Surface Residue Cover Research Articles

Vertical tillage effects on crop production and pest management in Pennsylvania

AbstractWithin the last four decades, widespread transition to no‐till corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] production in Pennsylvania has improved soil conservation and soil quality but can result in residue and pest management challenges. To effectively manage residue in no‐till cropping systems, some growers have adopted vertical tillage, a residue management practice characterized by cutting and incorporating crop residue within the top 5–10 cm of soil. Despite few studies documenting effects on crop production and soil conservation, vertical tillage has become widespread. Replicated on‐farm trials were conducted over a 2‐year period in 2021–2022 to improve grower and consultant decision‐making regarding the role of vertical tillage relative to continuous no‐till on southeast Pennsylvania farms located within the environmentally sensitive Chesapeake Bay Watershed. We assessed the effects of vertical tillage on corn residue cover, winter annual weed abundance, slug damage, and soybean performance in 40 paired strip trials comparing spring vertical tillage to no‐till using three different vertical tillage tools used by farmer cooperators. Vertical tillage equipment type is a driver of variation in changes to surface residue cover. Baseline surface residue cover was similar among no‐till strips, but a greater proportion (32%) of strips had mean surface residue cover levels below a 60% conservation program compliance threshold when a Kuhn‐Krause Excelerator was used. Relative to no‐till, vertical tillage resulted in a 50% reduction in winter annual weed cover, a 24% reduction in slug damage, and no significant differences in soybean stand establishment or grain yield.

Standardization of spray technique for pre-emergence herbicides in ZT-wheat (Triticum aestivum) with surface residue cover

The present study was carried out at Regional Research Station, CCS Haryana Agricultural University, Karnal, Haryana during winter (rabi) seasons of 2019–20 and 2020–21. In this experiment, ZT-wheat (Triticum aestivum L.) was sown with happy seeder under surface residue load of 6 t/ha (chopped). Fourteen weed control treatments including pre-emergence herbicide (pendimethalin 1500 g/ha), sequential application of pre-emergence fb post-emergence (POE) herbicide (pendimethalin 1500 g/ha fb pinoxaden 50 g/ha), weedy check and weed-free were applied in a randomised block design (RBD) with 3 replications. Pre-emergence (PRE) herbicides were applied on the top of rice (Oryza sativa L.) residues using two water volumes (500 and 1000 litre/ha) with 3 types of nozzles (flat-fan, flood-jet and air-injection). Among weed species, Rumex dentatus (L.) and Phalaris minor (Retz.) showed significantly higher suppression under residue mulch and Medicago polymorpha (L). showed least suppression. Pendimethalin 1500 g/ha fb pinoxaden 50 g/ha (1000 l/ha) (Flood-jet) was statistically similar to weed-free in terms of grain yield, net returns and B:C ratio during both the years.

Biosolids and conservation tillage for rainfed wheat farming in dry Mediterranean climates

Biosolids are used in dryland wheat (Triticum aestivum L.) production in eastern Washington and other regions of the world as a source of nutrients and to increase soil organic carbon (SOC). Moreover, conservation tillage is promoted to reduce erosion and soil degradation. We explored the impacts of biosolids vs synthetic fertilizer in combination with undercutter (UC) conservation tillage vs tandem disk (TD) traditional tillage in an 8-yr field experiment in drought-prone region near Lind, WA (244 mm avg. annual precipitation). There were two sets of plots to allow for data collection each year in a 2-yr winter wheat (WW)-fallow rotation. Biosolids were applied at 6.5 mt/ha dry weight to meet the nutrient needs of two WW crops. Synthetic fertilizer plots received 56 kg N plus 11 kg S/ha for every wheat crop. Biosolids increased WW grain yield vs synthetic fertilizer by 25% one year but with no differences in other years or the 8-yr avg. Tillage method had no effect on WW grain yield nor grain yield components. Wheat kernel weight was lower and grain protein higher than desirable in biosolids plots, indicating excessive N because the application rate was too high for such a dry environment. Consistent year-long surface residue cover > 30% was achieved with UC tillage for government farm program conservation compliance, but this was not attained with TD tillage. In addition to highly desirable levels of P, biosolids provided significant quantities of the important soil micronutrients Zn, Mn, Cu, Fe. Biosolids application did not increase SOC in the surface 30 cm. This study demonstrated the application of biosolids combined with low-disturbance UC conservation tillage is an agronomically- and environmentally sound practice for dryland wheat production. We believe this is the driest rainfed environment in which biosolids for crop production have yet been evaluated.

