Wild oat (Avena fatua L.) and false cleavers (Galium spurium L.) are currently a challenge to manage in less competitive crops such as flax (Linum usitatissimum L.). Increasing the functional diversity in crop rotations can be an option to improve weed management. Nonetheless, this strategy had not been tested in flax in western Canada. A 5-yr (2015 to 2019) crop rotation study was carried at three locations in western Canada to determine the effect of diverse flax-based crop rotations with differences in crop species, crop life cycles, harvesting time, and reduced herbicides on managing A. fatua and G. spurium. The perennial rotation (flax–alfalfa [Medicago sativa L.]–alfalfa–alfalfa–flax) under reduced herbicide use was found to be the most consistent cropping system, providing A. fatua and G. spurium control similar to the conventional annual flax crop rotation (flax–barley [Hordeum vulgare L.]–flax–oat [Avena sativa L.]–flax) with standard herbicides. At Carman, this alfalfa rotation provided even better weed control (80% A. fatua, 75% G. spurium) than the conventional rotation. Furthermore, greater A. fatua control was identified compared with a conventional rotation in which two consecutive winter cereal crops were grown successfully in rotation (flax–barley–winter triticale [×Triticosecale Wittm. ex A. Camus (Secale × Triticum)]–winter wheat [Triticum aestivum L.]–flax). Incorporation of silage oat crops did not show consistent management benefits compared with the perennial alfalfa rotation but was generally similar to the conventional rotation with standard herbicides. The results showed that perennial alfalfa in the rotation minimized G. spurium and A. fatua in flax-cropping systems, followed by rotations with two consecutive winter cereal crops.

Research in Kansas from 1983 to 1986 evaluated early preplant (30 to 45 days) and late preplant (10 to 14 days) herbicide treatments for weed control before ridge-till planting in a soybean and sorghum rotation. Control of fall panicum and common lambsquarters at planting time averaged at least 95% for all early preplant and 92% for late preplant treatments. Where no preplant treatment was used, heavy weed growth in spring delayed soil dry-down, which resulted in poor ridge-till planting conditions and reduced plant stands, and ultimately reduced sorghum grain yields by 24% and soybean yields by 12%. Horsenettle population declined significantly, and honeyvine milkweed population increased. Smooth groundcherry populations fluctuated from year to year with no overall change.

A survey of 146 fields was conducted to investigate herbicide performance in winter wheat-producing areas of southwestern Nebraska during August and September of 1986. Only 55% of the fields received an excellent rating for weed control and stubble quality; one third rated as unacceptable. Weed control after wheat harvest was improved by planting ‘Bounty 310’, ‘Siouxland’, ‘Vona’, and ‘Centura’ winter wheat cultivars rather than ‘Mustang’, ‘Hawk’, ‘Pioneer 2656’, and ‘Wings'. Fertilizing winter wheat in the fall, planting wheat at the optimum date, high wheat stem density, using a winter wheat-corn-fallow rotation, not spraying herbicides after wheat harvest on days that it rained or air temperature exceeded 35 C, and spraying weeds when they were small also improved weed control in wheat stubble. Nine months after wheat harvest, fields treated with atrazine before July 16 had more volunteer wheat than fields treated later.

Studies were conducted from 1990 through 1994 near Tifton, GA, on the population dynamics of yellow nutsedge and certain annual weeds in peanut—corn and peanut—cotton rotations. Converse rotation sequences were included to eliminate year effects. Continuous fallow plots (noncrop) were included for comparison. Within each crop, including fallow, were 3 levels of weed management: low, moderate, and intensive. Weed densities and numbers of yellow nutsedge tubers were not affected by crop rotations, but they were affected by individual crops and weed management systems in each crop. Fallow plots, including those with intensive fallow weed management using tillage and nonselective herbicides, consistently contained more yellow nutsedge plants and tubers than other plots. Moderate and intensive weed control systems in peanut and cotton reduced yellow nutsedge densities and tubers, but only peanut yields were increased by intensive weed management. Weed management systems did not affect yellow nutsedge densities in corn, although yields were increased by moderate and intensive systems due to improved control of other weeds. Our results suggest that uninterrupted plantings of peanut, corn, or cotton with moderate levels of weed management are generally sufficient to suppress yellow nutsedge and allow for optimum crop yield. If fields are fallow, yellow nutsedge population densities and tubers will increase exponentially, even with intensive fallow weed management.

