Combined application of N-fixing PGPB and rice straw mulch compensates N immobilization by straw, improving crop growth

Chemical and Biological Technologies in Agriculture

Table 3 Mean values ± SE of the soil nitrogen content, ryegrass plant nitrogen content and increase in atmospheric N-fixation (ΔNdfa) obtained in microcosm conditions at the indicated sampling dates for the factors inoculation and the presence of mulching (in the case of ΔNdfa only for the factor inoculation)

Factor	Treatment	Soil nitrogen content				Plant nitrogen content		ΔNdfa
		April sampling		June sampling		September sampling		September sampling
		mg NH₄⁺/g⁻¹	mg NO₃⁻/g⁻¹	mg NH₄⁺/g⁻¹	mg NO³⁻/g⁻¹	(%)	(mg/plant)	(%)
Inoculation	Non-inoculated control	0.0171 ± < 0.01	0.1487 ± 0.02	0.0149 ± < 0.01	0.1415 ± < 0.01	1.02 ± 0.11	17.34 ± 1.12	–	–
	Azotobacter chroococcum SM199	0.0211 ± < 0.01 ns	0.2176 ± 0.03***	0.0288 ± < 0.01***	0.2215 ± 0.01***	1.14 ± 0.14*	28.38 ± 1.38**	8.58	± 2.43 ns
	Azotobacter chroococcum SM232	0.0265 ± < 0.01***	0.1908 ± 0.02*	0.0276 ± < 0.01***	0.2146 ± 0.02***	1.18 ± 0.07**	33.04 ± 0.72***	7.03	± 3.86 ns
	Azotobacter salinestris SM662	0.0262 ± < 0.01***	0.2433 ± 0.02***	0.0254 ± < 0.01***	0.2296 ± 0.03***	0.84 ± 0.07**	17.22 ± 0.69 ns	2.33	± 0.80 ns
	Azotobacter chroococcum SM700	0.0196 ± < 0.01 ns	0.2090 ± 0.04**	0.0198 ± < 0.01*	0.1783 ± 0.02*	1.01 ± 0.11 ns	22.82 ± 1.13*	2.18	± 0.68 ns
	Azospirillum brasilense Az39	0.0242 ± < 0.01***	0.1778 ± 0.03 ns	0.0198 ± < 0.01*	0.1415 ± 0.01 ns	1.13 ± 0.18*	23.50 ± 1.86*	3.45	± 1.01 ns
Mulch	Non-mulching control	0.0214 ± < 0.01	0.2525 ± 0.01	0.0226 ± < 0.01	0.1548 ± < 0.01	1.30 ± 0.05	25.74 ± 0.53
	Mulching	0.0234 ± < 0.01*	0.1432 ± 0.01***	0.0228 ± < 0.01 ns	0.2208 ± 0.01***	0.81 ± 0.03***	20 ± 0.32**

Asterisks indicate the level of significance of the difference between the mean values of each treatment and its corresponding control, according to Dunnett’s test. Significance levels: ***p < 0.001; **0.001 < p < 0.01; *0.01 < p < 0.05; ns, not significant.