Use of a biochar-based formulation for coating corn seeds

Figures & data

Table 1. Selected properties of the two biochar types used in the study

Properties	Biochar
	Coconut	Hardwood
Organic carbon (% of total of dry mass)	78.0	86.6
Hydrogen/carbon ratio	0.50	0.30
Total nitrogen (% of total of dry mass)	0.54	0.91
Total ash (% of total of dry mass)	3.32	5.11
pH	6.49	8.86
Electrical conductivity (dSm^−1)	0.35	0.37

Figure 1. Corn seed germination and seed water uptake studies were carried out using a specifically designed test tube system (left). Seeds (A: control; B: dewaxed; C: commercially treated; D: biochar treated) were secured between two cotton plugs at the junction of two test tubes held together by a threaded sleeve created with a 3D printer.

Figure 2. Examples of measurement of the apparent contact angles of sessile water drops on the surface of untreated corn seeds (A) and seeds that were coated with the hardwood biochar (B). Measurements were also conducted on samples of corn seed that were coated with a commercial polymer (C) and seed which were subjected to the removal of the external waxy layer (D, dewaxed seeds).

Figure 3. Water uptake by untreated corn seeds (control) and by seeds that were coated with hardwood (HW) or coconut (CN) biochar. Measurements are also included of samples of seed that were coated with a commercial polymer and seeds that were subjected to the removal of the external waxy layer (dewaxed seeds). Each point represents mean ± STD (n = 3).

Table 2. Wettability of corn seeds was measured as reduced apparent contact angle of sessile water drops on the surface of seeds that were either untreated (control) or subjected to treatments with two types of biochar (hardwood, HW, and coconut, CN, biochar). Measurements included samples of seeds that were coated with a commercial polymer and seeds that were subjected to the removal of the external waxy layer (dewaxed seeds). Data are presented as mean ± STD. Values followed by the same letter are not significantly different (P < 0.05; LSD)

Seeds	Apparent contact angle (°)
Untreated	90.67 ± 3.28 a
Dewaxed	64.45 ± 10.14 b
Commercially coated	74.02 ± 7.26 c
Coated with HW Biochar	25.51 ± 6.77 d
Coated with CN Biochar	24.33 ± 5.01 d

Table 3. Germination and mean germination time of untreated seeds (control) compared with seeds that were coated with hardwood (HW), coconut (CN) biochar, a commercial polymer or seeds which were subjected to removal of the external waxy layer (dewaxed seeds). Data are presented as mean ± STD. Values followed by the same letter in the same column are not significantly different (P < 0.05; LSD)

Seeds	Germination	Mean germination time
	(%)	(h)
Untreated	99.2 ± 2.2 a	44.1 ± 0.9 a
Commercially coated	98.9 ± 1.2 a	43.0 ± 1.2 a
Dewaxed	99.0 ± 2.0 a	40.1 ± 0.8 b
Coated with HW biochar	99.2 ± 1.5 a	37.0 ± 0.7 c
Coated with CN biochar	99.5 ± 2.2 a	36.4 ± 0.5 c

Table 4. Aspergillus flavus propagules recovered during the germination process from untreated (control) seeds, and from seeds coated with hardwood (HW) biochar, coconut (CN) biochar, commercial polymer or subjected to the removal of the external waxy layer (dewaxed seeds). Data are presented as mean ± STD. Values followed by a letter are not significantly (P < 0.05) different from other values followed by the same letter (ANOVA)

	A. flavus (number of propagules per seed)
	2 d	4 d	7 d
Untreated	25.2 ± 2.9 a	32.3 ± 1.7 b	42.1 ± 3.2 c
Commercially coated	26.1 ± 3.1 a	39.4 ± 2.8 b	44.0 ± 2.8 c
Dewaxed	24.9 ± 2.9 a	29.1 ± 2.0 b	39.9 ± 1.8 c
Coated with HW biochar	23.5 ± 3.0 a	29.6 ± 2.6 b	40.5 ± 3.3 c
Coated with CN biochar	21.2 ± 2.9 a	31.1 ± 1.5 b	42.0 ± 3.0 c

Table 5. Size of the soil Aspergillus flavus population and percent aflatoxigenicity of isolates recovered from plots planted with untreated corn seeds and corn seeds coated with one of two types of biochar (hardwood, HW, and coconut, CN). In both years, samples were collected at the beginning (Apr.) and at the end (Sept.) at the end of the corn growing season. Aflatoxin contamination of harvested corn kernels and yield are reported. Data are presented as mean ± STD. For each year, values followed by a letter are not significantly (P < 0.05) different from other values followed by the same letter (ANOVA)

Year/Seed treatment	Propagule density (log 10  g^−1)		Aflatoxigenic isolates (%)		Aflatoxins (ng·g^−1)	Yield (q·ha^−1)
	Apr.	Sept.	Apr.	Sept.
2020
Untreated	3.9 ± 0.2 a	4.1 ± 0.8 b	36.3 ± 0.1 a	39.2 ± 0.4 b	0.8 ± 0.1 a	12.3 ± 1.4 a
Coated with HW biochar	3.4 ± 0.1 a	4.0 ± 0.4 b	30.2 ± 0.3 a	38.0 ± 0.2 b	0.6 ± 0.1 a	11.3 ± 0.9 a
Coated with CN biochar	3.5 ± 0.2 a	3.9 ± 0.3 b	32.2 ± 0.4 a	35.9 ± 0.5 b	0.4 ± 0.1 a	11.8 ± 0.8 a
2021
Untreated	3.7 ± 0.3 a	4.4 ± 0.5 b	35.3 ± 0.2 a	37.1 ± 0.1 a	3.3 ± 0.2 a	11.2 ± 0.8 a
Coated with HW biochar	3.6 ± 0.5 a	4.4 ± 0.8 b	38.8 ± 0.1 a	34.3 ± 0.2 a	3.6 ± 0.2 a	10.2 ± 2.4 a
Coated with CN biochar	3.2 ± 0.7 a	4.1 ± 0.4 b	37.9 ± 0.1 a	38.7 ± 0.3 a	3.0 ± 0.4 a	10.8 ± 0.7 a