A sorghum-sudangrass hybrid [Sorghum bicolor (L.) Moench. x Sorghum sudanense (P.) Stapf. ‘DEKALB SX17+’] (SSH) and foxtail millet [Setaria italica (L.) Beauv.] (FM) were evaluated for their effects on weed populations when grown for forage and as land conditioners prior to late-summer, no-till planting of alfalfa (Medicago sativa L. ‘Arc’). Both grasses established well in no-till situations, except for FM when excessive mulch impeded seed placement or seedling summer-annual weeds were not destroyed at planting time. SSH was the better competitor; after both were planted into a dense stand of seedling summer-annual weeds, SSH outyielded the weeds while FM did not. Both grasses suppressed weeds and enhanced subsequent alfalfa establishment. Obtaining adequate alfalfa stands was not a problem in no-till seedings: seedling populations often exceeded 300/m2 3 to 6 weeks after planting. Lack of adequate weed control was associated with stand losses in which disease was also a factor. Biennial and perennial broadleaf species were the predominant weeds. Prior cropping of SSH or FM is a valuable option for growers wishing to establish alfalfa without tillage, particularly when summer forage is useful.

Of 78 biotypes of wild radish (Raphanus raphanistrum) collected from Western Australia (WA), 42% were resistant and 14% intermediate to acetolactate synthase (ALS)-inhibiting herbicides. Based on the LD50 and GR50 ratios, the resistant biotype K96071 was 81-fold more resistant to chlorsulfuron and 114- to 116-fold more resistant to metosulam than the susceptible biotype K96041. More resistant biotypes were found in northern zones than in southern zones of WA. Resistant biotypes evolved after five applications of chlorsulfuron in a predominantly cereal–lupin rotation. Where resistant biotypes were found, ALS-inhibiting herbicides were not rotated with herbicides with different modes of action as frequently as in fields with susceptible biotypes. Cross-resistance to chlorsulfuron and metosulam was found in the resistant biotypes even though only 15% of the 78 biotypes were exposed to two applications of metosulam over a 10-yr period. All 78 biotypes were effectively controlled by simazine and 2,4-D amine.

A survey of 174 fields was conducted during August and September of 1998 to investigate effects of cultural and herbicide practices on postharvest weed control in winter wheat stubble fields across western and southern Nebraska. Seventy-four percent of the fields were seeded at rates of 67 to 100 kg/ha, with 60% of the wheat seeded in rows spaced 25 cm apart. Wheat seeded in east–west rows contained 98% more stinkgrass and 82% more tumble pigweed than wheat seeded in north–south rows. Sixty-nine percent of winter wheat stubble fields were rated excellent for weed control. Postharvest weed control with herbicides was not affected by row spacing. In western Nebraska, density of tumble pigweed and Russian thistle was greater when wheat seeding rate was 50 kg/ha than at higher seeding rates. Short-stature winter wheat cultivars had greater densities of Pennsylvania smartweed and toothed spurge than taller cultivars. The most common winter wheat cultivars were ‘Arapahoe’ (34%) and ‘Alliance’ (17%). Weed control was positively correlated with number of winter wheat stems per square meter (r = 0.22∗∗). Density of several weed species was greater in fields seeded with a disk than with a hoe drill. The most common crop rotations sampled were winter wheat–corn–fallow (50%), winter wheat–fallow (18%), and winter wheat–corn–soybean (13%). Winter wheat yields and wheat stem densities were greater and weed density was less when winter wheat was seeded after an 11- to 14-mo fallow period rather than a 0- to 5-mo period.

Three field trials were conducted in south Georgia under irrigated conditions in 2002/2003 and 2003/2004 to evaluate the effects of imazapic residues on oat growth and yield. Imazapic at 70 g ai/ha was applied during the first weeks of May, June, July, August, and September to bare soil. No additional tillage was performed after the herbicide application. Oats (cv. Coker 227) were planted the first week of October. Oat plant populations were not reduced by any timing of imazapic. Generally, oat plant heights and forage yields were reduced when imazapic was applied in August and September (1–2 mo before planting). Grain yields were not reduced by any timing of imazapic. Results of these tests suggest that the current 18-mo rotational restriction for oats following an application of imazapic could be reduced to 4 mo.

