John M. Laflen

Nitrate Movement Through the Soil Profile in Relation to Tillage System and Fertilizer Application Method

ABSTRACT AN experiment was performed to determine the movement of NOa-N through no-till and moldboard-plowed field plots. On the plowed plots, NOa-N (about 150 kg/ha) was surface broadcasted either before or after tillage; on the no-till plots, only surface application of NO3-N without tillage was used. Two rains of 12.7 and 6.35 cm (2.3 cm/h) were applied about one day apart with a rainfall simulator to the 5x5 m plots. Soil sampling down to 150 cm was performed before and after rainfall for soil water content and N03-N analyses. Results showed that plots under no-till maintained significantly higher N03-N amounts in the 0- to 30-cm layer, with 40% of the N03-N initially present still there after 12.7 cm of rain and 33% remaining after the additional 6.35 cm of rain. The corresponding numbers for the moldboard-plow plots were 19 and 9%. The amount of N03-N leached from the 150-cm profile with 12.7 cm of rain was also less (29 kg/ha) for the no-till compared with moldboard-plowed plots (122 kg/ha).

Soil and Water Loss from Conservation Tillage Systems

ABSTRACT A rainfall simulator was used to evaluate the effects of six different tillage practices on soil and water losses from continuous corn for three soils in Iowa. Soil loss decreased as tillage decreased. Percent of soil covered by corn residue explained between 78 and 89 percent of the variance in erosion among tillage systems. The effect of non-uniformly distributed corn residue on controlling erosion was greater than expected based on a published mulch factor. Runoff amounts decreased as residue cover increased for two of the three soils studied. No critical slope length limits were found for the tillage practices, soils, slopes, and slope lengths studied except for till-planting on the Ida soil. As sediment concentra-tions increased, mean sediment size increased for one soil, decreased for a second soil, and was unrelated to sediment concentration for the third soil.

Tillage System Effects on Sediment and Nutrients in Runoff from Small Watersheds

ABSTRACT TWO conservation tillage systems were studied and compared with the conventional (plow-disk-plant) tillage system. Runoff, soil loss, and nutrient losses dur-ing the 1973-75 growing seasons were measured for six small, paired watersheds planted to continuous corn (runoff and soil loss for the year, 1972, when conservation tillage systems were being established were also measured). Fifty-nine percent of the soil surface under ridge-planting and 11 percent under till-planting were covered with crop residue, compared to less than 2 per-cent for conventional planting. Conservation tillage systems on the average reduced runoff about 40 percent and reduced soil loss from 60 to 90 percent. Total losses of nitrogen and phosphorus (total P in sediment measured only in 1973) were mostly associated with soil loss and consequently were decreased for conservation tillage systems. Solution phosphorus losses and concen-trations and available P concentrations in sediment (measured in 1974 and 1975) increased with residue cover. Several factors could be responsible, including decreased fertilizer incorporation, selective erosion pro-cesses, and the residue being a phosphorus source. Corn yield data are given.

Environmental Effects of Applying Composted Organics to New Highway Embankments: Part 1. Interrill Runoff and Erosion

