Effect of Fertilization on Soil Fertility and Individual Stand Biomass in Strip Cut Moso Bamboo (Phyllostachys edulis) Forests

Abstract

Strip cutting has emerged as a new, efficient, and mechanized bamboo forest management model. To shorten the recovery period in strip cutting management, improve bamboo resource quality, prevent soil degradation, and achieve sustainable management, we selected on-year pure Moso bamboo (Phyllostachys edulis) forests for an 8-meter-wide strip cut. Three fertilization methods were applied in a complete two-factor experiment, including spreading, cave, and bamboo stump fertilization, at three fertilization dosages of 600, 900, and 1200 kg/ha (N:P:K = 3.5:1:2). We investigated the effects of different fertilization treatments on the biomass of new bamboo shoots and soil fertility to provide a reference for identifying the optimal fertilization scheme. The results showed that fertilization treatment increased the individual stand biomass of new Moso bamboo shoots, with a decreasing trend in the proportion of branches and leaves and an increasing proportion of culms in biomass allocation. Fertilization treatment significantly increased the total nitrogen, phosphorus, and potassium and available phosphorus contents in the soil. Overall, fertilization at 900 kg/ha using the spreading method showed the best results in promoting individual plant biomass recovery (5% increase in culm proportion and 4.12 kg increase in biomass per plant) and restoring soil fertility (increase the contents of TN, TP, TK, and AP in the entire soil layer) after strip cutting Moso bamboo forests, which addresses these pertinent issues in the strip cut management model.

1. Introduction

The Moso bamboo (Phyllostachys edulis) is an important forest resource widely distributed in southern China and has multiple benefits. Traditional bamboo forest harvesting follows a selective cutting method: “cutting the old and leaving the young, cutting the small and leaving the big, cutting the dense and leaving the sparse, cutting the weak and leaving the strong” [1]. This approach requires operators to be highly able to identify target bamboo and have considerable experience. With societal development and urbanization, rural labor resources are becoming scarce, affecting the labor-intensive management model of traditional Moso bamboo forests and hindering the improvement and upgradation of the bamboo industry.

Based on the physiological integration characteristics of Moso bamboo as a cloned plant, scholars have recently proposed a strip cutting management model. This model offers advantages, such as centralized production, mechanized operation, and reduced bamboo production costs. By setting harvest and reserved areas, the mother bamboo in the reserved areas supplies water and nutrients underground to the bamboo shoots and young bamboo in the harvest areas, promoting their regeneration [2,3,4]. However, strip cutting causes a significant disturbance to Moso bamboo forests, leading to drastic changes in the environment and the expansion of the ecological niche of Moso bamboo. Additionally, because of its clonal integration, Moso bamboo absorbs more nutrients from the land to compensate for the material output caused by harvesting. Research on the natural recovery of new bamboo forests after strip cutting reveals a common phenomenon of “increased quantity, decreased quality”, where the number of new bamboo increases significantly, but the average diameter at breast height (DBH) and average height under the branches decrease considerably. Furthermore, analysis of the main soil nutrients revealed a significant decrease in total nitrogen and potassium contents under 8-meter-wide strip cutting, indicating a deficiency in soil nutrient reservoirs. These are some of the current problems associated with strip cutting [5,6,7,8].

Fertilization, an important measure in bamboo forest management, involves artificially adding substantial amounts of nutrients to the forest within a short period. This helps to compensate for the productivity output of the forest caused by the cloning compensation effect of the mother bamboo in the reserved area and changes in the microenvironment, such as those of light and temperature. Additionally, because of the directional nutrient preferences of Moso bamboo rhizomes, more rhizomes from the reserved area enter the harvest area to generate new shoots, facilitating the rapid recovery of the harvest area and shortening the restoration period of the strip cutting management model. Studies have suggested that a high nitrogen and high potassium fertilizer ratio can significantly improve the quality of Moso bamboo stands under strip cutting. The optimal fertilizer ratio was found to be N:P:K = 3.5:1:2 [9]; however, the best fertilization method and amount are yet to be determined.

From the perspective of strip cutting in Moso bamboo forests, this study sought to address two existing issues in the strip cut management model: the decline in the quality of new shoots and reduced soil fertility. Through well-designed and effective fertilization experiments, this study aimed to explore the impact of fertilization on soil fertility and individual stand biomass in strip cut Moso bamboo forests, providing valuable insights into the sustainable management of strip cutting.

2. Materials and Methods

2.1. Site Description

The study was conducted at the Yixing forest farm, Yixing City, Wuxi, Jiangsu Province, China (119°31′–120°03′ E, 31°07′–31°37′ N; Figure 1). This region is dominated by a low mountainous and hilly terrain, with an average elevation of approximately 100 m. The total area of the existing Moso bamboo forest is 672 ha, with a living growing stock of 100,000 m³ and a forest coverage rate of 97%. Most of the area consists of artificially established pure forests that exhibit distinct forest growth cycle patterns, including major (on-year) and minor (off-year) growth years [10]. The region falls under the influence of a north subtropical monsoon climate, characterized by warm and humid conditions throughout the year, with an average annual temperature of 15.8 °C and an average annual precipitation of 1184 mm. The primary forest management practices in the study area include selective harvesting of mature bamboo at age class IV (IV du) and above, disease and pest control, and the removal of weeds and deadwood [11,12].

2.2. Experiment Design

In 2022, 30 rectangular strip cutting plots were established in an on-year Moso bamboo forest with consistent initial bamboo density, slope, and elevation, in addition to similar site quality and stand structure. Strip cutting was performed along contour lines with a width of 8 m and length of 20 m, creating 30 plots. Basic information of sample area is shown in

Table 1. Basic information on the sample area in the Moso bamboo forest.

