Effects of gravel on the evaluation of soil organic carbon density in Pinus massoniana plantations.

Gravel (>2 mm) is one of the main parameters for estimating soil carbon pool. To assess the effects of gravel on soil bulk density (BD) and organic carbon density (SOCD) in Pinus massoniana plantations, we estimated the BD and SOCD at the 0-10, 10-20 and 20-40 cm soil depths of 131 plots under two different conditions, with and without removing gravel. The BD of each soil layer after removing gravel was 0.58-1.57, 0.60-1.67, and 0.59-1.75 g·cm-3, respectively, which was significantly lower than that before removing gravel. Gravel increased the BD by 6.5%-6.8%. The SOCD of each soil layer before removing gravel was 8.93-65.97, 7.63-59.08, and 8.79-94.53 t·hm-2, respectively, which was higher than that after removing gravel. Overall, by neglecting the effect of gravel, SOCD was overestimated by 4.9%-11.8%. As gravel content increased, the relative deviation in the estimated BD and SOCD among different methods increased. When the gravel content was higher than 20%, the estimated SOCD at soil layer of 0-40 cm showed a significant difference between neglecting gravel and removing gravel, with the former being 29.7%-47.4% higher than the latter. In conclusion, gravel markedly affected the estimations of BD and SOCD. It was recommended that SOCD should be estimated by the method that not only uses the BD after removing gravel but also considers gravel as a correction factor (especially when gravel content is above 20.0%) to avoid overestimation of soil carbon pool.

Effects of mixed substrates of different agricultural and forestry residues on the cutting seedlings of Thuja sutchuenensis.

To screen environment-friendly seedling cultivation substrates which could replace peat and with less cost, we compared the effects of different agricultural and forestry residue mixed substrates on cutting propagation of Thuja sutchuenensis, in an experiment following randomized block design. There were five types of mixed substrates, including peat + vermiculite + perlite (T1), edible mushroom residue (EMR) + vermiculite + perlite (T2), carbo-nized rice husk (CRH) + vermiculite + perlite (T3), EMR + slag + sawdust (T4) and CRH + EMR + slag (T5). The results showed that the bulk density of T3 was the lowest, followed by T2, which significantly differed from other mixed substrates. The non-capillary porosity of T2 was significantly greater than that of T1, while the capillary porosity and the total porosity of T2 was lower than T1 and T3, respectively. T2 had the highest contents of total nitrogen, total phosphorus, total potassium, alkali-hydrolyzed nitrogen, available phosphorus, substrate moisture and the highest pH, which differed significantly from other mixed substrates in most chemical indicators. The membership function values of rooting rate and growth indicators of cuttings with different mixed substrates were in order of T2 > T3 > T1> T5 > T4. Most indicators with larger grey relation values were physical indicators. The top five indicators were capillary water capacity, total potassium, field water capacity, maximum water capacity, and total porosity, with both capillary water capacity and total potassium content ranking first. In general, the physicochemical properties, rooting rate, and growth characteristics of cuttings under T2 were better than those of other mixed substrates. The capillary water capacity and total potassium were the main factors affecting rooting and growth of cuttings. At the early stage of cutting, the physical properties of mixed substrate had greater effect on rooting rate and growth of cuttings than the chemical properties. Overall, our results suggested that T2 should be preferred in the cutting propagation of T. sutchuenensis.