Showing papers in "Journal of Soil and Water Conservation in 2015"

Sequestering carbon and increasing productivity by conservation agriculture

Abstract: T he quantum jump in food production and progress toward elimination of mass starvation have been driven by mechanization of plowing and other farm operations, introduction of input-responsive varieties, use of chemical fertilizers along with herbicides and pesticides, increase in supplemental irrigation, and reliance on information and communication technology. Notable among the consequences of the agricultural revolution between 1960 and 2015 are increase in (1) human population from 3 billion to 7.3 billion (United Nations 2014); (2) atmospheric concentration of carbon dioxide (CO2) from 316 ppm to 400 ppm (IPCC 2014); (3) global temperature by 0.12°C (0.22°F) per decade (IPCC 2014); (4) problems of soil degradation by erosion, salinization, depletion of soil organic matter (SOM), and nutrient imbalance (Bai et al. 2008); (5) depletion, pollution, and eutrophication of natural waters; and (6) risk of extinction of soils (Tenseson 2014) and species. Yet, food production must be increased by another 1 billion t (1.1 billion tn) by 2050, while also restoring the degraded soils and ecosystems, reducing net anthropogenic emissions, and improving the environment. Plow-based agriculture has exacerbated the problems of accelerated soil erosion by water and wind, oxidation of SOM, and decline in soil structure (aggregation) and tilth. The plow-related problems…

Cover crop adoption in Iowa: The role of perceived practice characteristics

Abstract: Cover crops are widely viewed by the soil and water conservation community to be an effective means for reducing soil erosion and nutrient loss and increasing soil health, yet relatively few farmers have adopted the practice. Despite the widespread recognition of cover crops' benefits and increased promotional efforts, there have been very few peer-reviewed studies focused on farmer perspectives on or adoption of cover crops. This study, which ana- lyzed data from a survey and in-depth interviews with Iowa farmers, examined the roles that perceived practice characteristics, perspectives on potential facilitating factors, and crop and livestock diversity play in cover crop adoption among Iowa farmers. As expected, perceived benefits were strongly associated with cover crop use. Measures of crop and livestock diversity were also positive predictors of adoption. In addition, farmers who endorsed strengthening of facilitating factors such as educational and technological infrastructure to support cover crop use were more likely to have adopted cover crops. Farmers who perceived higher lev- els of risks associated with cover crop use, on the other hand, were less likely to use them. Results suggest that research and promotional efforts should focus on both raising awareness of potential benefits and quantifying and communicating potential risks and risk abatement strategies. Helping farmers to better understand (1) the benefits of cover crops and how they can be enhanced, and (2) the potential risks and ways that they can be minimized might allow farmers to more effectively weigh the probable benefits and costs of cover crop use. The find- ings further suggest that farmers believe that better facilitating infrastructure, in the form of technical assistance (e.g., agricultural retailers and custom operators) and education, is needed to support the widespread adoption of cover crops.

What is causing the harmful algal blooms in Lake Erie

Abstract: I n the early to mid-1990s, Lake Erie was regarded as one of the great water quality success stories stemming from the Clean Water Act. Annual total phosphorus (TP) loading to the lake decreased from nearly 30,000 t (33,069 tn) in the late-1960s to less than 11,000 t (12,125 tn) by 1990 (Richards and Baker 1993). These reductions in TP loading were achieved through permitting of point sources and through conservation efforts to decrease sediment loss from agricultural fields. While TP loads to Lake Erie have remained relatively stable since the mid-1990s, soluble phosphorus (SP) loads have been steadily increasing. The harmful and nuisance algal blooms (HNABs) that paralyzed regional tourism and fishing industries decades ago have reappeared and have been linked with the amount of SP transported to the lake (Davis et al. 2009). In August of 2014, HNABs in Lake Erie became a national headline when microcystin toxin produced by cyanobacteria was discovered and approximately 400,000 residents in Ohio were left without drinking water. There has been much debate among researchers, conservationists, and industry representatives on the specific causes of the increased HNABs in Lake Erie. Our objective here is to document many of the recently suggested theories that…

Conservation tillage is not conservation agriculture

Abstract: A LOOMING COLLISION: GLOBAL POPULATION AND FOOD SECURITY As world population increases and food production demands rise, keeping our soil healthy and productive while protecting the environment is of paramount importance for agriculture. The expanding global population—expected to reach 9.5 billion people by 2050 (United Nations 2014)—is putting tremendous pressure on the finite land area and resources for agricultural production, and pending climate extremes exacerbate the challenge of food security for both developed and developing countries. Despite the lessons of history, soil erosion is still a major problem in agricultural production systems. Efforts to control land degradation and soil erosion can be traced over the last 10,000 years; humankind has been building on the ruins of the past tillage and monoculture concepts at our peril (Lal et al. 2007; Montgomery 2007a, 2007b). Montgomery (2007b) describes the effects of poor soil management and erosion on several past civilizations. Once thriving, these civilizations eventually collapsed due to erosion, salinization, nutrient depletion, and other types of soil degradation. Tillage for soil preparation for planting and cultivation, by loosening soil and easing its transport by wind or water, induces and increases erosion. We are losing soil faster than nature can make it. In fact,…

A system approach to conservation agriculture

Abstract: D wight D. Eisenhower, 34th US President (1953 to 1961), summarized the plow dilemma by stating, “Farming looks mighty easy when your plow is a pencil and you are a thousand miles from corn field” (Eisenhower 1956). Despite great progress in agriculture since the 1950s, farming may now pose even bigger challenges because of the increasing demand for food, feed, fiber, and fuel in the 21st century. The challenges of farming are exacerbated by a changing and uncertain climate, increase in risks of soil degradation by erosion and other processes driven by decline in soil organic carbon (SOC) concentration and pool, increase in dependence on energy-based inputs such as fertilizers and pesticides, high risks of shifts in spectrum of pests and pathogens, and decrease in availability of soil and water resources because of diversion to nonagricultural uses. Hence, there is a growing emphasis on sustainable intensification, climate-resilient and eco-efficient agroecosystems, and the linkage of farming and soil management to sustainable development goals (United Nations 2014). Research on and adoption of conservation agriculture (CA) started during the 1960s. Presently, the literature is replete with merits, limitations, and uncertainties of no-till (NT) systems (table 1). It is because of these limitations and uncertainties…

