Response of hydroponic lettuce to aeration, nitrate and potassium in the nutrient solution

Figures & data

Table 1. Treatments applied to lettuce plants grown in a floating hydroponic system to assess the effects of aereation of the nutrient solution and the ${\mathrm{N}\mathrm{O}}_3^{-}$/K concentration.

Nutrient solution	N meq L^−1	K meq L^−1
Aereated	12	8.5
	15	7
	12	2.85
Non-aereated	12	8.5
	15	7
	12	2.85

Table 2. Main effects of aeration and the ${\mathrm{N}\mathrm{O}}_3^{-}$/K concentration in the nutrient solution on root growth parameters and water consumption in lettuce plants grown in a floating hydroponic culture.

		Root fresh weight (g)	Root dry weight (g)	Root volume (cm^3)	Root length(cm)	Water consumption L/5 plants/36 days
Aerated	Aerated	38.2a	2.22	39.7a	56.3a	16.0a
	Nonaerated	33.7b	2.36	36.1b	38.0b	13.4b
${\mathrm{N}\mathrm{O}}_3^{-}$/K concn. meq L^−1	12/8.5	35.3ab	2.26	38.5	49.1	14.5
	15/7	39.5a	2.34	39.4	47.3	15.1
	12/2.85	33.1b	2.22	35.8	44.9	14.5
ANOVA	Aeration	p = 0.031	p = 0.097	p = 0.050	p = 0.001	p = 0.001
	${\mathrm{N}\mathrm{O}}_3^{-}$/K	p = 0.040	p = 0.248	p = 0.256	p = 0.567	p = 0.334
	Interaction	p = 0.534	p = 0.765	p = 0.687	p = 0.512	p = 0.717

Note: Means followed by the same letter indicated non-significant differences according to Duncan’s multiple comparison test at p < 0.05.

Table 3. Main effects of aeration and the ${\mathrm{N}\mathrm{O}}_3^{-}$/K concentration in the nutrient solution on leaf growth parameters and firmness in lettuce plants grown in a floating hydroponic culture.

		Leaf fresh weight (g)	Leaf dry weight (g)	Leaf length (cm)	Leaf firmness (gr cm^−2)
Aerated	Aerated	257a	10.70a	34.8a	3.06
	Nonaerated	204b	8.80b	32.2b	3.40
${\mathrm{N}\mathrm{O}}_3^{-}$/K concn. meq L^−1	12/8.5	223	10.00	33.4	3.11
	15/7	246	9.76	34.2	3.25
	12/2.85	223	9.40	32.9	3.32
ANOVA	Aeration	p = 0.003	p = 0.008	p = 0 .001	p = 0.171
	${\mathrm{N}\mathrm{O}}_3^{-}$/K	p = 0.340	p = 0.725	p = 0.118	p = 0.749
	Interaction	p = 0.386	p = 0.590	p = 0.863	p = 0.318

Note: Means followed by the same letter indicated non-significant differences according to Duncan’s multiple comparison test at p < 0.05.

Figure 1. Effect of the ${\mathrm{N}\mathrm{O}}_3^{-}$/K concentration and aeration/non aeration of the nutrient solution en leaf potassium concentration (Aeration: p = 0.001; ${\mathrm{N}\mathrm{O}}_3^{-}$/K: p = 0.001; Interaction: p = 0.050) and accumulation (Aeration: p = 0.001; ${\mathrm{N}\mathrm{O}}_3^{-}$/K: p = 0.001; Interaction: p = 0.001) in lettuce plants grown in a floating hydroponic system. FW = fresh weight. Bars represent the standard error of the mean (n = 4).

Table 4. Main effects of aeration and the ${\mathrm{N}\mathrm{O}}_3^{-}$/K concentration in the nutrient solution on leaf nitrogen (N), total N accumulation, calcium (Ca) and magnesium (Mg) concentration in lettuce plants grown in a floating hydroponic culture. Nitrogen, Ca and Mg are on a dry weight basis.

		N (mmol kg^−1)	Total N (mg kg^−1 fresh weight)	Ca (mmol kg^−1)	Mg (mmol kg^−1)
Aerated	Aerated	2675	1575	198	114.0a
	Nonaerated	2496	1501	186	82.1b
${\mathrm{N}\mathrm{O}}_3^{-}$/K concn. meq L^−1	12 /8.5	2587	1653	184b	91.5b
	15/7	2578	1453	183b	92.0b
	12/2.85	2581	1508	210a	111.5a
ANOVA	Aeration	p = 0.252	p = 0.477	p = 0.120	p = 0.001
	${\mathrm{N}\mathrm{O}}_3^{-}$/K	p = 0.994	p = 0.291	p = 0.010	p = 0.012
	Interaction	p = 0.915	p = 0.273	p = 0.660	p = 0.725

Note: Means followed by the same letter indicated non-significant differences according to Duncan’s multiple comparison test at p < 0.05.

Figure 2. Effect of the ${\mathrm{N}\mathrm{O}}_3^{-}$/K concentration and aeration/non aeration of the nutrient solution on leaf phosphorus concentration in lettuce plants grown in a floating hydroponic system (Aeration: p = 0.001; ${\mathrm{N}\mathrm{O}}_3^{-}$/K: p = 0.050; Interaction: p = 0.024). Bars represent the standard error of the mean (n = 4).

Table 5. Main effect of aeration and the ${\mathrm{N}\mathrm{O}}_3^{-}$/K concentration in the nutrient solution on gas exchange parameters and leaf temperature in lettuce plants grown in a floating hydroponic culture.

		Photosynthesis rate (µmol CO2 m^−2 s^−1)	Stomatic conductance (cm s^−1)	Transpiration rate (µg cm^−2 s^−1)	Leaf temperature (°C)
Aerated	Aerated	13.3b	0.46b	11.1b	25.8
	Nonaerated	14.9a	0.51a	12.0a	26.1
${\mathrm{N}\mathrm{O}}_3^{-}$/K concn. meq L^−1	12/8.5	13.8	0.46b	11.2b	26.0
	15/7	14.2	0.48ab	11.5b	26.1
	12/2.85	14.4	0.52a	12.0a	25.9
ANOVA	Aeration	p = 0.001	p = 0.031	p = 0.001	p = 0.338
	${\mathrm{N}\mathrm{O}}_3^{-}$/K	p = 0.389	p = 0.026	p = 0.016	p = 0.904
	Interaction	p = 0.581	p = 0.716	p = 0.717	p = 0.374

Note: Means followed by the same letter indicated non-significant differences according to Duncan’s multiple comparison test at p < 0.05.