plant height, rootshoot ratio and biomass production was recorded when 75% compost level was applied. Overall, Acacia performed better with 100% of compost application in field trail and 75% of compost application in pot trial. The results of this study demonstrated the positive effects of compost on the growth of Acacia. The seedling development was improved considerably with different levels having greater percentage of organic fertilizer and it was concluded that compost improves soil fertility and it should be used as organic fertilizer in farming and forestry practices for improving crop growth and yield.

Natural isotopic abundance in soil and foliar can provide integrated information related to the long-term alterations of carbon (C) and nitrogen (N) cycles in forest ecosystems. We evaluated total carbon (TC), total nitrogen (TN), and isotopic natural abundance of C (δ13C) and N (δ15N) in soil and foliar of coniferous plantation (CPF), natural broadleaved forest (NBF), and mixed forest stands at three different soil depths (i.e., 0–10, 10–20, and 20–40 cm). This study also explored how soil available nutrients are affected by different forest types. Lutou forest research station, located in Hunan Province, central China, was used as the study area. Results demonstrated that the topsoil layer had higher TC and TN content in the mixed forest stand, resulting in a better quality of organic materials in the topsoil layer in the mixed forest than NBF and CPF. In general, soil TC, TN, and δ15N varied significantly in different soil depths and forest types. However, the forest type did not exhibit any significant effect on δ13C. Overall, soil δ13C was significantly enriched in CPF, and δ15N values were enriched in mixed forest. Foliar C content varied significantly among forest types, whereas foliar N content was not significantly different. No big differences were observed for foliar δ15N and δ13C across forest types. However, foliar δ13C and δ15N were positively related to soil δ13C and δ15N, respectively. Foliar N, soil and foliar C:N ratio, soil moisture content (SMC), and forest type were observed as the major influential factors affecting isotopic natural abundance, whereas soil pH was not significantly correlated. In addition, forest type change and soil depth increment had a significant effect on soil nutrient availability. In general, soil nutrient availability was higher in mixed forest. Our findings implied that forest type and soil depth alter TC, TN, and soil δ15N, whereas δ13C was only driven by soil depth. Moreover, plantations led to a decline in soil available nutrient content compared with NBF and mixed forest stands.