W. D. Reynolds

Indirect estimation of near-saturated hydraulic conductivity from readily available soil information

Application of process-based water flow and solute transport models is often hampered by insufficient knowledge of soil hydraulic properties. This is certainly true for dual- or multi-porosity models that account for non-equilibrium flow of water in macropores, where the saturated ‘matrix’ hydraulic conductivity is a particularly critical parameter. Direct measurement is possible, but this is impractical for larger scale studies (i.e. catchment or regional), where estimation methods (pedotransfer functions) are usually required. This paper presents pedotransfer functions for hydraulic conductivity at a pressure head of � 10 cm, K10, based on measurements of near-saturated hydraulic conductivity made with tension infiltrometers in 70 soil horizons at 37 different sites in

Managing tile drainage, subirrigation, and nitrogen fertilization to enhance crop yields and reduce nitrate loss.

Improving field-crop use of fertilizer nitrogen is essential for protecting water quality and increasing crop yields. The objective of this study was to determine the effectiveness of controlled tile drainage (CD) and controlled tile drainage with subsurface irrigation (CDS) for mitigating off-field nitrate losses and enhancing crop yields. The CD and CDS systems were compared on a clay loam soil to traditional unrestricted tile drainage (UTD) under a corn (Zea Mays L.)-soybean (Glycine Max. (L.) Merr.) rotation at two nitrogen (N) fertilization rates (N1: 150 kg N ha(-1) applied to corn, no N applied to soybean; N2: 200 kg N ha(-1) applied to corn, 50 kg N ha(-1) applied to soybean). The N concentrations in tile flow events with the UTD treatment exceeded the provisional long-term aquatic life limit (LT-ALL) for freshwater (4.7 mg N L(-1)) 72% of the time at the N1 rate and 78% at the N2 rate, whereas only 24% of tile flow events at N1 and 40% at N2 exceeded the LT-ALL for the CDS treatment. Exceedances in N concentration for surface runoff and tile drainage were greater during the growing season than the non-growing season. At the N1 rate, CD and CDS reduced average annual N losses via tile drainage by 44 and 66%, respectively, relative to UTD. At the N2 rate, the average annual decreases in N loss were 31 and 68%, respectively. Crop yields from CDS were increased by an average of 2.8% relative to UTD at the N2 rate but were reduced by an average of 6.5% at the N1 rate. Hence, CD and CDS were effective for reducing average nitrate losses in tile drainage, but CDS increased average crop yields only when additional N fertilizer was applied.

Nitrous oxide and carbon dioxide emissions from monoculture and rotational cropping of corn, soybean and winter wheat

It is well established that nitrous oxide (N2O) and carbon dioxide (CO2) emissions from agricultural land are influenced by the type of crop grown, the form and amount of nitrogen (N) applied, and the soil and climatic conditions under which the crop is grown. Crop rotation adds another dimension that is often overlooked, however, as the crop residue being decomposed and supplying soluble carbon to soil biota is usually from a different crop than the crop that is currently growing. Hence, the objective of this study was to compare the influence of both the crop grown and the residues from the preceding crop on N2O and CO2 emissions from soil. In particular, N2O and CO2 emissions from monoculture cropping of corn, soybean and winter wheat were compared with 2 -yr and 3-yr crop rotations (corn-soybean or corn-soybean-winter wheat). Each phase of the rotation was measured each year. Averaged over three growing seasons (from April to October), annual N2O emissions were about 3.1 to 5.1 times greater in monocu...

Effects of selected conditioners and tillage on the physical quality of a clay loam soil

Field-crop yields are below their genetic and climatic potentials on many fine-textured soils due to low organic carbon content (OC), high bulk density (ρb), low hydraulic conductivity (Ks), insufficient air capacity (AC) and low plant-available water capacity (PAWC). Although soil conditioners derived from municipal, agricultural and industrial wastes are frequently used to improve soils, their effects on overall soil physical quality are still poorly understood. Hence, the objective of this laboratory soil core study was to determine for a Brookston clay loam the effectiveness of masonry sand, greenhouse rockwool waste, yard waste compost and swine manure compost for improving soil physical quality relative to “ideal” levels proposed in the literature, and relative to “benchmark” levels found in the soil under virgin conditions, long-term conventional tillage and long-term no-tillage. The virgin soil produced near-surface (0.05–0.15 m depth) values for ρb(0.88 Mg m-3), AC (0.19 m3m-3) and PAWC (0.22 m3m...

