Nutrient leaching under zero tension in a subtropical clonal eucalypt plantation on a sandy soil in South Africa

Figures & data

Table 1: Basic soil physical and chemical properties of the top 1.0 m (in 0.20 m increments) at the start of the study

	Soil depth (m)
Physical/chemical property	0–0.2	0.2–0.4	0.4–0.6	0.6–0.8	0.8–1.0
Bulk density (g cm^−3)	1.53	1.55	1.57	1.59	1.61
Clay (%)	2.5	2.3	2.2	1.8	2.0
Sand (%)	94.5	95.3	96.0	95.9	96.2
Silt (%)	3.0	2.4	1.8	2.3	1.7
pH (KCl)	4.35	4.31	4.33	4.36	4.37
Organic content (Walkley-Black) (g kg^−1)	4.3	2.7	2.1	1.8	1.6
Total Kjeldahl-nitrogen (g kg^−1)	0.39	0.37	0.28	0.35	0.30
Phosphorus (Bray-2) (mg kg^−1)	2.61	1.60	1.49	1.95	3.04
K^+(cmolc kg^−1)	0.02	0.03	0.04	0.03	0.03
Ca^2+(cmolc kg^−1)	0.45	0.46	0.49	0.91	0.51
Mg^2+(cmolc kg^−1)	0.20	0.22	0.24	0.28	0.23
Na^+(cmolc kg^−1)	0.03	0.03	0.04	0.04	0.04
Exchangeable acidity (cmolc kg^−1)	0.31	0.31	0.33	0.36	0.36
Cation exchange capacity (cmolc kg^−1)	0.93	0.94	1.03	1.49	1.03
Acid saturation (%)	25	29	32	34	36

Figure 1: Soil solution, rainfall and canopy drainage NH₄-N (a), NO₃-N (c) and organic-N (e) concentrations measured at 15 cm depth, and NH₄-N (b), NO₃-N (d) and organic-N (f) concentrations measured at 50 cm and 100 cm depths for felled and standing crop areas of the study site. Dashed vertical lines represent (A) felling, (B) residue burning, (C) planting and (D) canopy closure. Error bars represent a single SD across each treatment

Figure 2: Soil solution and volume weighted rainfall and canopy drainage K⁺ (a), Ca²⁺ (c), Mg²⁺ (e) and Na⁺ (g) concentrations recorded at 15 cm depth and K⁺ (b), Ca²⁺ (d), Mg²⁺ (f) and Na⁺ (h) concentrations recorded at 50 and 100 cm depths for felled and standing crop areas of the study site. Vertical shaded areas represent (A) felling, (B) residue burning, (C) planting and (D) canopy closure. Error bars represent a single SD across each treatment

Table 2: Nutrient leaching (kg ha^–1) beyond 1.0 m depth for felled and standing crop areas of the study between felling and planting and at six-month intervals after planting. Different superscript letters denote a significant difference between treatments for each period at LSD_0.05

Nutrient	New crop time period	Nutrient leaching in each treatment (kg ha^−1)			P-value	Nutrients added with rainfall (kg ha^−1)
		Standing crop	Burn	No burn
NH4-N	Felling to planting Planting to 6 months 6 to 12 months 12 to 18 months Felling to 12 months	1.2^a 1.0^a 0.0^a 1.0^a 2.2^a	1.0^a 0.5^a 0.5^b 0.4^a 2.1^a	1.0^a 2.4^b 0.2^c 0.3^a 3.5^b	0.094 0.009 <0.001 0.057 0.001	4.3 6.8 1.5 2.7 12.6
NO3-N	Felling to planting Planting to 6 months 6 to 12 months 12 to 18 months Felling to 12 months	0.4^a 0.5^a 0.0^a 0.4^a 0.9^a	5.3^b 26.2^b 0.4^b 0.4^a 31.9^b	5.3^b 10.9^c 0.4^b 0.7^a 16.6^c	<0.001 <0.001 0.042 0.182 0.001	1.8 2.0 0.9 0.7 4.7
Organic-N	Felling to planting Planting to 6 months 6 to 12 months 12 to 18 months Felling to 12 months	0.2^a 3.5^ab 0.2^a 3.8^a 3.9^a	1.2^a 2.4^a 2.1^b 3.2^a 5.7^b	1.2^a 6.2^b 3.2^b 3.8^a 10.5^b	<0.001 <0.001 0.001 0.3280.008	2.5 4.2 0.9 1.3 7.6
K	Felling to planting Planting to 6 months 6 to 12 months 12 to 18 months Felling to 12 months	3.4^a 9.3^a 0.4^a 16.1^a 13.1^a	21.8^b 89.0^b 8.0^b 10.1^b 118.8^b	21.8^b 104.2^c 6.0^c 9.6^b 132.0^c	<0.001 <0.001 <0.001 0.005 <0.001	4.8 5.4 3.5 3.7 13.7
Ca	Felling to planting Planting to 6 months 6 to 12 months 12 to 18 months Felling to 12 months	3.5^a 2.9^a 0.2^a 4.9^a 6.6^a	23.9^b 67.6^b 2.4^b 5.8^a 93.9^b	23.9^b 55.1^b 3.5^c 5.9^a 82.5^b	<0.001 0.001 <0.001 0.149 <0.001	2.0 7.7 1.2 1.9 10.9
Mg	Felling to planting Planting to 6 months 6 to 12 months 12 to 18 months Felling to 12 months	5.9^a 8.4^a 0.7^a 17.8^a 15.1^a	45.6^b 62.2^b 4.1^b 6.8^b 111.9^b	45.6^b 58.6^b 4.6^b 7.7^b 108.7^b	<0.001 <0.001 0.455 <0.001 <0.001	1.8 0.9 1.1 1.0 3.8
Na	Felling to planting Planting to 6 months 6 to 12 months 12 to 18 months Felling to 12 months	22.7^a 35.3^a 2.8^a 81.2^a 60.7^a	141.6^b 157.5^b 10.1^b 18.4^b 309.3^b	141.6^b 149.3^b 8.2^c 19.1^b 299.1^b	<0.001 0.182 <0.001 <0.001 <0.001	23.1 29.7 7.5 9.9 60.3

