Short-Term Effects of Biogas Digestates and Pig Slurry Application on Soil Microbial Activity

Table 5

Calculated parameters from soil respiration curves after amendment with four types of biogas digestates (BD-A, BD-B, BD-C, and BD-D) and pig slurry (PS). is the time of maximum respiration activity after amendment and the maximum peak height () is the respiration rate at that time. Specific growth rate (µ) was calculated according to ISO/DIS 17155 (i.e., on a log₁₀ basis). The C utilization rate is the cumulative respired C during the 12 days of incubation. Values not sharing the same letters (a–e) are statistical significantly different ( < 0.05).

Residue; type	Amendment rate; (kg -N ha^−1)	(h)	(mg CO2 h^−1)	Specific growth rate ()	Utilization rate of C; (% of added C)
BD-A	17.5	55.0^c	0.046^e	0.013^d	39.8^a
	35	57.4^b	0.078^de	0.017^d	28.5^abc
	70	62.1^b	0.141^de	0.017^d	30.9^ab
	140	66.2^a	0.287^d	0.019^d	32.5^ab
BD-B	17.5	—	—	—	—^2
	35	≤8.5^1	≥0.068^1	—	21.8^bcd
	70	18.4^f	0.117^de	0.018^d	16.6^d
	140	19.6^f	0.259^de	0.022^d	19.0^cd
BD-C	17.5	—	—	—	—^2
	35	≤8.5^1	≥0.175^1	—	13.7^d
	70	14.6^g	0.249^de	0.067^bc	19.4^cd
	140	18.1^f	0.668^c	0.057^bc	30.9^ab
BD-D	17.5	≤8.5^1	≥0.037^1	—	13.7^d
	35	≤8.5^1	≥0.088^1	—	15.7^cd
	70	≤8.5^1	≥0.202^1	—	15.0^d
	140	≤8.5^1	≥0.405^1	—	16.9^d
PS	17.5	12.6^g	0.232^de	0.090^a	32.2^ab
	35	20.8^f	0.519^c	0.053^c	27.8^abc
	70	29.2^e	1.111^b	0.060^bc	31.1^ab
	140	36.5^d	2.233^a	0.074^ab	31.4^ab

Maximum respiration occurred before or at time of stabilization of the respirometer readings. Average values from the first reliable reading (at 8.5 h) are reported but were not used in the statistical tests.
²Data points in the respiration measurements were frequently below the detection limit.
—: Data not obtainable.