Effect of tillage and water table control on evapotranspiration, surface runoff, tile drainage and soil water content under maize on a clay loam soil

Two tillage and two water table control treatments under continuous maize cropping were evaluated over a 3-year period (1992–1994) for their effects on evapotranspiration, surface runoff (SR), tile drainage (TD) and soil water content in the root-zone on a clay loam soil in southern Ontario. The tillage treatments included soil saver (SS, reduced tillage) and moldboard plow (MP, conventional tillage). The water table control treatments included controlled drainage-subirrigation (CDS) and regular tile drainage (DR). There was no significant difference (P<0.05) in evapotranspiration estimates between the SS and MP tillage treatments. The SS tillage increased SR compared with MP tillage during the non-cropping periods in 1993 and 1994, but not in 1992. Relative to MP, the SS tillage increased soil profile water content during the cropping period but decreased soil profile water content during the non-cropping period in 1992. The CDS treatment produced significantly higher (P<0.05) evapotranspiration and soil water content than the drainage treatment during the dry 1993 and 1994 years, but not during the wet 1992 year. The CDS treatment also had significantly lower (P<0.05) TD and higher SR than the drainage treatment. For all the treatments, over 65% of SR and TD occurred in the 5 month non-cropping period from November to March. Of the total annual water input (precipitation and/or subirrigation) to the field site, 8% was partitioned to SR, 30% was partitioned to TD, 55% was removed by crop and soil evapotranspiration and 7% was accounted for by changes in soil profile water content.

Reducing Nitrate Loss in Tile Drainage Water with Cover Crops and Water-Table Management Systems

Nitrate lost from agricultural soils is an economic cost to producers, an environmental concern when it enters rivers and lakes, and a health risk when it enters wells and aquifers used for drinking water. Planting a winter wheat cover crop (CC) and/or use of controlled tile drainage-subirrigation (CDS) may reduce losses of nitrate (NO) relative to no cover crop (NCC) and/or traditional unrestricted tile drainage (UTD). A 6-yr (1999-2005) corn-soybean study was conducted to determine the effectiveness of CC+CDS, CC+UTD, NCC+CDS, and NCC+UTD treatments for reducing NO loss. Flow volume and NO concentration in surface runoff and tile drainage were measured continuously, and CC reduced the 5-yr flow-weighted mean (FWM) NO concentration in tile drainage water by 21 to 38% and cumulative NO loss by 14 to 16% relative to NCC. Controlled tile drainage-subirrigation reduced FWM NO concentration by 15 to 33% and cumulative NO loss by 38 to 39% relative to UTD. When CC and CDS were combined, 5-yr cumulative FWM NO concentrations and loss in tile drainage were decreased by 47% (from 9.45 to 4.99 mg N L and from 102 to 53.6 kg N ha) relative to NCC+UTD. The reductions in runoff and concomitant increases in tile drainage under CC occurred primarily because of increases in near-surface soil hydraulic conductivity. Cover crops increased corn grain yields by 4 to 7% in 2004 increased 3-yr average soybean yields by 8 to 15%, whereas CDS did not affect corn or soybean yields over the 6 yr. The combined use of a cover crop and water-table management system was highly effective for reducing NO loss from cool, humid agricultural soils.

