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One laboratory and three field experiments were conducted to determine physiological mechanisms through which barley (Hordeum vulgare L.) monocrops and barley-pea (Pisum sativum L.) intercrops suppressed growth and seed production of two weedy species of mustard (Brassica kaber (DC) L.C. Wheeler and B. hirta Moench). The study quantified the negative effects of nitrogen (N) and light deficits on mustard's photosynthetic performance, and the reduction in mustard's access to N and light resources that resulted from the presence of barley and pea. The work demonstrated that crop competition for resources was paralleled by reductions in mustard's photosynthetic performance, above-ground biomass and seed production. It also showed that the negative effects of the crops on mustard's resource status, photosynthetic performance, and yield could be overcome, at least partially, by application of N fertilizer or use of a pea cultivar that intercepted less light. Mustard suffered most from crop competition when N fertilizer was not applied and when a long-vined pea cultivar that produced abundant leaf area was used in the intercrop mixtures. Instantaneous measurements of net photosynthesis, made on individual leaves early in the growing season, predicted 59–74% of the variation in mustard's final above-ground biomass and seed production.

Surplus nitrogen (N) in ground and surface water is of concern in intensive agricultural regions. Surplus N leaches during lengthy periods where annual crop systems are used in temperate regions. This paper presents a model to estimate the surplus N available for leaching to ground water beneath agricultural systems and applies the model to watersheds in an intensive maize and soybean production system. The model utilizes commonly available georeferenced data on soils, crops, and livestock, making it applicable to watersheds in many regions. The model links stocks of N in soil, crops, livestock, fertilizer and the atmosphere. Nitrogen flow centers on exchange between the soil N stocks. Nitrogen mineralization rates are defined for three soil organic matter pools, crop residue, and manure based on carbon:N ratios. Nitrogen exports from the system are harvested crops, livestock and losses to the atmosphere. Application of the model in 26 Iowa watersheds finds surpluses of 18 to 43 kg-N/ha. Surpluses exceeded measured annual nitrate-N loads in regional streams by amounts equivalent to denitrification rates in groundwater. Deficits in soil N were sufficiently small to suggest that the system is in equilibrium with soils of the region.

[1] Agricultural land uses impact leachable nitrogen (N) and erosion, indicators of the potential for nitrate and sediment contamination of water resources. This paper evaluates the potential impact of alternative land uses on leachable N, soil organic nitrogen (SON) and erosion in western Iowa watersheds using a combination of widely available models and georeferenced data. The alternative land uses increase land area under perennial cover, integrate livestock with cropping systems, and reduce inorganic fertilizer use. We used the Water Erosion Prediction Program (WEPP) to estimate erosion and a N-budget model to estimate leachable N and changes in SON. The N model described here is widely applicable because it utilizes commonly available georeferenced data on soils, crops, and livestock. Maximum annual erosion rates were estimated to be 22 Mg ha−1 under current conditions, double the regional maximum at which soil is maintained as a medium for plant growth (T). Under alternative land uses, erosion was between 1.1 Mg ha−1 and 5.5 Mg ha−1, well below T. Annual leachable N was as much as 43 kg ha−1 for current conditions, but consistently less than15 kg ha−1 under alternative land uses. Maximum SON losses were 23 kg N ha−1 under current conditions while SON increased by as much as 18 kg N ha−1 under alternative land uses. These results indicate that erosion may be minimized, leachable N could be decreased and SON may be increased by better accounting of N inputs and altering the distribution and species composition of crop and pasture systems.

Introduction Since 1990, the American market for organic foods has grown at a rate of 20% per year or more, and is now worth at least $7 billion annually. Price premiums paid to farmers for organically produced crops can increase their value substantially compared with conventionally produced crops. The potential economic advantages for organic production, coupled with increasing concerns about environmental and human health impacts of conventional farming practices, have sparked interest by farmers and researchers in the development of best management practices for organic farming systems.

During the past quarter century, growing numbers of government policy makers, scientists, consumers, and farmers have expressed concerns over the impacts of conventional farming practices on environmental quality, human health, and the economic viability of farm families and rural communities. Particularly in western Europe, and to a certain extent in the USA, Canada, and other countries, these concerns have begun to translate into changes in public policy, research priorities, and market opportunities that favor the development of low-external-input (LEI) and organic farming systems. For example, during the 1980s in Sweden, a >50% reduction in agricultural pesticide use was mandated and achieved through coordinated sets of regulations, research and extension education activities, and economic incentives (Bellinder et al., 1994; Matteson, 1995). Similar approaches have been initiated in other European countries (Matteson, 1995). Concurrently, consumer demand for organic crop and livestock products has grown 20 to 25% per annum in the USA, many European countries, and Japan (Geier, 1998; Myers and Rorie, 2001). Sales of organic products in 2000 were estimated at $7.8 billion in the USA (Myers and Rorie, 2001) and at least $7.5 billion in Europe and the UK (Soil Association, 2001). Continued growth is expected in the amount of land managed with LEI and organic methods and in associated economic activity.