Soil biology for resilient, healthy soil

Abstract: hat is a resilient, healthy soil? A resilient soil is capable of recovering from or adapt-ing to stress, and the health of the living/biological component of the soil is cru-cial for soil resiliency. Soil health is tightly coupled with the concept of soil quality (table 1), and the terms are frequently used interchangeably. The living component of soil or soil biota represents a small fraction (<0.05% dry weight), but it is essential to many soil functions and overall soil qual-ity. Some of these key functions or services for production agriculture are (1) nutrient provision and cycling, (2) pest and patho-gen protection, (3) production of growth factors, (4) water availability, and (5) for-mation of stable aggregates to reduce the risks of soil erosion and increase water infiltration (table 2). Soil resources and their inherent biological communities are the foundation for agricultural production systems that sustain the human population.The rapidly increasing human popula-tion is expanding the demand for food, fiber, feed, and fuel, which is stretching the capacity of the soil resource and contrib-uting to soil degradation. Soil degradation decreases a soil’s production capacity to directly supply human demands and decreases a soil’s functional capacity to per -form numerous critical services, which are valued in trillions of US dollars (Pimental et al. 1997). The ability to reverse degra-dation of soil resources and improve soil services is intimately related to the abil-ity to promote the biological functioning or health of the soil. Although this report primarily considers soil microorganisms, we fully acknowledge the importance of higher soil organisms to the mainte-nance of soil health and provision of soil services, but leave those phyla to future discourse. Emerging tools and technolo-gies have become available to dramatically advance our understanding of microscopic soil biota and provide the foundation to manage soil organisms to enhance primary productivity, provide multiple ecological services, rejuvenate soil resilience, and sus-tain long-term soil resource quality.

Biomass production of 12 winter cereal cover crop cultivars and their effect on subsequent no-till corn yield

Abstract: Cover crops can improve the sustainability and resilience of corn (Zea mays L.) and soybean (Glycine max L. Merr.) production systems. At present, the most widely used cover crops in corn–soybean systems in the upper Midwest United States have been winter cereals. However, there have been isolated reports of corn yield reductions following winter rye (Secale cereale L.) cover crops, and the risk of corn yield reductions will reduce the likelihood of farmers adopting cover crops. Although the exact mechanism is unknown and there are many possible causes of corn yield reductions following winter cereal cover crops, we hypothesize that there may be differences among winter cereal species or cultivars in their effect on corn yield. Additionally, there have been no evaluations of shoot growth and nitrogen (N) uptake of winter cereal cultivars used as cover crops in the upper Midwest. Seven winter rye cultivars, 2 winter triticale (× Triticosecale Wittmack) cultivars, and 3 winter wheat (Triticum aestivum L.) cultivars were planted following soybean harvest and grown as a winter cover crops preceding corn in four years to determine whether the 12 cultivars differed in (1) biomass production and N uptake, and (2) impact on corn yield, harvest population, and other yield parameters. The 12 cover crop cultivars differed in each of the four years for shoot dry weight, shoot N concentration, and total shoot N content. In general, the winter rye cultivars had greater shoot biomass, lower shoot N concentrations, and higher total shoot N contents than the winter triticale and winter wheat cultivars. The winter cereal cultivars decreased corn yield in two of the four years, and the yield effect varied among cultivars. Some cultivars of all three species caused corn yield decreases, with no indication that winter rye had a greater effect than did winter wheat or winter triticale. Four winter rye cultivars did not significantly reduce corn yield in either of the two years in which yield was reduced. In general, the decreases in corn yield following the winter cereal cover crops were related to decreases in harvest population and increases in the number of barren plants, but were not strongly related to cover crop shoot dry weight within years. Our study shows that there are genotypic differences among winter cereal cultivars for their performance as cover crops and their effect on corn yields.

Soil carbon sequestration and aggregation by cover cropping

Abstract: Agriculture is the foundation of human civilization. Transition from hunter-gatherer to settled agriculture, as evidenced by the use of crude implements for tilling and harvesting, may have occurred in modern day Iraq and elsewhere around 11,000 years ago (Troeh et al. 2004). The beneficial role of growing cover crops in improving soil productivity had been recognized for at least three millennia and probably longer. Use of cover crops as green manure had been advocated in most ancient cultures (e.g., Indus Valley and Middle East) to improve soil fertility. In China, for example, use of cover cropping dates back to the Zhou dynasty 3,000 years ago (Lipman 1912; Pieters 1927; Meisinger et al. 1991). Cato, a Roman philosopher during the 3rd century BC, advocated the use of green manure and compost to improve soil productivity (Winiwater 2006; Brevik and Hartemink 2010). By the 4th century AD, grain yields of wheat ( Triticum aestivum ) in Rome declined drastically due to the lack of cover cropping and were hardly 270 to 400 kg ha−1 (4 to 6 bu ac−1), and that of barley ( Hordeum vulgare ) were only 220 to 320 kg ha−1 (195.8 to 285.1 lb ac−1; Paine and Harrison 1993). Therefore, during 395…

Trade-offs between winter cover crop production and soil water depletion in the San Joaquin Valley, California