The economic feasibility of soybeans, grain sorghum, and corn in annualrotation with winter wheat using reduced tillage and no-tillage systems inthe Central Great Plains was evaluated, with continuous wheat and grainsorghum also analyzed. Net returns were calculated using simulated yield andprice distributions based on historical yields, two historical annual priceseries, and 2011 costs. Stochastic Efficiency with Respect to a Function wasused to determine the preferred strategies under various risk preferences.The no-till wheat-soybean and reduced-till wheat-soybean systems are thefirst and second most preferred, regardless of the level of riskaversion.

Conservation agricultural systems rely on three principles to enhance ecosystem services: (1) minimizing soil disturbance, (2) maximizing soil surface cover and (3) stimulating biological activity. In this paper, we explore the concept of diversity and its role in maximizing ecosystem services from managed grasslands and integrated agricultural systems (i.e., integrated crop–livestock–forage systems) at the field and farm level. We also examine trade-offs that may be involved in realizing greater ecosystem services. Previous research on livestock production systems, particularly in pastureland, has shown improvements in herbage productivity and reduced weed invasion with increased forage diversity but little response in terms of animal production. Managing forage diversity in pastureland requires new tools to guide the selection and placement of plant mixtures across a farm according to site suitability and the goals of the producer. Integrated agricultural systems embrace the concept of dynamic cropping systems, which incorporates a long-term strategy of annual crop sequencing that optimizes crop and soil use options to attain production, economic and resource conservation goals by using sound ecological management principles. Integrating dynamic cropping systems with livestock production increases the complexity of management, but also creates synergies among system components that may improve resilience and sustainability while fulfilling multiple ecosystem functions. Diversified conservation agricultural systems can sustain crop and livestock production and provide additional ecosystem services such as soil C storage, efficient nutrient cycling and conservation of biodiversity.

Producers in the semi-arid Dark Brown Chernozemic (Typic Boroll) soil zone of the Canadian Prairie are contemplating changes to land-use practices, moving away from conventional high-input production systems that specialize in one or two annual grain crops to more diversified and extended cropping systems that use reduced-input and organic management practices. This study examined the economic merits of nine cropping systems, consisting of a factorial combination of three input management methods and three levels of cropping diversity. It was conducted over the 1996–2007 period on a loam soil at Scott, Saskatchewan. The input treatments were: (1) high input (HIGH), which used conventional tillage and full recommended rates of fertilizers and pesticides ‘as required’; (2) reduced input (RED), which used conservation tillage and integrated weed and nutrient management practices in an effort to lower requirements for fuel, fertilizers and pesticides; and (3) organic input (ORG), which used tillage, non-chemical pest control, higher seeding rates, delayed seeding and legume crops to replenish soil nutrients. The crop diversity treatments included: (1) a fallow-based rotation with low crop diversity (LOW); (2) a diversified annual rotation of cereal, oilseed and pulse grains (DAG); and (3) a diversified rotation using annual grains and perennial forages (DAP). All crop rotations were 6 years in length. At the 2007 input costs and prices, average net returns and 12-year net present values were higher for organic than for non-organic treatments, with the ORG input/LOW crop diversity system being the most profitable (net returns=$234 ha−1 yr−1 and net present value=$1953 ha−1). Net returns averaged about 10% less for ORG/DAG compared to the most profitable system, and about 22% less for HIGH/DAG and RED/DAG (the best non-organic systems). The DAP treatments that included forage were not economically competitive with the other treatments, often producing economic losses. The relative profitability of the organic treatments was highly dependent on the existence of organic price premiums. When price premiums for organic crops were reduced to less than 70% of the 2007 levels, the organic treatments were less profitable than the comparable non-organic treatments. The organic treatments also experienced significantly lower (and often negative) net returns compared to the non-organic treatments during completion of the 3-year organic certification period. We estimated that it required 5–7 years after completion of certification for the organic treatments to break even with the comparable non-organic treatments. Thereafter the organic treatments produced consistently higher net earnings. Production costs averaged 16% lower with ORG management compared to the HIGH-input treatments, but we found little difference in total costs between the respective HIGH- and RED-input treatments. The organic treatments also displayed lower income variability than the non-organic treatments, with the ORG/LOW system being preferred by risk-averse producers, who do not subscribe to all-risk crop insurance, and with the ORG/LOW and ORG/DAG systems preferred by low and medium risk-averse producers when having the added financial protection from the Canada/Saskatchewan all-risk crop insurance program.