Early corn stand count of different cropping systems using UAV-imagery and deep learning

Optimum plant stand density and uniformity is vital in order to maximize corn (Zea mays L.) yield potential. Assessment of stand density can occur shortly after seedlings begin to emerge, allowing for timely replant decisions. The conventional methods for evaluating an early plant stand rely on manual measurement and visual observation, which are time consuming, subjective because of the small sampling areas used, and unable to capture field-scale spatial variability. This study aimed to evaluate the feasibility of an unmanned aerial vehicle (UAV)-based imaging system for estimating early corn stand count in three cropping systems (CS) with different tillage and crop rotation practices. A UAV equipped with an on-board RGB camera was used to collect imagery of corn seedlings (~14 days after planting) of CS, i.e., minimum-till corn-soybean rotation (MTCS), no-till corn-soybean rotation (NTCS), and no-till corn-corn rotation with cover crop implementation (NTCC). An image processing workflow based on a deep learning (DL) model, U-Net, was developed for plant segmentation and stand count estimation. Results showed that the DL model performed best in segmenting seedlings in MTCS, followed by NTCS and NTCC. Similarly, accuracy for stand count estimation was highest in MTCS (R2 = 0.95), followed by NTCS (0.94) and NTCC (0.92). Differences by CS were related to amount and distribution of soil surface residue cover, with increasing residue generally reducing the performance of the proposed method in stand count estimation. Thus, the feasibility of using UAV imagery and DL modeling for estimating early corn stand count is qualified influenced by soil and crop management practices.

Mapping Tillage Practices Using Spatial Information Techniques.

Monitoring tillage practices is important for explaining soil quality and yield trends, and their impact on environmental quality. However, a common problem in sustainable residue management is scarcity of accurate residue maps. Because predictive insights on soil quality dynamics across a spatial domain are vital, this entry explicates on a new remote sensing-based technique for assessing surface residue cover. Here, an empirical model for mapping surface residue cover was created by integrating line-transect % residue cover field measurements with information gleaned from ground spectroradiometers and Advanced Wide-Field Sensor (AWiFS) satellite imagery. This map was validated using non-photosynthetic vegetation (NPV) fractional component extracted by spectral mixture analysis (SMA). SMA extracts fractional components of sensed signals in imagery, which within agricultural fields are NPV, green vegetation, bare soil, and shade. A stepwise linear regression between residue estimates by line transect and map generated using satellite imagery had R2 = 87%. Upon map categorization according to surface residue for a single AWiFS imagery encompassing an area of 836,868 ha, but focused on corn (Zea mays) fields within South Dakota, revealed that <4% of these corn fields had >15% surface residue cover left in the field by November 2009. Findings such as these may guide policy on soil quality, which is directly correlated with residue management. In the future, the spatial distribution of surface residues remaining after harvest in field planted with other crops and other seasons will be mapped. Besides, the efficacy of integrating hyperspectral sensor data to enhance accuracy will be investigated.

Simulating the effects of conventional versus conservation tillage on soil water, nitrogen dynamics, and yield of winter wheat with RZWQM2