Abstract: Cover crops are currently not widely used in annual crop production systems in California9s semiarid Central Valley due to concerns about lost opportunity costs and uncertainties about water use. From 1999 through 2014, we quantified cover crop biomass production for a variety of mixtures under winter precipitation and limited supplemental irrigation. In a separate study, we also determined changes in soil water storage under three cover crop mixtures compared to fallowed plots during two (2013 and 2014) winter periods to investigate tradeoffs associated with water use by cover crops in this region. Over the 15 years of the project that were characterized by recurring drought, a total of 22.8 Mg ha−1 (20,360 lb ac−1) of aboveground cover crop biomass was produced with a total precipitation of 209 and 20 cm (82 and 8 in) of supplemental irrigation applied in 1999, 2012, and 2014. Cover crop biomass varied from 0.39 Mg ha−1 (348 lb ac−1) in the low precipitation period (winter of 2006 to 2007) to 9.34 Mg ha−1 (8,340 lb ac−1; winter of 2000 to 2001). Soil water storage in the sampled depth (0 to 90 cm [0 to 35 in]) for the fallow and each of the cover crop mixtures was compared each year from January to March, the primary growing period for cover crops in this region. Net soil water storage increased during this period by 4.8 and 4.3 cm (1.9 and 1.7 in) in 2013 and 2014, respectively, for the fallow system, but in the cover crop mixture plots, there was no additional water storage. Instead, water use by the cover crop mixes resulted in a negative water balance over the cover crop growth period on an average of 0.47 and 0.26 cm (0.19 and 0.10 in) in 2013 and 2014, respectively. Thus, compared to the fallow system, cover crops depleted 5.3 and 0.67 cm (2.1 and 0.26 in) and more water from the 0 to 90 cm (0 to 35 in) profile in 2013 and 2014, respectively. From this long-term systems research, we conclude that while vigorous growth of winter cover crops in the Central Valley of California may not be possible in all years due to low and erratic precipitation patterns, there may be benefits in terms of providing ground cover, residue, and photosynthetic energy capture in many years. However, cover crop biomass production may come at a cost of soil water depletion in this semiarid, drought-prone region.

Conservation effects on soil quality indicators in the Missouri Salt River Basin

Abstract: The Conservation Effects Assessment Project (CEAP) was initiated in 2002 to quantify the potential benefits of conservation management practices throughout the nation. Within the Central Claypan Region of Missouri, the Salt River Basin was selected as a benchmark watershed for soil and water quality assessments. This study focuses on two objectives: (1) assessing soil quality for 15 different annual cropping and perennial vegetation systems typically employed in this region, and (2) evaluating relationships among multiple measured soil quality indicators (SQIs). Management practices included annual versus perennial vegetation, and varying grass species composition (cool-season versus warm-season), tillage intensity (no-till versus mulch-till), biomass removal, rotation phase, crop rotation (corn [Zea mays L.]–soybean [Glycine max L. Merr] versus corn–soybean–wheat [Triticum aestivum L.]) and incorporation of cover crops into the rotation. Soil samples were obtained in 2008 from 0 to 5 cm (0 to 2 in) and 5 to 15 cm (2 to 6 in) depth layers. Ten biological, physical, chemical, and nutrient SQIs were measured and scored using the Soil Management Assessment Framework (SMAF). Across SQIs, biological and physical indicators were the most sensitive to management effects, reflecting significant differences in organic carbon (C), mineralizable nitrogen (N), β-glucosidase, and bulk density. In the 0 to 5 cm layer, perennial systems demonstrated the greatest SMAF scores, ranging from 93% to 97% of the soil9s inherent potential. Scores for annual cropping systems ranged from 78% to 92%: diversified no-till, corn–soybean–wheat rotation with cover crops (92%) > no-till, corn–soybean rotation without cover crops (88%) > mulch-till corn–soybean rotation without cover crops (84%). Conversely, in the 5 to 15 cm layer, no-till cropping systems scored lower for overall soil function (58% to 61%) than mulch-till systems (65% to 66%). In the 0 to 5 cm layer, biological soil quality under the diversified no-till system with cover crops was 11% greater than under no-till without cover crops, and 20% greater than under mulch-till without cover crops. The effect of rotation phase was primarily reflected in 64% lower mineralizable N following corn relative to soybean. Additionally, soil nutrient function was significantly affected by biomass removal. The results of this study demonstrate that the benefits of conservation management practices extend beyond soil erosion reduction and improved water quality by highlighting the potential for enhanced soil quality, especially biological soil function. In particular, implementing conservation management practices on marginal and degraded soils in the claypan region can enhance long-term sustainability in annual cropping systems and working grasslands through improved soil quality.

Reducing hypoxia in the Gulf of Mexico: Reimagining a more resilient agricultural landscape in the Mississippi River Watershed

Abstract: I n 1972 President Nixon signed the Clean Water Act (CWA) into law, making clean water a public right and establishing a goal that the nation's waters should be both “fishable and swimmable.” It is considered by many to be the most important and effective environmental law ever passed. Before the CWA, two-thirds of US waterways were considered unsafe for fishing and swimming, and waste from households, municipalities, factories and power plants, including sewage, livestock processing, waste oil, and chemicals, flowed untreated into rivers, streams, and lakes. The law reduced the discharge of sewage and other industrial point source pollution into waterways, but most agricultural nonpoint source pollution, the greatest source of water pollution today, was exempted. The agriculture exemption, called “one of the last, great intractable problems of environmental law,” results in an inconsistent system for addressing water pollution, with regulation for the majority of urban sources and a voluntary, incentive-based system for much of agriculture (Laitos and Ruckriegle 2013). Despite more than 40 years of largely voluntary efforts by federal, state, and local government, and tens of billions of US dollars of investment in conservation, nationwide progress on nutrient control has not yet been achieved. Concentrations of nitrogen (N)…

Progress and perspectives with cover crops: Interpreting three years of farmer surveys on cover crops

Abstract: I n September of 2012, as a record-setting drought impacted farms across the United States, reports of an interesting nature kept popping up related to cover crops. A number of farmers who were using cover crops had started fall harvest and were finding that their corn ( Zea mays L.) and soybean ( Glycine max [L.] Merr.) fields planted after cover crops seemed to have better yields, in some cases with a sizeable benefit. This ran counter to the prevailing thought at the time among many farm advisors, which was that cover crops would hurt commodity yields in a dry year. To find out if there was indeed something going on with yield benefits from cover crops, some modest funding support was provided from the North Central Region Sustainable Agriculture Research and Education (SARE) program to the Conservation Technology Information Center (CTIC), a nonprofit based in Indiana with a history of doing survey work related to conservation practices, to conduct a survey of farmers who were using cover crops. The results of that survey, particularly with crop yields, proved eye-opening to many people around the country and actually contributed to changes in federal crop insurance policy pertaining to cover crops. A total of…