Treatment	Longitude	Latitude	Aspect	Slope (°)	Altitude (m)
C600–C1200	119°45′20″ E	31°15′37″ N	Southwest	3	80
S600–S1200	119°45′14″ E	31°15′40″ N	Northeast	9	102
B600–B1200	119°45′12″ E	31°15′43″ N	Southwest	17	138
CK1–CK3	119°45′10″ E	31°15′42″ N	Northeast	13	127

. The same width of the reserved plots was set on both sides of the strip cut plots. The function of the reserved plots was to transport nutrients to support the growth and development of the new bamboo in the SC through the underground whip root system [9].

The experiment employed a two-factor (fertilization methods and fertilization dosages), three-level complete factorial design (three fertilization methods were used: spreading, cave, and bamboo stump fertilization). Fertilization dosages were set at 600, 900, and 1200 kg/ha with nine treatments, each with three replications. Additionally, three strip cutting plots were left unfertilized as control treatments (CK), and the specific procedures for the three fertilization methods were as follows:

• Spreading fertilization: Compound fertilizer was evenly spread in the plots 2–3 days after precipitation during the fertilization period.
• Cave fertilization: Twenty holes were dug within each plot (10–20 cm deep), evenly distributed in two rows, and equal amounts of fertilizer were added to each hole.
• Bamboo stump fertilization: The internodes of the bamboo stumps within the harvest area were hollowed out, and compound fertilizer was applied to the cavities, reaching the bottom. The cavities were then covered with the topsoil.

These treatments were denoted as S, C, and B, respectively. Three commonly used commercial fertilizers were used: urea (with N content ≥ 46%), calcium superphosphate (with P₂O₅ content ≥ 12%), and potassium chloride (with K₂O content ≥ 60%). The ratio of these fertilizers was maintained at N:P:K = 3.5:1:2. Fertilization was performed in February, May, and September 2022. The same fertilization levels were maintained for each application, following the experimental design.

2.3. Biomass Survey

An aboveground biomass survey was conducted in November 2022. A standard tree analysis method was employed to calculate the average DBH of new bamboo in each plot. Of the new bamboo, standard bamboo of the corresponding size was selected, cut, and stripped of the branches and leaves. The bamboo culms, branches, and leaves were weighed separately. Standard branches were selected from the upper, middle, and lower layers of the Moso bamboo canopy and returned to the laboratory for analysis. According to the height of the cut bamboo, the culm was divided into segments every 2 m. The fresh weight was measured for each segment, and a segment of the bamboo culm from the upper end of each section was returned to the laboratory for morphological analysis. The dry weight was determined to calculate the individual plant biomass of Moso bamboo after drying in an oven at 105 °C for 30 min followed by 75 °C until a constant weight was achieved.

2.4. Soil Fertility Survey

The soil fertility survey was conducted during the stable soil conditions period in the Moso bamboo stand in the autumn–winter season, specifically in November 2022. A five-point sampling method was employed within each plot to collect soil samples at 0–10, 10–20, and 20–40 cm depths. Soil samples from the same location and depth were mixed thoroughly to create composite samples for each depth in each plot. The samples were divided into four equal portions using the quartering method. The selected indicators and methods for determination included soil total nitrogen (TN) content determined using the Kjeldahl method, soil alkali-hydrolyzable nitrogen content (AN) determined using the alkaline diffusion method, soil total phosphorus (TP) content determined using the alkaline fusion-molybdenum antimony anti-colorimetric method, soil available phosphorus (AP) content determined using the ammonium fluoride extraction-molybdenum antimony anti-colorimetric method, soil total potassium (TK) content determined using the alkaline fusion-flame photometer method, soil available potassium (AK) content determined using the ammonium acetate extraction-flame photometer method, soil organic carbon (SOC) content determined using the potassium dichromate oxidation-external heating method, soil sucrase (SC) activity determined using the 3,5-dinitrosalicylic acid colorimetric method, soil acid phosphatase (ACP) activity determined using the sodium phenyl phosphate colorimetric method, and soil catalase (CAT) enzyme activity determined using the potassium permanganate titration method [10].

2.5. Data Analyses

Data were processed using Microsoft Excel 2016 (Microsoft Corporation, Redmond, WA, USA). Statistical analyses were performed using SPSS version 20.0 (SPSS Inc., Chicago, IL, USA). Data statistics and graph construction were conducted using Microsoft Office Excel 2016 (Microsoft Corporation) and Origin21 (OriginLab, Northampton, MA, USA). One-way analysis of variance (ANOVA), least significant difference (LSD), and Duncan’s test were used to determine significant differences (α = 0.05) between biomass and soil properties in the ten treatments (nine fertilization treatments and CK). Homogeneous variance and assumptions of normality were examined using Leven and Shapiro–Wilk tests, respectively. Two-way analysis of variance (two-way ANOVA), including main effect analysis, interaction effect analysis, simple effect analysis, and post hoc multiple comparisons (LSD method), analyzes the total and available soil nutrients under different fertilization treatments.

3. Results

3.1. Total Soil Nutrients

As soil depth increased, TN exhibited a significant (p < 0.05) decreasing trend. TK also showed a decreasing trend, although the difference was not significant (p > 0.05) in the deeper soil layers (

Table 2. Total and available soil nutrients in Moso bamboo stands based on the fertilization method and dosage treatment.

