Post-Harvest Sugarcane Residue Management Strategies Studied Under Rainfall Simulator for Reduced Soil Erosion and Loss of Agrochemicals.

Carol Bronick, Lloyd Southwick and James FoussSoil and Water Research, 4115 Gourrier Avenue, Baton Rouge, LA 70808

ABSTRACTRetention of post-harvest residue has been shown to reduce runoff, erosion and off-site

migration of agrochemicals; however the optimal level of residue retention needs to be evaluated in light of planned bio-energy plants utilizing sugarcane for ethanol production. Greenhouse and field rainfall simulations on Cancienne silt loam in microplots representing typical sugarcane management practices were used to assess residue management (100%, 20% and 0% residue swept into furrows). Fertilizer (220 kg/ha applied as 32% solution) was applied in a knife cut and soil was repacked over the cut. Commonly used pesticides (pendimethalin and atrazine) were applied. Runoff and sediments were collected and analyzed for pesticides and nutrients. Sediment and pendimethalin losses increased with decreasing rates of residue retention; pendimethalin is commonly associated with sediments. Losses of nitrate and atrazine, which are associated with the water phase of runoff, increased with increasing residue. These results suggest that maintaining a high percent (>20%) residue retention swept into rows will reduce erosion and some agrochemicals while reaching acceptable levels of bio-mass harvest for bio-energy production. Residue management for N and atrazine is important under these soils to avoid losses to surface water and the environment.

INTRODUCTIONImproved understanding of residue management is essential to understanding the role

of residue in reducing off-site migration of pesticides and nutrients and the viability of sugarcane residue use in bio-energy production. The extent to which post-harvest sugarcane residue can be removed without negatively impacting soil erosion and off-field transport of agrochemicals, crop yield, soil parameters needs to be evaluated. The influence of residue on N cycling is complicated and in many cases indirect. Residue coverage tends to alter soil temperature and moisture which in turn influence microbial processes such as nitrification, mineralization and denitrification, which control the availability of nitrate for off site migration (Thorburn et al., 2005). The reduced scale of greenhouse microplot simulations and the complexity of field conditions make the applicability of data from greenhouse microplot simulations to study field conditions unclear.

OBJECTIVESCompare erosion and agrochemical loss under

• different levels of post harvest residue retention and management • field and greenhouse rainfall simulations

RESULTS

• Bare soil had highest erosion and lowest nitrate loss in all field and greenhouse studies. In greenhouse beds, bare soil had lowest atrazine and highest pendimethalin losses.

• Full swept residue retention reduced erosion and pendimethalin and increased nitrate and atrazine loss in runoff. Pendimethalin tends to associate with sediment while nitrate and atrazine occur in the water phase. The increased organic matter from residue contributes to an increased mineralization and greater probability of nitrate loss (Thorburn et al., 2004).

• Partial, swept residue tended to reduce erosion in comparison to bare soil; however, the results were highly variable and not statistically significant. Higher retention rates (>20%) should be evaluated.

CONCLUSIONS

• Erosion: Residue retention reduced erosion under both greenhouse and field experiments—although the decreased plot size may highlight some dynamics while masking others.

• Nitrogen can be immobilized by residue, making it unavailable for crop plants, or mineralized, making it mobile. Residue improved soil conditions for N mineralization and resulted in increased N loss in runoff.

• Atrazine loss increased with residue treatment in greenhouse microplots

• Pendimethalin loss decreased with residue treatment in greenhouse microplots

• Microplot experiments may be more important for indicating trends caused by treatments than for providing absolute values.

REFERENCESGrigg, B. C., J. L. Fouss, and L. M. Southwick. 2005. Impacts of Sugarcane Post-Harvest Residue Management on Runoff, Soil Erosion, and Nitrate

loss. ASAE Annual International Meeting, paper 052136. Pfaff, J. D., D. P. Hautman, and D. J. Munch. 1997. Method 300.1: Determination of inorganic anions in drinking water by ion chromatography.

Cincinnati, Ohio: USEPA, ORD, NERL.Thorburn, P.J., H.L. Horan and J.S. Biggs. 2004. Nitrogen management following crop residue retention in sugarcane production. SuperSoil 2004,

the 3rd Australian New Zealand Soils Conference.Thorburn, P.J., E.A. Meier and M.E. Probert. 2005. Modelling nitrogen dynamics in sugarcane systems: Recent advances and applications. Field

Crops Research 92: 337-351.

AcknowledgementsThe authors express their appreciation to Dr. Timothy Appelboom, Kelvin Lewis, Gary Foster, Chris Borron, John

Canady for their assistance in these studies.

Field rainfall simulationMATERIALS AND METHODSCancienne silt loam (fine-silty, mixed, superactive, nonacid, hyperthermic fluvaquentic

epiaquepts - formerly included with the Commerce series) from the St. Gabriel Research Station, Louisiana Agricultural Experiment Station was used for both greenhouse and field rainfall simulations. Field plots were established between mounded rows (approximately 1.5m) and 1.8 m long (2.7m2). Greenhouse beds were established (0.6m x 1.5m x 0.2m) with sieved (5mm) soil (Grigg et al., 2005). Post harvest sugarcane residue was collected from the previous harvest and air-dried and applied to greenhouse and field plot treatments were full residue (5Mg/ha), partial residue (1 Mg/ha) and control (no residue to simulate burned residue). Rainfall was simulated for 30 minutes, approximately 80mm/hr in the field and 110mm/hr in the greenhouse. Prior to each rainfall simulation soil samples were collected for moisture analysis. During rainfall events runoff was pumped into graduated, plastic carboys and total volume was determined at the end of the rainfall. Runoff was analyzed for solids, nutrients and pesticides. Nitrate-N, NO2-N and PO4-P concentrations (mg/L) were determined using ion chromatography and USEPA Method 300 (Pfaff et al., 1997). Runoff and soil extracts samples were analyzed for atrazine and pendimethalin by gas chromatography.

DISCUSSIONNitrogen cycling is complex, influenced by organic matter, temperature and moisture.

Residue cover improves both moisture and temperature for increased N mineralization. Cancienne soils are somewhat poorly drained and moderate to slowly permeable, leaving the nitrate available for runoff. These results are similar to short-term experiments and simulations by Thorburn et al. (2004). These results suggest that substances carried in the water phase of runoff, such as nitrate and atrazine, may be increased by residue under high soil moisture, poor soil profile drainage conditions. Sediment, and associated pendimethalin, will be decreased through residue retention.

Table 1. Annualized soil loss (Mg/ha/yr) in field and greenhouse rainfall simulations.

Table 2. Annualized nitrate loss (kg/ha/yr) in field and greenhouse rainfall simulations.

9.2b9.2bFull Swept

11.5a33.1aPartial Swept

14.0a37.3a*Bare

GreenhouseField

24.1a36.1aFull Swept

17.9b18.7abPartial Swept

10.6c15.5b*Bare

GreenhouseField

19c

39b

56a*

Pendimethalin

349A Full Swept

321ABPartial Swept

258B**Bare

Atrazine

Table 3. Atrazine and pendimethalin loss in greenhouse rainfall simulations (g/ha).

*Small letters indicate significant differences between treatments (p=0.05)**Capitol letters indicate significant differences between treatments (p=0.1)

Erosion Nitrate Pesticide

Greenhouse rainfall simulation