L. B. Owens

Modeling soil carbon transported by water erosion processes.

Long-term monitoring is needed for direct assessment of soil organic carbon (SOC), soil, and nutrient loss by water erosion on a watershed scale. However, labor and capital requirements preclude implementation of such monitoring at many locations representing principal soils and ecoregions. These considerations warrant the development of diagnostic models to assess erosional SOC loss from more readily obtained data. The same factors affect transport of SOC and mineral soil fraction, suggesting that given the gain or loss of soil minerals, it may be possible to estimate the SOC flux from the data on erosion and deposition. One possible approach to parameterization is the use of the revised universal soil loss equation (RUSLE) to predict soil loss and this multiplied by the per cent of SOC in the near-surface soil and an enrichment factor to obtain SOC loss. The data obtained from two watersheds in Ohio indicate that a power law relationship between soil loss and SOC loss may be more appropriate. When measured SOC loss from individual events over a 12-year period was plotted against measured soil loss the data were logarithmically linear (R2=0·75) with a slope (or exponent in the power law) slightly less than would be expected for a RUSLE type model. The stable aggregate size distribution in runoff from a plot scale may be used to estimate the fate of size pools of SOC by comparing size distributions in the runoff plot scale and river watershed scales. Based upon this comparison, a minimum of 73 per cent of material from runoff plots is deposited on the landscape and the most stable carbon pool is lost from watershed soils to aquatic ecosystems and atmospheric carbon dioxide. Implicit in these models is the supposition that water stable soil aggregates and primary particles can be viewed as a tracer for SOC. Copyright

Role of lumbricus terrestris (L.) burrows on quality of infiltrating water

Abstract Long-term watershed studies at the North Appalachian Experimental Watershed, Coshocton, Ohio have shown that when corn ( Zea mays L.) is planted in soil covered by the residue of the previous crop (i.e. no-tillage management), surface runoff from summer storms is greatly reduced. In addition, the residue cover provides a favorable environment for various soil invertebrates, especially earthworms. During high-intensity rainstorms, some of the water that infiltrates in no-till corn fields moves rapidly downward in burrows made by the earthworms Lumbricus terrestris L. Samplers were developed for collecting infiltrating rain water flowing in L. terrestris burrows at a depth of 45cm below the soil surface. With annual surface applications of 175 kg N ha −1 as NH 4 NO 3 , concentrations of NO 3 -N in water flowing in individual burrows during growing season storms ranged up to 152 mg l −1 . Concentrations of NO 3 -N tended to be lowest after prolonged wet soil conditions and highest after intermittent warm, dry periods. Distilled water poured directly into the surface openings of L. terrestris burrows and immediately collected as it drained into samplers, contained up to 40 mg of NO 3 -N I −1 , a value greater than that measured in many of the samples resulting from natural rain storms. Water and herbicide mixtures poured through L. terrestris burrows showed that the linings of the burrow, or drilosphere, may contribute nitrogen to the infiltrating water while greatly reducing the concentrations of atrazine and alachlor.

Effect of cropland management and slope position on soil organic carbon pool at the North Appalachian Experimental Watersheds

Soil organic matter is strongly related to soil type, landscape morphology, and soil and crop management practices. Therefore, long-term (15–36-years) effects of six cropland management systems on soil organic carbon (SOC) pool in 0–30 cm depth were studied for the period of 1939–1999 at the North Appalachian Experimental Watersheds (<3 ha, Dystric Cambisol, Haplic Luvisol, and Haplic Alisol) near Coshocton, OH, USA. Six management treatments were: (1) no tillage continuous corn with NPK (NC); (2) no tillage continuous corn with NPK and manure (NTC-M); (3) no tillage corn–soybean rotation (NTR); (4) chisel tillage corn–soybean rotation (CTR); (5) moldboard tillage with corn–wheat–meadow–meadow rotation with improved practices (MTR-I); (6) moldboard tillage with corn–wheat–meadow–meadow rotation with prevalent practices (MTR-P). The SOC pool ranged from 24.5 Mg ha −1 in the 32-years moldboard tillage corn (Zea mays L.)–wheat (Triticum aestivum L.)–meadow–meadow rotation with straight row farming and annual application of fertilizer (N:P:K = 5:9:17) of 56–112 kg ha −1 and cattle (Bos taurus) manure of 9 Mg ha −1 as the prevalent system (MTR-P) to 65.5 Mg ha −1 in the 36-years no tillage continuous corn with contour row farming and annual application of 170–225 kg N ha −1 and appropriate amounts of P and K, and 6–11 Mg ha −1 of cattle manure as the improved system (NTC-M). The difference in SOC pool among management systems ranged from 2.4 to 41 Mg ha −1 and was greater than 25 Mg ha −1 between NTC-M and the other five management systems. The difference in the SOC pool of NTC-M and that of no tillage continuous corn (NTC) were 16–21 Mg ha −1 higher at the lower slope position than at the middle and upper slope positions. The effect of slope positions on SOC pools of the other management systems was significantly less ( < 5M g ha −1 ). The effects of manure application, tillage, crop rotation, fertilizer rate, and soil and water conservation farming on SOC pool were accumulative. The NTC-M treatment with application of NPK fertilizer, lime, and cattle manure is an effective cropland management system for SOC sequestration.