Compost stability is one of the most important criteria used to evaluate compost quality. Several of the most popular methods to quantify stability are based on measurements of aerobic respiration of oxygen to carbon dioxide. This study compared two closed-vessel respiration techniques. In both methods, the evolved CO2 was absorbed by sodium hydroxide (NaOH), leading to a pressure drop in the container. The conventional technique measures absorbed CO2 by titrating the NaOH trap, limiting measurement frequency by the need to manually remove and replace the trap. The pressure sensor method (PSM) uses a datalogger to record pressure differences in the vessel, allowing several observations each hour. Samples of bedded swine manure compost (n=125) were analyzed using both the PSM and the titration method (TM). Each compost sample was also analyzed for total solids, volatile solids (VS), pH and electrical conductivity. Respiration results obtained using the PSM were compared with those obtained using the TM, with each method run on split compost samples under the same environmental conditions. Respiration rates measured by PSM and TM were highly correlated (R2 = 0.92). Respiration rates ranged from 3.64 to 10.77 mg CO2-C gVS-1 d-1, varying with feedstock and the extent of prior composting. Decreases in volatile solids and/or increases in composting time resulted in decreases in the respiration rate, but the effect of pH and electrical conductivity was not clear. For the PSM, detailed time series data also allowed dynamic observation of important changes in the respiration rate throughout the course of incubation. PSM is a sensitive and reliable method to quantify compost respiration and stability.

Introduction In 1938, C.E. Leighty described crop rotation as “the most effective means yet devised for keeping land free of weeds.” Despite the accumulation of a considerable amount of evidence to support this assertion, little has been learned over the past six decades about why, mechanistically, cropping system diversity suppresses weeds. The field experiment and modeling work described here were initiated to address this issue and focused particularly attention on the question of whether diverse rotations can achieve effective weed control through greater reliance on ecological interactions, such as seed predation, rather than herbicides.

The goal of this three-year project is to identify, promote, and assist farmers in adopting integrated crop and livestock farming systems that reduce costs, minimize negative environmental impacts, increase market opportunities and increase profits for small and mid-size family farms. The project uses a holistic systems approach that evaluates six inter-related elements: economic impact, marketing opportunities, community impact, ecosystem impact, farmer adoption, and information transfer. This paper deals with ecosystem impacts of changes in land-use, crop rotations, and farm management. A number of existing simulation models for crop growth, livestock performance, soil erosion, nitrogen dynamics, tillage and manure management, and energy consumption are being used to evaluate impacts of alternative management strategies on indicators of ecosystem sustainability. Databases on soil and weather needed for these models are clustered and interconnected by means of web-based interfaces. This paper describes the models to be integrated, initial scenarios for future land-use, our approach to defining representative farms, the current status of the web based model development, and some results.

Concerns over environmental and human health impacts of conventional weed management practices, herbicide resistance in weeds, and rising costs of crop production and protection have led agricultural producers and scientists in many countries to seek strategies that take greater advantage of ecological processes and thereby allow a reduction in herbicide use. This book provides principles and practices for ecologically based weed management in a wide range of temperate and tropical farming systems. After examining weed life histories and processes determining the assembly of weed communities, the authors describe how tillage and cultivation practices, manipulations of soil conditions, competitive cultivars, crop diversification, grazing livestock, arthropod and microbial biocontrol agents, and other factors can be used to reduce weed germination, growth, competitive ability, reproduction and dispersal. Special attention is given to the evolutionary challenges that weeds pose and the roles that farmers can play in the development of new weed-management strategies.