The movement and distribution of the soil water and nitrogen are significantly influenced by tillage management. However, the dynamics of soil water and nitrogen due to changes in tillage and surface residue cover can be difficult to characterize due to limitations in field experimentation. The objective of this study was to quantify the differences in the soil water and nitrogen balance in the 0–100 cm soil profile, winter wheat (Triticum aestivum L.) yield, water productivity (WP) and nitrogen use efficiency (NUE) that occur when conventional tillage (CT) was changed to four types of conservation tillage treatments (no-tillage [NT], subsoiling tillage [ST], no-tillage with straw [NS] and subsoiling tillage with straw [SS]). Experimental data from 2011 to 2016 collected in Henan province, China on a sandy loam soil was used to calibrate and validate the Root Zone Water Quality Model (RZWQM2). Then the model was used to simulate four tillage systems (NT, NS, ST, SS) that were then compared with CT. The agreement index (d) between simulated and measured soil water content, soil nitrate concentration, and grain yield ranged between 0.71 and 0.93. The root means square error (RMSE) of the soil water content and nitrate concentration was in the range 0.02–0.03 cm cm−1and 5.5–10.3 mg kg−1, respectively. When CT was converted to NT from 2011 to 2016, the model simulated a 9.1 % reduction in annual water loss and a 55.6 % decrease in nitrogen leaching loss and simulated significant increase in average grain yield, WP and NUE. Replacing CT with NT appears to be the best of the four alternative conservation tillage conversion strategies in Henan Province of China.

Influence of tillage depth of a cultivator on the incorporation of crop residues of winter barley in a chernozem soil

Summary Although crop residues contribute to erosion control, the influence of the tillage depth (TD) on their incorporation has not been studied extensively. The main objective of this study was to determine the differences in the amount and distribution of incorporated crop residues and surface residue coverage if the TD of a cultivator is varied (0.10, 0.20, or 0.30 m). The experiment was carried out on a chernozem soil with winter barley residues in 2016 in Groß-Enzersdorf (Lower Austria). Individual soil cores, each 0.05 m long, were removed using a special device. No significant differences were observed for the incorporated crop residues up to a depth of 0.35 m between the three TDs. The mean values of the incorporated crop residues at a TD of 0.10, 0.20, or 0.30 m were 11.64, 13.30, and 10.82 t/ha, respectively. The distribution of crop residues in the individual depth segments (DSs) showed a main concentration of more than 90% at a depth of 0.10 m and a significant decrease in deeper layers. This stratification was independent of the TD. Therefore, a shallower TD is sufficient for straw management on a chernozem soil in the production area of Marchfeld, which also enables a reduction in draft and, consequently, fuel consumption and processing costs.

Effects of conservation tillage drills on soil quality indicators in a wheat–oilseed rape rotation: organic carbon, earthworms and water‐stable aggregates

AbstractThe effects of five conservation tillage drills with crop residue levels covering between 17% and 79% of the soil, and tillage depths ranging from 25 to 200 mm, were examined over 3 years. The tillage systems ranged from a relatively disruptive Farm System to a Low Disruption system, with three intermediate treatments labelled Sumo DTS, Claydon and Mzuri. The study involved field sites on a clay or clay loam soil, where winter wheat and oilseed rape were grown in rotation. In the clay field, the Mzuri and Low Disruption treatments, which produced the highest residue coverage, showed the greatest increase in surface total soil organic carbon (1.1 and 0.48 Mg C ha−1, respectively) between years 1 and 3. The least disruptive tillage system also resulted in the highest density of earthworms (181–228 m−2), and the most disruptive system produced the lowest densities (75–98 m−2). In the third year, the least disruptive system also showed a higher proportion of water‐stable aggregates (29.8%) than the other treatments (22.7%–25.3%). Linear regressions showed positive relationships of both soil organic carbon and earthworm density with surface residue cover, and of the proportion of water‐stable aggregates with soil organic carbon.

Conservation Tillage Impacts and Adaptations in Irrigated Corn Production in a Humid Climate

Core Ideas No‐till land management (NT) decreases corn production in a humid climate. The reasons for reduced yield were investigated by integrating system models with experiments. Soil N deficiencies under NT possibly contributed to the yield decrease. Split application or enhancing N rate can compensate for the yield decrease under NT. We initiated a long‐term experiment in 2008 on 1.25‐ha farm‐scale plots to assess the production impacts of no‐till with full residue retention (NT) system over a conventional tillage (CT) system under irrigated corn (Zea mays L.) production on a Dundee silt loam soil in a humid climate. Data collected in the experiment from 2009 to 2015 were mainly confined to grain yield at harvest. In 2016 and 2017, additional data were collected including soil surface crop residue mass and soil surface residue cover; corn leaf area index (LAI) and biomass; soil water, temperature, N, C, and bulk density (Db); and the corn phenology. In 7 out of 9 yr (2009–17), harvested grain yields under NT were significantly lower than those harvested under CT. To investigate the possible reasons for the yield decreases under NT, we integrated the experiment with the Root Zone Water Quality Model to synthesize information on the various components in the system. The N loss to runoff and deep percolation, denitrification caused by higher soil water content, and a low N mineralization rate caused by lower soil temperatures under NT potentially contributed to the observed grain yield decrease under this treatment. Simulations showed that an additional N application at 40 kg ha−1 at planting or a split application of 50 kg ha−1 at planting and the remaining 174 kg ha−1 in the second week of May could make the yield return under NT comparable to that under CT.

