The effects of subsurface irrigation at different soil water potential thresholds on the growth and transpiration of Populus tomentosa in the North China Plain

Figures & data

Figure 1. Soil water potential (SWP) variation under (a) T₂₅, (b) T₅₀ and (c) T₇₅ treatments and (d) precipitation in 2010 and 2011. SWP data gaps in (a), (b) and (c) are due to data lost. Dashed lines in (a), (b) and (c) represent the target thresholds of −25, −50 and −75 kPa, respectively. Due to equipment failure, a large amount of precipitation was not recorded in August 2011

Figure 2. Soil water content (SWC) dynamics at 100 and 120 cm depths under different SWP treatments in 2011. The short solid bars represent irrigation events and the long bar indicates a rainfall of 83 mm

Figure 3. Dynamics of groundwater level from August 2009 to October 2012. Dashed lines indicate the depth of 100, 200, 300 and 400 cm

Table 1. Monthly precipitation and reference crop potential evapotranspiration (ET₀) in the experiment site from April to October 2008–2011

Attribute	Year	Month
		4	5	6	7	8	9	10
ET0 (mm)	2008		139	115	98	92	81	64
	2009	97	131	144	95	82	64	75
	2010	80	111	114	101	70	61	59
	2011	96	105	116	97	72	51	47
	Mean	91	121	122	98	79	64	61
Precipitation (mm)	2008		25	40	145	44	43	22
	2009	5	78	134	180	122	88	0
	2010	15	11	83	187	438	36	9
	2011	18	42	72	160	89^a	90	16
	Mean	13	39	82	168	202^b	64	12

^aDue to equipment failure, a large amount of precipitation was not recorded

^bCalculated using only the data of 2008–2010

Figure 4. Mean daily transpiration of Populus tomentosa on a ground area basis (E) under different treatments in 2010

Figure 5. Monthly basal area at breast height (ABH) increments of P. tomentosa under different treatments in 2010 and 2011. Data are means of randomly selected trees within each treatment

Table 2. Adjusted mean increments of above-ground dry biomass (ADB) per hectare in different treatments in 2010 and 2011

Treatment	ADB increment^a (mg ha^−1)
	2010	2011
T25	17.5(1.2) a	14.3(1.2) ab
T50	15.3(1.2) a	14.5(1.1) ab
T75	14.1(1.2) ab	14.8(1.1) a
CK	11.4(1.2) b	11.2(1.1) b

Data are means (standard error). Different lower-case letters within the same column in the same year indicate significant difference at P < 0.05 according to LSD test