Linking supplementary data to soil P levels and stratification

1. Linking supplementary data to soil P levels and stratification GLPF Grant- Team meeting #5 July 23-24, 2013

2. Hypotheses • We would find increased P stratification with: • Recent manure application • No soil inversion • Broadcast fertilizer application • We would find increased P stratification with poorly drained soils belonging to hydrologic soil groups C/D (not examining today)

3. Statistical analysis • Used analysis of variance (ANOVA) followed by a Tukeytest when possible • Differences in means • Used Kruskal Wallis (KW) followed by a Dunn’s test when unequal variances or non-normal data • Differences in ranks • Each figure depicts the mean or average value ± 95% confidence intervals • 95% certain the mean is in this range

4. Influence of tillage used for corn Total

5. Influence of tillage used for corn Total Ratio Difference • Reduced tillage had lower mean total 0-8”soil P (39ppm) compared to mulch tillage (44ppm; ANOVA, P=0.019) • Inversion tillage had a lower mean stratification, both in terms of the ratio (1.36 vs. 1.53; KW, P=0.03) and difference (11ppm vs. 18ppm; KW, P=0.001)

6. Combined tillage practices

7. Combined tillage practices Total Ratio Difference • Lower soil P levels in reduced till corn followed by mulch till (35ppm) compared to other tillage practices (42ppm; ANOVA P<0.001) • Yet, no significant differences in stratification across tillage practices (ratio: KW, P=0.16; difference: KW, P=0.08)

8. Fertilizer application method Total Ratio Difference • Lumped all broadcast and all banding, regardless of season • Banding lead to higher soil P levels (mean= 37ppm vs. 41ppm; MW, P=0.024) • However, broadcast had higher levels of stratification (ratio: 1.56 vs. 1.48, MW, P=0.001; difference: 17ppm vs. 15ppm, MW, P=0.015)

9. Manure application history Total Ratio Difference • Frequent manure application lead to higher mean soil P (58ppm), and any history of application had higher levels (47ppm) compared to no known applications (38ppm; KW P<0.001) • Although the ratio had significant differences, the pattern is difficult to interpret (KW P=0.001) • The difference between top and total was higher for recent application of manure (25ppm vs 16ppm, KW P=0.02)

10. Combined manure, tillage, fertilizer application

11. Combined manure, tillage, fertilizer application • Manure application tended to result in higher mean soil P (51ppm vs. 39ppm) • Banding had higher soil P in reduced till corn/no-till (45ppm) compared to broadcast (36ppm) • Trend in others ANOVA P<0.001

12. Combined manure, tillage, fertilizer application • Ratio was lowest under inversion tillage and reduced till corn/no-till with banding (1.4) compared to reduced till with broadcast (1.6; KW P=0.007) • Difference was highest with manure application (25ppm) and lowest with inversion (12ppm; KW P=0.006)

13. Classification and Regression Tree (CART) analysis • Next step in analyzing these data • Hypothetical example: • We tended to find higher soil test P with recent manure application and banded fertilizer application Recent manure application? yes no Banded fertilizer application? yes no STP = 51 ppm n=120 Other potential factors? Soil type, tillage, slope? STP = 41 ppm n=382 yes no

14. Classification and Regression Tree (CART) analysis • We tended to find lower stratification with inversion tillage, higher stratification with recent manure application and broadcast fertilizer Inversion tillage? yes no Ratio = 1.35 Diff = 11ppm n=61 Recent manure application? yes no Broadcast fertilizer application? yes no Ratio = 1.60 Diff = 27ppm n=120 Other potential factors? Soil type, tillage, slope? Ratio = 1.55 Diff = 16ppm n=206 yes no

15. Questions?