Net and gross nitrification in tea soils of varying productivity and their adjacent forest and vegetable soils

Figures & data

Table 1. Selected basic properties of the tested soils

Soil type	pH^# (H2O)	Organic C (%)	Total N (%)	C/N	Microbial biomass C^# (mg kg^−1)	−N^# (mg kg^−1)	−N^# (mg kg^−1)	Available P (mg kg^−1)	Exchangeable K (mg kg^−1)
HTP	3.32 ± 0.07c	3.93 ± 0.52a	0.38 ± 0.04a	10.37 ± 0.65b	277.9 ± 61.7b	68.5 ± 7.6 ab	0.8 ± 0.4c	556 ± 28a	220 ± 29b
MTP	3.43 ± 0.04c	2.13 ± 0.28b	0.20 ± 0.02b	10.56 ± 0.63b	211.1 ± 8.7 cd	47.4 ± 2.8b	2.2 ± 0.3 ab	118 ± 18c	213 ± 25b
LTP	3.89 ± 0.03b	1.71 ± 0.08b	0.15 ± 0.02c	11.48 ± 1.53b	151.7 ± 18.7d	13.4 ± 0.9c	1.9 ± 0.4b	68 ± 8d	138 ± 19c
F	4.01 ± 0.05b	0.86 ± 0.08c	0.09 ± 0.01d	10.21 ± 1.59b	258.5 ± 22.2 bc	22.3 ± 0.6c	3.1 ± 0.7a	Tr. e	98 ± 9c
V	7.18 ± 0.24a	3.50 ± 0.36a	0.23 ± 0.03b	14.61 ± 0.56a	584.3 ± 34.5a	84.6 ± 15.3a	0.3 ± 0.4c	171 ± 31b	551 ± 114a
HTP, high tea production; MTP, middle tea production; LTP, low tea production; F, forest; V, vegetable; H2O, purified water; C, carbon; N, nitrogen; , nitrate; , ammonium; P, phosphorus; K, potassium. ^#Soil pH, microbial biomass C, −N and −N were determined by using fresh soils after a pre-incubation period. Other soil parameters were determined by using air-dried soils. Different letters within same column indicate significant difference of mean value at p < 0.05. Data are mean ± standard deviation (SD) (n = 3).

Figure 1. Nitrate change in different soils incubated without nitrogen (N) fertilizer. Soil types: HTP, high tea production; MTP, middle tea production; LTP, low tea production; F, forest; V, vegetable. –N, nitrate N. Vertical bars show standard deviations.

Table 2. Net nitrification rates (mg kg⁻¹ d⁻¹) with nitrogen (N) fertilizer (ammonium sulfate) and without N, incubated for 3 and 35 d in different types of soils

	Net nitrification rate in 3 d			Net nitrification rate in 35 d
Soil type (ST)	−N	+N	Sig. between −N and + N	−N	+N	Sig. between −N and +N
HTP	10.39 ± 3.75a	8.06 ± 0.74b		1.97 ± 0.18a	6.83 ± 0.01a	***
MTP	2.94 ± 0.26bc	9.05 ± 3.69b	*	1.55 ± 0.01b	2.28 ± 0.09c	**
LTP	0.53 ± 0.12c	2.57 ± 0.65c	*	0.29 ± 0.00c	1.51 ± 0.01d	***
F	0.69 ± 0.27c	0.04 ± 0.59c		0.37 ± 0.04c	0.64 ± 0.03e	*
V	3.45 ± 1.41b	65.13 ± 2.58a	***	1.43 ± 0.25b	6.14 ± 0.05b	**
ANOVA test (F value)
ST	354***			806***
T	371***			1865***
ST × T	342***			344***
Soil type HTP, high tea production; MTP, middle tea production; LTP, low tea production; F, forest; V, vegetable. Different letters within same column indicate significant difference of mean value at p < 0.05. Data are mean ± SD (n = 3). ANOVA test: ST, soil type, T, treatments between –N and +N. *, ** and *** denote significant difference at p < 0.05, p < 0.01 and p < 0.001, respectively.

Figure 2. Mineral nitrogen (N) change in different soils incubated with ammonium sulfate. Soil types: HTP, high tea production; MTP, middle tea production; LTP, low tea production; F, forest; V, vegetable. –N, ammonium N. Vertical bars show standard deviations.

Figure 3. Gross nitrification rate and nitrate consumption in different soils. Soil types: HTP, high tea production; MTP, middle tea production; LTP, low tea production; F, forest; V, vegetable. –N, ammonium N. Vertical bars show standard deviations. Different letters denote significant differences (p < 0.05) between gross nitrification rate and microbial consumption rate in the same soil.

Figure 4. Relationships between nitrogen (N) application rate and net (a) and gross (b) nitrification rates.