J. F. Moncrief

Snowmelt runoff, sediment, and phosphorus losses under three different tillage systems.

In cold climates, snowmelt runoff often exceeds rainfall runoff during the year. Conservation tillage practices may be effective in reducing runoff during the cropping season but not during the snowmelt period. A plot study was conducted on a cropped hillslope to assess how tillage practices affect snowmelt runoff and the associated losses of sediment, phosphorus (P), and chemical oxygen demand (COD). Tillage systems were fall moldboard and chisel plowing with spring disking, and a ridge till system utilizing only the tillage associated with summer row cultivation. Tillage and planting were done up and down the slope. Ridge tilled plots had higher fall residue cover, retained more snow, had less surface roughness, and consequently produced more runoff than the moldboard plow treatment. The amount of runoff from chisel plowed plots was similar to runoff from ridge tilled plots despite a relatively rough surface and moderate amount of residue cover. Phosphorus losses in runoff were higher for the ridge till and chisel plow systems than for the moldboard plow system. For all tillage systems, soluble P represented a major portion (75%) of the total P loss in snowmelt runoff. Although erosive losses in snowmelt were low, the P losses were substantial and merit consideration in studies evaluating management systems impact on surface water quality in regions where snowmelt runoff is important.

Effect of subsoiling and subsequent tillage on soil bulk density, soil moisture, and corn yield☆

Abstract Many producers use subsoilers periodically to alleviate suspected compaction caused by traffic from tillage, planting, and harvesting equipment. In the fall of 1988 a study was initiated in the upper Midwest region of the USA near Morris, Minnesota to study the effects of a one-time subsoiling and its interaction with four subsequent primary tillage systems (fall moldboard plowing, fall chisel plowing, spring disking, and no-tilling) on soil compaction, soil moisture, penetrometer resistance, and corn ( Zea mays L.) growth and grain yield. The experiment was established on a Hamerly clay loam (Aeric Calciaquoll)-Aastad clay loam (Pachic Udic Haploboroll) complex. Subsoiling was performed in the fall of 1988 and the study was cropped to continuous corn from 1989 to 1991 on a site that had been farmed many years by normal 6-row, 76-cm row width equipment. Results show that subsoiling had very little effect on plant growth and no effect on grain yield over three cropping seasons following the subsoiling operation. Subsoiling had significant effects on soil bulk density and volumetric soil moisture content in 1989, but by 1990–1991 these effects were not significant. Volumetric soil moisture content generally increased in relation to soil bulk density increases. Tillage impacted surface residue accumulation, but did not affect soil bulk density, volumetric soil moisture, or grain yield. Results from this study indicate that subsoiling soils does not necessarily result in better yields or better soil moisture availability, particularly if compaction problem are not evident.

Prevalence and initiation of preferential flow paths in a sandy loam with argillic horizon

Numerous studies have reported on preferential solute transport, giving evidence that preferential flow is widespread. However there has been little field documentation of the relative importance of different preferential transport mechanisms. This study used a dye tracer to examine the extent and relative importance of different preferential transport mechanisms in a glacial outwash-derived soil that is used extensively for high input agriculture in central Minnesota, USA (Verndale sandy loam: coarse loamy over sandy, mixed, frigid, Udic Argiborolls). Experimental treatments included three initial soil water contents (WET, MEDIUM, and DRY) and three dye solution application rates (FLOOD, SPRINKLER-High, and SPRINKLER-Low). Thirteen cm of FD&C Blue no. 1 (also known as Brilliant Blue FCF) food dye solution (200 g l−1) were applied to replicated 1 m×1 m plots in a recently tilled 5 year old alfalfa stand and to two additional plots with no history of alfalfa. Vertical soil profile faces were exposed at 10-cm increments across each plot. Extensive and deeper preferential dye movement occurred under FLOOD conditions regardless of initial soil moisture or recent vegetation history. The two SPRINKLER rates generally resulted in relatively shorter preferential flow paths (PFPs). Within-plot variability of dye patterns—including depth and number of PFPs—was very high. Most PFPs observed were associated with roots and decayed roots, or with patterns in the abruptness and topography of the boundary between the Ap and Bt horizons. Open burrows were uncommon, but contributed to extensive preferential flow in the two NO-ALFALFA plots. Our findings indicate that preferential transport is prevalent under the variety of application rate and soil moisture conditions evaluated, and that observable soil features appear to be initiators of the majority of the PFPs. Only a few (10 of 126) of the profiles excavated had preferential flow paths that were not associated with visible soil features. The observed high variability gives support to the idea that observations of spatial variability in pesticide transport studies is due to preferential transport. Our initial goal of elucidating the relationship between rate of application and the relative number and depth of PFPs was aimed at evaluating water flow patterns. However, subsequent research found that dye retardation was increased at slower application rates, indicating that the dye patterns we observed were due to both the rate and the pattern of water movement. As a result, we caution that our findings of generally deeper and more extensive preferential dye transport under the higher velocity FLOOD application rate do not necessarily indicate more extensive preferential water (or non-adsorbing solute) transport at this rate compared to the intermittent SPRINKLER rate. It is possible that our observations may be indicative of patterns in movement of adsorbed solutes such as pesticides, however this contention would require further research.