Because of expanding markets for high-value niche crops, opportunities have increased for the production of medicinal herbs in the USA. An experiment was conducted in 2001 and 2002 near Gilbert, IA, to study crop performance, weed suppression, and environmental conditions associated with the use of several organic mulches in the production of two herbs, catnip (Nepeta cataria L.) and St. John’s wort (Hypericum perforatum L. ‘Helos’). Treatments were arranged in a completely randomized design and included a positive (hand-weeded) control, a negative (nonweeded) control, oat straw, a flax straw mat, and a nonwoven wool mat. Catnip plant height was significantly greater in the oat straw than the other treatments at 4 wk through 6 wk in 2001; at 4 to 8 wk in 2002, catnip plant height and width was significantly lower in the negative control compared with the other treatments. Catnip yield was significantly higher in the flax straw mat than all other treatments in 2001. In 2002, St. John’s wort yields were not statistically different in any treatments. All weed management treatments had significantly fewer weeds than the non-weeded rows in 2002. Total weed density comparisons in each crop from 2 yr showed fewer weeds present in the flax straw and wool mat treatments compared with positive control plots. There was no significant weed management treatment effect on the concentration of the target compounds, nepetalactone in catnip and pseudohypericin–hypericin in St. John’s wort, although there was a trend toward higher concentrations in the flax straw treatment.

Two field experiments were conducted to investigate effects of soil conditions and crop genotypes on canopy relations and yield responses of two crops (barley and field pea) and a weed (white mustard) sown in trispecific mixtures. Treatments involved variations in nitrogen supply, water supply and pea genotype. Photosynthetic surface area and seed yield of pea were increased by increasing water supply, but were unaffected or diminished by increasing nitrogen supply. ‘Century’ pea produced about four times more surface area than ‘Alaska’ pea. Under irrigated, low-nitrogen conditions, seed yields of the two pea varieties were similar, but under high-nitrogen conditions, seed yield of the smaller variety declined significantly. Under high-nitrogen conditions, the larger ‘Century’ pea constituted a large proportion of the upper levels of the mixed-species canopies, while the smaller ‘Alaska’ pea was overtopped and shaded by mustard. Increasing nitrogen or water supply increased photosynthetic surface area of barley, but most of these increases occurred at canopy levels where only small amountse of photosynthetically active radiation ( par ; or Qpa) were available. Increasing nitrogen supply had a much stronger positive effect on barley seed yield than did increasing water supply. Use of ‘Century’ pea rather than the smaller ‘Alaska’ pea decreased barley's photosynthetic surface area, access to Qpa, and seed yield; these effects were particularly pronounced under low-nitrogen conditions. In terms of canopy development, Qpa interception, and yield, nitrogen fertilizer benefitted mustard much more than it did either crop species. Averaged across irrigation regimes, pea genotypes, and years, application of N increased mustard biomass by 472%, but increased total crop seed yield only 31%. Increasing water supply had much less effect than nitrogen fertilizer on mustard's production of photosynthetic surface area and biomass. Use of ‘Century’ pea rather than the smaller ‘Alaska’ pea resulted in increased shading and decreased growth of mustard. Results of the experiments indicate that soil conditions, the relative values and desired yields of the different component crops, and the degree of priority placed on weed suppression should all bear on the choice of appropriate crop varieties for intercropping systems. When the snaller ‘ALaska’ pea was used in the intercrop/weed mixtures, a large total amount of crop seed (pea + barley) was produced under high-water, low-nitrogen conditions. Total crop seed yield was greatest, however, when the larger ‘Century’ pea was used in the mixtures and nitrogen fertilizer was applied. Mustard produced very little biomass under the former conditions, but produced a substantial amount of biomass under the latter conditions.

Transdisciplinary weed research (TWR) is a promising path to more effective management of challenging weed problems. We define TWR as an integrated process of inquiry and action that addresses complex weed problems in the context of broader efforts to improve economic, environmental and social aspects of ecosystem sustainability. TWR seeks to integrate scholarly and practical knowledge across many stakeholder groups (e.g. scientists, private sector, farmers and extension officers) and levels (e.g. local, regional and landscape). Furthermore, TWR features democratic and iterative processes of decision-making and collective action that aims to align the interests, viewpoints and agendas of a wide range of stakeholders. The fundamental rationale for TWR is that many challenging weed problems (e.g. herbicide resistance or extensive plant invasions in natural areas) are better addressed systemically, as a part of broad-based efforts to advance ecosystem sustainability, rather than as isolated problems. Addressing challenging weed problems systemically can offer important new leverage on such problems, by creating new opportunities to manage their root causes and by improving complementarity between weed management and other activities. While promising, this approach is complicated by the multidimensional, multilevel, diversely defined and unpredictable nature of ecosystem sustainability. In practice, TWR can be undertaken as a cyclic process of (i) initial problem formulation, (ii) 'broadening' of the problem formulation and recruitment of stakeholder participants, (iii) deliberation, negotiation and design of an action agenda for systemic change, (iv) implementation action, (v) monitoring and assessment of outcomes and (vi) reformulation of the problem situation and renegotiation of further actions. Notably, 'purposive' disciplines (design, humanities and arts) have central, critical and recurrent roles in this process, as do integrative analyses of relevant multidimensional and multilevel factors, via multiple natural and social science disciplines. We exemplify this process in prospect and retrospect. Importantly TWR is not a replacement for current weed research; rather, the intent is to powerfully leverage current efforts. Public domain – authored by a U.S. government employee

