1. Effects of reduced tillage on vertical phosphorus stratification and availability
Clain Jones, Chengci Chen, Evette Allison, and Karnes Neill Montana State University
Prepared for 2007 American Society of Agronomy Conference

2. Background
Tillage has previously been found to affect available soil P levels (Selles et al. 1999) and vertical P stratification (Grant and Bailey, 1994), yet almost no studies have been conducted on calcareous soils.
No research located on effects of CT and NT on P uptake (prior to 2006). Phosphorus uptake and P fertilizer needs could be affected by tillage effects on:
1. P stratification (both vertical and horizontal) 2. Temperature 3. Moisture 4. Nitrogen availability 5. Yield
Differences in P stratification and uptake between CT and NT would indicate need for different P rates.

3. Questions
1. Are there differences in vertical stratification of available P between tilled and no-till systems in calcareous soils?
2. Is P uptake different between tillage systems?
3. Should P rates be adjusted for different tillage systems?

4. Materials and Methods
Location: Central Ag. Research Ctr., Moccasin, Montana
Existing study on tillage, cropping system (fallow, spring wheat, spring pea, winter pea forage  winter wheat), and nitrogen rate (0, 45, 90, 135 kg N/ha)
Tillage treatments:
9 year no-till (NTNT)
30+ year CT (CTCT) – Sweep till, 1 pass/year (Reduced T?)
NT following CT (CTNT)
CT following 9 year no-till (NTCT)
P fertilized with the seed (2-2.5 cm deep) each year

5. Study Location

6. Photo: nris.mt.gov

7. Photo: C. Chen, 2007
Spring Wheat
Fallow (NTNT)
Spring Pea
Winter Pea

8. Soil Sampling and Analysis
Fallow soils sampled Sept. 2005
Soil increments: Every 3 cm from 0 to 30 cm
Five soils composited per plot (4 replicates)
Analyses: Olsen P (top 30 cm) and sequential P fractions (top 15 cm)

9. Sequential Extractions
All in 1:30 soil:water suspensions, shaken 16 h, and centrifuged
Resin-P
Anion exchange resin capsule, extracted w/ 2M HCl (high availability)
Bic-P
0.5 M NaHCO3, pH 8.5 (high availability)
NaOH-P
0.1 M NaOH (moderate availability)
HCl-P
1 M HCl (low availability)

10. P uptake
Tissue P analyzed from winter wheat harvested in 2006 from same plots as soil sampled (90 kg N/ha treatment).
Tissue P analyzed in spring pea (grain) and winter pea (forage) harvested in 2007 (0 and 90 kg N/ha in 2006).

11. Results

12. Olsen P Distribution

13. Resin P Distribution

14. (averaged over 0-15 cm depth)
P Fractions
(averaged over 0-15 cm depth) b b b a

15. 2006 Winter Wheat Aboveground P Uptake
Note: Winter wheat fertilized with 10 kg P/ha

16. 2007 Winter Pea Aboveground P Uptake
WP not fertilized. Means of P uptake for 8 subplots per treatment

17. 2007 Spring Pea Grain P Uptake
SP not fertilized. Means of P uptake for 8 subplots per treatment.

18. Relevance of P Uptake
Our results, combined with research from other recent studies (Lupwayi et al. 2006; Schwab et al. 2006), suggest that P fertilizer rates do not need to be adjusted based on tillage system.

19. Summary
Stratification of Olsen P was greater in long-term NT than CT, yet all tillage treatments had much higher P levels near the surface.
Long term NT had significantly lower 0.1 M NaOH-P than long term CT (0-15 cm depth).
All other P fractions were not significantly different among tillage treatments.
Aboveground P uptake was not different among tillage treatments.
The results, combined with other recently published studies, suggest that P rate recommendations do not need to consider type of tillage system.

20. Acknowledgments This study was funded by the following:
Montana Fertilizer Advisory Committee

21. QUESTIONS?