Submitted to: Soil Tillage Research Organization International Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: February 7, 2000
Publication Date: February 7, 2000
Interpretive Summary: The adoption of conservation tillage has grown steadily in North America in recent times. Reduced erosion and increased water retention under conservation tillage might decrease the sediment-bound pollutants to surface waters helping water pollution containment efforts. Greater infiltration may, however, cause accelerated leaching of groundwater contaminants. This concern is real in the Southeast where use of conservation tillage, such as no-till, and animal waste, such as poultry litter, is increasing on major crops like cotton and soybeans. In a study designed to address this concern, we found similar nitrate-nitrogen losses through sub-surface drains between no-till and conventional tillage cotton. But slightly higher losses were observed in cotton fertilized with poultry litter compared to that fertilized with ammonium nitrate. This may have been due to greater than the 50% expected N mineralization from poultry liter. Concentrations of nitrate-nitrogen reached between 20 and 30 mg L- following fertilizer application but reduced to below 5 mg L-1 later in the season. Dissolved ortho-phosphate, which can be of concern when groundwater discharges into streams, generally remained below 0.1 mg L-1 in all treatments. Those concerned with effects of no-till cotton and poultry litter use in the Southeast would find these results encouraging.
Technical Abstract: Risk of ground water contamination by nutrients, notably nitrate-nitrogen (NO3-N) might increase under conservation tillage. Leaching of dissolved ortho-phosphate (Ortho-P) can also be a concern when groundwater discharges into a stream nearby. We conducted a study in 1997 and 1998 near Watkinsville, GA, to evaluate NO3-N and Ortho-P losses through subsurface drainage from no-till (NT) and conventional tillage (CT) cotton fertilize with either conventional fertilizer (CF) or poultry litter (PL). Limited rainfall precluded significant drainage in the 1998 cotton season. Total NO3-N loss were similar between CT and NT in 1997 (mean 8.9 and 8.2 kg ha- 1, respectively; P>0.73), but different between PL and CF (mean 10.3 and 6.5 kg ha-1, respectively, P=0.009). The difference may have been due to greater N mineralization than expected from PL. Peak NO3-N concentrations reached 20 to 30 mg L-1 from CT, 10 to 15 mg L-1 from NT, and 10 to 20 mg L-1 in both PL and CF plots during the first two months after N application, and then fell to below 5 mg L-1 late in the season. Disolved ortho-phosphate concentration remained below 0.1 mg L-1 for all but one drainage event. These are encourage results for producers engaged in cotton production under no-till with poultry litter with respect to water quality.