Weed management is a critically important activity on both agricultural and non-agricultural lands, but it is faced with a daunting set of challenges: environmental damage caused by control practices, weed resistance to herbicides, accelerated rates of weed dispersal through global trade, and greater weed impacts due to changes in climate and land use. Broad-scale use of new approaches is needed if weed management is to be successful in the coming era. We examine three approaches likely to prove useful for addressing current and future challenges from weeds: diversifying weed management strategies with multiple complementary tactics, developing crop genotypes for enhanced weed suppression, and tailoring management strategies to better accommodate variability in weed spatial distributions. In all three cases, proof-of-concept has long been demonstrated and considerable scientific innovations have been made, but uptake by farmers and land managers has been extremely limited. Impediments to employing these and other ecologically based approaches include inadequate or inappropriate government policy instruments, a lack of market mechanisms, and a paucity of social infrastructure with which to influence learning, decision-making, and actions by farmers and land managers. We offer examples of how these impediments are being addressed in different parts of the world, but note that there is no clear formula for determining which sets of policies, market mechanisms, and educational activities will be effective in various locations. Implementing new approaches for weed management will require multidisciplinary teams comprised of scientists, engineers, economists, sociologists, educators, farmers, land managers, industry personnel, policy makers, and others willing to focus on weeds within whole farming systems and land management units.

This paper deals with ecosystem, social, and economic impacts of changes in land-use, crop rotations, and farm management in two counties in western Iowa. In this region, expansion of farm size, increase in the average age of farmers, and reductions in labor availability have been continuous processes, caused by agro-economic and social factors over the last several decades. The landscape of the Loess rolls in western Iowa includes fields with hill slopes ranging from 0 to beyond 14%. Many of the soils are highly erodible. A two-year rotation of corn-soybeans is currently the most common cropping system, and results in considerable soil loss from bare soils in winter and spring. On many farms livestock production has dramatically decreased or disappeared entirely over the last 25 years. Our project focuses on re-integration of crop and livestock production. Our main goal is to investigate the ecological impacts of replacing chemical fertilizers by animal manure and of including perennial crops and pastures in the cropping system. The I-FARM simulation model is being used to estimate the ecological effects of various crop and livestock production systems at the farm scale. When using local land-use data and the simulation model, we are able to predict effects of alternative cropping systems and livestock production at the county scale on soil loss, nutrient balances, and associated labor requirement. The paper will show some results of simulations in terms of crop diversity patterns, livestock to be raised in a closed system at the county level, fertilizer replaced by manure, farm labor required, erosion and nutrient control, and economic consequences. We also present some social trends.

(1) The hypothesis that intercrops have fewer, smaller weeds than their component sole crops was tested by sowing pure and mixed crops of barley and field pea at commercial densities and at double these densities in two fields near Ithaca, New York, U.S.A. The effect of these cropping systems on the species composition of associated weeds was also investigated. (2) For both sole crops and intercrops weed productivity decreased and crop productivity increased with higher crop density. (3) Crop treatments had no effect on weed numbers relative to unplanted control treatments. (4) For both highand low-density treatment series, weed productivity decreased in the order unplanted controls > pea sole crops > intercrops > barley sole crops. Weed productivity in the high-density intercrop, formed by sowing together the two low-density sole crops, was not significantly different from weed productivity in the low-density barley sole crop. (The estimated difference+S.E. was 0 77+21 8 g m-2.) (5) Weed suppression by barley may have resulted from competition for soil moisture since weeds which grew in barley sole crops or barley/pea intercrops had lower predawn water potentials than weeds in unplanted controls or in pea sole crops. (6) Within both density series, above-ground crop productivity decreased in the order barley > intercrop > pea. Yield of the high-density intercrop was nearly equal to the sum of yields of the two low-density sole crops. (7) Relative abundance of the major weed species differed among crop treatments. In general, the most dominant weed species was more suppressed than other species as crop productivity increased. This response is explained in terms of a dominance hierarchy.