Water and solute movement in soil as influenced by macropore characteristics

In most contaminant transport modeling studies, only the macropores that are visible at the soil surface are considered. Furthermore, it is assumed that these macropores are straight and continuous throughout the soil profile. Little is known on the importance of other types of macropore continuity and tortuosity on preferential movement of contaminants through soils. This paper describes the results of a laboratory study dealing with macropore continuity effects on breakthrough curves (BTCs) and solute distribution in a Forman loam (fine-loamy mixed Udic Haploborolls) soil. BTCs were obtained under a constant hydraulic head of 0.08 m from a 2-D column (slab) containing artificial macropores. The input solution contained 1190 mg l−1 KBr, 10 mg l−1 Rhodamine WT, and 100 mg l−1 FD&C Blue #1. The continuity types studied were: macropore open at the soil surface–open at the bottom of the column (O–O), open–closed (O–C), closed–open (C–O), and closed–closed (C–C). A treatment without macropore served as a control. As expected, the solution in the O–O treatment reached the bottom of the macropore about 100 times faster by bypassing most of the soil matrices. As a result, the breakthrough time for O–O treatments was much faster than any other continuity treatments. Both the O–O and O–C type macropores favored earlier breakthrough, smaller apparent retardation coefficient (R′), deeper center of mass, and higher anisotropy in tracer concentrations in the horizontal direction than the C–O, C–C, and the Control treatment. The C–C macropore was favored in deeper penetration of tracer only when another macropore was present nearby. The importance of macropore continuity increased with an increase in the adsorption coefficient of the tracers.

Effects of Polymer-coated Urea on Nitrate Leaching and Nitrogen Uptake by Potato

Increasing groundwater nitrate concentrations in potato (Solanum tuberosum L.) production regions have prompted the need to identify alternative nitrogen management practices. A new type of polymer-coated urea (PCU) called Environmentally Smart Nitrogen (Agrium, Inc., Calgary, AB) is significantly lower in cost than comparable PCUs, but its potential to reduce nitrate leaching and improve fertilizer recovery has not been extensively studied in potato. In 2006 and 2007, four rates of PCU applied at emergence were compared with equivalent rates of soluble N split-applied at emergence and post-hilling. Additional treatments included a 0 N control, two PCU timing treatments (applied at preplant or planting), and a soluble N fertigation simulation. Nitrate leaching, fertilizer N recovery, N use efficiency (NUE), and residual soil inorganic N were measured. Both 2006 and 2007 were low leaching years. Nitrate leaching with PCU (21.3 kg NO(3)-N ha(-1) averaged over N rates) was significantly lower than with split-applied soluble N (26.9 kg NO(3)-N ha(-1)). The soluble N fertigation treatment resulted in similar leaching as PCU at equivalent N rates. Apparent fertilizer N recovery with PCU (65% averaged over four rates) tended to be higher than split-applied soluble N (55%) at equivalent rates (p = 0.059). Residual soil N and NUE were not significantly affected by N source. Under the conditions of this study, PCU significantly reduced leaching and tended to improved N recovery over soluble N applied in two applications and resulted in similar N recovery and nitrate leaching as soluble N applied in six applications.

Role of macropore continuity and tortuosity on solute transport in soils: 2. Interactions with model assumptions for macropore description

The impact of macropore description on solute transport predictions in soils is not well understood. A 2-D Galerkin finite element model was used to compare different approaches for describing macropore flow in soil. The approaches were: a modification of the hydraulic conductivity function (Hydraulic function), the lumping of all macropores into one single straight macropore (Lumping), the use of an exchange factor between microporosities and macroporosities that occupy the same area (Dual porosity), and a detailed description of each macropore (Full description, base case). Simulated breakthrough curves were obtained with domains that contained one or more macropores of different shapes under both steady state and transient flow conditions. The Hydraulic function approach was not sensitive to macropore continuity and tortuosity. When the macropores were open at the soil surface and the solute was surface applied, the first three approaches underestimated both breakthrough curves and solute distribution in the profile compared to the Full description approach. When the solute was initially incorporated in the soil, the first three approaches overestimated the breakthrough curves compared to the Full description approach. The first three approaches also underestimated the heterogeneity of solute distribution in the profile compared to the Full description approach, mostly when the macropores were tortuous. The differences between predicted breakthrough curves with different approaches decreased with an increase in tortuosity and a decrease in surface continuity. To simplify macropore description, the Dual porosity approach was the better of the first three approaches for predicting breakthrough curves provided the exchange factor between macropores and matrix porosity was available.

An integrative analysis of the role of atmospheric deposition and land management practices on nitrogen in the US agricultural sector.