Sediment transport capacity and its response to hydraulic parameters in experimental rill flow on steep slope

Abstract: Sediment transport capacity must be considered when developing physical models of soil erosion. The effects of related hydraulic parameters (e.g., flow discharge, slope gradient, and flow velocity), and of force predictors (e.g., shear stress, stream power, and unit stream power) on sediment transport capacity in rill erosion are still poorly known on the farmland of the Loess Plateau in China where rill erosion is common. We conducted a series of experiments to simulate and evaluate the sediment transport capacity of rill flow in a nonerodible rill flume. The test sediment was the loessial soil of the farmland of the Loess Plateau. Five flow discharges ranging from 0.22 to 0.67 × 10−3 m2 s−1 (0.00237 to 0.00721 ft2 sec−1) and five slope gradients ranging from 15.8% to 38.4% were tested. Sediment transport capacity increased with both flow discharge and slope gradient, as expected, but was more sensitive to flow discharge than to slope gradient, unlike other similar studies. Mean flow velocity, related to the flow discharge, was strongly correlated with sediment transport capacity (r2 = 0.93). Stream power was the best predictor of sediment transport capacity; shear stress and unit stream power, with critical values of 0.55 W m−2 and 0.02 m s−1 (0.04 mi hr−1) respectively, were poor predictors. An empirical equation of sediment transport capacity of the loessial soil for rill flow was developed. Our results present a different view, compared to previous studies, of the relationship of sediment transport capacity with discharge and slopes, especially with lower discharges, steep slopes, and loessial soil. Further study should be conducted to evaluate the performance of farmland soil at various slopes and discharges.

Identifying new deep-rooted plant species suitable as undersown nitrogen catch crops

Abstract: A five-year field study was conducted in order to identify and test plant species suitable as undersown nitrogen (N) catch crops. With the aim of maximizing the catch crop effect against N leaching loss, the main focus was on identifying species with deeper rooting than ryegrass (Lolium perenne L.), which is typically used for this purpose. More than 20 species from 9 plant families were studied as undersown catch crops in spring barley (Hordeum vulgare L.). The root and shoot biomass production, N uptake, carbon (C) to N ratio, root distribution, rooting depth, and reduction of soil nitrate-N (NO3-N) were measured, and observations of general performance as undersown catch crops were made. During barley growth only small differences in root growth among the catch crops was observed. Later, during autumn, striking differences in root growth appeared, and while ryegrass had few roots below 0.8 m (31.5 in) depth, a number of species showed high root intensities in the soil layer from 0.8 to 1.6 m (31.5 to 63.0 in). Dyer9s woad (Isatis tinctoria L.) and viper9s bugloss (Echium vulgare L.) showed high root intensities even at 1.6 to 2.4 m (63.0 to 94.5 in). The measured differences in root growth were significantly related to the ability of the different species to deplete soil NO3-N from deeper soil layers. Dyer9s woad, which was the most efficient, reduced soil NO3-N content in November to 15 kg N ha−1 (13 lb N ac−1) in the 0 to 2.5 m (0 to 98.4 in) soil layer compared to 53 kg N ha−1 (47 lb N ac−1) under ryegrass and 62 kg N ha−1 (55 lb N ac−1) without a catch crop, and most of this difference occurred below 1 m (39.4 in) depth. There were many other differences among the species in terms of growth, N uptake, root/shoot ratio, and C/N ratio—differences that may be of interest for their use as catch crops for N management. One major effect was that legumes took up far more N than the other species and also produced more biomass than most others. However, none of the four legumes were among the deep-rooted species identified; they were among the shallowest rooted species with a root distribution close to that of ryegrass.

Does grazing of cover crops impact biologically active soil carbon and nitrogen fractions under inversion or no tillage management

Abstract: Cover crops are a key component of conservation cropping systems. They can also be a key component of integrated crop-livestock systems by offering high-quality forage during short periods between cash crops. The impact of cattle grazing on biologically active soil carbon (C) and nitrogen (N) fractions has not received much attention. We investigated the impacts of tillage (conventional disk and no tillage) and cover crop management (ungrazed and grazed) on biologically active soil C and N fractions from biennial sampling during seven years of continuous management. Soil microbial biomass C was unaffected by cover crop management under conventional tillage, but was enhanced with grazing compared with no grazing under no tillage at a depth of 0 to 6 cm (0 to 2.4 in), as well as at 0 to 30 cm (0 to 12 in). The same effect occurred for the flush of carbon dioxide (CO2) following rewetting of dried soil during 3 days of incubation at a depth of 0 to 6 cm only, while it occurred for cumulative C mineralization during 24 days of incubation at a depth of 0 to 30 cm only. Grazing effects on net N mineralization during 24 days of incubation and residual soil inorganic N were nonexistent. All biologically active fractions of soil C and N were highly stratified with depth under no tillage and less so under conventional tillage. Cumulative stocks of soil C and N fractions to a depth of 0 to 30 cm were generally not significantly different between cover crop management systems, nor between tillage systems, except for (1) lower soil microbial biomass C with than without grazing under conventional tillage, (2) greater soil microbial biomass C with than without grazing under no tillage, and (3) lower cumulative C mineralization during 24 days under no tillage than under conventional tillage. Grazing of cover crops can be recommended as a strategy to promote greater adoption of cover cropping throughout the southeastern United States.

