Effect of K-type and Ca-type artificial zeolites applied to high sodic soil on the growth of plants different in salt tolerance

Abstract

The present study aimed to investigate the effects of K-type and Ca-type artificial zeolites on the growth and water and element absorptions of kidney bean (Phaseolus vulgaris L.), tomato (Lycopersicon esculentum Mill), maize (Zea mays L.) and beet (Beta vulgaris L.) in high sodic soil. Tottori sand dune soil, which was used as a control, was converted to high sodic soil mixed with salts. Each type of zeolite was mixed into the high sodic soil at rates of 0, 1, 2 and 5%. The results showed that kidney bean, tomato and maize died in high sodic soil 25–27 days after transplanting (DAT), whereas beet survived, although its growth was extremely suppressed at 26 DAT. The addition of Ca-type zeolite improved growth in all of the tested plants. Even 4 DAT the growth of beet was improved by recovery of water absorption, and growth of tomato was improved by recovery of Ca and K absorptions and cation balance, and restriction of Na absorption. Growth of kidney bean and maize improved at 11 or 13 DAT by recovery of water absorption and Ca and K absorptions. After 4 DAT, water absorption and P and K absorptions of beet were highly recovered compared with those of the other plants; beet growth improved to a large degree. The ameliorative effect of 5% Ca-type zeolite was lower than that of 2% in tomato, maize and beet because the excessive uptake of Ca restricted P transport from root to shoot, and high electrical conductivity of the soil solution restricted water uptake. Even 1% K-type zeolite addition suppressed growth of beet at 4 DAT, and the addition of 2% or 5% of K-type zeolite suppressed the growth of tomato and maize 11 or 13 DAT. Higher concentrations of HCO⁻ ₃ and CO²⁻ ₃, and pH of the soil solution of K-type zeolite treatments might inhibit water absorption by roots.

Key words:

• artificial zeolite
• element absorption
• pH
• sodic soils
• water absorption

INTRODUCTION

Salinization and sodication of soils are major problems in farming in arid and semi-arid regions. The low osmotic potential in saline soil (electrical conductivity > 4 dS m⁻¹) inhibits water uptake by plants (Lea-Cox and Syvertsen 1993). Plant growth is extremely restricted in sodic soil (exchangeable sodium percentage > 15 and pH > 8.5) by the toxicity of Na and B (Maas 1984), by the decrease in K, Ca and Mg uptake (Bernstein et al. 1974, Perez-Alfocea et al. 1993), and by the low availability of Fe, Mn, Zn and Cu (Page et al. 1996).

The disposal of coal fly ash, which is generated in thermal power plants, is a serious environmental problem (Clarke 1994). As the artificial zeolite that is produced from coal ash is abundant in Ca and/or K, we expect that the addition of zeolite can ameliorate plant growth in sodic soils. The addition of K and Ca has been shown to ameliorate plant growth in high Na conditions (Grieve and Fujiyama 1987).

Most studies related to the hazards of NaCl (Grattan and Grieve, 1999) and the response of plants to Na have been investigated using solution cultures. However, solution culture cannot reproduce the soil condition. We reproduced sodic soils with high concentrations of Na⁺, CO²⁻ ₃ and HCO⁻ ₃ from sandy soil. The addition of 5% (w/w) of both zeolites improved growth in beet, which is salt tolerant and grows in a wide range of sodicity levels (Yamada et al. 2002) and Ca-type zeolite saved maize (moderately salt sensitive) and can be grown in high sodic soils (M. Yamada et al., unpubl. data, 2000). However, the ameliorative effect of zeolites at an early stage remains unclear because, in general, any effects were analyzed approximately 50 days after transplanting. In the present study, therefore, the effect of zeolites on plant growth was investigated from 4 days to 4 weeks after transplanting. Application of artificial zeolite is attractive if it can improve the growth of glycophytes, which are generally salt sensitive. In this study, we also examined tomato and kidney bean, which are moderately salt sensitive and salt sensitive, respectively (Maas 1984). As the addition of 5% K-type, and Ca-type zeolite in particular, was excessive for maize growth in a low sodic soil (M. Yamada et al., unpubl. data, 2000), we included treatments of 1% and 2% of both types of zeolites in this study.