Rapid Changes in Soil Carbon and Structural Properties Due to Stover Removal from No-Till Corn Plots

Harvesting corn (Zea mays L.) stover for producing ethanol may be beneficial to palliate the dependence on fossil fuels and reduce CO2 emissions to the atmosphere, but stover harvesting may deplete soil organic carbon (SOC) and degrade soil structure. We investigated the impacts of variable rates of stover removal from no-till (NT) continuous corn systems on SOC and soil structural properties after 1 year of stover removal in three soils in Ohio: Rayne silt loam (fine-loamy, mixed, active, mesic Typic Hapludults) at Coshocton, Hoytville clay loam (fine, illitic, mesic Mollic Epiaqualfs) at Hoytville, and Celina silt loam (fine, mixed, active, mesic Aquic Hapludalfs) at South Charleston. This study also assessed relationships between SOC and soil structural properties as affected by stover management. Six stover treatments that consisted of removing 100, 75, 50, 25, and 0, and adding 100% of corn stover corresponding to 0 (T0), 1.25 (T1.25), 2.50 (T2.5), 3.75 (T3.75), 5.00 (T5), and 10.00 (T10) Mg ha−1 of stover, respectively, were studied for their total SOC concentration, bulk density (&rgr;b), aggregate stability, and tensile strength (TS) of aggregates. Effects of stover removal on soil properties were rapid and significant in the 0- to 5-cm depth, although the magnitude of changes differed among soils after only 1 year of stover removal. The SOC concentration declined with increase in removal rates in silt loams but not in clay loam soils. It decreased by 39% at Coshocton and 30% at Charleston within 1 year of complete stover removal. At the same sites, macroaggregates contained 10% to 45% more SOC than microaggregates. Stover removal reduced >4.75-mm macroaggregates and increased microaggregates (P < 0.01). Mean weight diameter (MWD) and TS of aggregates in soils without stover (T0) were 1.7 and 3.3 times lower than those in soils with normal stover treatments (T5) across sites. The SOC concentration was negatively correlated with &rgr;b and positively with MWD and LogTS. Stover removal at rates as low as 1.25 Mg ha−1 reduced SOC and degraded soil structure even within 1 year, but further monitoring is needed to establish threshold levels of stover removal in relation to changes in soil quality.

Impact of Glyphosate-Tolerant Soybean and Glufosinate-Tolerant Corn Production on Herbicide Losses in Surface Runoff

Residual herbicides used in the production of soybean [Glycine max (L.) Merr] and corn (Zea mays L.) are often detected in surface runoff at concentrations exceeding their maximum contaminant levels (MCL) or health advisory levels (HAL). With the advent of transgenic, glyphosate-tolerant soybean and glufosinate-tolerant corn this concern might be reduced by replacing some of the residual herbicides with short half-life, strongly sorbed, contact herbicides. We applied both herbicide types to two chiseled and two no-till watersheds in a 2-yr corn-soybean rotation and at half rates to three disked watersheds in a 3-yr corn/soybean/wheat (Triticum aestivum L.)-red clover (Trifolium pratense L.) rotation and monitored herbicide losses in runoff water for four crop years. In soybean years, average glyphosate loss (0.07%) was approximately 1/7 that of metribuzin (0.48%) and about one-half that of alachlor (0.12%), residual herbicides it can replace. Maximum, annual, flow-weighted concentration of glyphosate (9.2 microg L(-1)) was well below its 700 microg L(-1) MCL and metribuzin (9.5 microg L(-1)) was well below its 200 microg L(-1) HAL, whereas alachlor (44.5 microg L(-1)) was well above its 2 microg L(-1) MCL. In corn years, average glufosinate loss (0.10%) was similar to losses of alachlor (0.07%) and linuron (0.15%), but about one-fourth that of atrazine (0.37%). Maximum, annual, flow-weighted concentration of glufosinate (no MCL) was 3.5 microg L(-1), whereas atrazine (31.5 microg L(-1)) and alachlor (9.8 microg L(-1)) substantially exceeded their MCLs of 3 and 2 microg L(-1), respectively. Regardless of tillage system, flow-weighted atrazine and alachlor concentrations exceeded their MCLs in at least one crop year. Replacing these herbicides with glyphosate and glufosinate can reduce the occurrence of dissolved herbicide concentrations in runoff exceeding drinking water standards.