Many lessons in long-term cropping systems experiments are learned from practical experience. I have conducted large-scale, long-term, multidisciplinary dryland and irrigated cropping systems experiments with numerous colleagues at university and government research stations and in farmers' fields in the USA and in developing countries for 25 years. Several practical lessons learned through the years are outlined in this short commentary. While some of these lessons learned may be intrinsically obvious, results of many cropping systems experiments have not been published in scientific journals due to fatal flaws in experimental design, improper transitioning between phases of the experiment and many other reasons. Ongoing active support by stakeholders is critical to maintain funding for long-term cropping systems studies. Problems and unexpected challenges will occur, but scientists can often parlay these into opportunities for discovery and testing of new hypotheses. Better understanding and advancement of stable, profitable and sustainable cropping systems will be critical for feeding the world's projected 10 billion people by the mid-21st century.

Sustainable cropping systems use crop diversity as a foundation to reduce the environmental impacts of agrichemicals and risks of pest and disease outbreaks. Although greater diversity in the agricultural landscape is an important goal, the decisions of individual farmers determine the diversity of crops used in each farming system. Therefore, it is essential to gain an understanding of important factors in farmers' decisions as part of any proposed solution to low crop diversity. Our objective was to develop and test an integrated socioeconomic model of farmers' decisions on crop rotations as an indicator of overall crop diversity. The model incorporated measures of farmers' attitudes, net household income, control over decisions, social norms, and regional location to address the social, economic, and environmental factors of crop diversity. Mail survey responses from 197 farmers from a western Corn Belt county in 1998 supplied the data for the analysis. Location had the strongest influence on crop diversity in the model, on the basis of a standardized beta statistic of 0.46 in the ordinary least squares regression analysis. Farmers in the region with the highest degree of sloping land had significantly higher crop diversity than farmers in the most productive, relatively flat area. Lower household net income and positive attitudes toward crop rotations were also associated with higher crop diversity. We believe social norms and control would exert more influence in uncertain decisions. The results of this study suggest that, to maintain and possibly expand crop diversity in the future, targeting farmers in sloping landscapes with positive attitudes toward rotations would be the best approach to focus economic incentives for diverse crop rotations and technical support from Extension. In any effort to support crop diversity greater than a typical cornsoybean rotation, it is also critical to preserve integrated forage/crop/livestock systems. Further adaptation and application of our behavioral model in other settings would help to better evaluate, understand, and target the integrated decisions people make relative to crop diversity.

The Wisconsin Integrated Cropping Systems Trial has been comparing different farming systems on two farm sites in southern Wisconsin since 1989. Inexplicable differences in the yields of corn grown in three systems stimulated research on the relationship between yield and the dynamics of root growth. The three systems were continuous corn with mineral fertilizer (CS1), corn—soybean—winter wheat—red clover (CS3), and corn—oat + alfalfa—alfalfa with dairy manure applied (CS5). Four or five sequential root samplings were taken each growing season on two sites for 3 years. Soil monoliths were taken from around the base of the plant and washed out over a 1-mm sieve. Estimates were obtained of the length and health of roots from different nodes that were attached to the crown of the plant. The seasonal accumulation of root length was estimated by summing the maximal root length produced at each root node. Corn grown in monoculture averaged 7.5 Mg of grain/ha, which was similar to corn grown after red clover green manure (7.3 Mg/ha) but less than corn grown after alfalfa with manure (8.5 Mg/ha). Contrary to expectations, corn grown in monoculture averaged 26% more root length over the season than CS3 and 12% more length than CS5. The differences were mostly due to increased production of later sets of roots (nodes 6–9) for the corn in monoculture. However, for the first sets of nodes (seminal—node 5) the percentage of healthy roots was lower in the monoculture system (59%) than in CS3 (63%) or CS5 (76%). The increased root growth associated with corn grown in monoculture may be a response to poor root health. Regressions with root growth accounted for a large amount of the variation in grain yields. Corn grown after alfalfa with manure achieved higher yields with less roots than did corn grown in monoculture. Yields in the former system plateaued at root lengths of 1 cm/cm3 and greater, producing grain yields that ranged from 8 to 10 Mg/ha. Corn grown in CS1 and CS3 showed curvilinear responses with calculated yield maxima of 8.7 and 9.9 Mg/ha at root lengths of 2.12 and 1.74 cm/cm3, respectively. Intensifying the use of rotations and organic manures seemed to increase the ability of the corn rooting system to support grain yields. The cause for this greater efficiency is not yet clear, though root health may be an important factor.