Nitrogen recovery by cover crops in relation to time of planting and growth termination

Abstract: Residual fertilizer nitrogen (N) in soil represents a potential environmental contaminant because of the risk of nitrate (NO3) leaching into ground water. Winter annual grass cover crops can conserve residual soil N; however, their ability to recover N greatly varies with management. A two-year field experiment in the North Carolina Coastal Plain on a State fine sandy loam (fine-loamy, mixed, thermic Typic Hapludult) compared dry matter (DM), N accumulation, and soil inorganic N following rye (Secale cereale L.), winter wheat (Triticum aestivum L.), triticale (Triticum secale L.), black oats (Avena strigosa L.), and fallow (native weeds) in relation to planting (October, November, and December) and growth termination (early March, early April, and late April/early May) dates and levels of residual soil N. Cover crop DM and N accumulations decreased with successive planting date delays (November and December) for each growth termination date in the following spring. In 2000, cumulative DM yields of October- and November-planted cover crops were 3.17 Mg ha−1 (1.41 tn ac−1) and 3.74 Mg ha−1 (1.66 tn ac−1), respectively, which were significantly greater than those of December-planted cover crops (1.90 Mg ha−1 [0.84 tn ac−1]) at the second growth termination date (early April). Cover crop N accumulation increased with a delay in growth termination, although the interaction between cover crop species and the planting date varied. October planting of rye and triticale showed greater N accumulation at a March growth termination date, averaging 37.8 kg N ha−1 (33.7 lb N ac−1) for rye and 37.6 kg N ha−1 (33.5 lb N ac−1) for triticale; these values were 7.8% and 14.1% higher than those of black oat and wheat, respectively, at the same planting and growth termination dates. November-planted wheat showed in the highest N accumulation (average, 57.9 kg N ha−1 [51.7 lb N ac−1]) at the late April/early May termination date; this was 3.8% to 7.9% higher than that of other species. In contrast, black oat showed a greater ability to scavenge soil residual N with a late planting and growth termination date combination (average, 58.7 kg N ha−1 [52.4 lb N ac−1]). The cover crop planting date affected soil inorganic N distribution at each termination date, with an October planting date resulting in lower soil profile inorganic N levels than November and December planting dates. Lower soil inorganic N concentrations were strongly associated with increases in cover crop DM and N accumulation for each growth termination date. These results should help growers identify the best niche for a cover crop with respect to recovering residual soil N in their various rotations.

Remote sensing to monitor cover crop adoption in southeastern Pennsylvania

Abstract: In the Chesapeake Bay Watershed, winter cereal cover crops are often planted in rotation with summer crops to reduce the loss of nutrients and sediment from agricultural systems. Cover crops can also improve soil health, control weeds and pests, supplement forage needs, and support resilient cropping systems. In southeastern Pennsylvania, cover crops can be successfully established following corn (Zea mays L.) silage harvest and are strongly pro- moted for use in this niche. They are also planted following corn grain, soybean (Glycine max L.), and vegetable harvest. In Pennsylvania, the use of winter cover crops for agricultural con- servation has been supported through a combination of outreach, regulation, and incentives. On-farm implementation is thought to be increasing, but the actual extent of cover crops is not well quantified. Satellite imagery can be used to map green winter cover crop vegetation on agricultural fields and, when integrated with additional remote sensing data products, can be used to evaluate wintertime vegetative groundcover following specific summer crops. This study used Landsat and SPOT (System Probatoire d' Observation de la Terre) satellite imagery, in combination with the USDA National Agricultural Statistics Service Cropland Data Layer, to evaluate the extent and amount of green wintertime vegetation on agricultural fields in four Pennsylvania counties (Berks, Lebanon, Lancaster, and York) from 2010 to 2013. In December of 2010, a windshield survey was conducted to collect baseline data on winter cover crop implementation, with particular focus on identifying corn harvested for silage (expected earlier harvest date and lower levels of crop residue), versus for grain (expected later harvest date and higher levels of crop residue). Satellite spectral indices were successfully used to detect both the amount of green vegetative groundcover and the amount of crop residue on the surveyed fields. Analysis of wintertime satellite imagery showed consistent increases in vegetative groundcover over the four-year study period and determined that trends did not result from annual weather variability, indicating that farmers are increasing adoption of practices such as cover cropping that promote wintertime vegetation. Between 2010 and 2013, the occurrence of wintertime vegetation on agricultural fields increased from 36% to 67% of corn fields in Berks County, from 53% to 75% in Lancaster County, from 42% to 65% in Lebanon County, and from 26% to 52% in York County. Apparently, efforts to promote cover crop use in the Chesapeake Bay Watershed have coincided with a rapid increase in the occurrence of wintertime vegetation following corn harvest in southeastern Pennsylvania. However, despite these increases, between 25% and 48% of corn fields remained without substantial green vegetation over the wintertime, indicating further opportunity for cover crop adoption.

A modeling approach to evaluate the impact of conservation practices on water and sediment yield in Sasumua Watershed, Kenya

Abstract: Degradation of agricultural watersheds often reduces their capacity to provide ecosystem services such as sediment retention, flow regulation, and water quality improvement. Soil and water conservation practices can be used to enhance the capacity of watersheds to produce these services. The objective of this study was to evaluate the impact of agricultural conservation practices on water and sediment yield using the Soil and Water Assessment Tool (SWAT) model. The study area was Sasumua Watershed (107 km2 [43 mi2]), where land degradation has affected watershed9s capacity to regulate flow and maintain water quality. The model was calibrated and validated for streamflow at the watershed outlet. Data on annual average erosion rates for the area was used to constrain soil erodibility factor (KUSLE) and practice erodibility factor (PUSLE) parameters during sediment calibration while measured three month sediment concentration data was used for validation. Model performance was assessed using the coefficient of determination (r2), Nash-Sutcliffe efficiency coefficient (ENS) and percent bias (PBIAS). Results gave monthly streamflow r2 values of 0.80 and 0.85, ENS values of 0.74 and 0.81, and PBIAS values of ±5% and ±6% during the calibration and validation. The model also satisfactorily simulated daily sediment concentrations with an r2 value of 0.54. However, ENS and PBIAS values were low, which was attributed to the short duration of measurement. The validated model was used to simulate sediment yield for the period 1970 to 2010. Mean annual watershed sediment yield was 40,934 t y−1 (90,243,096 lb yr−1). The impacts of filter strips, contour farming, parallel terraces, grassed waterways, and their combinations on water and sediment yield were simulated by adjusting relevant model parameters. The effectiveness of filter strips increased nonlinearly with width being optimum at 30 m (98.4 ft). A combination of 30 m (98.4 ft) wide filter strips and grassed waterways reduced sediment yield by 80%; parallel terraces, 10 m (32.8 ft) filter strips, and grassed waterways reduced sediment yield by 75%; 10 m (32.8 ft) filter strips and grassed waterways reduced yield by 73%; contour farming and grassed waterways reduced yield by 66%; and grassed waterways reduced yield by only 54%. Parallel terraces reduced surface runoff by 20% and increased base flow by 12%, while contour farming reduced surface runoff by 12% and increased base flow by 6.5%. Implementation of conservation practices can reduce sediment yield and increase water yield marginally. The results give an insight into the implications of the present land use management practices and can be used to devise ecologically sound watershed management and development plans.