Stock and distribution of total and corn-derived soil organic carbon in aggregate and primary particle fractions for different land use and soil management practices

Land use, soil management, and cropping systems affect stock, distribution, and residence time of soil organic carbon (SOC). Therefore, SOC stock and its depth distribution and association with primary and secondary particles were assessed in long-term experiments at the North Appalachian Experimental Watersheds near Coshocton, Ohio, through δ13C techniques. These measurements were made for five land use and soil management treatments: (1) secondary forest, (2) meadow converted from no-till (NT) corn since 1988, (3) continuous NT corn since 1970, (4) continuous NT corn-soybean in rotation with ryegrass since 1984, and (5) conventional plow till (PT) corn since 1984. Soil samples to 70-cm depth were obtained in 2002 in all treatments. Significant differences in soil properties were observed among land use treatments for 0 to 5-cm depth. The SOC concentration (g C kg−1 of soil) in the 0 to 5-cm layer was 44.0 in forest, 24.0 in meadow, 26.1 in NT corn, 19.5 in NT corn-soybean, and 11.1 in PT corn. The fraction of total C in corn residue converted to SOC was 11.9% for NT corn, 10.6% for NT corn-soybean, and 8.3% for PT corn. The proportion of SOC derived from corn residue was 96% for NT corn in the 0 to 5-cm layer, and it decreased gradually with depth and was 50% in PT corn. The mean SOC sequestration rate on conversion from PT to NT was 280 kg C ha−1 y−1. The SOC concentration decreased with reduction in aggregate size, and macro-aggregates contained 15 to 35% more SOC concentration than microaggregates. In comparison with forest, the magnitude of SOC depletion in the 0 to 30-cm layer was 15.5 Mg C/ha (24.0%) in meadow, 12.7 Mg C/ha (19.8%) in NT corn, 17.3 Mg C/ha (26.8%) in NT corn-soybean, and 23.3 Mg C/ha (35.1%) in PT corn. The SOC had a long turnover time when located deeper in the subsoil. Additional research is needed to understand association of SOC with particle and aggregate size fractions and temporal changes and depth-distribution with regard to land use and soil management.

Water quality response times to pasture management changes in small and large watersheds

To interpret the effects of best management practices on water quality at a regional or large watershed scale, likely response times at various scales must be known. Therefore, four small (≤1 ha [≤2.5 ac]) watersheds, in rotational grazing studies at the North Appalachian Experimental Watershed near Coshocton, Ohio, were used to study management impacts on water quality and response times. Surface runoff was sampled on an event basis; groundwater discharge was sampled monthly from springs developed where a perching clay layer outcropped at the soil surface. In four large watersheds ranging from 18 to 123 ha (44 to 303 ac), base flow was over 50% of annual stream flow and approximately 20% of annual precipitation. Nitrate-N loads in base flow were 31% to 59% of total annual NO3-N load in stream flow. When the N fertilization rate in a “medium fertility” area that contains two small watersheds was increased from 56 to 168 kg ha-1 y-1 (50 to 150 lb ac-1 yr-1), NO3-N concentrations in groundwater discharge responded little in four years. Then NO3-N levels in groundwater discharge increased for 10 years. With discontinuation of N fertilization, NO3-N concentrations in groundwater discharge returned to pre-N increase levels after six years. In a “high fertility” grazing area with a similar perched water table, 224 kg N ha-1 (200 lb ac-1) was applied annually. Concentrations of NO3-N increased to >10 mg L-1 (ppm) after five years. Legumes were then interseeded into the grass forage, and mineral N fertilization was discontinued. Nitrate-N concentrations in groundwater discharge returned to their pre-fertilization levels after about five years. This multi-year response of groundwater discharge quality to management change in small watersheds indicates that the response time for measurable change in multi-square-mile watersheds will be equally long, if not longer, and trends will be muted.