Treatments	Soil Layer	TN	TP	TK	AN	AP	AK
	(cm)	(g/kg)	(g/kg)	(g/kg)	(mg/kg)	(mg/kg)	(mg/kg)
C600	0–10	1.92 ± 0.06 Abc	0.33 ± 0.02 Aab	9.13 ± 0.15 Cb	130.50 ± 1.87 Ac	4.66 ± 0.20 Aab	42.97 ± 3.17 Ab
	10–20	1.52 ± 0.06 Bb	0.34 ± 0.02 Aa	9.87 ± 0.02 Bcd	83.40 ± 8.79 Bb	2.61 ± 0.29 Bb	36.27 ± 1.45 Ba
	20–40	1.00 ± 0.02 Cb	0.36 ± 0.03 Aa	10.20 ± 0.04 Abc	38.82 ± 4.35 Cb	1.30 ± 0.14 Cbc	32.16 ± 1.24 Ba
C900	0–10	1.90 ± 0.12 Abc	0.34 ± 0.01 Aab	9.40 ± 0.13 Bb	141.79 ± 2.78 Ac	5.02 ± 0.21 Aa	41.38 ± 2.47 Ab
	10–20	1.42 ± 0.22 Bbc	0.33 ± 0.02 Aa	9.70 ± 0.06 Bcd	90.35 ± 3.08 Bb	2.34 ± 0.51 Bb	33.64 ± 3.13 ABa
	20–40	0.83 ± 0.08 Cbc	0.34 ± 0.02 Aab	10.81 ± 0.06 Ab	47.06 ± 3.57 Cb	1.43 ± 0.13 Bbc	28.18 ± 1.78 Ba
C1200	0–10	2.19 ± 0.03 Aab	0.39 ± 0.02 Aa	10.63 ± 0.82 Aa	150.90 ± 1.12 Abc	4.69 ± 0.45 Aab	48.51 ± 2.51 Aab
	10–20	1.87 ± 0.05 Ba	0.37 ± 0.00 Aa	11.27 ± 0.30 Ab	89.21 ± 10.47 Bb	2.85 ± 0.26 Bb	34.84 ± 4.65 Ba
	20–40	1.28 ± 0.06 Ca	0.38 ± 0.01 Aa	11.87 ± 0.14 Aa	55.76 ± 2.24 Cb	2.09 ± 0.04 Ba	32.60 ± 3.65 Ba
S600	0–10	2.02 ± 0.05 Abc	0.27 ± 0.02 Abc	9.85 ± 0.39 Aab	143.28 ± 8.53 Ac	4.93 ± 0.06 Aab	39.09 ± 1.53 Ab
	10–20	1.66 ± 0.22 Aab	0.27 ± 0.01 Aab	10.07 ± 0.37 Ac	84.91 ± 7.44 Bb	2.73 ± 0.24 Bb	31.58 ± 3.21 Ba
	20–40	1.11 ± 0.17 Bab	0.27 ± 0.04 Abc	10.89 ± 0.21 Ab	48.47 ± 3.66 Cb	1.60 ± 0.01 Cb	19.63 ± 0.56 Ca
S900	0–10	2.29 ± 0.07 Aa	0.37 ± 0.03 Aab	10.76 ± 0.88 Aa	159.94 ± 2.59 Ab	5.33 ± 0.09 Aa	47.43 ± 1.84 Ab
	10–20	1.79 ± 0.05 Bab	0.36 ± 0.03 Aa	11.97 ± 0.27 Aa	89.96 ± 14.29 Bb	3.04 ± 0.09 Bb	41.97 ± 1.25 Aa
	20–40	1.18 ± 0.22 Cab	0.37 ± 0.01 Aa	12.12 ± 0.16 Aa	52.71 ± 17.65 Bb	1.25 ± 0.11 Cbc	38.92 ± 2.73 Aa
S1200	0–10	2.09 ± 0.02 Ab	0.31 ± 0.07 Ab	10.64 ± 0.60 Aa	163.32 ± 6.45 Ab	4.79 ± 0.27 Aab	45.68 ± 1.98 Ab
	10–20	1.71 ± 0.17 Bab	0.29 ± 0.08 Aab	11.05 ± 0.24 Ab	75.19 ± 14.16 Bb	3.97 ± 0.12 Ba	33.98 ± 0.18 Ba
	20–40	1.12 ± 0.03 Cab	0.29 ± 0.05 Ab	11.26 ± 0.32 Aab	49.28 ± 11.85 Bb	1.17 ± 0.05 Cc	30.04 ± 0.31 Ca
B600	0–10	1.84 ± 0.06 Ac	0.31 ± 0.01 Ab	9.09 ± 0.09 Cb	141.47 ± 8.56 Ac	4.25 ± 0.30 Ab	38.97 ± 0.97 Ab
	10–20	1.50 ± 0.11 Bb	0.32 ± 0.02 Aab	9.53 ± 0.15 Bcd	77.89 ± 9.39 Bb	3.46 ± 0.40 Aab	34.13 ± 0.97 Ba
	20–40	1.16 ± 0.06 Cab	0.30 ± 0.01 Ab	10.13 ± 0.02 Abc	43.19 ± 0.73 Cb	1.21 ± 0.17 Bbc	27.04 ± 0.72 Ca
B900	0–10	1.77 ± 0.24 Ac	0.25 ± 0.05 Abc	10.34 ± 0.20 Aab	150.38 ± 2.99 Abc	4.31 ± 0.06 Ab	38.06 ± 0.60 Ab
	10–20	1.46 ± 0.12 Abc	0.26 ± 0.04 Ab	10.43 ± 0.25 Ab	67.55 ± 5.75 Bb	3.58 ± 0.06 Bab	31.02 ± 1.89 Ba
	20–40	0.93 ± 0.07 Bbc	0.25 ± 0.02 Abc	10.74 ± 0.03 Abc	54.63 ± 3.40 Bb	1.34 ± 0.13 Cbc	30.71 ± 0.40 Ba
B1200	0–10	1.84 ± 0.04 Ac	0.26 ± 0.02 Abc	10.70 ± 0.48 Aa	144.37 ± 4.10 Ac	5.31 ± 0.42 Aa	36.02 ± 0.22 Ab
	10–20	1.14 ± 0.30 Ac	0.27 ± 0.05 Aab	11.32 ± 0.29 Ab	71.09 ± 10.95 Bb	3.98 ± 0.05 Ba	35.70 ± 1.00 Aa
	20–40	0.74 ± 0.19 Abc	0.23 ± 0.04 Ac	10.93 ± 0.43 Ab	61.51 ± 11.37 Bab	1.49 ± 0.09 Cbc	30.52 ± 1.43 Ba
CK	0–10	1.81 ± 0.07 Ac	0.27 ± 0.00 Abc	9.38 ± 0.37 Ab	179.03 ± 8.94 Aa	0.85 ± 0.41 Ac	58.34 ± 9.56 Aa
	10–20	1.20 ± 0.09 Bc	0.24 ± 0.02 Bb	9.54 ± 0.39 Ad	122.72 ± 22.24 Ba	0.75 ± 0.65 Ac	42.39 ± 9.16 Ba
	20–40	0.74 ± 0.12 Cc	0.24 ± 0.02 Bc	9.94 ± 0.74 Ac	78.84 ± 14.73 Ca	0.40 ± 0.30 Ad	35.93 ± 9.25 Ba