Construction of new highways can lead to challenges when attempting to re-establish vegetation on right-of-ways. Lack of vegetation can leave soil exposed and subject to increased runoff and soil erosion. Therefore, the Iowa Department of Transportation and the Iowa Department of Natural Resources sponsored a study to evaluate the use of composts applied as mulch blankets to decrease runoff and erosion. This article evaluates interrill runoff and erosion between three types of compost (biosolids, yard waste, and bio-industrial byproducts) and two soil conditions (existing compacted subsoil (control) and imported topsoil) on a 3:1 highway embankment. Composts were applied as 5 and 10 cm blankets on the surface of the control, and topsoil was placed on the surface of the control at a depth of 15 cm. Treatments were replicated six times over a two-year period for both bare soil and six weeks following planting of an Iowa DOT-specified cover crop. Rainfall was applied at an average intensity of 95 mm h-1 using a rainfall simulator, and sampling was conducted for 1 h after runoff began. All compost treatments were effective at reducing interrill erosion rates under the conditions simulated in this study. In addition, the three compost media required 30 min or longer to produce runoff, while the two conventional soils produced runoff within the first 8 min. The depth of compost application was only a factor for the runoff rate on unvegetated treatments. In this case, the 5 cm depth had a significantly greater runoff rate than the 10 cm depth. Both 5 and 10 cm compost applications had similar effects on interrill erosion rates. Although the steady-state interrill erosion rates of all three composts were 3% to 24% of the steady-state interrill erosion rates of the two soils on unvegetated treatments, and 0.1% to 30% of the steady-state interrill erosion rates of the two soils on vegetated treatments, the type of compost was also a factor in interrill erosion control. The yard waste compost was the coarsest of the three compost materials, and on unvegetated plots had a steady-state interrill erosion rate that was 17% and 33% of the steady-state interrill erosion rates of biosolids and bio-industrial compost, respectively. Interrill erodibility factors were calculated for all treatments and fell within the range of experimental rangeland values (10,000 to 2,000,000 kg sec/m4) that are used in the Water Erosion Prediction Project.

Environmental Effects of Applying Composted Organics to New Highway Embankments: Part 2. Water Quality

An oversupply of composted organics, and imposition of new federal regulations governing stormwater discharges from construction sites, motivated the Iowa Department of Natural Resources (IDNR), and the Iowa Department of Transportation (Iowa DOT) to sponsor a study of the potential water quality impacts of using compost to control runoff and erosion on highway construction sites. Test areas treated with 5 and 10 cm deep blankets (unincorporated) of three types of compost (biosolids, yard waste, and bio-industrial byproducts) were constructed on a new highway embankment with a 3:1 sideslope and subjected to simulated rainfall intensity of approximately 100 mm h-1. Concentrations and total masses of N, P, K, and nine metals in runoff from compost-treated areas were compared to those in runoff from embankment areas receiving two conventional runoff and erosion control methods typically used by the Iowa DOT (light tillage and seeding of native embankment soil, or application of 15 cm of imported topsoil followed by seeding). Simulations were replicated six times under both vegetated and unvegetated conditions, and the first hour of runoff was sampled to determine concentrations and total masses of soluble and adsorbed nutrient and metals. The applied composts generally contained much greater pollutant concentrations than either of the two soils used in the conventional treatments, and runoff from unvegetated plots treated with compost also contained significantly greater concentrations of soluble and adsorbed Zn, P, and K, and adsorbed Cr and Cu, than runoff from the two conventional treatments. In accordance with previously reported soil erosion research, runoff from all test plots was sampled periodically during the first hour of runoff. Due to their significantly greater infiltration capacity, however, compost-treated areas required significantly greater amounts of rainfall than conventionally treated areas to produce 1 h of runoff. In light of this significant difference in the amount of rain applied, the total mass of pollutants contained in runoff generated by equal amounts of rainfall was judged a more equitable basis for comparing the treatments. Runoff samples collected during the first 30 min of rainfall (equivalent to a 25-year return period storm at the applied intensity of 100 mm h-1) were used for this purpose, and the resulting total masses of individual quantifiable soluble and adsorbed contaminants in runoff from conventionally treated areas were at least 5 and 33 times, respectively, those in runoff from compost-treated areas. Based on these results, blanket applications of compost can be used to reduce runoff and erosion from construction sites without increasing nutrients and metals in stormwater runoff.