MATERIALS AND METHODS

Preparation and chemical analysis of soil

The experimental set up for the current study was similar to that described by Yamada et al. (2002). Tottori sand dune soil was used for this experiment. The soil was converted into saline high sodic soil (HSO) by adding 0.2, 0.2 and 1.5 cmol kg⁻¹ CaCl₂·2H₂O, MgSO₄·7H₂O and Na₂CO₃, respectively. A non-sodicated control soil (CO) was also included. Air-dried K-type or Ca-type zeolites (Kimura Chemical Plants, Amagasaki City, Japan) were uniformly applied to the HSO at rates of 1, 2 and 5% (equivalent to 10, 20 and 50 g kg⁻¹). These treatments were denoted as KZ1, KZ2 and KZ5 and CAZ1, CAZ2 and CAZ5, respectively. Four kilograms of soil was placed into each 4 L pot. Basal doses of NH₄NO₃, NH₄H₂PO₄ and K₂SO₄ were also applied at rates of 0.36, 0.18 and 0.13 cmol kg⁻¹ soil. Potassium was not applied in the KZ treatments. The treatments were replicated four times. The pH, electrical conductivity (EC) and concentration of cations and anions in both zeolites and those for saturation extracts of soils before plant cultivation were measured and the exchangeable sodium percentage (ESP) was calculated as described previously (Yamada et al. 2002).

Cultivation and chemical analysis of plants

Kidney bean (Phaseolus vulgaris L. cv. Naaru), tomato (Lycopersicon esculentum Mill cv. Saturn), maize (Zea mays L. cv. Yellow dent) and beet (Beta vulgaris L. cv. Sugarmangold) were grown in the glass-dome of the Arid Land Research Center, Tottori University, Tottori, Japan, where the maximum temperature was kept below 30°C in 2000. Seeds were sown in 6 cm diameter vinyl pots filled with CO soils and then seedlings were transplanted to the 4 L pots. One to 15 shoots were harvested at 4 days after transplanting (DAT), 11 or 13 DAT (11–13 DAT) and 25, 26 or 27 DAT (25–27 DAT). At the last sampling, the roots were also harvested. The sowing, transplanting and sampling dates are shown in Table 1. Fresh and dry weights of plant species were measured and the water deficit (WD) of shoots was calculated as described previously (Yamada et al. 2002). The K, Na, Ca and Mg concentrations (cmol kg⁻¹, hereafter referred to by the element name with a subscript c) of shoots and roots were measured as described previously (Yamada et al. 2002) at 4 DAT and 25–27 DAT. The P concentration (P_c) of shoots and roots was determined by the vanado-molybdate yellow method. The concentration ratios of Na to K, Ca and Mg of shoots were calculated at 4 DAT and the ratio of Na to (K + Ca + Mg) was also calculated at 25–27 DAT. The relative dry weight and mineral uptakes of each treatment to CO were calculated at 25–27 DAT. Data were analyzed statistically and the means were compared using Duncan's new multiple range test (P < 0.05).

RESULTS

Chemical properties of soil

In HSO, the Na⁺, CO²⁻ ₃ and HCO⁻ ₃ concentrations for saturation extracts were extremely high, whereas the Ca²⁺, Mg²⁺ and K⁺ concentrations were lower than those in CO (Table 2). The CAZ treatments increased cation concentrations and decreased CO²⁻ ₃ and HCO⁻ ₃ concentrations,

Table 1 Date of sowing, transplanting and sampling of each plant species in 2000

Plant	Sowing	Transplanting	Sampling
			1st	2nd	3rd
Kidney bean	30-Aug	8-Sep	12-Sep (4)	19-Sep (11)	4-Oct (26)
Tomato	3-Aug	31-Aug	4-Sep (4)	11-Sep (11)	25-Sep (25)
Maize	5-Aug	11-Aug	15-Aug (4)	24-Aug (13)	7-Sep (27)
Beet	25-Aug	14-Sep	18-Sep (4)	27-Sep (13)	10-Oct (26)
Numbers in parentheses refer to the days after transplanting.