Strip Tillage Implements for Single and Twin Row Peanut

Core Ideas Grower interest in conservation tillage and cover crops remains high for peanut.Twin rows improved yields and peanut grade compared to single rows.Peanut performance did not vary across strip tillage implements.Twin rows with strip tillage and a cover crop is a productive option for peanut. Soil degradation and rising production costs have prompted grower interest in conservation tillage with cover crops for peanut (Arachis hypogaea L.). Our objective was to evaluate single and twin row peanut production across three different strip tillage implements (KMC, Orthman, Unverferth) with and without a rye (Secale cereale L.) cover crop in Headland, AL, and Tifton, GA, during 2012 to 2014. Surface residue cover following planting, plant populations, peanut yield, total sound mature kernels (TSMK), and soil penetration resistance (PR) for the cultivar Georgia 06G were compared across cover crop treatments, tillage implements, and row patterns. Surface residue exceeded 60% at both locations in the rye treatment. Plant populations were greater across the fallow treatment and the twin row pattern at both locations. Twin rows increased yield compared with single rows in Headland (360 kg ha−1) and Tifton (&gt;1000 kg ha−1) and also improved grade (TSMK) at both locations. Strip tillage implements had no effect on peanut plant parameters. At planting, soil PR was greater with a cover crop only at Headland; whereas implements reduced soil PR in 2012 (Orthman) and 2014 (Unverferth). At harvest, soil PR differences were only observed in 2013. The KMC and Unverferth implements maintained less resistance compared with Orthman at Headland, whereas cover crop reduced PR at Tifton. Peanut performance did not differ in response to one strip tillage implement over the other; however, results show strip tillage with a cover crop and twin row management improves peanut production across the Southeast.

Soil surface cover on irrigated rotations for potato ( Solanum tuberosum L.), dry bean ( Phaseolus vulgaris L.), sugar beet ( Beta vulgaris L.), and soft white spring wheat ( Triticum aestivum L.) in southern Alberta

Soil surface cover (crop residue and fall-seeded cover crops) during the nongrowing season is an important tenet of sustainable agriculture, reducing wind and water erosion risk and enhancing soil water conservation. Expansion of irrigated row crop production, namely, potato (Solanum tuberosum L.), dry bean (Phaseolus vulgaris L.), and sugar beet (Beta vulgaris L.), in southern Alberta in the late 1990s prompted a 12-year (2000 to 2011) study to evaluate rotations and soil management systems for improved soil quality. The study compared conservation (CONS) and conventional (CONV) management systems in three- to six-year rotations. Conservation management included cover crops; reduced tillage; feedlot manure compost addition; and solid-seeded, narrow-row dry bean production. Beginning in the third year of the study (2002), surface residue cover was estimated each spring prior to tillage or seeding. Averaged over 10 years (2002 to 2011), residue cover was significantly higher on CONS (15.6%) versus CONV (7.1%) management. Cover was significantly higher where wheat (Triticum aestivum L.) was the previous crop (33.7%) compared to narrow-row dry bean (9.7%), which was significantly higher than potato and sugar beet (6.5% to 6.7%), which were in turn significantly higher than wide-row bean (3.6%). Inclusion of a fall rye (Secale cereale L.) cover crop after potato or dry bean increased residue cover close to or more than 30%, the threshold required to reduce wind erosion risk. Long-term replacement of cereals with lower residue-producing crops (e.g., potato, dry bean, and sugar beet) on irrigated rotations in southern Alberta should be considered judiciously in light of potential negative effects on surface residue cover.

Can legumes provide greater benefits than millet as a spring cover crop in southern Queensland farming systems?