Interest in developing more sustainable cropping systems has led to renewed interest in legumes as N sources for crops. We conducted a 2-year study to compare the effects of green manure, green manure plus fertilizer, and fertilizer on wheat yield and N leaching potential. In 1991–92, wheat following corn and receiving 0, 45, or 90 kg N/ha was compared with wheat planted after plowing the autumn regrowth of red clover/johnsongrass hay (supplemented with alfalfa) that supplied 107 kg total N/ha. In 1992–93, wheat following corn and receiving 90 kg N/ha was compared with wheat following hay regrowth that either received fertilizer N at 45 kg/ha or 90 kg N/ha or was supplemented with alfalfa (total of 123 kg N/ha). Yield with only green manure averaged 65% of yield with 90 kg N/ha. Yields with green manure plus 45 or 90 kg N/ha were not different from yield with 90 kg N only. The first year, soil to a depth of 30 cm declined from as high as 40 kg/ha in the fall to less than 10 kg/ha as wheat growth increased in the spring. In contrast, concentration averaged 20 kg/ha throughout the growing season. Trends in soil inorganic N were similar the second year. Profile nitrate distribution indicated a greater potential for N leaching with fertilizer than with green manure. Soil from the site was used in a laboratory incubation study to determine the rate of N mineralization from white clover at 10°C. An average of 80% of the clover N was recovered as soil inorganic N; however, in the field study, recovery (soil inorganic N in the 0 to 30-cm zone + Nin above-ground wheat biomass) was only 21%. Supplementing green manures with spring applications of fertilizer N could decrease the leaching loss without decreasing wheat yield.

Sustainable rainfed cropping systems are needed in the Pacific Northwest of the United States to reduce or eliminate wind and water erosion, improve soil quality, and control weeds with reduced chemical inputs. A grass seed cropping system is excellent for improving soil quality and for controlling erosion, and can be grazed by sheep to produce meat and wool Tilla ge and residue management methods that create a rough surface to reduce wind and water erosion and increase water infiltration include: use of a chisel to create large clods; leaving residue on the surface; and use of the Paratill to shatter the soil to increase water infiltration with little disturbance of the soil surface. Including a legume in the rotation may help to break disease cycles, add N and C to the soil, and improve soil biological properties. The use of surface residues and tillage to control erosion and increase water infiltration may demand new approaches to weed contro I Rhizobacteria that attack the roots of weeds but not of wheat may reduce the need for chemica I herbicides. Research being conducted on these techniques in the Pacific Northwest of the United States and in other countries should soon result in guidelines for sustainable agricultural systems for the dryland, rainfed areas of the world.

We conducted a field experiment within a low-input reduced tillage trial to determine how a cover crop affects inoculum levels of vesicular-arbuscular mycorrhizal (VAM) fungi. Plots with and without the hairy vetch cover crop were established on September 30, 1993, under moldboard plow (MP), chisel-disk (CD), and no-till (NT) treatments in low-input (LI) management, and MP in conventional (CONV) management. We conducted a 3-week colonization assay in the greenhouse with bahiagrass seedlings to assess the relative colonization potential of the soils in the fall and following spring. Hairy vetch roots were colonized by indigenous VAM fungi by 65 days after planting, with plants from NT being more colonized than plants from MP or CD plots. Spore populations were greater in the LI than in the CONV system. The beneficial effect of the cover crop on VAM spore populations in soil was manifested in the spring, with the Glomus type group more abundant in plots with cover than without it. The greenhouse bioassay showed that colonization potential of spring 1994 soil samples was higher in plots with cover than without cover for both the LI and CONV systems. Just one season of an overwintering cover crop of hairy vetch increased the inoculum of VAM fungi the following spring before the next cash crop was planted.

