Efficient conservation and sustainable use of crop diversity is critical to support global food and nutritional security with ex situ collections stored in over 800 genebanks in 115 countries. The challenge is to manage those collections for long-term conservation of crop diversity and sustainable use to respond to global challenges of food security and climate change. The Genebank Standards for Plant Genetic Resources for Food and Agricutlure (Genebank Standards) form the overall framework for curation of ex situ crop collections, allowing considerable flexibility to develop customized approaches to conserving different crops. Stratified curation involves strategically tailoring curation to specific genebank goals, crops, priorities and resources for each accession based on all available information to prioritize accessions for long-term conservation. It implies using scarce resources where they are most needed and recognizes that accessions can be (a) fully curated to international standards; (b) partially curated for storage for a limited time; (c) archived and stored but no longer curated and available from the genebank; or (d) historical and removed entirely from the genebank. The stratified approach is consistent with the Genebank Standards and the policy framework of the International Treaty on Plant Genetic Resources for Food and Agriculture. Stratified curation encourages curators to make difficult decisions on accession management to better respond to challenges of curating large collections of crop diversity.

Granular temporal and spatial scale observations of conservation practices are essential for identifying changes in the production systems that improve soil health and water quality and inform long-term agricultural research and adaptive policy development. In this study, we demonstrate an innovative use of farmer practice survey data and what can be uniquely known from a detailed survey that targets specific farm groups with a regional focus over multiple consecutive years. Using three years of survey data (n = 3914 respondents), we describe prevailing crop rotation, tillage, and cover crop practice use in four Midwestern US states. Like national metrics, the results confirm dominant practices across the landscape, including corn-soybean rotation, little use of continuous no-till, and the limited use of cover crops. Our detailed regional survey further reveals differences by state for no-till and cover crop adoption rates that were not captured in federal datasets. For example, 66% of sampled acreage in the Midwest has corn and soybean rotation, with Illinois having the highest rate (72%) and Michigan the lowest (41%). In 2018, 20% of the corn acreage and 38% of the soybean acreage were in no-till, and 13% of the corn acres and 9% of the soybean acres were planted with a cover crop. Cover crop adoption rates fluctuate from year to year. Results demonstrate the value of a farmer survey at state scales over multiple years in complementing federal statistics and monitoring state and yearly differences in practice adoption. Agricultural policies and industry heavily depend on accurate and timely information that reflects spatial and temporal dynamics. We recommend building an agricultural information exchange and workforce that integrates diverse data sources with complementary strengths to provide a greater understanding of agricultural management practices that provide baseline data for prevailing practices.

A 2-yr field experiment was conducted to explore the effects on weed growth and crop productivity of intercropping sweet corn with summer savory. Five cropping patterns were set up: sweet corn alone (16 seeds m−2, in rows, 75 cm apart), summer savory alone (40 seeds m−2, broadcasted), and three intercropping ratios of 75% sweet corn, 25% summer savory (75%C:25%S), 50%C:50%S, and 25%C:75%S, of plant densities used in respective monocultures. When intercropping, weed biomass decreased as the proportion of summer savory increased, with a reduction of 48%, 61%, and 70 % in 75%C:25%S, 50%C:50%S, and 25%C:75%S, respectively, compared to sweet corn alone. In parallel, sweet corn yield was higher under intercropping compared to its monoculture and increased as the proportion of summer savory decreased, with yield increases compared to corn monoculture of 38%, 32%, and 15% in the first year and 48%, 23%, and 14 % in the second year in 75%C:25%S, 50%C:50%S, and 25%C:75%S, respectively. However, the intercropping pattern had the opposite effect on summer savory yield, with a significant reduction in yield with an increasing ratio of sweet corn. Our results indicate that intercropping sweet corn with summer savory can increase both weed suppression and yield of sweet corn compared to crop monoculture.

Increasing crop diversity has been proposed to increase the sustainability of cropping systems. If producers are to adopt these systems, they should also be economically viable. In this study conducted near Mandan, North Dakota, four no-till cropping systems with varying levels of crop diversity were evaluated over a 12-yr period to quantify system effect on crop productivity, input use, production costs, and economic risks and returns. Cropping system treatments included a small grain–fallow rotation (SG–Fallow) and a continuous spring wheat (Triticum aestivum L.) rotation (Cont SW) as baseline low-diversity rotations, a small grain–winter wheat (T. aestivum L.)–sunflower (Helianthus annuus L.) rotation (SG–WW–Sun), a 5-yr rotation (Five Year) and a dynamic rotation (Dynamic). The SG–Fallow rotation was significantly less productive and less profitable on average than the other rotations, as measured by gross returns and net returns, respectively. However, SG–Fallow also used significantly less inputs than the other rotations. Production costs for the Cont SW and SG–WW–Sun rotations showed a significant increasing trend over time, while production costs for the Five Year rotation showed a significantly lower and slight decreasing trend over the period, with cost trends for the SG–Fallow and Dynamic rotations intermediate to these. Net returns tended to increase and relative economic risk tended to decrease as crop diversity increased from SG–Fallow and Cont SW to SG–WW–Sun, Five Year and the Dynamic system. Results from this study suggest that more diverse rotations can maintain or increase crop productivity and enhance economic viability.