Cover crops grown during fallows can increase organic matter inputs, improve soil surface cover to reduce erosion risk, and enhance rainfall infiltration. An experiment compared a chemical fallow control with six different cover crops terminated at either 60 or 90 days after sowing. The commercial choice of millet (Echinochloa esculenta) was compared with two summer legumes (lablab (Lablab purpureus) and soybean (Glycine max)), and three winter legumes (field pea (Pisum sativum), faba bean (Vicia faba) and common vetch (Vicia sativa)). Cover crop biomass growth, atmospheric nitrogen (N) fixation, surface residue cover, and soil water and mineral N dynamics during the growth period and subsequent fallow were measured. Soil water and N availability and yield of wheat crops following the experimental treatments were simulated over a 100-year climate record using APSIM. Both experiments and simulations found the legumes inferior to millet as spring-sown cover crops, because they were slower to accumulate biomass, required later termination and provided groundcover that was less persistent, resulting in lower soil water at the end of the fallow. After 90 days of growth, the summer legumes, lablab and soybean, produced the most biomass and fixed more N (up to 25 kg N/ha) but also extracted the most soil water and mineral N. Legume N fixation was low because of high soil mineral N status (&gt;100 kg N/ha) and occurred only when this had been depleted. At the end of the subsequent fallow in April, soil water was 30–60 mm less and soil mineral N 80–100 kg/ha less after both millet and 90-day terminated summer legume cover crops than the chemical fallow control. Simulations predicted soil-water deficits following legume cover crops to be &gt;50 mm in the majority of years, but soil mineral N was predicted to be lower (median 80 kg N/ha) after millet cover crops. In conclusion, monoculture legume cover crops did not provide advantages over the current commercial standard of millet, owing to less effective provision of groundcover, low N fixation and possibly delayed release of N from residues. Further work could explore how legumes might be more effectively used as cover crops to provide N inputs and soil protection in subtropical farming systems.

Impact of irrigation, surface residue cover and plant population on sugarbeet growth and yield, irrigation water use efficiency and soil water dynamics

Currently, sugarbeet producers in western Nebraska are facing the challenge of reducing their irrigation water usage due to ground water pumping restrictions and the unpredictable amount of rainfall that is available from year to year. Therefore, there is an increasing interest in developing season long deficit irrigation strategies for sugarbeet, the main objective of this study. The other objectives were to determine the impact of surface residue and plant population on sugarbeet production. Three field trials were conducted in eight consecutive cropping seasons (2008–2015). The average root and sugar yield for the full irrigation treatment were equal to 71.11 and 11.08Mgha−1, respectively during the 6 years of the two irrigation studies (2008–2013) while applying 75% and 50% ETc on average caused 9% and 11% yield reduction, respectively (2008–2011). Plots under full irrigation treatment and rainfed showed highest and lowest water depletion, respectively. Overall based on six years of data (2008–2013), stressing moderate and severe late in growing season produced 1.03 and 1.87Mgha−1 more sugar while consuming about 13mm less water than imposing same level of stress early in season. The residue covered plots produced 0.29Mgha−1 more sugar yield than bare soil plots on average across treatments and years. Overall, higher population rates resulted in higher sugarbeet yield. Findings of this research will deliver insight for sugarbeet irrigation management.

Quantification and Mapping of Surface Residue Cover for Maize and Soybean Fields in South Central Nebraska