Values are presented as mean ± standard deviation (n = 3). Different lowercase letters indicate significant differences between different treatments in the same soil layer, and different capital letters indicate significant differences between different soil layers in the same treatment (p < 0.05). TN, total nitrogen; TP, total phosphorus; TK, total potassium; AN, alkali-hydrolyzable nitrogen; AP, available phosphorus; AK, available potassium.

). Regardless of soil depth, all treated groups showed a significant (Table 2, p < 0.05) increase in the overall nutrient content compared with CK. Fertilization methods have main effects in TP for all depth soil layers, TN for the 0–40 cm layer and TK for the 20–60 cm layer (

Table 3. Two-way analysis of variance analysis of total and available soil nutrients under different fertilization methods and treatment dosages: F and p values.

	Soil Layer	F (Methods)	p (Methods)	F (Dosages)	p (Dosages)	F (Methods × Dosages)	p (Methods × Dosages)
	(cm)
TN	0–10	15.090	0.001	1.932	0.200	3.979	0.040
	10–20	7.031	0.014	0.018	0.982	3.514	0.054
	20–40	3.776	0.064	1.256	0.330	5.888	0.013
TP	0–10	8.389	0.009	0.314	0.738	3.496	0.055
	10–20	4.491	0.044	0.119	0.889	2.556	0.112
	20–40	17.269	0.001	0.949	0.423	5.012	0.021
TK	0–10	2.876	0.108	10.206	0.005	1.197	0.376
	10–20	16.043	0.001	50.007	0.000	16.308	0.000
	20–40	23.877	0.000	36.638	0.000	11.648	0.001
AN	0–10	12.768	0.002	14.106	0.002	2.246	0.144
	10–20	3.839	0.062	0.302	0.747	0.830	0.538
	20–40	0.730	0.509	3.141	0.092	0.702	0.610
AP	0–10	3.277	0.085	2.433	0.143	5.373	0.017
	10–20	24.061	0.000	11.272	0.004	2.000	0.178
	20–40	11.699	0.003	8.548	0.008	16.532	0.000
AK	0–10	22.731	0.000	3.869	0.061	7.657	0.006
	10–20	1.329	0.312	0.639	0.550	6.213	0.011
	20–40	1.434	0.288	20.511	0.000	22.273	0.000

p (methods) < 0.05, the main effect exists, and the fertilization method has a differential relationship with the nutrient content under the soil layer. p (dosages) < 0.05, the main effect exists, and the fertilization dosage has a differential relationship with the nutrient content under the soil layer. p (methods × dosages) < 0.05, an interaction exists.

and

Table 4. The effect of fertilization methods on total and available soil nutrients in Moso bamboo stands under different fertilization dosages.