Historic Assessment of Agricultural Impacts on Soil and Soil Organic Carbon Erosion in an Ohio Watershed

Agricultural management affects soil and soil organic carbon (SOC) erosion. The effect was assessed for a watershed (0.79 ha, 10% slope steepness, 132 m slope length) at the North Appalachian Experimental Watershed research station near Coshocton, Ohio, from 1951 to 1998. The agricultural management included: (i) plow-till corn (Zea mays L.)-wheat (Triticum aestivum L.)-meadow-meadow rotation (CWMM) from 1951 to 1970, (ii) plow-till continuous corn (CC) from 1971 to 1975, (iii) meadow (M) from 1976 to 1983, and (iv) no till corn-soybean (Glycine max (L.) Merr) rotation (CS) from 1984 to 1998. Soil erosion was assessed by sediment collection, the Revised Universal Soil Loss Equation (RUSLE), and the 137Cesium (137Cs) method. The SOC erosion was computed as a product of the soil erosion multiplied by the SOC content of 1.51% in the surface soil and by the SOC enrichment ratio of 1.71 except for the proportional equation of the 137Cs method. Sediment collection measurements indicated that the annual soil and SOC erosion rates (Mg ha−1 yr−1) for the corn cycles were, respectively, 1.55 and 0.040 for CWMM, 5.88 and 0.15 for CC, 0.63 and 0.016 for CS, and 2.34 and 0.060 for the entire period. The rates were, respectively, 0.35 and 0.009 for wheat cycles, 0.63 and 0.016 for soybean cycles, and essentially zero for meadow. Furthermore, the rates for the crop rotation periods were, respectively, 0.50 and 0.013 for CWMM, 5.88 and 0.15 for CC, 0.63 and 0.016 for CS, and 1.02 and 0.026 for the entire study period. The estimates by the RUSLE and proportional equation were 3 to 14 and 10 to 55 times the sediment values, respectively. However, the estimates by the revised exponential equation were 1 to 3 times the sediment values.

Pastureland Conservation Effects Assessment Project: Status and expected outcomes

The Conservation Effects Assessment Project (CEAP) is a multiagency scientific effort to quantify environmental outcomes of conservation practices applied to private agricultural lands. The program is anticipated to help shape future conservation policies, programs, and practices. The integrated landscape approach will focus on enhanced ecological resilience and sustainable agricultural production, both of which are essential to maintaining livelihoods and meeting global food needs (Nowak and Schnepf 2010). Principal components of CEAP include (1) detailed syntheses of scientific conservation literature; (2) a national assessment of conservation effects on ecosystem services; and (3) detailed investigations of conservation practices at various scales, including paddock, landscape, and water-shed levels. The CEAP effort on grazing lands began in rangeland in 2006 (Weltz et al. 2008) with a synthesis of the scientific literature on key rangeland conservation practices (Briske forthcoming). A CEAP effort on pastureland, primarily in the eastern and central United States, began in 2008. A literature synthesis documenting the science behind key conservation practices (Nelson forthcoming) revealed that scientific support exists for most conservation practices on pastureland, but critical knowledge, data, and technology gaps remain, including the following: Comprehensive assessments of effects of grazing management on a broad suite of…

Runoff water quality during drought in a zero-order georgia piedmont pasture: nitrogen and total organic carbon.

Approximately 11% of the Southern Piedmont (1.8 million ha) is used for pasture and hay production, mostly under low-input management. Few studies have investigated in the region long-term nitrogen and carbon losses in surface runoff, which can be significant. We present 1999 to 2009 hydrologic and water quality data from a rotationally grazed, 7.8-ha, zero-order pasture (W1) near Watkinsville in the Georgia Piedmont. Annual rainfall was 176 to 463 mm below the long-term average (1240 mm) in 7 of the 11 yr. There were 20 runoff events during 86 mo of below-average rainfall (deficit period), compared with 54 events during 46 mo of nondeficit period. Mean event flow-weighted concentration (in mg L) was 0.96 for nitrate-nitrogen (NO-N), 0.97 for ammonium-nitrogen (NH-N), 3.70 for total nitrogen (TN), and 9.12 for total organic carbon (TOC) ( = 43-47; limited due to instrument problem). Nutrient loads (in kg ha per event) averaged 0.04 for NO-N, 0.03 for NH-N, 0.19 for TN, and 0.54 for TOC. Total loads for N and TOC were 6 to 11 times greater from nondeficit than from deficit periods. The observed N concentrations, while well below maximum drinking water standard limits, could pose risk for eutrophication, which can be stimulated at lower concentrations. However, the ability of headwater streams, such as the one downstream of W1, to reduce nutrient concentrations might partially alleviate this concern. The results of this study point to the need to use a long-term dataset that includes measurements made in drought and wet years when evaluating the efficacy of water quality standards.