The past, present, and future of the cover crop industry

Abstract: HISTORICAL COVER CROP USE The use of the crops we commonly refer to as cover crops can be traced back over the millennia. Ancient civilizations depended on their use to enhance the growth of crops they cultivated for food. Native Americans utilized a concept called “Three Sisters” where corn ( Zea mays L.), edible beans, and squash were grown together as the benefits of diversity were realized. This strategy established a foundation of the effectiveness of the synergy of mixed species that is so prevalent in cover cropping today. Cover crops were used nearly two hundred years before World War II. In fact, you could argue that the first US president, George Washington, who was also a well-known farmer by trade, was one of the foremost promoters in America for cover crops. His crop rotations were strategically listed to include “crops grown to eat and sell” and “crops grown to replenish the soil.” Clover, grass, and buckwheat ( Fagopyrum esculentum Moench) were listed as those he incorporated into his cropping system (Mount Vernon Ladies' Association 2015). Many farmers in the new frontier were farming the land for a dozen years or so only to observe the soil erode and become less productive…

Cover crops in the agricultural systems of the Argentine Pampas

Abstract: T he Argentine Pampas (figure 1) is located in the south cone of South America (31° to 39° S and 58° to 65° W). The region extends along 55 to 60 million ha (135 to 148 million ac) and was originally covered with temperate grasslands. The region shows several similarities as well as differences with their equivalent grassland of North America. In a simplified picture, the climate is humid in the east and subhumid/semiarid in the west. Rainfall varies from 1,200 mm y−1 (47 in yr−1) in the east to 500 mm y−1 (20 in yr−1) in the west. Fall and spring/summer are the rainier seasons but there is considerable variability in monthly and annual precipitation. The Pampas is classified as mesothermal, with average temperature around 14°C (57.2°F) in the south and 20°C (68°F) in the north. Winters can be cold, especially in the south, where it sometimes snows, but soils never become frozen. Most soils of the Pampas were developed from loess-like sediments and are mainly Mollisols. From east to west, soils are mainly Argiudolls, Hapludolls, and Haplustolls, and in some localized areas Natraquolls. Other less representative soils are Alfisols, Vertisols, and Entisols (Lavado and Taboada 2009). The Pampas is…

Using hedgerow biodiversity to enhance the carbon storage of farmland in the Fraser River delta of British Columbia

Abstract: Hedgerows (also known as field margins, shelterbelts, or windbreaks) have the potential to help mitigate greenhouse gas emissions from agricultural activities through carbon (C) sequestration in the woody biomass of trees and shrubs as well as in the soil. A first step to understanding the sequestration potential is to quantify the biomass C and soil C storage. In the Fraser Valley of British Columbia, Canada, a hedgerow stewardship program incentivizes farmers to plant hedgerows to create habitat for biodiversity conservation and to improve ecosystem services such as climate change mitigation. This study evaluated the efficacy of hedgerows to store C in woody biomass and soil relative to remnant hedgerows (RH) and neighboring production fields with annual crops. We measured soil C (equivalent soil mass) and soil aggregate stability in both hedgerows and production fields, while biomass C and species diversity were calculated for the trees and shrubs in the two hedgerow types. There was no significant difference in the biomass C in the two hedgerow types, despite age differences with planted hedgerows (PH) having a mean total above- and belowground biomass of 76 ± 32 t C ha−1 (33.8 ± 14.2 tn C ac−1) and RH 124 ± 21 t C ha−1 (55.3 ± 9.3 tn C ac−1). Aggregate stability was similar in both hedgerow types, and was significantly greater than neighboring production fields. Woody vegetation biodiversity was significantly greater in PH than RH for richness, Shannon, and Simpson measures. Planted hedgerows stored significantly greater soil C than RH to 1.2 t m−2 (1.1 tn yd−2) standard soil mass with values being 175.9 ± 13.2 t C ha−1 (78.4 ± 5.8 tn C ac−1) and 132.7 ± 7.3 t C ha−1 (59.1 ± 3.2 tn C ac−1), respectively. Soil C in PH was 40% greater than that of their neighboring production fields. Soil C was significantly correlated with the Shannon and Simpson diversity of the hedgerow shrubs and trees indicating that planting hedgerows, with improved woody vegetation biodiversity, may have a positive effect on their greenhouse gas mitigation potential on farmland.

Absentee landowners of agricultural land: Influences upon land management decision making and information usage

Abstract: Ownership of agricultural land by absentee owners (individuals who do not reside permanently on their land) is on the rise worldwide, yet researchers and conservation practitioners know very little about these landowners, what influences their land management decisions, and their use of varying land management information sources. Our study focuses on (1) how absentee landowners vary in terms of influences upon their decision making regarding land management and (2) how, or if, this variance predicts sources of conservation information landowners use regarding their land. The findings show three distinct groups of absentee landowner classes: (1) Minimal Recreationists, (2) Moderates, and (3) Recreation and Conservationists. While recreation on the land dominates as the most powerful influence upon decision making regarding land management, conservation was not a prominent land management motivation in two of the three classes. These groups of landowners correspond with differing information usage patterns, with Recreation and Conservationists the most likely to use information from conventional sources (e.g., influential individuals, agricultural organizations, and conservation agencies) while the other two groups have negative relationships with almost all of the information sources. We discuss strategies for tailoring and delivering conservation messages to these diverse absentee landowner groups.

