Water table management reduces tile nitrate loss in continuous corn and in a soybean-corn rotation.

Craig F Drury,Chin S Tan,Thomas W Welacky,Thomas O Oloya,John D Gaynor,John W Daniel Reynolds

doi:10.1100/tsw.2001.268

Abstract

Water table management systems can be designed to alleviate soil water excesses and deficits, as well as reduce nitrate leaching losses in tile discharge. With this in mind, a standard tile drainage (DR) system was compared over 8 years (1991 to 1999) to a controlled tile drainage/subirrigation (CDS) system on a low-slope (0.05 to 0.1%) Brookston clay loam soil (Typic Argiaquoll) in southwestern Ontario, Canada. In the CDS system, tile discharge was controlled to prevent excessive drainage, and water was pumped back up the tile lines (subirrigation) to replenish the crop root zone during water deficit periods. In the first phase of the study (1991 to 1994), continuous corn (Zea mays, L.) was grown with annual nitrogen (N) fertilizer inputs as per local soil test recommendations. In the second phase (1995 to 1999), a soybean (Glycine max L., Merr.)-corn rotation was used with N fertilizer added only during the two corn years. In Phase 1 when continuous corn was grown, CDS reduced total tile discharge by 26% and total nitrate loss in tile discharge by 55%, compared to DR. In addition, the 4-year flow weighted mean (FWM) nitrate concentration in tile discharge exceeded the Canadian drinking water guideline (10 mg N l) under DR (11.4 mg N l), but not under CDS (7.0 mg N l). In Phase 2 during the soybean-corn rotation, CDS reduced total tile discharge by 38% and total nitrate loss in tile discharge by 66%, relative to DR. The 4-year FWM nitrate concentration during Phase 2 in tile discharge was below the drinking water guideline for both DR (7.3 mg N l) and CDS (4.0 mg N l). During both phases of the experiment, the CDS treatment caused only minor increases in nitrate loss in surface runoff relative to DR. Hence CDS decreased FWM nitrate concentrations, total drainage water loss, and total nitrate loss in tile discharge relative to DR. In addition, soybean-corn rotation reduced FWM nitrate concentrations and total nitrate loss in tile discharge relative to continuous corn. CDS and crop rotations with reduced N fertilizer inputs can thus improve the quality of tile discharge water substantially.

Highlights

Tile drainage has enabled farmers to plant earlier in the spring and harvest later in the fall, which has led to increased flexibility in crop type and field operations as well as enhanced crop productivity
controlled tile drainage/subirrigation (CDS) effectively decreased tile flow volume, nitrate concentration in tile drainage water, and total amount of nitrate lost through the tile discharge relative to DR
Under CDS, the flow weighted mean (FWM) nitrate concentrations of tile drainage water were less than the drinking water guideline (10 mg N l1) in both phases of the study (i.e., 7.0 mg N l1 in Phase 1 and 4.0 mg N l1 in Phase 2) (Table 1)

Summary

Introduction

Tile drainage has enabled farmers to plant earlier in the spring and harvest later in the fall, which has led to increased flexibility in crop type and field operations as well as enhanced crop productivity. Subirrigation, and tile drainage volumes were recorded continuously from May 1991 to October 31, 1994 (Phase 1) and from May 1, 1995 until April 30, 1999 (Phase 2) by Neptune T-10 water meters[10]. During Phase 1, the FWM nitrate concentration of tile drainage water from the DR treatment (11.4 mg N l1) was greater than that from corresponding CDS treatment (7.0 mg N l1 ), amounting to a 39% reduction for CDS (Table 1).

Results

Conclusion