Table 2 Chemical properties of the soils before cultivation

	Concentration (cmolc kg^−1) for saturation extracts										EC (dS m^−1)	pH	ESP	Classification
	K^+	Na^+	Ca^2+	Mg^2+	CI	NO^− 2	CO^− 3	CO^2− 3	HCO^− 3	SO^2− 4
CO	0.15 b	0.06 a	0.44 c	0.51 c	0.31 b	0.00 a	0.29 c	0.55 e	0.000 a	0.01 a	3.9 a	6.23 a	−5 a	nSa • nSo
HSO	0.04 a	1.43 b	0.00 a	0.00 a	0.36 b	0.00 a	0.28 c	0.60 f	0.015 c	0.26 d	5.2 c	9.93 d	78 g	Sa • So
HSO-KZ1	0.04 a	1.37 b	0.01 a	0.01 a	0.09 a	0.07 b	0.05 a	0.07 a	0.024 d	0.26 d	3.9 a	9.89 d	58 e	nSa • So
HSO-KZ2	0.08 ab	1.45 b	0.01 a	0.00 a	0.09 a	0.07 b	0.05 a	0.07 a	0.035 e	0.28 e	4.2 a	10.03 d	62 e	Sa • So
HSO-KZ5	2.36 b	1.20 b	0.00 a	0.00 a	0.34 b	0.00 a	0.29 c	0.41 c	0.062 f	0.34 f	5.0 b	10.43 e	69 f	Sa • So
HSO-CAZ1	0.07 ab	2.43 d	0.08 b	0.02 a	0.16 a	0.12 d	0.09 b	0.12 b	0.008 b	0.13 c	6.5 d	8.39 c	46 d	Sa • So
HSO-CAZ2	0.07 ab	1.93 c	0.08 b	0.02 a	0.13 a	0.10 c	0.07 ab	0.09 ab	0.008 b	0.13 c	5.6 c	8.52 c	39 c	Sa • So
HSO-CAZ5	0.10 ab	2.42 d	0.71 d	0.07 b	2.15 c	0.00 a	0.30 c	0.47 d	0.000 a	0.05 b	9.8 e	7.95 b	22 b	Sa • So
Different letters indicate significant differences at P < 0.05 using Duncan's new multiple range test. CO, control soil; HSO, high sodic soil; KZ1, KZ2, KZ5, CAZ1 CAZ2 and CAZ5, 1, 2 and 5% (w/w) K-type or Ca-type zeolite treatments, respectively; EC, electrical conductivity; ESP, exchangeable sodium percentage; nSa • nSo, non-saline • non-sodic soil (EC < 4.0 and ESP < 15); nSa • So, non-saline • sodic soil (EC<4.0 and ESP>15); Sa • So, saline • sodic soil (EC > 4.0 and ESP > 15) (US Salinity Laboratory Staff 1954).

ESP and pH. The CAZ5 doubled the EC level of the soil compared with HSO. The KZ treatments increased the CO²⁻ ₃ and HCO⁻ ₃ concentration and decreased the Cl⁻ and SO²⁻ ₄ concentration and EC for saturation extracts of soil. In HSO-KZ2 and HSO-KZ5, the pH was higher than 10.

Plant growth

Even by 4 DAT, the shoot dry weight of maize and beet in HSO was significantly smaller than in CO (Table 3). At 11–13 DAT, the relative dry weight of whole plants of beet, tomato, kidney bean and maize in HSO to CO was 0.36, 0.36, 0.20 and 0.18. After 11–13 DAT, the