The area cultivated under conservation tillage practices such as no-till and minimal tillage has recently increased in Midwestern states, including Nebraska. This increase, consequently, resulted in changes in some of the impacts of cropping systems on soil, such as enhancing soil and water quality, improving soil structure and infiltration, increasing water use efficiency, and promoting carbon sequestration. However, there are no methods currently available to quantify the percent crop residue cover (CRC) and the area under conservation tillage for maize and soybean at large scales on a continuous basis. This research used Landsat-7 (ETM+) and Landsat-8 (OLI) satellite data to evaluate six tillage indices [normalized difference tillage index (NDTI), normalized difference index 7 (NDI7), normalized difference index 5 (NDI5), normalized difference senescent vegetative index (NDSVI), modified CRC (ModCRC), and simple tillage index (STI)] to map CRC in eight counties in south central Nebraska. A linear regression CRC model showed that NDTI performed well in differentiating the CRC for different tillage practices at large scales, with a coefficient of determination (R2) of 0.62, 0.68, 0.78, and 0.07 for 25 March, 18 April, 28 May, and 6 June 2013 Landsat images, respectively. A minimum NDTI method was then used to spatially map the CRC on a regional scale by considering the timing of planting and tillage implementation. The measured CRC data were divided into training (calibration) and testing (validation) datasets. A CRC model was developed using the training dataset between minimum NDTI and measured CRC with an R2 of 0.89 (RMSD = 10.63%). A 3 x 3 matrix showed an overall accuracy of 0.90 with a kappa coefficient of 0.89. About 26% of the maize area and 15% of the soybean area had more than 70% CRC in south central Nebraska. This research and the procedures presented illustrate that multi-spectral Landsat images can be used to estimate and map CRC (error within 10.6%) on a regional scale and continuous basis using locally developed tillage practice versus crop residue algorithms. Further research is needed to incorporate soil and residue moisture content into the CRC versus tillage index to enhance the accuracy of the models for estimating CRC.

Soil erosion and surface runoff under strip tillage for sugar beet (Beta vulgaris L.) in Central Europe

Soil erosion due to cultivation of row crops on soils with a high silt content can result in hazardous on-site and off-site damages. An effective and sustainable soil protection measure is to reduce the intensity of tillage. On-farm trials were conducted to compare the effect of strip tillage (ST), full-width reduced tillage (RT) and intensive tillage (IT) systems on surface runoff and soil loss in sugar beet crops grown on four typical loess sites in hilly regions of southern Germany in 2014 and 2015. Heavy rainfall (24mm 20min−1) was simulated in the 4–6 leaf stage of sugar beet with a small portable nozzle rainfall simulator. Observed data were used to establish soil loss ratios for ST as part of the cropping and management factor of RUSLE.Compared to IT, surface runoff was 55% and 92% lower for RT and ST, respectively, caused by increased water infiltration presumably due to (i) higher earthworm activity and (ii) the absence of negative effects of reduced tillage intensity on penetration resistance. Moreover, reducing tillage intensity increased surface residue cover, initial water content and organic carbon content in the topsoil layer.Soil loss was 85% and 98% lower for RT and ST compared to IT, respectively, as a result of (i) decreased runoff rates, (ii) higher stability of aggregates against the impact of raindrops and (iii) reduced velocity of the runoff flow and thereby lower sediment concentrations. Based on residue cover, the soil loss ratio calculated for ST agreed well with values established for other tillage systems.Overall, reducing tillage intensity by strip tillage was proven to offer environmental benefits due to reduced surface runoff and soil loss. In addition, plant-available water likely increases through enhanced infiltration.

Effect of sugarcane cropping systems on herbicide losses in surface runoff

Herbicide runoff from cropping fields has been identified as a threat to the Great Barrier Reef ecosystem. A field investigation was carried out to monitor the changes in runoff water quality resulting from four different sugarcane cropping systems that included different herbicides and contrasting tillage and trash management practices. These include (i) Conventional – Tillage (beds and inter-rows) with residual herbicides used; (ii) Improved – only the beds were tilled (zonal) with reduced residual herbicides used; (iii) Aspirational – minimum tillage (one pass of a single tine ripper before planting) with trash mulch, no residual herbicides and a legume intercrop after cane establishment; and (iv) New Farming System (NFS) – minimum tillage as in Aspirational practice with a grain legume rotation and a combination of residual and knockdown herbicides.Results suggest soil and trash management had a larger effect on the herbicide losses in runoff than the physico-chemical properties of herbicides. Improved practices with 30% lower atrazine application rates than used in conventional systems produced reduced runoff volumes by 40% and atrazine loss by 62%. There were a 2-fold variation in atrazine and >10-fold variation in metribuzin loads in runoff water between reduced tillage systems differing in soil disturbance and surface residue cover from the previous rotation crops, despite the same herbicide application rates. The elevated risk of offsite losses from herbicides was illustrated by the high concentrations of diuron (14μgL−1) recorded in runoff that occurred >2.5months after herbicide application in a 1st ratoon crop. A cropping system employing less persistent non-selective herbicides and an inter-row soybean mulch resulted in no residual herbicide contamination in runoff water, but recorded 12.3% lower yield compared to Conventional practice. These findings reveal a trade-off between achieving good water quality with minimal herbicide contamination and maintaining farm profitability with good weed control.