Soil Layer	Dosages	Methods	TN	TP	TK	AN	AP	AK
(cm)	(kg/ha)		(g/kg)	(g/kg)	(g/kg)	(mg/kg)	(mg/kg)	(mg/kg)
0–10	600	C	1.92 ± 0.06 a*	0.33 ± 0.02 A*	9.13 ± 0.15 A	130.50 ± 1.87 A*	4.66 ± 0.20 a	42.97 ± 3.17 a*
		S	2.02 ± 0.05 a*	0.27 ± 0.02 A*	9.85 ± 0.39 A	143.28 ± 8.53 A*	4.93 ± 0.06 a	39.09 ± 1.53 a*
		B	1.84 ± 0.06 a*	0.31 ± 0.01 A*	9.09 ± 0.09 A	141.47 ± 8.56 A*	4.25 ± 0.30 a	38.97 ± 0.97 a*
	900	C	1.90 ± 0.12 b*	0.34 ± 0.01 A*	9.40 ± 0.13 A	141.79 ± 2.78 B*	5.02 ± 0.21 ab	41.38 ± 2.47 b*
		S	2.29 ± 0.07 a*	0.37 ± 0.03 A*	10.76 ± 0.88 A	159.94 ± 2.59 A*	5.33 ± 0.09 a	47.43 ± 1.84 a*
		B	1.77 ± 0.24 b*	0.25 ± 0.05 A*	10.34 ± 0.20 A	150.38 ± 2.99 B*	4.31 ± 0.06 b	38.06 ± 0.60 b*
	1200	C	2.19 ± 0.03 a*	0.39 ± 0.02 A*	10.63 ± 0.82 A	150.90 ± 1.12 A*	4.69 ± 0.45 a	48.51 ± 2.51 a*
		S	2.09 ± 0.02 b*	0.31 ± 0.07 A*	10.64 ± 0.60 A	163.32 ± 6.45 A*	4.79 ± 0.27 a	45.68 ± 1.98 a*
		B	1.84 ± 0.04 b*	0.26 ± 0.02 A*	10.70 ± 0.48 A	144.37 ± 4.10 A*	5.31 ± 0.42 a	36.02 ± 0.22 b*
10–20	600	C	1.52 ± 0.06 A*	0.34 ± 0.02 A*	9.87 ± 0.02 a*	83.40 ± 8.79 A	2.61 ± 0.29 A*	36.27 ± 1.45 a
		S	1.66 ± 0.22 A*	0.27 ± 0.01 A*	10.07 ± 0.37 a*	84.91 ± 7.44 A	2.73 ± 0.24 A*	31.58 ± 3.21 a
		B	1.50 ± 0.11 A*	0.32 ± 0.02 A*	9.53 ± 0.15 a*	77.89 ± 9.39 A	3.46 ± 0.40 A*	34.13 ± 0.97 a
	900	C	1.42 ± 0.22 A*	0.33 ± 0.02 A*	9.70 ± 0.06 c*	90.35 ± 3.08 A	2.34 ± 0.51 A*	33.64 ± 3.13 b
		S	1.79 ± 0.05 A*	0.36 ± 0.03 A*	11.97 ± 0.27 a*	89.96 ± 14.29 A	3.04 ± 0.09 A*	41.97 ± 1.25 a
		B	1.46 ± 0.12 A*	0.26 ± 0.04 A*	10.43 ± 0.25 b*	67.55 ± 5.75 A	3.58 ± 0.06 A*	31.02 ± 1.89 b
	1200	C	1.87 ± 0.05 A*	0.37 ± 0.00 A*	11.27 ± 0.30 a*	89.21 ± 10.47 A	2.85 ± 0.26 B*	34.84 ± 4.65 a
		S	1.71 ± 0.17 A*	0.29 ± 0.08 A*	11.05 ± 0.24 a*	75.19 ± 14.16 A	3.97 ± 0.12 A*	33.98 ± 0.18 a
		B	1.14 ± 0.30 A*	0.27 ± 0.05 A*	11.32 ± 0.29 a*	71.09 ± 10.95 A	3.98 ± 0.05 A*	35.70 ± 1.00 a
20–40	600	C	1.00 ± 0.02 a	0.36 ± 0.03 a*	10.20 ± 0.04 b*	38.82 ± 4.35 A	1.30 ± 0.14 a*	32.16 ± 1.24 a
		S	1.11 ± 0.17 a	0.27 ± 0.04 b*	10.89 ± 0.21 a*	48.47 ± 3.66 A	1.60 ± 0.01 a*	19.63 ± 0.56 b
		B	1.16 ± 0.06 a	0.30 ± 0.01 ab*	10.13 ± 0.02 b*	43.19 ± 0.73 A	1.21 ± 0.17 b*	27.04 ± 0.72 a
	900	C	0.83 ± 0.08 a	0.34 ± 0.02 a*	10.81 ± 0.06 b*	47.06 ± 3.57 A	1.43 ± 0.13 a*	28.18 ± 1.78 b
		S	1.18 ± 0.22 a	0.37 ± 0.01 a*	12.12 ± 0.16 a*	52.71 ± 17.65 A	1.25 ± 0.11 a*	38.92 ± 2.73 a
		B	0.93 ± 0.07 a	0.25 ± 0.02 b*	10.74 ± 0.03 b*	54.63 ± 3.40 A	1.34 ± 0.13 a*	30.71 ± 0.40 b
	1200	C	1.28 ± 0.06 a	0.38 ± 0.01 a*	11.87 ± 0.14 a*	55.76 ± 2.24 A	2.09 ± 0.04 a*	32.60 ± 3.65 a
		S	1.12 ± 0.03 a	0.29 ± 0.05 b*	11.26 ± 0.32 b*	49.28 ± 11.85 A	1.17 ± 0.05 b*	30.04 ± 0.31 a
		B	0.74 ± 0.19 b	0.23 ± 0.04 b*	10.93 ± 0.43 b*	61.51 ± 11.37 A	1.49 ± 0.09 b*	30.52 ± 1.43 a

Interaction, simple effects analysis, and differences between different treatments are represented by different lowercase letters; no interaction, one-way analysis of variance, differences between different treatments represented by different capital letters (p < 0.05). The significant main effect is represented by “*”.

). Fertilization dosages have main effects in TK for all depth soil layers, but no main effects for TN and TP were noted (Table 3 and

Table 5. The effect of fertilization dosages on total and available soil nutrients in Moso bamboo stands under different fertilization methods.