Table 3 Dry weight (g plant−1) of the shoots and roots of the plants

	Shoots	Shoots	Shoots	Roots
Kidney bean	4 DAT	11 DAT	26 DAT	26 DAT
CO	0.086 a	0.303 d	1.49 b	0.336 c
HSO	0.073 a	0.062 a	dead	dead
HSO-KZ1	0.076 a	0.081 ab	dead	dead
HSO-KZ2	0.078 a	0.084 ab	dead	dead
HSO-KZ5	0.074 a	0.069 a	dead	dead
HSO-CAZ1	0.079 a	0.115 bc	0.24 a	0.031 b
HSO-CAZ2	0.085 a	0.131 c	0.28 a	0.077 b
HSO-CAZ5	0.081 a	0.119 bc	0.28 a	0.068 a
Tomato	4 DAT	11 DAT	25 DAT	25 DAT
CO	0.032 ab	0.140 d	1.12 c	0.120 c
HSO	0.029 ab	0.051 a	dead	dead
HSO-KZ1	0.033 b	0.038 a	dead	dead
HSO-KZ2	0.027 a	0.031 a	dead	dead
HSO-KZ5	0.031 ab	0.025 a	dead	dead
HSO-CAZ1	0.034 b	0.089 b	0.28 a	0.059 b
HSO-CAZ2	0.040 c	0.100 c	0.36 b	0.051 b
HSO-CAZ5	0.031 ab	0.073 b	0.23 a	0.031 a
Maize	4 DAT	13 DAT	27 DAT	27 DAT
CO	0.075 d	0.499 d	3.47 c	1.90 b
HSO	0.059 bc	0.091 a	dead	dead
HSO-KZ1	0.055 b	0.082 a	dead	dead
HSO-KZ2	0.052 ab	0.077 a	dead	dead
HSO-KZ5	0.045 a	0.071 a	dead	dead
HSO-CAZ1	0.066 cd	0.242 c	0.83 a	0.54 a
HSO-CAZ2	0.066 cd	0.270 c	1.33 b	0.84 a
HSO-CAZ5	0.052 ab	0.181 b	0.69 a	0.49 a
Beet	4 DAT	13 DAT	26 DAT	26 DAT
CO	0.023 d	0.095 d	0.437 d	0.102 cd
HSO	0.014 b	0.034 b	0.066 b	0.012 a
HSO-KZ1	0.010 a	0.014 a	0.032 ab	0.005 a
HSO-KZ2	0.010 a	0.013 a	0.022 a	0.003 a
HSO-KZ5	0.009 a	0.012 a	0.013 a	0.002 a
HSO-CAZ1	0.019 c	0.072 c	0.304 c	0.095 c
HSO-CAZ2	0.017 c	0.075 c	0.337 c	0.121 d
HSO-CAZ5	0.017 bc	0.065 c	0.305 c	0.072 b
Different letters indicate significant differences at P < 0.05 using Duncan's new multiple range test. CO, control soil; HSO, high sodic soil; KZ1, KZ2, KZ5, CAZ1 CAZ2 and CAZ5, 1, 2 and 5% (w/w) K-type or Ca-type zeolite treatments, respectively; DAT, days after transplanting.

Table 4 Water deficit (%) of plant shoots

	4 DAT	11 DAT	26 DAT
Kidney bean
CO	0.00 a	0.00 a	0.00 a
HSO	3.23 cd	24.5 bc	–
HSO-KZ1	3.17 bcd	13.1 d	–
HSO-KZ2	3.93 d	39.0 cd	–
HSO-KZ5	4.40 d	30.9 d	–
HSO-CAZ1	1.09 ab	–0.70 ab	4.48 a
HSO-CA72	1.48 abc	–0.85 ab	–0.52 a
HSO-CAZ5	1.71 abc	–0.74 ab	–1.38 a
Tomato
CO	0.00 a	0.00 a	0.00 a
HSO	1.22 ab	2.30 b	–
HSO-KZ1	2.36 c	5.80 b	–
HSO-KZ2	3.32 d	3.76 b	–
HSO-KZ5	3.69 d	4.81 b	–
HSO-CAZ1	0.85 ab	1.15 a	0.26 a
HSO-CAZ2	0.96 ab	1.20 a	0.16 a
HSO-CAZ5	1.14 b	1.93 a	–1.87 a
Maize
CO	0.00 a	0.00 a	0.00 a
HSO	2.87 c	7.90 b	–
HSO-KZ1	3.63 cd	7.77 b	–
HSO-KZ2	4.03 d	9.94 b	–
HSO-KZ5	5.50 e	8.20 b	–
HSO-CAZ1	3.29 cd	2.12 a	–0.67 a
HSO-CAZ2	1.86 b	1.64 a	1.02 a
HSO-CAZ5	3.80 cd	2.62 a	0.97 a
Beet
CO	0.00 a	0.00 a	0.00 a
HSO	2.49 a	5.58 a	1.35 ab
HSO-KZ1	6.69 b	14.0 b	3.14 ab
HSO-KZ7	11.0 d	23.0 c	4.00 b
HSO-KZ5	15.8 e	28.0 c	9.82 c
HSO-CAZ1	0.26 a	0.09 a	–0.22 a
HSO-CAZ7	0.16 a	–0.18 a	–0.26 a
HSO-CAZ5	0.62 a	0.53 a	0.67 ab
Different letters indicate significant differences at P < 0.05 using Duncan's new multiple range test. CO, control soil; HSO, high sodic soil; KZ1, KZ2, KZ5, CAZ1 CAZ2 and CAZ5, 1, 2 and 5% (w/w) K-type or Ca-type zeolite treatments, respectively; DAT, days after transplanting.

maize, kidney bean and tomato plants were dead, and beet growth was considerably restricted in HSO.