Effects of corn residue and herbicide placement on herbicide runoff losses

ABSTRACT RAINFALL simulation was used to determine the ef-fects of corn residue on the soil surface, and her-bicide placement relative to it, on herbicide runoff losses. The herbicides propachlor, atrazine, and alachlor were applied above or below residue to plots with 0, 375, 750, and 1500 kg/ha corn residue. A 2-h rain of 127 mm was simulated. For plots with no residue, average time to runoff was 11 min, runoff was 63 mm, soil loss 11 t/ha, and herbicide losses 7 percent of the amounts applied. Increased residue amounts increased time to runoff and decreased runoff, erosion, and herbicide losses such that time to runoff for the greatest residue amount was 30 min, and runoff, soil loss, and herbicide losses were 18 mm, 1 t/ha, and 1 percent, respectively. At least 84 per-cent of the herbicide losses were in the dissolved phase. Herbicide placement had little or no effect on concentra-tions of herbicides in runoff water and sediment. Her-bicide concentrations in water and sediment were negatively correlated with time to runoff.

Evaluation of Revegetation from Blanket Applied Composts on a Highway Construction Site

Compost has been evaluated as a stormwater best management practice for erosion control, but site revegetation is the ultimate goal of most stormwater plans. In this study, three different composts applied as a surface layer or mulch at two depths of 5 and 10 cm were compared with topsoil and subsoil as a medium for crop growth and weed suppression during revegetation of a highway right-of-way. Compost was shown to be as effective as topsoil and subsoil controls for crop growth, while significantly reducing growth of weed species. There were no significant differences between 5- and 10-cm depths of composts, indicating that the shallower depth would be adequate for establishing a cover crop and achieving weed suppression. Compost mulches offer promising opportunities for crop and weed management during revegetation of roadsides and other disturbed landscapes.

ENVIRONMENTAL EFFECTS OF APPLYING COMPOSTED ORGANICS TO NEW HIGHWAY EMBANKMENTS: PART III. RILL EROSION

Control of stormwater runoff and soil erosion on highway construction sites is a concern for state departments of transportation and municipalities. Composted organics are viewed as an alternative approach to improve construction site soils and to reduce runoff and soil erosion. The objective of this study is to evaluate the use of blanket-applied composted organics on rill erosion as compared to soils. Rill erosion was measured on three composted organics applied at 5 and 10 cm depths, a topsoil treatment (15 cm application), and the existing soil (control) on a highway embankment with a three-to-one sideslope (33%). Treatments were tested using rainfall simulation at a target rate of 100 mm/h and simultaneously adding five inflows at the top of the rill on both vegetated and unvegetated plots. Rill erosion on blanket-applied compost treatments was measured, and the usefulness of the shear stress model for predicting rill erosion on compost-treated areas was assessed. Rill erodibilities and critical shear values were calculated for all treatments using the shear stress model that was originally developed for soil. Rill erodibilities were higher on topsoil-treated plots than on control and compost-treated areas. Yard waste had significantly lower rill erodibility than all other compost and soil treatments. There were no significant differences between critical shear values for the composts and soil. Yard waste compost exhibited greater resistance to rill formation than the biosolids and bio-industrial composts or the two soils. Low R2 values for compost erodibility and critical shear suggest that the shear stress model used in this analysis is not well suited for use with composted organics. Detachment caused by flotation of low-density particles, and bridging caused by coarse particles lodging farther down the slope, are believed to be two rill erosion mechanisms in compost that the shear stress model does not adequately address.

Estimating the Impact of Biomass Harvest on Soil Erosion Using the WEPP Model

Biomass in the form of crop residue has the potential to be a new energy source and an alternative to fossil fuels because of its high energy content and availability. In order for crop residue to be a competitive energy source, the sustainability of such a program must be evaluated. The effect of removing crop residue from traditional row crop fields after the harvest of the grain raises concerns over the effects it will have on soil erosion and soil fertility. The Water Erosion Prediction Project (WEPP) model was used in this project to estimate the effect that harvesting crop residue could have on soil erosion. The erosion at different crop residue removal rates was compared on different soils and on different slopes. The simulation showed that soil type had a smaller effect on erosion than did slope or biomass removal rate.