Potassium and phosphorus have no effect on severity of charcoal rot of soybean

Figures & data

Fig. 1 Maximum air temperatures and precipitation for the months of April through October for 2008 to 2010 at Jackson and Milan, TN. The set of numbers in the x-axis indicates the monthly total precipitation.

Table 1. Probability of greater values of F resulting from Type III tests of fixed effects P and K from colony forming units (CFU) of Macrophomina phaseolina and soil from soybean tissue from two locations (Milan and Jackson, TN, USA) during 2008, 2009 and 2010 obtained from SAS PROC MIXED analysis.

		Effect of P				Effect of K
		Tissue CFU		Soil CFU		Tissue CFU		Soil CFU
Effect	DF	F Value	Pr > F	F Value	Pr > F	F Value	Pr > F	F Value	Pr > F
Year	2	7.21	***	3.63	*	13.12	***	0	NS
Location	1	24.43	***	17.3	***	0.66	NS	0.1	NS
Year×Location	2	1.68	NS	4.03	**	1.71	NS	0.2	NS
Treatment	5	0.95	NS	2.32	*	0.22	NS	1.1	NS
Year×Treatment	10	0.72	NS	0.77	NS	0.59	NS	1.4	NS
Location×Treatment	5	0.29	NS	1.12	NS	0.78	NS	0.8	NS
Year×Location×Treatment	10	0.67	NS	1.03	NS	0.54	NS	0.7	NS

*, significant effect P ≤ 0.05; **, significant effect P ≤ 0.01; ***, significant effect P ≤ 0.001; NS, non-significance at P ≤ 0.05.

Table 2. Location-by-year interaction on soil colony forming units (CFU) from soybean grown in Jackson and Milan, TN, USA in 2008, 2009 and 2010.

	Soil CFU
Location	2008	2009	2010
Milan	42 A	73 A	68 A
Jackson	41 A	40 B	40 B

Different letters indicate significant differences among location plots within year based on P rates analysed by least significant differences at P ≤ 0.05.

Fig. 2 (Colour online) Trends of phosphorus (expressed as P₂O₅₎ and potassium fertilizer (expressed as K₂O) on CFU g⁻¹ of tissue (A and B) and soil (C and D) at Jackson (filled circles and solid lines) and Milan (open circles and dashed lines); filled and open circles are actual CFUs; dashed and solid lines are regression lines. Phosphorus was applied at six rates: 0, 22, 45, 67 and 90 kg P₂O₅ ha⁻¹; and K was applied at six rates: 0, 45, 90, 134 and 179 kg K₂O ha⁻¹ with the sixth level applied for both equal to the recommended fertilizer application rate based on annual soil P and K testing in 2008, 2009 and 2010 at Jackson and Milan, TN, USA.

Table 3. Effect of phosphorus and potassium fertilizer rates on colony forming units per gram of M. phaseolina from tissue and soil at Jackson and Milan, TN, USA in 2008 through 2010.

Nutrient	Location	Year	Slope	Standard Error of Slope	R^2 (%)	F-value	P-value
				Tissue CFU^−g
Phosphorus	Jackson	2008	35.8	69.1	9.68	0.27	0.61
Phosphorus	Jackson	2009	−10.1	21.2	2.45	0.23	0.64
Phosphorus	Jackson	2010	76.8	86.2	24.75	0.79	0.39
Potassium	Jackson	2008	18.9	104	23.75	0.86	0.37
Potassium	Jackson	2009	19.2	70	49.91	3.05	0.10
Potassium	Jackson	2010	−16.7	121.3	0.0	0.11	0.75
Phosphorus	Milan	2008	60.7	20.3	26.14	0.34	0.57
Phosphorus	Milan	2009	44.8	11	2.92	0.41	0.53
Phosphorus	Milan	2010	103.5	51.1	26.5	0.73	0.41
Potassium	Milan	2008	−3.6	19.7	0.12	0.03	0.86
Potassium	Milan	2009	25.8	13.6	51.07	3.59	0.08
Potassium	Milan	2010	−68.2	37	70.05	3.41	0.08
				Soil CFU
Phosphorus	Jackson	2008	0.18	0.15	31.63	0.82	0.55
Phosphorus	Jackson	2009	−0.05	0.11	2.45	0.88	0.52
Phosphorus	Jackson	2010	−0.03	0.08	11.6	0.65	0.67
Potassium	Jackson	2008	−0.07	0.17	41.06	0.16	0.97
Potassium	Jackson	2009	0.1	0.35	49.91	1.21	0.35
Potassium	Jackson	2010	0.07	0.22	7.06	0.86	0.53
Phosphorus	Milan	2008	−0.01	0.08	0.29	0.41	0.83
Phosphorus	Milan	2009	0.22	0.06	2.92	3.4	0.03*
Phosphorus	Milan	2010	−0.18	0.09	24.94	0.42	0.83
Potassium	Milan	2008	0.04	0.11	3.7	1.27	0.33
Potassium	Milan	2009	0.13	0.07	51.07	1.29	0.32
Potassium	Milan	2010	0.07	0.13	42.86	2.25	0.10

*, significant effect at P ≤ 0.05.