Surface Energy Balance, Evapotranspiration, and Surface Coefficients During Non-Growing Season in a Maize-Soybean Cropping System

<abstract> Surface energy balance components, including actual evapotranspiration (ET), were measured in a reduced-till maize-soybean field in south central Nebraska during three consecutive non-growing seasons (2006/2007, 2007/2008, and 2008/2009). The relative fractions of the energy balance components were compared across the non-growing seasons, and surface coefficients (K_c) were determined as a ratio of measured ET to estimated alfalfa (ET_r) and grass (ET_o) reference ET (ET_ref). The non-growing season following a maize crop had 25% to 35% more field surface covered with crop residue as compared to the non-growing seasons following soybean crops. Net radiation (R_n) was the dominant surface energy balance component, and its partitioning as latent heat (LE), sensible heat (H), and soil heat (G) fluxes depended on field surface and atmospheric conditions. No significant differences in magnitude, trend, and distribution of the surface energy balance components were observed between the seasons with maize or soybean surface residue cover. The cumulative ET was 196, 221, and 226 mm during the three consecutive non-growing seasons. Compared to ET_ref, the cumulative total measured ET was 61%, 63%, and 59% of cumulative total ET_o and 43%, 46%, and 41% of cumulative total ET_r during the three consecutive seasons. The type of residue on the field surface had no significant effect on the magnitude of ET. Thus, ET was primarily driven by atmospheric conditions rather than surface characteristics. The coefficient of determination (R²) for the daily ET vs. ET_r data during the three consecutive non-growing seasons was only 0.23, 0.42, and 0.42, and R² for ET vs. ET_o was 0.29, 0.46, and 0.45, respectively. Daily and monthly average K_c values varied substantially from day to day and from month to month, and exhibited interannual variability as well. Thus, no single K_c value can be used as a good representation of the surface coefficient for accurate prediction of ET for part or all of the non-growing season. A good relationship was observed between monthly total measured ET vs. monthly total ET_ref. The R² values for monthly total ET vs. monthly total ET_ref data ranged from 0.71 to 0.89 for both ET_r and ET_o. Using pooled data for monthly total ET vs. monthly total ET_ref, R² was 0.78 for ET_r and 0.80 for ET_o. The slopes (S) of the best-fit line with intercept for the monthly total ET vs. monthly total ET_ref data were consistent for all three non-growing seasons, with S = 0.45 ±0.05 for ET_r and S = 0.62 ±0.08 for ET_o. The parity in R² and S across the three non-growing seasons suggests that the same regression equation can be used to approximate non-growing season ET for field surfaces with both maize and soybean crop residue covers. Considering the extreme difficulties in measuring ET during winter in cold and windy climates with frozen and/or snow-covered conditions, the approach using a linear relationship between monthly total ET vs. monthly total ET_ref appears to be a good alternative to using a surface coefficient to approximate non-growing season monthly total ET. The conclusions of this research are based on the typical dormant season conditions observed at the research location and may not be generally transferable to other locations with different climatic and surface conditions.

New Insights on using Fallout Radionuclides to Estimate Soil Redistribution Rates

The fallout radionuclides such as ¹³⁷Cs have been widely accepted and used in the past 40 yr to provide quantitative soil redistribution estimates at a point scale. Recently their usefulness has been questioned by a few researchers challenging the validity of the key assumption that the spatial distribution of fallout radionuclides in soil is initially uniform. The objective of this work is to reconcile the opposing views by examining the assumption and by developing a new concept for correctly interpreting soil redistribution rates estimated with the tracing technique. This review shows that the spatial uniformity assumption is invalid due to ¹³⁷Cs redistribution caused by spatial variations in rainfall interception, vegetation type and cover, surface residue cover, water infiltration rates, and micro-topography. Thus, the commonly used method of comparing a point ¹³⁷Cs inventory with the reference mean inventory for estimating soil redistribution rate for that point is flawed. Soil redistribution rate estimated for a sampling point is not the true erosion rate because random spatial variation of the radionuclide inventory at the point is erroneously attributed to an effect of soil redistribution. Fortunately, such spatial variations at points are typically random in nature, and therefore can be resolved statistically by increasing independent sample number and by interpreting soil redistribution rate in terms of mean value for a uniform area or slope position, as the random spatial errors of the radionuclide inventories tend to be averaged out.