The KZ treatments significantly decreased shoot dry weight of beet and KZ5 decreased the weight of maize already at 4 DAT (Table 3). After 11–13 DAT, the KZ treatments suppressed growth of beet continuously, and also tended to suppress growth in maize and tomato. The CAZ treatments significantly increased shoot dry weight of beet and CAZ2 also increased the weight of tomato at 4 DAT. After 11–13 DAT, the CAZ treatments significantly improved growth in all the examined plants.

Table 5 Concentration of elements (cmol kg−1) in plant shoots 4 days after transplanting

	P	K	Na	Ca	Mg
Kidney bean
CO	7.79 bc	99.4 b	1.08 a	26.9 d	32.1 d
HSO	8.01 c	68.8 a	72.0 cd	7.50 a	12.6 a
HSO-KZ1	7.10 ab	70.3 a	45.9 bc	7.50 a	11.7 a
HSO-KZ2	7.28 abc	76.4 a	90.1 d	8.98 a	14.7 b
HSO-KZ5	6.97 ab	75.1 a	68.0 cd	9.36 a	12.6 a
HSO-CAZ1	7.58 abc	94.7 b	14.0 a	17.0 b	19.8 c
HSO-CAZ2	7.05 ab	99.6 b	7.89 a	21.7 c	19.8 c
HSO-CAZ5	6.87 a	103 b	6.39 a	36.7 e	20.5 c
Tomato
CO	8.37 b	106 c	13.2 a	46.2 c	62.5 d
HSO	8.69 b	49.5 a	162 c	28.6 a	36.4 ab
HSO-KZ1	8.32 b	53.5 a	156 c	24.5 a	34.5 a
HSO-KZ2	8.25 b	53.8 a	167 c	26.5 a	33.7 a
HSO-KZ5	8.00 b	66.1 b	166 c	26.0 a	33.8 a
HSO-CAZ1	7.81 b	64.0 b	123 b	34.7 b	38.1 bc
HSO-CAZ2	7.33 ab	67.5 b	108 b	36.6 b	37.7 bc
HSO-CAZ5	6.26 ab	65.9 b	104 b	53.2 d	39.9 c
Maize
CO	22.3 c	92.7 d	0.06 a	14.1 d	30.6 e
HSO	17.4 b	32.2 a	21.9 b	3.86 a	21.0 b
HSO-KZ1	15.0 ab	30.2 a	29.6 c	3.08 a	17.2 a
HSO-KZ2	17.5 b	31.6 a	18.2 b	3.38 a	20.7 b
HSO-KZ5	16.2 b	33.0 a	6.73 a	3.09 a	17.2 a
HSO-CAZ1	13.7 a	46.5 b	51.2 d	5.54 b	23.3 c
HSO-CAZ2	16.8 b	60.3 c	53.1 d	8.20 c	26.0 d
HSO-CAZ5	15.3 ab	59.1 c	32.4 c	15.0 d	24.0 cd
Beet
CO	20.9 a	155 b	124 a	17.7 b	58.7 b
HSO	24.7 ab	75.6 a	229 bc	10.6 a	37.3 a
HSO-KZ1	34.9 c	98.3 a	198 b	11.4 a	38.5 a
HSO-KZ2	32.0 bc	96.7 a	196 b	12.2 a	39.5 a
HSO-KZ5	35.8 c	98.8 a	194 b	13.1 a	42.6 a
HSO-CAZ1	25.4 ab	81.0 a	255 c	10.7 a	37.5 a
HSO-CAZ2	28.2 abc	90.2 a	321 d	13.3 a	45.4 a
HSO-CAZ5	21.2 a	85.9 a	276 cd	22.6 c	45.0 a
Different letters indicate significant differences at P < 0.05 using Duncan's new multiple range test. CO, control soil; HSO, high sodic soil; KZ1, KZ2, KZ5, CAZ1 CAZ2 and CAZ5, 1, 2 and 5% (w/w) K-type or Ca-type zeolite treatments, respectively.

The ameliorative effect was significantly larger in CAZ2 than in CAZ5 and on roots than on shoots, except for kidney bean. The relative dry weight of whole plants of beet, maize, tomato and kidney bean in CAZ2 to that in the control was 0.85, 0.40, 0.33 and 0.20, at 25–27 DAT.

Water status

Among the treatments, the water deficit (WD) in kidney bean, tomato and beet was found to be: CAZ1 ≒ CAZ2 ≒ CAZ5 < HSO < KZ1 < KZ2 ≒ KZ5 at 4 DAT (Table 4). The WD of maize differed and was in the order: CAZ2 < HSO ≒ CAZ1 ≒ CAZ5 < KZ1 ≒ KZ2 < KZ5 at 4 DAT.