Soil Layer	Methods	Dosages	TN	TP	TK	AN	AP	AK
(cm)		(kg/ha)	(g/kg)	(g/kg)	(g/kg)	(mg/kg)	(mg/kg)	(mg/kg)
0–10	C	600	1.92 ± 0.06 b	0.33 ± 0.02 A	9.13 ± 0.15 A*	130.50 ± 1.87 C*	4.66 ± 0.20 a	42.97 ± 3.17 b
		900	1.90 ± 0.12 b	0.34 ± 0.01 A	9.40 ± 0.13 A*	141.79 ± 2.78 B*	5.02 ± 0.21 a	41.38 ± 2.47 b
		1200	2.19 ± 0.03 a	0.39 ± 0.02 A	10.63 ± 0.82 A*	150.90 ± 1.12 A*	4.69 ± 0.45 a	48.51 ± 2.51 a
	S	600	2.02 ± 0.05 a	0.27 ± 0.02 A	9.85 ± 0.39 A*	143.28 ± 8.53 A*	4.93 ± 0.06 a	39.09 ± 1.53 b
		900	2.29 ± 0.07 a	0.37 ± 0.03 A	10.76 ± 0.88 A*	159.94 ± 2.59 A*	5.33 ± 0.09 a	47.43 ± 1.84 a
		1200	2.09 ± 0.02 a	0.31 ± 0.07 A	10.64 ± 0.60 A*	163.32 ± 6.45 A*	4.79 ± 0.27 a	45.68 ± 1.98 a
	B	600	1.84 ± 0.06 a	0.31 ± 0.01 A	9.09 ± 0.09 B*	141.47 ± 8.56 A*	4.25 ± 0.30 b	38.97 ± 0.97 a
		900	1.77 ± 0.24 a	0.25 ± 0.05 A	10.34 ± 0.20 A*	150.38 ± 2.99 A*	4.31 ± 0.06 b	38.06 ± 0.60 a
		1200	1.84 ± 0.04 a	0.26 ± 0.02 A	10.70 ± 0.48 A*	144.37 ± 4.10 A*	5.31 ± 0.42 a	36.02 ± 0.22 a
10–20	C	600	1.52 ± 0.06 A	0.34 ± 0.02 A	9.87 ± 0.02 ab*	83.40 ± 8.79 A	2.61 ± 0.29 A*	36.27 ± 1.45 a
		900	1.42 ± 0.22 A	0.33 ± 0.02 A	9.70 ± 0.06 b*	90.35 ± 3.08 A	2.34 ± 0.51 A*	33.64 ± 3.13 a
		1200	1.87 ± 0.05 A	0.37 ± 0.00 A	11.27 ± 0.30 a*	89.21 ± 10.47 A	2.85 ± 0.26 A*	34.84 ± 4.65 a
	S	600	1.66 ± 0.22 A	0.27 ± 0.01 A	10.07 ± 0.37 c*	84.91 ± 7.44 A	2.73 ± 0.24 B*	31.58 ± 3.21 b
		900	1.79 ± 0.05 A	0.36 ± 0.03 A	11.97 ± 0.27 a*	89.96 ± 14.29 A	3.04 ± 0.09 B*	41.97 ± 1.25 a
		1200	1.71 ± 0.17 A	0.29 ± 0.08 A	11.05 ± 0.24 b*	75.19 ± 14.16 A	3.97 ± 0.12 A*	33.98 ± 0.18 b
	B	600	1.50 ± 0.11 A	0.32 ± 0.02 A	9.53 ± 0.15 c*	77.89 ± 9.39 A	3.46 ± 0.40 A*	34.13 ± 0.97 a
		900	1.46 ± 0.12 A	0.26 ± 0.04 A	10.43 ± 0.25 b*	67.55 ± 5.75 A	3.58 ± 0.06 A*	31.02 ± 1.89 a
		1200	1.14 ± 0.30 A	0.27 ± 0.05 A	11.32 ± 0.29 a*	71.09 ± 10.95 A	3.98 ± 0.05 A*	35.70 ± 1.00 a
20–40	C	600	1.00 ± 0.02 ab	0.36 ± 0.03 a	10.20 ± 0.04 c*	38.82 ± 4.35 B	1.30 ± 0.14 b*	32.16 ± 1.24 a*
		900	0.83 ± 0.08 b	0.34 ± 0.02 a	10.81 ± 0.06 b*	47.06 ± 3.57 AB	1.43 ± 0.13 b*	28.18 ± 1.78 a*
		1200	1.28 ± 0.06 a	0.38 ± 0.01 a	11.87 ± 0.14 a*	55.76 ± 2.24 A	2.09 ± 0.04 a*	32.60 ± 3.65 a*
	S	600	1.11 ± 0.17 a	0.27 ± 0.04 b	10.89 ± 0.21 b*	48.47 ± 3.66 A	1.60 ± 0.01 a*	19.63 ± 0.56 c*
		900	1.18 ± 0.22 a	0.37 ± 0.01 a	12.12 ± 0.16 a*	52.71 ± 17.65 A	1.25 ± 0.11 b*	38.92 ± 2.73 a*
		1200	1.12 ± 0.03 a	0.29 ± 0.05 ab	11.26 ± 0.32 ab*	49.28 ± 11.85 A	1.17 ± 0.05 b*	30.04 ± 0.31 b*
	B	600	1.16 ± 0.06 a	0.30 ± 0.01 a	10.13 ± 0.02 b*	43.19 ± 0.73 A	1.21 ± 0.17 a*	27.04 ± 0.72 a*
		900	0.93 ± 0.07 ab	0.25 ± 0.02 a	10.74 ± 0.03 a*	54.63 ± 3.40 A	1.34 ± 0.13 a*	30.71 ± 0.40 a*
		1200	0.74 ± 0.19 b	0.23 ± 0.04 a	10.93 ± 0.43 a*	61.51 ± 11.37 A	1.49 ± 0.09 a*	30.52 ± 1.43 a*

Interaction, simple effects analysis, and differences between different treatments are represented by different lowercase letters; no interaction, one-way analysis of variance, differences between different treatments represented by different capital letters (p < 0.05). The significant main effect is denoted by “*”.