Interactive effects of composts and liquid pig manure with added nitrate on soil carbon dioxide and nitrous oxide emissions from soil under aerobic and anaerobic conditions

The composting process results in immobilization of inorganic N. When high-Ndemanding crops are grown in compost- amended soils, additional N fertilizer is often applied. The combination of elevated nitrate levels from N fertilizer and high C inputs from the compost may result in enhanced greenhouse gas emissions. Hence, the objective of this laboratory incubation study was to characterize CO2 and N2O emissions from a Brookston clay loam soil that has received organic amendments in the presence or absence of added nitrate. The organic amendments included urban yard waste compost (YWC), liquid pig manure + wheat straw compost (PMC), and liquid pig manure (LPM). The nitrate treatments included added nitrate (100 mg KNO3-N kg soil-1) or no added nitrate. Total CO2 emissions during aerobic incubation followed the pattern: YWC > LPM > PMC > control (no organic amendments) for both nitrate treatments. Nitrate addition increased CO2 emissions from the YWC- and LPM-amended soils by 9 and 43%, respectively, but ha...

Influence of composts and liquid pig manure on CO2 and N2O emissions from a clay loam soil

Application of raw animal manure to agricultural land has resulted in environmental and health problems. Alternatives, such as composting, are now being developed to alleviate this situation. However, very little information is available regarding the fate of composts when added to fine-textured and poorly drained soils, especially with respect to the initial decomposition of composts and their effects on soil-derived CO2 and N2O emissions. We evaluated food waste compost (FW), yard waste compost (YW), liquid pig manure (LPM), LPM + yard waste compost (PMY) and LPM + wheat straw compost (PMS). Red clover (Trifolium pratense L.) (RC) and an unamended control soil were also tested. The solid amendments were divided into ground and unground treatments. Carbon dioxide emissions were increased relative to the control soil for all treatments except PMY. Total CO2 emissions over the 144-h incubation from unground material followed the pattern (P RC (554 mg CO2-C kg-1 soil) ...

Nitrogen mineralization and uptake by ryegrass in a clay loam soil amended with composts or liquid pig manure

Although composted liquid pig manure is increasingly being applied to agricultural soils, little is known about its impacts on N dynamics (mineralization, denitrification, immobilization, and plant uptake) in the crop root zone compared to liquid pig manure (LPM) or other types of composts. A greenhouse pot experiment was conducted to determine N mineralization and plant uptake in a ryegrass-cropped clay loam soil that had been amended with either LPM, LPM + wheat straw compost (PMS), or yard waste compost (YWC). Over a 20-wk growth period, plant biomass was increased relative to the control by 164% for LPM, 64.3% for YWC, and 39.6% for PMS. However, the recovery of amendment N in the ryegrass was low and variable at 3.3% for PMS (12.7 mg N kg-1), 3.7% for YWC (21.5 mg N kg-1), and 15.3% for LPM (90.9 mg N kg-1). Although gains and losses of mineral N occurred primarily within the first 8 wk, assimilation of amendment N by the ryegrass appeared to continue throughout the entire growth period. High amounts...

Solute dynamics and the Ontario nitrogen index: II. Nitrate leaching 1

Abstract: Nitrogen (N) leaching from soil into surface and ground waters is a concern in humid areas of Canada. As a result, N management protocols, including the Ontario N Index, are widely used to identify N leaching risk, although field assessment remains limited. Nitrogen fertilizer and chloride (Cl) tracer were fall-applied to five agricultural soils in Ontario with different textures and hydrologic soil groups (HSG) to assess the Ontario N Index and characterize inorganic N movement over 1 yr. The treatments included three N rates (0, 100, and 200 kg N ha-1) plus Cl tracer and 200 kg N ha-1 rate without Cl. After spring thaw, N loss from the crop root zone (top 60 cm) ranged from 68% for Brookston clay loam to 99% for Harrow sandy loam. A strong linear relationship between apparent N recovery and apparent Cl recovery indicated that N loss from the root zone occurred primarily by downward leaching. Leaching was controlled by the minimum measured saturated hydraulic conductivity (Ksat), and good estimates of N leaching were obtained using a quasi-theoretical relationship between N loss and Ksat. We concluded that Ontario N Index estimates of N leaching risk might be improved by including site-specific measurements of Ksat.