Exploring the potential for top-dressing bread wheat with ammonium chloride to minimize grain yield losses under drought

Figures & data

Table 1. Chemical and physical composition of the soil used for plant growth.

Characteristic	Unit	Value
Color		Dark gray
Gravel	%	5
Texture		Sandy
Ammonium nitrogen	mg kg^–1	20
Nitrate nitrogen	mg kg^–1	89
Phosphorus Colwell	mg kg^–1	25
Potassium Colwell	mg kg^–1	275
Sulfur	mg kg^–1	128.1
Organic carbon	%	1.66
Conductivity	dS m^–1	0.440
pH level (CaCl2)	pH	6.4
pH level (H2O)	pH	6.7
DTPA copper	mg kg^–1	2.26
DTPA iron	mg kg^–1	19.96
DTPA manganese	mg kg^–1	14.86
DTPA zinc	mg kg^–1	1.07
Exc. aluminum	mg kg^–1	9
Exc. calcium	mg kg^–1	880
Exc. magnesium	mg kg^–1	232
Exc. potassium	mg kg^–1	250
Exc. sodium	mg kg^–1	242
Boron hot CaCl2	mg kg^–1	30
Chloride	mg kg^–1	155.7

Table 2. Experimental time line and analysis over the growing period.

Parameter	Days after sowing	Action
Sowing	0	Seeds sown into pots
Fertilizer treatments	47	100 mL supplied to a single pot
Dry down begins	59	Watering to predetermined GWC/VWC
Measurements	70	Photosynthesis measurement and leaf harvests
Re-watering	74	Droughted plants rewatered
Measurements	77	Photosynthesis measurements
Maturity harvest	140	Plants harvested once completely dry

Table 3. Fertilizer treatments supplied to the soil at 47 DAS.

Drought conditions (D)		Watered conditions (W)
Identifier	Treatment	Identifier	Treatment
D	Untreated	W	Untreated
D + KCl	1.52 mmol KCl	W + KCl	1.52 mmol KCl
D + NC4Cl	1.52 mmol NH4Cl	W + NC4Cl	1.52 mmol NH4Cl
D + NH4HCO3	1.52 mmol NH4HCO3	W+ NH4HCO3	1.52 mmol NH4HCO3

Table 4. Wheat growth responses to drought and fertilization at maturity, mean ± SEM (n = 6).

		Tiller number plant^−1		Spike number^† plant^−1		Shoot biomass (g plant^−1)		Thousand grain weight (g)		Flowering^‡ (days after sowing)
	Treatment	W	D	W	D	W	D	W	D	W	D
RAC875	Untreated	5.0^a	6.8^ab	4.7^ab	6.0^ab	6.4^abcd	6.9^abcd	46.6^abcd	51.9^abcd	75.0^ab	74.8^ab
	KCl	5.8^ab	6.0^ab	4.8^ab	5.0^ab	6.8^abcd	5.4^ab	52.6^bcd	52.5^abcd	74.3^ab	72.2^ab
	NH4Cl	5.2^a	8.2^ab	5.2^ab	7.2^ab	6.9^abcd	6.8^abcd	49.8^abcd	46.9^abcd	74.3^ab	72.7^ab
	NH4HCO3	5.2^a	5.0^a	4.7^ab	3.7^a	7.4^abcd	3.5^a	50.0^abcd	51.9^abcd	73.4^ab	71.0^a
Gladius	Untreated	5.0^a	5.3^a	4.7^ab	4.2^ab	6.8^abcd	4.2^a	45.8^abcd	48.2^abcd	76.2^ab	74.3^ab
	KCl	5.2^a	6.7^ab	4.5^ab	5.2^ab	6.1^ab	5.5^abc	47.7^abcd	48.3^abcd	73.8^ab	70.8^a
	NH4Cl	5.3^a	6.2^ab	4.5^ab	5.0^ab	5.9^abc	5.6^abc	44.1^abcd	47.1^abcd	75.0^ab	74.7^ab
	NH4HCO3	5.0^a	7.8^ab	4.5^ab	6.3^ab	5.5^abc	6.5^abcd	43.4^abcd	49.6^abcd	74.0^ab	72.5^ab
Mace	Untreated	7.3^ab	8.3^ab	7.0^ab	6.7^ab	10.3^bcd	10.2^abcd	42.4^ab	53.2^bcd	78.2^b	78.7^b
	KCl	7.5^ab	10.2^b	6.8^ab	6.8^ab	11.0^d	11.0^d	45.2^abcd	54.7^d	78.2^b	76.7^ab
	NH4Cl	7.8^ab	9.2^ab	7.0^ab	6.5^ab	9.9^bcd	7.7^abcd	40.9^a	54.1^cd	77.5^ab	76.3^ab
	NH4HCO3	7.5^ab	9.3^ab	7.3^b	7.5^b	10.0^cd	9.4^bcd	42.5^abc	52.4^abcd	77.3^ab	77^ab
Genotype		<0.001		<0.001		<0.001		<0.05		<0.001
D/W		<0.001		n.s.		0.013		<0.001		n.s.
Fertilizer		n.s.		n.s.		n.s.		n.s.		n.s.
Genotype × D/W		n.s.		n.s.		n.s.		n.s.		n.s.
Genotype × fertilizer		n.s.		< 0.1		< .05		n.s.		n.s.
D/W × fertilizer		n.s.		n.s.		n.s.		n.s.		n.s.
Genotype × D/W× fertilizer		n.s.		n.s.		n.s.		n.s.		n.s.

The same superscript letters within a column indicate no significant difference between means whilst different letters indicate significant differences at p < 0.05. ‘Genotype’ indicates the three genotypes examined here: RAC875, Mace and Gladius. ‘D/W’ indicates the watering regimes applied including drought (D) and watered (W). ‘Fertilizer’ indicates the treatments applied including untreated, NH₄Cl, KCl, and NH₄HCO₃.

^†Spike number includes fertile and sterile spikes.

^‡Flowering was measured at anthesis.

Figure 1. The effect of drought and fertilizer treatments on grain number and yield. Three genotypes (RAC875, Gladius and Mace) were grown to maturity and the following components measured. (a, b) Grain number, (d–e) grain yield, and (c, f) % loss of grain number and grain yield under drought (W/D*100) (n = 6, mean ± SEM). Statistical significance within a graph is indicated by different letters determined by two-way ANOVA with Bonferroni post-hoc analysis (p < 0.05).

Figure 2. The physiological effect of drought and fertilization. The flag leaf from the main stem was assessed for (a, b) stomatal conductance, (c, d) photosynthesis, and (d, e) carbon isotope discrimination (Δ¹³C) in three wheat genotypes (RAC875, Gladius and Mace) at 70 days after sowing (n = 6, mean ± SEM). Statistical significance within a graph is indicated by different letters determined by two-way ANOVA with Bonferroni post-hoc analysis (p < 0.05). Graphs without letters indicate that means were not significantly different.

Figure 3. The effects of drought and fertilization on flag leaf accumulation of potassium and chloride. The concentration of (a, b) chloride and (c, d) potassium in the leaf below the flag leaf (FL-1) of three wheat genotypes (RAC875, Gladius and Mace) at 70 days after sowing (n = 6, mean ± SEM). Statistical significance within a graph is indicated by different letters determined by two-way ANOVA with Bonferroni post-hoc analysis (p < 0.05). Graphs without letters indicate that means were not significantly different.