Table 6 Concentration of elements (cmol kg−1) and ratio of Na to (K + Ca + Mg) in beet 26 days after transplanting

	P	K	Na	Ca	Mg	Na/(K + Ca + Mg)
Beet shoots
CO	14.1 c	173 e	47 a	22.9 e	77.1 d	0.17 a
HSO	2.24 a	23.3 a	336 de	6.1 a	25.0 ab	6.23 d
HSO-KZ1	2.17 a	19.4 a	346 ef	11.2 bc	26.3 ab	6.40 d
HSO-KZ2	1.87 a	23.8 a	300 cd	11.6 bc	21.1 a	5.73 d
HSO-KZ5	4.19 b	44.5 b	259 c	21.7 e	31.9 b	2.65 b
HSO-CAZ1	17.0 d	139 d	99 b	42.5 f	56.7 c	0.41 a
HSO-CAZ2	17.7 d	47.6 b	384 f	9.65 b	32.8 b	4.27 c
HSO-CAZ5	13.3 c	67.9 c	292 c	24.8 e	34.1 b	2.30 b
Beet roots
CO	7.48 b	31.0 c	3.0 a	21.3 a	12.4 ab	0.05 a
HSO	1.38 a	9.88 a	57.8 be	14.9 a	15.4 bc	1.72 bc
HSO-KZ1	1.75 a	5.40 a	66.3 cd	14.2 a	16.5 bcd	1.96 c
HSO-KZ2	1.88 a	3.76 a	69.6 de	13.9 a	14.2 abc	2.20 c
HSO-KZ5	1.35 a	2.93 a	32.4 b	15.9 a	9.95 a	1.19 abc
HSO-CAZ1	2.36 a	21.9 b	40.8 be	17.0 a	16.9 cd	0.74 ab
HSO-CAZ2	3.06 a	21.9 b	38.5 b	17.9 a	16.3 bcd	0.68 ab
HSO-CAZ5	2.94 a	33.9 c	39.1 b	35.9 b	20.1 d	0.44 a
Different letters indicate significant differences at P < 0.05 using Duncan's new multiple range test. CO, control soil; HSO, high sodic soil; KZ1, KZ2, KZ5, CAZ1 CAZ2 and CAZ5, 1, 2 and 5% (w/w) K-type or Ca-type zeolite treatments, respectively.

In all the tested plants, the water status in the CAZ treatments was found to be similar to that in CO at 11–13 DAT up to 25–27 DAT. The KZ treatments significantly increased the WD in beet until 26 DAT and tended to increase WD in tomato at 11 DAT.

Absorption of elements

At 4 days after treatment

The K_c, Ca_c and Mg_c of shoots in HSO were significantly lower than those of CO in all tested plants (Table 5). Under HSO, the Na_c of maize was tremendously increased and that of kidney bean increased 67-fold, tomato by 12-fold and beet by 1.8-fold compared to CO. The KZ1 and KZ2 did not differ for element concentrations, regardless of the plant species. The KZ5 decreased significantly the Na_c and Mg_c of shoots in maize. The K_c of shoot in KZ treatments was the same as HSO, although K-fertilizer was not supplied to all of the tested plants. The CAZ1, CAZ2, and especially CAZ5, increased Ca_c, K_c and Mg_c in all plant species except beet. The CAZ treatments decreased Na_c of shoots in kidney bean and tomato, but increased the concentration in maize. In beet, the Ca_c of shoots in CAZ5 was twice that in HSO.

At 25, 26 or 27 days after treatment

In beet, the P_c and K_c of shoots and roots and the Ca_c and Mg_c of shoots in the CAZ treatments was considerably higher than the concentrations in HSO (Table 6). The relative K uptake in the roots and P uptake in the shoots in the CAZ treatments compared with CO in beet were also considerably higher than the concentrations in the other plants (Fig. 1). The relative P uptake in the shoots in CAZ5 compared with CO of tomato and maize was markedly lower than in CAZ1 and CAZ2.