). Using the spreading fertilization method, no significant (p > 0.05) differences in 0–10 cm soil nutrients were observed among the different fertilization dosages. However, in the 10–40 cm soil layer, the 900 kg/ha fertilization dosage leads to the highest TK content (Table 5). Under the 900 kg/ha fertilization dosage, the spreading fertilization method significantly (p < 0.05) increased TN in the 0–10 cm soil layer and TK in the 10–20 cm soil layer (Table 4).

3.2. Available Soil Nutrients

As soil depth increased, AN, AP, and AK, the three types of available nutrients, showed a significant (p < 0.05) decreasing trend (Table 2). In all soil layers, all fertilization treatments significantly increased AP content compared with that of CK (p < 0.05). Fertilization methods have main effects on AN and AK in the 0–10 cm soil layer and AP in the 10–20 cm soil layer (Table 3 and Table 4). Fertilization dosages have main effects in AN in the 0–10 cm soil layer, AP in the 10–40 cm soil layer, and AK in the 20–40 cm soil layer (Table 3 and Table 5). Under the 900 kg/ha fertilization dosage, the AN, AP, and AK contents in the 0–10 cm soil layer subject to the spreading fertilization method are all the highest (Table 4).

3.3. Soil Organic Carbon

SOC decreased significantly (Figure 2, p < 0.05) with increasing soil depth. In the 0–10 and 10–20 cm soil layers, the S900 treatment resulted in the highest SOC. However, in the 20–40 cm soil layer, SOC did not differ significantly among the different fertilization treatments (Figure 2, p > 0.05).

3.4. Main Enzyme Activities in the Soil

In the 0–10 cm soil layer, S600 and S900 treatments significantly (Figure 3, p < 0.05) reduced SC activity. The activities of CAT and ACP in fertilized soil did not significantly (Figure 3, p > 0.05) differ from those in CK. There is no regular variation between treatments in different soil layers. Overall, SC, CAT, and ACP decrease with increasing soil depth.

3.5. New Bamboo Stand Biomass and Allocation

Regarding total individual bamboo stands biomass, the plots under the spreading fertilization treatment method showed an overall higher biomass than that of CK with the peak occurring in the S900 treatment. Compared with CK, the S900 treatment increased the biomass per plant by 4.12 kg and increased the proportion of culm per plant by 5%. Under different fertilization treatments, the biomass allocation patterns showed a trend of increased culm proportions and decreased branch and leaf proportions compared with those of CK (Figure 4).

4. Discussion

In the strip cutting management of Moso bamboo forests, the deficiency in soil nutrient reserves, specifically the decline in total and available nutrients, is one of the challenges that fertilization treatments aim to address [13,14]. Total nutrients directly reflect the impact of nutrient input and are influenced by disturbances, such as harvesting and management practices. This is attributed to the capacity of the soil to absorb and retain nutrients, with soil aggregates playing a pivotal role in retaining ion nutrients and supporting productivity [15]. Strip cutting alters the forest environment through canopy gaps, affecting light conditions, microclimate, and understory vegetation growth, subsequently affecting soil physical characteristics. This results in decreased soil density, increased soil porosity, and enhanced water-holding capacity and capillary porosity, leading to better nutrient retention. However, introducing considerable amounts of inorganic fertilizers could negatively affect soil physical attributes, including porosity and soil structure [16], implying there is a certain threshold for the increase in nutritional components after fertilization. In this study, under the spreading fertilization method, the threshold for soil total nutrients was reached at 900 kg/ha, where the total nutrients at various soil depths exceeded those at 1200 kg/ha (Table 2 and Table 5, p < 0.05). For cave and bamboo stump fertilization at 900 and 1200 kg/ha, respectively, the overall soil total nutrients showed similar patterns, with no significant improvements observed with increasing fertilization dosages. Among the different fertilization methods, spreading resulted in the highest soil total nutrients in the 0–10 cm soil layer, whereas the cave treatment resulted in the highest total nutrients in the 10–20 cm soil layer. In the spreading method, fertilizer is directly applied to the surface of the forest, with nutrients primarily entering the deeper soil layers through settling and leaching. Cave fertilization targets the middle and deeper soil layers where Moso bamboo roots are predominantly distributed. Comparatively, bamboo stump fertilization resulted in lower total soil nutrients, indicating less effective supplementation of soil nutrient deficiencies in strip cut Moso bamboo forests. Nonetheless, previous studies have suggested that bamboo stump fertilization enhances soil fertility postharvest [17]. Compared with bamboo stump fertilization, the spreading and cave methods are more suitable for implementing strip cutting and postharvest fertilization of Moso bamboo forests with gentle slopes and moderate densities. With increasing soil depth, AN, AP, and AK exhibited a significant decreasing trend (Table 2, p < 0.05). However, regarding different fertilization methods and dosages, varying nutrient input by altering the amount of fertilizer or changing the location of nutrient input through different fertilization methods resulted in neither consistent trends nor significant differences in available nutrients.