Soil quality evaluation under different land management practices

Sustainable agricultural production requires prudent management backed by reliable information that accurately elucidates the complex relationships between land management practices and soil quality trends. Therefore, this study investigates the influence of management on soil properties acquired at different depths, and yields, at five different field sites within Ohio, USA. The principal management systems considered were no till with or without manure and cover crops, natural vegetation (NV) or forest, and conventional tillage (CT) defined as farms with surface residue cover (<30 %). Analyses of variance (ANOVA), correlation analyses, stepwise regression, and the principal component analyses (PCA) were used to elucidate and model the link between four different management practices and the soil physical and chemical properties. The ANOVA results indicate that the available water capacity and electrical conductivity (EC) were the major variables affected by management. In contrast, soil pH, bulk density (ρ b), porosity, soil organic carbon (SOC), and total nitrogen (TN), were invariable with management, yet only pH and EC did not significantly vary with the interaction of soil type and management effects. In comparison, the PCA results suggest that SOC, TN, porosity, ρ b, and EC were the major determining factors controlling yield variability. Interestingly, the derived models revealed that the highest yields, notably 10 and 2.7 Mg ha−1 for corn (Zea mays L.) and soybean (Glycine max (L.) Merr.) occurred in soils under CT management. Quantifying the nexus between soil properties and management choices as demonstrated in this study, can provide critical insight for sustainable agricultural production.

Tidal Flat and Sand Beach Remediation: Choosing Remediation Techniques to Speed Ecological Recovery of Habitats Still Impacted 20 Years after the Gulf War Oil Spill

ABSTRACT After nearly 20 years of limited natural recovery following the Gulf War oil spill, surveys were conducted in 2009-2010 to identify where oil has persisted and ecological recovery has been slow along the Arabian Gulf coastline of Saudi Arabia. In 2011-2013, large-scale remediation projects were executed on 3 locations totaling 155 hectares of tidal flats and sand beaches to speed ecological recovery. Targeted remediation techniques were used as tools to meet the following goals: 1) increase suitable habitat for grazers and burrowing infauna; 2) reduce total petroleum hydrocarbon levels; and 3) improve physical processes (drainage) and reduce associated stressors such as ponding. Three principal techniques were developed and utilized along sheltered and moderately exposed tidal flats: 1) tilling of oiled sediments using tines (rake) or disc harrow attachment, followed by manual removal of remaining surface oil; 2) complete physical removal and disposal of the surface or cohesive subsurface oiling layers; and 3) tilling areas contained within berms while flooded to liberate liquid oil that was subsequently recovered by skimming/vacuuming. The first technique was considered appropriate when there was a well-defined gradient between hardened surface oiling and lightly oiled subsurface sediments, within sandy tidal flats, and where sediment conservation was a priority. This technique resulted in 20% additional oiled surface residue cover, which was removed manually. Resulting sediment loss was minimal. Goals 1, 2 and 3 were met. The second technique was preferred when there was a dry cohesive oiled layer either on the surface or beneath a layer of clean sand and where sediment conservation was not a priority. Excavation of oiled sediments resulted in high sediment loss by physical removal; however, goals 1 and 2 were clearly achieved. Additional re-grading including possible sediment replacement was required to achieve goal 3. The third technique was considered the optimal method when there was a high level of subsurface liquid oiling within tidal flats, and if sediment conservation was a priority. Goal 1 was achieved by breaking up surface barriers. To achieve goals 2 and 3, multiple tilling passes were required to liberate and remove liquid oil. Monitoring results show that while oil levels varied across remediated sites, a trend in reduction was common throughout. Short- and long-term ecological responses are being monitored.