Cation balance

The cation balance was not affected by KZ2 in kidney bean, tomato or maize, but a slightly decreased Na/K, Na/Ca and Na/Mg was observed in beet (Fig. 2). The CAZ2 greatly reduced the Na/K, Na/Ca and Na/Mg of shoots in kidney bean and halved it in tomato. In beet, the CAZ2 did not affect the cation balance at 4 DAT (Fig. 2), but Na/(K + Ca + Mg) of shoot in CAZ treatments was lower than HSO at 26 DAT (Table 6). In maize, Na/K, Na/Ca and Na/Mg in HSO were the lowest of all the tested plants. The CAZ2 increased Na/Mg and Na/ K at 4 DAT, but its value was lower than that recorded for the other plants (Fig. 2).

DISCUSSION

As the ESP of HSO was very high (78), glycophytes might suffer from Na toxicity and reduced absorption of Ca, Mg and K. The high pH condition (> 9.9) of HSO may damage roots and have a bad influence on water and nutrition absorption. In this study, growth reducing factors and the effect of zeolite addition were discussed from early stages after transplanting in HSO treatments.

The addition of Ca-type zeolite improved growth in all of the tested plants, although the improving factors

Figure 1  Relative dry weight (DW) and mineral uptake in the Ca-type zeolite (CAZ) treatment compared to the control. Different letters indicate differences at P < 0.05 using Duncan's new multiple test. (□) CAZ1, (░) CAZ2 and (▒) CAZ5 refer to the 1, 2 and 5% (w/w) Ca-type zeolite treatments, respectively. Error bars are standard deviation. DAT, days after transplanting.

varied among plant species. In kidney bean, the HSO treatment resulted in the highest WD and lowest Mg_c among the four species. The Na_c increase and Ca_c decrease in the HSO treatment followed those recorded in maize, although growth inhibition was not observed at 4 DAT (Tables 3,4,5). The dry weight in HSO, however, decreased with markedly high WD at 13 DAT (Tables 3,4). Deteriorated nutritional status and water status just after transplanting, therefore, had a negative influence on growth afterwards. Although the CAZ treatments suppressed Na absorption and increased the absorption of K, Ca and Mg and improved cation balance, and improved water status at 4 DAT, the growth improvement was observed 13 DAT. The ameliorative effect of CAZ treatments on kidney bean was lower than that observed for the other plant species at 26 DAT. This might be because of the extremely lower relative uptake of K in root and Mg in shoot in CAZ compared with that in CO at 26 DAT in kidney beans compared with the other plant species (Fig. 1).

In tomato, growth did not decrease in HSO at 4 DAT, despite the deteriorated nutritional status (Tables 3,5). As the growth proceeded, however, the nutritional status became worse followed by deterioration of water

Figure 2  Concentration ratios of Na to K, Ca and Mg in shoots 4 days after transplanting (□) CO, (▪) HSO, (░) KZ2 and (▒) CAZ2 refer to control soil, high sodic soil and 2% (w/w) K-type or Ca-type zeolite treatments, respectively. Different letters indicate differences at P < 0.05 using Duncan's new multiple test. Error bars are standard deviation.

absorption, and finally growth decreased at 11 DAT. Even at 4 DAT, dry weight in CAZ2 was significantly higher, and that in CAZ1 trended to be higher, than that in HSO. The CAZ treatments could not improve water status, but increased absorption of Ca and K and decreased absorption of Na and improved cation balance, which might result in improved growth (Tables 3,4,5). Tomato showed the lowest WD among the four species in HSO until 11 DAT, and decreases in WD in the CAZ treatments were smaller than those recorded in the other species, indicating that the effect of improved water absorption was lowest in tomato.

In maize, the increase in Na_c and decrease in Ca_c and K_c were markedly higher in HSO at 4 DAT, and water absorption was severely inhibited, and these were the main causes of growth reduction (Tables 3,4,5). The CAZ treatments did not improve water status at 4 DAT. They improved K and Ca status, but enhanced absorption of Na and growth did not change. At 13 DAT, the CAZ treatments improved water status and as a consequence growth was improved. Not only recovery of K and Ca absorptions but also that of water absorption are necessary for improvement of growth of maize in HSO.