SOC is a crucial indicator of soil fertility and directly influences soil fertility, water retention capacity, soil structure, and biodiversity. In the present study, SOC in the 20–40 cm soil layer was significantly lower than that in the 0–20 cm soil layer (Figure 2, p < 0.05). This can be attributed to the higher microbial activity in the 0–20 cm soil layer, where root exudates from crops decay and form organic colloids, leading to higher SOC and active component contents. However, as soil depth increases, the fixation effect of organic colloids weakens [18]. The C1200, S900, and S1200 treatments significantly increased SOC in the 0–10 cm soil layer. The application of inorganic fertilizers helps to improve the activity of soil surface SOC [19]. However, in the 20–40 cm soil layer, the treatments and CK did not significantly differ, indicating that the fertilization treatments did not significantly affect SOC in deeper soil layers. This finding is consistent with those reported by Liu et al. [20].

The results showed a significant decreasing trend in the main soil enzyme activities with increasing soil depth, consistent with the findings of other studies [21]. SC plays a crucial role in soil carbon cycling [22]. In the present study, the spreading fertilization treatment significantly reduced SC activity in the 0–10 cm soil layer (Figure 3, p < 0.05). The bamboo forest surface layer contains substantial amounts of litter, animal remains, and other organic matter, making it the primary source of soil humus. Consequently, microorganisms in the surface layer of the soil require higher relative activity to release more enzymes. Incidentally, the surface and shallow soil layers are the primary targets for fertilization treatments, reflecting the production capacity of SC and related microorganisms. There is a certain degree of inhibition under favorable nutrient conditions and abundant substrate availability. Soil CAT enzymes participate in the decomposition of harmful substances, such as hydrogen peroxide, and are related to soil resilience [23]. The CAT enzyme activity in the soil under fertilization treatments did not significantly differ from that of CK, indicating that fertilization treatment did not trigger soil resilience mechanisms. Soil ACP enzymes hydrolyze soil organic phosphorus into inorganic forms that plants can easily absorb and utilize. The current study showed that soil ACP activity in the fertilizer-treated plots did not significantly differ from that of CK; however, the AP content in the soil significantly increased (Figure 3, p < 0.05), conforming to the pattern where enzyme activity remains unchanged, but reaction rates accelerate with increasing substrate concentration.

Aboveground bamboo biomass is a primary product of bamboo forest management and serves as a significant indicator of bamboo quality and forest productivity [24]. Disturbances caused by strip cutting operations in bamboo forests can alter the original nutrient distribution and utilization patterns [8]. When plants experience changes in nutrient availability, they adjust their total biomass and allocation strategies [25]. After strip cutting, competition within the bamboo forest intensifies, resources become constrained, and postharvest regenerated bamboo exhibits prostrate growth characteristics to adapt optimally to the altered environment by adjusting organ biomass allocation. Under fertilization treatments, the nutrient environment of the stands improved, and the growth of Moso bamboo was no longer constrained. Existing research suggests two pathways through which fertilization increases bamboo biomass. One is direct nutrient uptake by plant organs, primarily potassium, which promotes the hardening and growth of branches, stems, and other organs [26]. The second pathway is enhanced photosynthesis, primarily through nitrogen uptake, which boosts chlorophyll synthesis and increases photosynthetic rates, leading to higher dry matter accumulation [27]. This enhancement also has a certain threshold. Under high nitrogen and potassium fertilization ratios and relatively high fertilization dosages (1200 kg/ha), individual bamboo stand biomass decreased, showing an unimodal trend of 900 > 1200 > 600 kg/ha (Figure 3). Regarding the allocation of newly generated biomass, fertilized strip cut bamboo stands showed an increase in culm biomass values and proportions, whereas leaf and branch biomass values and proportions decreased. This differs from the results of Xu et al. [28], who fertilized Quercus acutissima and Phoebe bournei seedlings. This discrepancy can be attributed to the specific characteristics of bamboo. In the initial growth stage, bamboo focuses primarily on rapid vertical growth, swiftly occupying the upper canopy space and then branching out and expanding its leaves. Therefore, unlike other tree species, Moso bamboo does not require significant investment in photosynthetic structures, such as leaves, because the excellent light conditions in the upper canopy space can meet its growth needs. Conversely, bamboo allocates more resources to culm growth to increase its height and strengthen its resistance to lodging and broken branches. To a certain extent, this demonstrates bamboo’s high plasticity in biomass allocation, indicating its strong adaptability to changes in nutrient environments [29].

This study is aimed at restoring soil fertility in forest land and improving the biomass of individual bamboo plants. However, there is still a gap in research in terms of explaining the fate and utilization efficiency of nutrients, and the experimental design did not consider the impact of forest edge effects. Therefore, in the future, research should focus on cost-effective, efficient, and economically friendly fertilization schemes for the restoration of forest productivity and guide actual production processes.

5. Conclusions

Fertilization significantly increased TN, TP, TK, and AP in the soil of a strip cut bamboo forest. This helped address soil nutrient deficiency to a certain extent. Among the different fertilization methods, spreading fertilizer promoted soil fertility restoration better than cave and bamboo stump fertilization. Spreading fertilizer at moderate rates yielded the best results in increasing individual bamboo stand biomass while also leading to decreased proportions of branches and leaves and increased proportions of culms in biomass allocation. Overall, the spreading fertilization method, at an application rate of 900 kg/ha, proved most effective in promoting postharvest soil fertility restoration and enhancing individual bamboo stand biomass in the context of strip cutting bamboo forest management. The use of the S900 fertilization method is the best suited to improve the individual bamboo stand biomass, prevent soil fertility decline, and achieve efficient and sustainable management.