Tree, Grass, and Crop Root Length Densities and Soil Water Content Within an Agroforestry Buffer System

1. Tree, Grass, and Crop Root Length Densities and Soil Water Content Within an Agroforestry Buffer System Ranjith Udawatta1, Stephen Anderson2, and Harold Garrett1 Center for Agroforestry1, Department of Soil, Environmental and Atmospheric Sciences2 School of Natural Resources, University of Missouri-Columbia.

2. Despite improvements in the use of soil conservation practices, crop rotations, and nutrient management programs, significant concerns still exist regarding soil erosion and nutrient losses in runoff from row crop production. In the US, states are required to implement water quality standards based on USEPA guidelines or other scientifically defensible methods (Ice and Binkley, 2003). Rationale

3. Such requirements result in increasing pressure for the development of economically and environmentally suitable guidelines to reduce NPSP from agricultural watersheds. • Recently, agroforesty has been suggested as an alternative to traditional row crop production for conservation and a source of additional income.

4. Effects of agroforestry practices on root distributions and changes in soil water content have received little attention in the temperate climatic zone. • This study will evaluate root length densities and changes in seasonal volumetric soil water content in agroforestry and grass buffer cropping systems.

5. Hypothesis: Permanent vegetation with deep roots and an extended transpiration period will change root distribution patterns and soil water content changes over time compared to row crops.

6. Study Design: Two paired watersheds in a corn-soybean rotation in northeast Missouri. Grass buffers consist of brome, redtop, and birdsfoot trefoil and were established in 1997. Pin oak, swamp white oak, and bur oak trees were planted in the center of grass buffers on the agroforestry watershed in 1997.

7. Data Collected Root length densities: Tree, Grass, and Corn areas to a 1 m depth in 2004. Volumetric soil water content in tree, grass and corn areas in 2004.

8. Study site location and 0.5 m interval contour lines. Gray bands indicate grass buffers and agroforestry buffers and grass waterways. Sampling Areas for Roots

9. At 5000 feet altitude in August 2002

10. At 5000 feet altitude in August 2002

11. 2003 2005

12. Study Design for Soil Water Monitoring Pin oak Data logger 10 m Buffer Senor depths 5 cm 10 cm Campbell Soil Water Content Reflectrometer sensors were installed on two transects. 20 cm Sensor locations 40 cm

13. Analysis Procedures Roots length densities by treatment were compared to examine differences among the three treatments. Roots length densities by depth and treatment were compared to examine differences in depth distribution of roots among the three treatments. Calibrated volumetric soil water content among the three treatments and depths were compared to evaluate treatment effects on seasonal soil water content.

14. RESULTS

15. Root Length Density from 0 to 1.0 m Depth by Treatment

16. Crop Root Length Density Between Two Buffers a a a a

17. Root Length Density Within Grass Buffers a a b

18. Vertical distribution of root length for corn, tree and grass treatments.

19. Vertical distribution of root length for pin oak, swamp white oak and bur oak

20. Monthly Precipitation and Corn Growing Period 670 mm Corn 5/22/04 Long-term precipitation

21. Soil Water Content for Tree, Grass, and Crop Areas from June 14 to November 30, 2004 5 cm Depth

22. Soil Water Content for Tree, Grass, and Crop Areas 6-14 to 11-30 5 cm 10 cm 20 cm 40 cm

23. Daily Precipitation During October 2004 Recharge Period

24. Soil Water Recharge (5 and 10 cm depths) 5 cm Depth 10 cm Depth

25. Soil Water Recharge (20 and 40 cm depths) 20 cm Depth 40 cm Depth

26. Summary • Tree and grass areas had more root length compared to the crop areas although the differences were not significant. • 2. Trees and grass had more roots in the subsurface horizons relative to the corn areas. • 3. Volumetric soil water content was significantly lower in the tree and grass areas compared to crop areas. This was attributed to the extended transpiration period for the trees and grass compared to corn.

27. The results of the study show that agroforestry buffers maintained lower seasonal soil water • content allowing more water recharge during storm events. • During recharge periods, soil under trees stored more water compared to soils under • corn. This could be attributed to greater differences in antecedent water content and possibly improved infiltration due to better soil physical properties such as porosity.

28. The differences in soil water content were smaller at the 20 and 40 cm depths. • 7. The 2004 average Missouri corn yield was • 7379 kg ha-1. The study watersheds had an average corn yield of 9050 kg ha-1. • 8. Incorporation of tree and grass buffers did not • reduce crop yields at this site in 2004 but improved soil water storage.

29. CONCLUSIONS Results indicate that agroforestry and grass buffer treatments can effectively reduce runoff and nutrient losses when incorporated directly into a corn-soybean rotation.

30. Acknowledgements We gratefully acknowledge the Missouri Department of Natural Resources, the Missouri Agricultural Experiment Station, the USDA-Agricultural Research Service, and the US-Environmental Protection Agency.

31. Thank You