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Irrigation and nitrogen application directly affect the availability and distribution of soil nutrients. Understanding the response of soil nutrients to long-term water–fertilizer coupling conditions is helpful to improve the management and use efficiency. Irrigation was divided into three gradient levels, which accounted for 45%, 60%, and 75% (W1, W2, and W3) of the field water holding capacity. Based on pure nitrogen, four levels of nitrogen application were set: 0.0, 101.6, 203.2, and 304.8 kg·hm−2 (N0, N1, N2, and N3). We measured tree height and diameter at breast height (DBH), and we analyzed the chemical properties of the soil at 0–40 cm depth, from 2007 to 2020. The ranges of DBH, tree height, individual volume, and stand volume were 5.80–25.25 cm, 6.10–16.47 m, 0.01–0.37 m3, and 11.76–481.47 m3·hm−2, respectively. The contents of organic matter, total nitrogen, available phosphorus, and available potassium in the soil ranged from 8.60 g·kg−1 to 18.72 g·kg−1, from 0.21 g·kg−1 to 0.79 g·kg−1, from 8.09 mg·kg−1 to 47.05 mg·kg−1, and from 90 mg·kg−1 to 322 mg·kg−1, respectively. Soil pH value decreased rapidly at a rate of 0.31 units per year for the first five years. Irrigation and nitrogen application, and their interaction, had significant (p < 0.01) effects on soil total nitrogen, available phosphorus, available potassium, and nitrate-nitrogen. We suggest maintaining the field water holding capacity above 60%, with a nitrogen application rate of 203.2 kg·hm−2, to save water, maintain soil fertility, and optimize soil nitrogen supply. Our study aimed to achieve scientific and accurate fertilization of Populus tomentosa stands over different periods, to alleviate the decline of soil fertility, and to improve the utilization rate of water and fertilizer through long-term nutrient monitoring. [ABSTRACT FROM AUTHOR]

Traditional methods to deal with thinning shreds (twigs, bark, etc.) include using them as fuelwood (artificially taken out of the forest) and stacking in situ natural decompositions (slow decomposition and nutrient return to the field). These methods will cause the loss of nutrients in the forest, and composting with additives can effectively promote nutrient circulation effectively. The purpose of our study was to explore the effects of composts of forest thinning shreds with different additives on soil and tree growth in semimature Pinus tabuliformis Carr. We selected four composts of forest thinning shreds (T1 adjustment of C/N and C/P + 0.2% priming; T2: adjustment of C/N and C/P + 0.2% common compost; T3: adjustment of C/N and C/P only; T4: raw material grinding of thinning shreds) and applied them in the volume of 900 g·m−2, which were made in the early stage. The soil nutrient content, microbial characteristics, and growing volume of Pinus tabuliformis were measured at 0.5, 1, and 1.5 years after fertilization. The soil became acid after one year of fertilization, having a great impact on the 0–20 cm soil layer. At 0.5 years of fertilization, the total nitrogen (TN) content of the soil with priming compost (T1) was 1.5 times higher than that of the control group (T5); the soil organic matter (SOM) was increased by 4.93–6.41 mg·kg−1. After one year of fertilization, the difference in the soil microbial carbon and nitrogen (MBC and MBN) content of each treatment decreased gradually. Soil sucrase activity was the highest after fertilization, and different composts had the greatest impact on urease activity in the 0–20 cm layer; the alkaline phosphatase (AKPase) activity of soil with common compost (T2) changed the most, and after 0.5 years of fertilization, the acid phosphatase (APase) activity of T1 in the two layers increased by 0.31 mg·g−1 and 0.1 mg·g−1, and the increase in of T2 was slightly lower than that of T1. There were significant differences in the number of bacteria, fungi, and actinomycetes compared to T1 and T2 with other treatments. T1 promoted the height growth (H) of trees three times higher than T5 and T2 promoted the growth of diameter at breast height (DBH) by 2.5 cm. The results showed that T1 and T2 had obvious effects on promoting soil nutrient content, microbial biomass accumulation, and forest growth, and the application of compost had no significant effect on promoting understory regeneration. The findings of this study show that using compost with priming can effectively increase the soil nutrient content, microbial activity, and quantity of Pinus tabuliformis effectively in terms of promoting the growth of trees and reducing the nutrient loss caused by thinning. [ABSTRACT FROM AUTHOR]

This study aimed to explore the effects of different additives on tending shreds of Platycladus orientalis (L.) Franco. Two different additives (priming 0.2% and common compost 0.2%) combined with C, N, and P adjustment of raw material treatments were tested on the temperature, moisture, EC, pH, lignocellulose degradation rate, nutrient content, and toxicity of compost. Priming made the compost temperature rise rapidly, and the peak temperature of the composting group with priming reached 51 °C. At the end of composting, the moisture in each treatment from high to low was in the order: common compost > priming > C/N, C/P adjustment only > control group. The increase of EC in the treatments with additives was great, and the peak value of EC in the treatment of priming was 1.30 ms·cm−1, which was 3.9 times higher than that of the control group. At the end of composting, the decomposition rate of cellulose in priming compost was 1.7 times higher than that in the control group, and the hemicellulose decomposition rate in the common compost group was 3.2 times higher than that in the control group. By the end of composting, the pH value of the composts in additive treatments was above 7.0, and the pH value of the priming treatment was the highest (7.5). The highest content of organic matter was found in the priming treatment, which was 52%, 1.7 times higher than that in the control group. The total nutrient content (TN + K2O + P2O5) of additive treatments was higher than 5.0%, and the priming treatment was 2.7% higher than that of the control group. By the end of composting, the germination rate and germination index ranged from 88% to 91% and 60% to 81%. Except for the control group, the C/N ratio of other treatments decreased to below 25. Additives can accelerate the decomposition of raw materials, shorten the composting cycle, and improve the quality of composts, and the effect of adding priming is the most significant. [ABSTRACT FROM AUTHOR]