Table 3: Aboveground nutrient pools at felling and canopy closure (trees and residues) and nutrient uptake with growth during felling to canopy closure of the new crop. Different superscript letters denote a significant difference (LSD_0.05; all P values are <0.001). The propagated SE is shown in parentheses

Pool or flux at each time	Treatment	Nutrient (kg ha^−1)
		N	P	K	Ca	Mg	Na
Nutrients contained in trees and residues
Felling	Standing crop	403.1 (11.7)	43.9 (2.1)	194.2 (10.5)	683.5 (28.0)	120.5 (4.6)	27 (1.2)
	Felled plots	294.7 (40.9)	25.7 (7.6)	112.2 (43.1)	605.4 (176.7)	103.9 (27.2)	18.9 (5.3)
Time of residue burning	No burn	232.3 (15.2)	11.0 (0.7)	23.0 (1.5)	448.6 (29.3)	60.9 (4.0)	2.6 (0.4)
	Burn (ash)	111.1 (53.4)	8.2 (3.9)	19.7 (9.5)	413.9 (198.9)	39.3 (18.9)	4.1 (2.0)
Canopy closure	Standing crop	381.9^a	46.2^a	203.1^a	688.4^a	114.2^a	28.3^a
	Burn	75.1^b	5.0^b	66.0^b	50.9^b	16.8^b	2.7^b
	No burn	241^c	12.0^c	68.9^b	553.2^c	49.7^c	5.9^c
Nutrient uptake into trees between felling and canopy closure
Standing crop	Litter fall	116.7 (20.7)	4.6 (0.8)	22.3 (5.1)	119 (22.2)	29.5 (5.8)	12.2 (2.7)
Standing crop	Tree uptake	15.1^a	2.6^a	13.4^a	35.3^a	5.9^a	1.5^a
Burn	Tree uptake	75.1^b	5.0^b	66.0^b	50.9^b	16.8^bc	2.7^b
No burn	Tree uptake	64.9^b	4.3^bc	57.6^b	42.5^c	14.8^c	2.4^b

Table 4: Soil nutrient pools at incremental depths between 0 and 1.0 m at the end of the study. Significant differences between treatments are shown as different superscripts between total pool sizes for each depth range (LSD_0.05)

Treatment	Soil depth	Total N (kg ha^−1)	Bray-2 extractable P (kg ha^−1)	Exchangeable base cation
				K	Ca	Mg	Na
Standing crop		1 248^a	8.4^a	34.6^a	350^a	79.5^a	29.8^a
Burn		1 130^a	11.6^a	67.5^ab	940^b	112.1^b	28.8^a
No burn	0–0.15	927^a	9.7^a	105.3^b	532^ac	98.3^ab	24.4^a
P-values		0.235	0.699	0.002	0.006	0.043	0.072
Standing crop		2 760^a	3.4^a	16.7^a	152^a	78.8^a	90.4^a
Burn		2 245^ab	4.1^a	8.3^a	247^a	82.2^a	63.6^b
No burn	0.15–0.5	1 778^b	6.4^a	23.2^a	234^a	72.9^a	57.4^b
P-values		0.014	0.411	0.196	0.257	0.902	<0.001
Standing crop		2 653^a	9.4^a	14.2^a	249^a	143.6^a	95.6^a
Burn		1 732^b	8.0^a	17.3^a	224^a	72.4^a	30.0^b
No burn	0.5–1.0	2 086^b	8.0^a	36.1^a	176^a	71.5^a	8.8^b
P-values		<0.001	0.818	0.652	0.468	0.410	<0.001
Standing crop		6 661^a	21.2^a	65.5^a	751^a	301.9^a	215.8^a
Burn		5 107^b	23.7^a	93.1^b	1 411^b	266.7^a	122.4^b
No burn	0–1.0	4 791^b	24.2^a	164.6^c	942^a	242.7^a	90.6^b
P-values		0.030	0.830	0.015	0.040	0.530	<0.001