Additions of anthropogenic nitrogen (N) compounds constitute one of the major classes of air pollutants of significance to human health and the environment. Reliance on wet deposition measurements alone can lead to considerable underestimates (by 40-60%) of the total (wet + dry) atmospheric N deposition. In addition, wet deposition of N are about 20% of the levels that are lost due to volatilization (primarily ammonia). Nevertheless, in the agricultural sectors of the Mississippi River basins, farm management practices, and recycling of N within cropping systems clearly outweigh the contributions of atmospheric deposition. As opposed to native vegetation and forests, there are no records of the negative effects of atmospheric N deposition on crop yield. Similarly, field studies on the interactions of atmospheric N compounds with the incidence and spread of pathogens does not permit any generalizations. Nitrogen applied as fertilizer affects disease probably more by its effect on the plant growth than by its effects on pathogens. In contrast, atmospheric nitrogen dioxide appears to be a stimulant of aphid performance. Under conditions of heavy weed infestation, N fertilization stimulates weed growth and competitiveness, rather than crop yield.

Performance of a variable tillage system based on interactions with landscape and soil

Understanding tillage system interaction with landscape variability is important in prescribing appropriate tillage systems that are profitable and environmentally sound. A three-year (1997–1999) study was conducted on a gently sloping, poorly drained lacustrine landscape to evaluate tillage, landscape, and soil interactions on grain yield. Tillage systems investigated were a reduced tillage (RT) system [no-tillage after soybean (Glycine max (L.) Merr), fall chisel plowing after corn (Zea mays (L.) var. mays)], and a conventional tillage (CT) system (fall chisel plowing after soybean and fall moldboard plowing after corn). Fall primary tillage was followed with a pre-plant field cultivation in the spring. Runoff and pollutant losses from the two tillage systems were also measured under a 63 mm h−1 simulated rainfall. Runoff and pollutant (total solids, chemical oxygen demand, total P, dissolved molybdate reactive P) losses were similar, or lower (6.6, 8.0, 7.7, 5.5, and 4.1 times, respectively) in the RT than the CT system. Tillage system, landscape elevation, and soil type interactions on crop yield varied depending upon whether it was a wet or dry growing season. Using the interactions, soybean yield differences among the modeled fixed-RT, fixed-CT, and variable tillage (VT) systems in a wet year were less than 0.1 Mg ha−1. During a dry year, corn yield was higher in the RT and the VT systems than in the CT system. When no new purchase of tillage equipment(s) is necessary to implement the RT, VT, or CT system, the modest yield benefits during relatively dry years, plus the improved runoff water quality by using reduced tillage system in all or part of the landscape, would justify the use of RT and VT systems over the CT system in the lacustrine landscape.

Predicting soil temperatures under a ridge-furrow system in the U.S. Corn Belt☆

Abstract A model is presented for predicting hourly soil temperatures under bare and residue plus plantcovered east-west oriented ridges in the Northern U.S. Corn Belt. The model is based on the implicit finite difference solution of a one-dimensional heat-flow equation. Two-dimensional soil temperature distribution under a ridge-furrow system is simulated by solving the one-dimensional heat-flow equation in vertical and horizontal directions, alternatively. Inputs needed for simulation are thermal diffusivity, and initial and boundary conditions. A procedure is suggested for estimating hourly upper boundary temperatures from daily maximum and minimum air temperatures. A constant temperature at the bottom boundary was justified by simulating soil temperatures in a deep profile. In general, the predicted soil temperatures under the bare ridge-furrow surface were within 2°C of the measured values; however, at some depths differences were as great as 4°C. Considering that soil temperatures are generally inputs to models (crop emergence and plant growth, nitrogen transformations and chemical degradation) that use at the minimum a daily time step, errors of 2–4°C in daily soil temperatures, in many cases, will lead to relatively minor errors in the final prediction of higher order processes.

Long-term conservation tillage and liquid dairy manure effects on corn. II. Nitrate concentration in soil water

Deterioration of ground and surface water quality has often been associated with failure to properly account for nitrogen (N) from manure and legumes in crop production. The objective of this study was to evaluate the effects of tillage, N source, and frequency of liquid manure application on NO3-N concentration of soil water under the root zone of corn (Zea mays L.). The experiment was conducted on a silt loam soil in southeast Minnesota, USA. Tillage and N treatments were initiated in 1982 and remained constant during the study. Tillage systems were chisel plowing plus secondary tillage with a field cultivator (CP) and no-tillage (NT). Nitrogen treatments were unfertilized control, inorganic fertilizer applied annually at 235 kg ha−1 for NT and 191 kg ha−1 for CP, and manure application of 284±20 kg ha−1 N (total N) annually and biennially (application every other year). Soil water for NO3-N analysis was sampled weekly from 1.5-m depth using suction samplers during the 1989 and 1990 growing seasons. For these two years, mean soil water NO3-N concentrations were 66 mg l−1 for annual inorganic fertilizer, 50 mg l−1 for annual manure and 11 mg l−1 for biennial manure treatments. Differences in NO3-N concentrations between annual manure and annual inorganic fertilizer treatments, and between annual manure and biennial manure treatments were statistically significant (P=0.05). Mean NO3-N concentrations averaged over annual inorganic fertilizer and annual manure treatments were 69 mg l−1 for CP and 50 mg l−1 for NT. With small supplemental fertilizer N, biennial manure application offers an alternative to annual application to minimize N leaching.