We analyzed two sets of farm policy options, representing different ideological approaches to government involvement in agriculture, to estimate their effects on the relative economic attractiveness of “sustainable” and “conventional” farming systems. The mandatory supply control approach, through strict acreage limitations on program crops, represents a strong government role in commodity supply management. The Normal Crop Acreage approach, on the other hand, allows farmers greater flexibility in deciding what crops to grow. We used economic models of five pairs of case study farms in different agroclimatic areas of South Dakota, covering corn-soybean, spring wheat, and winter wheat growing regions. Mandatory restrictions on the planted acreage of “program” crops, including soybeans, were found to favor the conventional systems, because they induced high prices for crops that predominate in conventional systems, especially com, soybeans, and wheat. In principle, however, mandatory acreage controls could require compliance with certain sustainable agriculture practices. Normal Crop Acreage (NCA) proposals can encourage greater use of sustainable farming systems. Where conventional corn and soybean production is relatively profitable, as in parts of eastern South Dakota, NCA options by themselves appear insufficient to induce changeovers to sustainable cropping systems. In wheat growing areas of northern and western South Dakota, however, where the two systems oflen are about equally profitable, NCA policies could promote sustainable systems, particularly if deficiency payments are not reduced for harvesting legumes and other non-program crops on NCA base. To have this positive effect, NCA policies must be introduced gradually and structured to limit adverse effects on the markets for legumes and other non-program crops that are important in sustainable rotations.

People are becoming more aware that our soil resources are as vulnerable to degradation as air or water, but criteria are needed to learn how soil quality is changing. Our objectives in this review are: (1) to illustrate that interactions between human and natural factors determine soil quality; (2) to identify indicators that can be used to evaluate human-induced effects on soil quality; and (3) to suggest soil and crop management strategies that will sustain or improve soil quality. The physical, chemical, and biological processes and interactions within the soil are critical factors affecting all indicators of soil quality. The biological processes are especially important because they provide much of the resiliency or buffering capacity to ameliorate stress. Presumably, no single soil or crop management practice will guarantee improved soil quality, but conservation tillage, cover crops, and crop rotations are practices that may be effective. Alley or narrow-strip cropping may facilitate adoption of several of those agronomic practices and increase temporal and spatial diversity across the landscape. To maintain or possibly improve soil quality and simultaneously address a growing waste disposal problem, we suggest that urban lawn and newspaper waste be evaluated as carbon sources. We conclude that the most critical factor, regardless of the soil and crop management strategy, is to recognize that carbon is an essential element for improving soil quality in the U.S. and around the world.

Farm programs influence the profitability of a crop rotation through five effects: (1) a deficiency payment (DP) effect, (2) an acreage reduction (ARP) effect, (3) a base effect, (4) a crop price effect, and (5) a risk reduction effect. This study initially examines ARP and DP effects of the 1985 Farm Bill on the relative profitability of a low-input rotation and a grain-intensive conventional rotation in Washington state over 1986–1990. In years of low deficiency payments or high foregone returns from ARP land, the low-input green manure rotation was competitive with the conventional rotation but lost its advantage in years of low ARP costs or high deficiency payments. Long-runincentives to maintain wheat base introduced a consistent bias against the low-input green manure rotation. Planting flexibility options proposed during the 1990 Farm Bill debate could reduce farm program barriers to green manure and other low-input rotations. The Bush Administration's Normal Crop Acreage (NCA) proposal, which was not accepted in the 1990 legislation, would have largely eliminated base erosion for the green manure rotation in this study. More importantly, non-ARP green manure acreage would have qualified for deficiency payments under the NCA, thereby sharply increasing the low-input rotation's relative profitability. Proposals like the NCA might receive further attention in the future due to environmental concerns, fiscal pressures, or possible trade agreements requiring multilateral phaseout of agricultural subsidies coupled to commodities.