Suspended sediment supply dominated by bank erosion in a low-gradient agricultural watershed, Wildcat Slough, Fisher, Illinois, United States

Abstract: The relative contributions from potential sediment sources to the suspended load of the Wildcat Slough, a headwater tributary in central Illinois, are estimated as a proxy for understanding sediment and nutrient transport in low gradient, intensively managed watersheds. Sediment and nutrient fluxes from agricultural areas to rivers have led to nitrate (NO3) concentrations that exceed US Environmental Protection Agency water quality standards and phosphorus (P) concentrations that promote algal growth, decreasing water quality across the state of Illinois. This study assesses contributions to the sediment load as a function of land use and channel morphology in Wildcat Slough, a low gradient, intensively managed 61.3 km2 (23.67 mi2) watershed in the Upper Sangamon River Basin of central Illinois, United States. Land use is dominated by row crop agriculture. Potential sediment sources include row crop fields, forest, floodplains, river banks, pastures, and grasslands. The majority of the stream is constrained within a deep, channelized ditch fed by tile drains. However, in the lowermost reaches, Wildcat Slough freely meanders and has established fluvial features including point bars and cut banks. A suite of tracers (delta carbon 13 [δ13C], phosphorus [P], magnesium [Mg], manganese [Mn], and carbon [C]) differ significantly between the potential sediment sources. An unmixing model uses the concentrations of the tracers in source samples and in suspended sediment collected during high discharge events to estimate the relative contribution from each source to the suspended load. The majority of suspended sediment was sourced from channel banks (40% to 65%) and forest (35% to 55%) with very little derived from the agricultural uplands (10% or less). The lack of sediment from uplands signifies a disconnect between the uplands and the channel, reflecting the low relief of the uplands and the dominance of tile drains in routing water to the channel. These findings suggest that efforts to limit the sediment-born nutrient load should focus on near-channel areas in meandering reaches. Best practices in similar landscapes may include installation of a buffer between meandering channel reaches and fertilized land, or limiting fertilizer application near channel banks, to diminish the inputs to the nutrient load via natural channel migration.

The 4Rs for cover crops and other advances in cover crop management for environmental quality

Abstract: H umans have used soil resources for thousands of years. Human use has degraded and eroded soil worldwide in ways that damage food production, biodiversity, and ecosystem services. A direct implication of soil degradation is that soil scarcity will become a critical future problem for global agricultural production. With limited new lands for cultivation worldwide and a projected increase in global population to 10 billion this century, long-term agricultural sustainability is an increasing global concern. To conserve soil, better agricultural methods that sustain the soil are needed (Montgomery 2007). Soil management must focus on regaining a balance in (1) organic carbon (C) inputs and losses, (2) soil erosion and production, and (3) release and loss of nutrients (Amundson et al. 2015). Soil does far more than just support farming and forestry. It stores C, filters water, transforms nutrients, and sustains plant and animal biodiversity by conservation of critical shrinking wildlife habitat. It is unclear how these essential processes will respond to agricultural intensification, or how they might be enhanced in tandem with farming (Banwart 2011). Fortunately, the recent renewed use of cover crops management practices can help address this problem. Cover crops have enormous potential to improve soil and water conservation…

Soil properties, bacterial community composition, and metabolic diversity responses to soil salinization of a semiarid grassland in northeast China

Abstract: Soil secondary salinization resulting from overgrazing is a serious environmental problem in arid or semiarid grasslands in northeast China, generally characterized by the dramatic increase of soil soluble salt content and the decrease of vegetative production. However, the process of soil degradation, especially the influence of soil salinization on soil physicochemical properties, enzyme activities, bacterial community composition, and metabolic diversity, has been less exhaustively assessed. This work aims to evaluate the effects of salinization level on the soil properties and to discuss the effects of metabolic profiles and bacterial community in salinized grasslands. Soil samples were collected from three grasslands with a gradient of salinization level (0.135%, 0.375%, and 1.063%, respectively). The soil properties were measured. Analysis of community level physiological profiles (CLPPs) and 16S rRNA gene denaturing gradient gel electrophoresis (DGGE) were used to determine the metabolic diversity and dominant species of a soil bacterial community, respectively. Soil moisture, porosity, total nitrogen (N) and phosphorus (P), available N and potassium (K), DNA content, microbial biomass, enzymatic activities (dehydrogenase, phosphomonoesterase, urease, and polyphenol oxidase), and metabolic function diversity all decreased significantly with an increase in salt content. Soil bulk density, pH, and available P concentration increased significantly. All of the aforementioned soil properties had significant linear relations with salt content and aboveground biomass (p

Cover cropping and the “4 per Thousand” proposal

Abstract: C limate change, caused by anthropogenic emissions through fossil fuel combustion and land use conversion including deforestation, is a major global issue of the twenty-first century. Estimates of anthropogenic emissions for 2014 include about 10 Pg (11 billion tn) of carbon (C) through fossil fuel combustion and ~1 Pg (1 billion tn) C from deforestation and land use conversion. Cumulative emissions of carbon dioxide (CO2) for the period of 144 years from 1870 to 2014 is estimated at 545 ± 55 Pg C (600 ± 61 billion tn C; 2,000 ± 200 Pg CO2 [2,200 ± 220 billion tn CO2]), about 75% from fossil fuel combustion and about 25% from land use change (Le Quere et al. 2014). Agricultural activities contribute, both directly and indirectly, about 30% of the total anthropogenic emissions (IPCC 2014). Therefore, agriculture must be integral to any agenda to mitigate the climate change. National commitments made thus far to reduce gaseous emissions may allow global temperatures to increase by 3°C (5.4°F) by 2100 (“How much warming” 2015), which far exceeds the 2°C (3.6°F) limit accepted by the Group of Eight (G-8) nations as per the L'Aquila Accord in 2009 (Reuters 2009). Therefore, there is an urgent need…

