Influence of Azolla (Azolla microphylla Kaulf.) compost on biogenic gas production, inorganic nitrogen and growth of upland kangkong (Ipomoea aquatica Forsk.) in a silt loam soil

Figures & data

Figure 1 Production of nitrous oxide (N₂O) during soil incubations sampled weekly. Value followed by different letters indicate significant different (least significant difference, LSD; P < 0.05). The error bars indicate the standard deviations. N, nitrogen.

Figure 2 Production of carbon dioxide (CO₂) during soil incubations sampled weekly. Value followed by different letters indicate significant different (least significant difference, LSD; P < 0.05). The error bars indicate the standard deviations.

Table 1 Levels of ammonium (NH₄⁺) (μg N g⁻¹) accumulated during incubation of the silt loam soil

	Concentration of NH4^+ (μg N g^−1) incubation time (week)
Treatments	1	2	3	4
Control	4.1^a	1.8^a	1.9^a	1.5^a
Azolla low	4.5^ab	2.6^a	2.5^ab	2.5^a
Azolla med	5.1^ab	2.7^a	3.5^ab	2.6^a
Azolla high	6.4^b	6.3^b	4.1^b	3.5^a
Urea	19.8^c	15.2^c	10.2^c	6.1^b

N, nitrogen. Values followed by different letters in each column indicate significant differences (least significant difference, LSD; P < 0.05).

Table 2 Levels of nitrate (NO₃^–) (μg N g⁻¹) accumulated during incubation of the silt loam soil

	Concentration of NO3^– (μg N g^−1) incubation time (week)
Treatments	1	2	3	4
Control	46.9^a	41.6^a	57.1^a	68.9^a
Azolla low	72.8^ab	89.4^b	84.3^b	126^b
Azolla med	74.3^b	90.2^b	88.5^b	146^b
Azolla high	82.8^b	98.6^b	116^c	158^b
Urea	63.0^ab	79.4^b	166^d	33.5^a

N, nitrogen. Values followed by different letters in each column are significantly different (least significant difference, LSD; P < 0.05).

Figure 3 Height (cm) of upland kangkong (Ipomoea aquatica Forsk.) grown in pots. Treatments are: control (no amendment), Azolla Compost low (80.3 g m⁻²), Azolla Compost medium (160.5 g m⁻²), Azolla Compost high (240.8 g m⁻²), Urea (10 g N m⁻²). Different letters refer to significant differences (least significant difference, LSD; P < 0.05).

Table 3 Plant biomass (dry weight, grams per pot) of aboveground upland kangkong (Ipomoea aquatica Forsk.) studied in a pot experiment. Soil treatments are the same as for Fig. 1. Different letters refer to significant differences (least significant difference, LSD; P < 0.05)

Treatments	Plant biomass (dry weight) (gram pot^–1)
Control	4.77^a
Azolla low	5.13^ab
Azolla med	5.30^ab
Azolla high	5.38^ab
Urea	5.42^b

Soil treatments are the same as for Fig. 3. Values followed by different letters in each column are significantly different (LSD, P < 0.05).