The beet WD value was not higher than those of the other plant species in HSO, presumably assuming that increased Na_c and decreased K_c, Ca_c and Mg_c would cause severe growth inhibition (Tables 3,4,5). However, beet growth was improved by CAZ treatments, although the increment of Ca_c and K_c was the smallest among the plant species and CAZ treatments increased Na_c (Tables 3,5). The larger decreases in WD as a result of the CAZ treatments might contribute to amelioration of the growth at 4 DAT (Table 4). Beet could quickly respond to the improved water status. At 26 DAT, the P_c of beet in HSO was much lower than that in CO, although there was no difference in available P concentration for saturation extracts of soil between CO and the other treatments (M. Yamada et al., unpubl. data, collected in 2000). Root growth of beet was markedly improved by CAZ treatments compared to shoot growth, which might result in increased P absorption and contribute to improved growth (Tables 3,6). In addition, CAZ treatments improved K uptake of root and the cation balance of shoots (Fig. 1, Table 6). These, as well as a marked improvement in water absorption, brought the highest growth improvement among the plant species (Tables 3,4).

The ameliorative effect of CAZ5 was lower than that of CAZ2 in tomato, maize and beet (Table 3). The Ca_c in CAZ5 was 2–3-fold higher than that in CAZ2 at 4 DAT in all tested species (Table 5) and this tendency continued to 25–27 DAT (Table 6, data shown for beet). In contrast, shoot P_c in beet and tomato in CAZ5 was lower than that in CAZ2 even at 4 DAT. At 25–27 DAT CAZ5 reduced P_c in the shoots by 51% for tomato, 75% for maize and 75% for beet compared to CAZ2. A lower relative P absorption in CAZ5 than in CAZ2 (Fig. 1) could be associated with inhibited P transport from root to shoot in the presence of excessive Ca under CAZ5. These results were supported by our previous unpublished findings for maize in low sodic soil and by the findings of Ruiz and Romero (1998). The WD in CAZ5 was higher than that in CAZ2 in tomato and maize until 11–13 DAT and in beet until 26 DAT because of the higher EC in CAZ5 (Table 2). These results indicated that the addition of CAZ5 was in excess for plants at HSO.

The CAZ treatments improved growth of all the tested plant species. Conversely, KZ treatments had significantly suppressed beet growth by 4 DAT and KZ5 and KZ2 suppressed the growth of tomato and maize by 13 DAT (Table 3). The concentrations of Fe, Mn, Zn and Cu in the shoots in the HSO and KZ treatments were higher than the critical level (data not shown). However, water status was aggravated in tomato and maize by KZ treatments at 4 DAT, and damaged growth later (11 or 13 DAT). A markedly high WD, even in KZ1, seriously damaged growth in beet at 4 DAT. In contrast, the WD of all the other tested plant species was lowered by the CAZ treatments (Table 4). The absorption of the elements was less affected by KZ treatment (Table 5). Thus, the effect of K-type and Ca-type zeolite on water status was opposite and only Ca-type zeolite improved nutritional status. Thus, these zeolites had quite a different effect on plant growth.

Why was the effect of both zeolites on water status so different? In KZ5 and KZ2, the concentration of HCO⁻ ₃ and CO²⁻ ₃ and the pH of soil solution were higher than in the HSO and CAZ treatments (Table 2), which might injure root growth and cause inhibition of water absorption (Table 4). Peiter et al. (2001) showed that HCO⁻ ₃ inhibited root elongation. Bie et al. (2004) suggested that NaHCO₃ was more toxic to lettuce growth than Na₂SO₄. In contrast, the addition of CAZ decreased the CO²⁻ ₃ and HCO⁻ ₃ concentration of soil solution (Table 2). It was considered that improved water uptake in the CAZ treatments resulted from the absence of root damage by CO²⁻ ₃ and HCO⁻ ₃. The higher sensitivity of the beet roots to the higher CO²⁻ ₃ and HCO⁻ ₃ concentrations in KZ treatments severely suppressed water absorption at 4 DAT, whereas the mitigated WD by the CAZ treatments was possibly accounted for by the morphologically fine absorption roots of beet (Osaki et al. 1995).

The addition of Ca-type zeolite could ameliorate the growth of glycophytes in high sodic soil from early stages by recovery of water status in beet, nutritional status in tomato, and both water and nutritional status in kidney been and maize. However, the addition of K-type zeolite suppressed the growth of beet, maize and tomato by inhibiting water absorption.

ACKNOWLEDGMENTS

The authors are grateful to Mr K. Ogawa and Mr Y. Kageyama (Kimura Chemical Plants), and Mr I. Ueyama, Mr T. Shimizu and Dr M. Irshad (Arid Land Research Center, Tottori University) for their assistance and English correction. This research was conducted as part of a research project entitled: “Research for the improvement of the saline soil by using artificial zeolites” sponsored by Kimura Chemical Plants, Japan.