Interpolation methods for improving the RUSLE R-factor mapping in Brazil

Abstract: Methods for Revised Universal Soil Loss Equation (RUSLE) rainfall erosivity factor (R-factor) predictions have been useful for land use planning in agricultural areas related to soil erosion risk map assessment, which is crucial at the regional scale. Many studies have focused on the R-factor prediction in Brazil and have utilized ordinary kriging and other methods, especially inverse square distance weighted (ISDW) predictions. For large regions with sparse sample rain-gauge network and complex atmospheric systems, such as Brazil, regression-kriging method arises as one that can produce reliable and improved results. The objective of this study was to compare the performance of (1) ordinary kriging; (2) co-kriging taking altitude as spatially distributed covariate; (3) ISDW; (4) multivariate regression model for R-factor as function of latitude, longitude, and altitude; and (5) regression-kriging. Daily pluviometric data sets from 928 rain gauges were used, considering the Modified Fournier Index (MFI) methodology for estimating the mean annual R-factor values for each rain gauge. From these stations, 155 were extracted randomly and used exclusively for statistical comparison of the methods. Regression-kriging method has demonstrated higher performance than the others, with mean absolute error of 11% compared to 15.8%, 16.2%, 19%, and 19.5%, respectively, for co-kriging, ordinary kriging, regression model, and ISDW. In addition, Willmott9s index D for regression-kriging was higher than 0.94 while for the others lower than 0.90, proving its greater prediction accuracy. Thus, regression-kriging method was the most reliable, producing the best practical map. With regard to other methods, co-kriging also produced acceptable results for developing R-factor maps for Brazil.

Water management for cucumber: Greenhouse experiment in Saudi Arabia and modeling study using SALTMED model

Abstract: A successful water management scheme for irrigated crops needs a holistic approach that considers water, crop, soil, and field management. Models can be very useful tools in this respect. Not only can they help in calculating crop water requirements and irrigation scheduling, but they can also be used to predict yields and soil salinization under different management scenarios. The SALTMED model has been developed for such an integrated management approach. To investigate how much water can be saved with minimum yield reduction, a controlled greenhouse experiment was established. Different water amounts were applied to cucumber (Cucumis sativus L.) ranging from 100% to 30% irrigation requirement. The SALTMED model has been employed using the observed data of soil water, soil salinity, and yield. The model was successfully calibrated using 100% crop evapotranspiration (ETc), soil water, and salinity data. This was followed by successful model validation using the other deficit irrigation treatments (80%, 60%, 40%, and 30% ETc). The results of calibration and validation of the SALTMED model showed that the model can simulate adequately soil water content, soil salinity, and final cucumber yield.

Switchgrass yield and stand dynamics from legume intercropping based on seeding rate and harvest management

Abstract: Intercropping legumes may reduce inputs and enhance sustainability of forage and feedstock production, especially on marginal soils. This approach is largely untested for switchgrass (Panicum virgatum L.) production, yet producer acceptance should be high given the traditional use of legumes in forage/agricultural systems. Our objectives were to evaluate three cool-season and two warm-season legumes and their required densities to influence yield and supply nitrogen (N) compared to three inorganic N levels (0, 33, and 66 kg N ha -1 (0, 30, and 60 lb N ac -1 )) at three locations in Tennessee (Knoxville (Sequatchie Silt Loam), Crossville (Lilly Loam), and Milan (Loring B2 Series)). Fall of 2010 seeded, cool-season legumes (red clover (Trifolium pratense L.), hairy vetch (Vicia villosa L.), ladino clover (Trifolium repens L.)), arrowleaf clover (Trifolium vesiculosum L.), and a spring of 2011 seeded, warm-sea- son legume (partridge pea (Chamaecrista fasciculate L.)) were interseeded into switchgrass at three (high, medium, and low) seeding rates each in two experiments. Harvest treatments were annual single, postdormancy biofuel (Experiment One) or integrated forage-biofuel (preanthesis and postdormancy; Experiment Two). Year one yield impacts were minimal. During the second harvest year, legumes increased yield versus Year 1; in general, yields for 33 and 67 kg N ha -1 did not differ from those for red clover, hairy vetch, ladino clover, or partridge pea (p < 0.05). Arrowleaf clover yields were not different from 0 kg N ha -1 . Forage biomass yields were generally more responsive to legumes (p < 0.05) than the biomass regime. Legume persistence after three years was generally greatest for ladino clover and partridge pea. Forage quality (switchgrass only) in some cases was positively influenced by legume treatments, notably hairy vetch and partridge pea (p < 0.05). Intercropping selected legumes in switchgrass may enhance forage quality and yield while reducing nonrenewable inputs, fertilizer costs, and emissions/runoff to air and groundwater.

Ammonia and nitrous oxide gas loss with subsurface drainage and polymer-coated urea fertilizer in a poorly drained soil

Abstract: Gaseous nitrogen (N) loss from denitrification and ammonia (NH3) volatilization from poorly drained soils in corn (Zea mays L.) production can be significant, diminish production, and lead farmers to apply a high rate of N. Nitrous oxide (N2O), a greenhouse gas that is emitted during denitrification, has a high global warming potential that contributes to climate change. Reducing gaseous N loss from poorly drained soils through drainage and N management in corn production is essential to minimizing the environmental impact and maintaining high yields. The objective of the study was to determine how subsurface tile drainage and applications of polymer-coated urea (PCU) affect soil N2O emissions and N fertilizer-induced NH3 volatilization loss from a claypan soil. Drainage water management treatments consisted of conventional subsurface tile drainage, managed subsurface tile drainage, and no-drainage in combination with N fertilizer source (noncoated urea [NCU] and PCU). Subsurface drainage treatments did not significantly (p ≤ 0.05) affect cumulative soil N2O emissions and NH3 volatilization loss compared to no-drainage. Averaged over 2010 to 2013, cumulative soil N2O emissions from PCU was 2% of applied N, and NCU was 4% of applied N. Yield-scaled soil N2O emissions were reduced 53% with PCU compared to NCU. The percentage fertilizer loss from NH3 volatilization was significantly (p ≤ 0.05) reduced from 2.8% with NCU to 0.8% with PCU. These results suggest that use of PCU may assist in reducing cumulative losses of N2O and NH3 from poorly drained claypan soils, but drainage systems operating under this study9s environmental conditions did not affect gaseous N losses.