Exotic crops—plant species grown in relatively small quantities and not traditionally cultivated in a country or region—are often intimately linked with the ethnic origins of their maintainers and are a principal source of culinary and nutritional diversity for many people. Recognizing that a wealth of exotic crop diversity and associated knowledge is held by small-scale growers in the UK, Garden Organic initiated the Sowing New Seeds project to capture and preserve some of this valuable resource by building a seed collection and knowledge base. To establish a sample of this diversity and knowledge, we undertook a survey at 31 allotment sites in the Midlands region of the UK with the objectives of identifying the exotic crops cultivated, characterizing the demography of those who grow them, understanding their direct use values, and assessing their potential indirect use value for the diversification and improvement of other crops. Results reveal that 26% of the food crops recorded are exotic and that they are grown by people belonging to 13 different ethnic groups. The majority save their own seed, indicating that these crops are performing well in the UK, with grower selection providing the basis for their continuing success. Further, most maintainers swap seed with other growers, indicating that exotic crops are likely to be gradually diversifying in response to different growing conditions—a positive sign for their value for local food security and as national genetic resources with potential for use in crop improvement programs. The research highlights the multitude of benefits that growers obtain through cultivating exotic crops, which are not only related to nutrition and culinary requirements, but also to general health and well-being, culture, and a range of other forms of life enrichment. It is critical that growers are encouraged and supported in continuing to cultivate, save and pass on their exotic crops to younger generations, as well as to protect allotments from development in order to maintain this important diversity adapted to local growing conditions. Importantly, many exotic crops currently grown on a small scale may enter into commerce, and thus expand the diversity of the UK's food crop base. Such a shift may be particularly important in the face of the increasingly detrimental impacts of climate change on crop production. We conclude that exotic crop diversity could be more important for future nutrition, health and food security than we currently appreciate.

Benefits of reduced tillage and diverse crop rotations include reversing soil C loss, and improving soil quality and function. However, adoption of these strategies is lagging, particularly in the Upper Midwest, due to a perception that reduced tillage lowers crop yields. Therefore, an 8-year comparison of these conservation systems with a conventional, tilled, 2-year rotation system was conducted to evaluate effects on yields, system productivity (measured with potential gross returns) and weed seed densities. This study compared conventional moldboard plow + chisel till (CT) to reduced strip-tillage + no-tillage (ST), each with a 2-year (2y) or 4-year (4y) crop rotation, abbreviated as CT-2y, CT-4y, ST-2y and ST-4y. The 2y rotation was corn (Zea mays L.) and soybean (Glycine max [L.] Merr.); the 4y rotation was corn, soybean, spring wheat (Triticum aestivum L.) underseeded with alfalfa (Medicago sativa L.) and alfalfa. Only corn grain was significantly influenced by tillage strategy; CT systems yielded more than ST systems, regardless of rotation. Soybean grain yields were similar among CT-2y, CT-4y, ST-4y and lowest in the ST-2y. Yields of wheat and alfalfa were the same under both tillage strategies. Weed seed densities were higher in wheat and alfalfa, followed by corn then soybean, but were not influenced by tillage or rotation, nor universally negatively correlated to yield. Due to greater corn yields, overall system productivity was highest in CT-2y, the same between CT-4y and ST-2y, and lowest in ST-4y. Within years, productivity of CT-2y was different from only one other system at a time in 3 of 8 years and had the same productivity as all systems in another 3 of 8 years. Additionally, the similarity of productivity among three of four systems in 6 of 8 years indicated reduced tillage and diverse rotations have potential for adoption. Results support the need for research on a rotational tillage strategy, i.e., moldboard plowing before corn, to improve overall productivity if using ST before soybean, wheat and alfalfa.

Weed management is evolving to include cultural tactics that reduce weed populations. This study near Brookings, SD, evaluated the effect of crop sequence and tillage on seedling emergence of common sunflower across years. In the third and fourth years of the study, seedling density was sevenfold greater after 2 yr of soybean with tillage compared with a 2-yr sequence of canola and winter wheat with no-till. Apparently, canola and winter wheat enhanced the natural decline of common sunflower seed density in soil, leading to fewer seedlings in following years. In the first year of the study, tillage increased seedling emergence of common sunflower compared with no-till; seedlings rarely emerged in canola or winter wheat. Most seedlings of common sunflower emerged in May, with more than 90% of seedlings emerging between May 7 and June 4. Cool-season crops grown with no-till may affect weed seed survival in soil in the western Corn Belt.

Producers in the semiarid Great Plains are exploring alternative crop rotations, with the goal of replacing winter wheat–fallow. In 1993, a study was established to compare performance of eight rotations comprised of various combinations with winter wheat (W), spring wheat (SW), dry pea (Pea), safflower (Saf), corn (C), sunflower (Sun), proso millet (M), or fallow (F). After 8 years, we characterized weed communities by recording seedling emergence in each rotation. Seventeen species were observed, with downy brome, kochia, horseweed, and stinkgrass comprising 87% of the community. Rotations with the least number of weed seedlings were W–F and SW–W–C–Sun; in comparison, weed density was six-fold higher in W–M. Density of downy brome and kochia was highest in W–M compared with other rotations, whereas stinkgrass and green foxtail were prominent in proso millet of the W–M and W–C–M rotations. Horseweed established readily in safflower and dry pea. In the semiarid Great Plains, designing rotations in a cycle of four that includes cool- and warm-season crops can be a key component of integrated weed management.

Over 175 growers in each of six states (Illinois, Indiana, Iowa, Mississippi, Nebraska, and North Carolina) were surveyed by telephone to assess their perceptions of the benefits of utilizing the glyphosate-resistant (GR) crop trait in corn, cotton, and soybean. The survey was also used to determine the weed management challenges growers were facing after using this trait for a minimum of 4 yr. This survey allowed the development of baseline information on how weed management and crop production practices have changed since the introduction of the trait. It provided useful information on common weed management issues that should be addressed through applied research and extension efforts. The survey also allowed an assessment of the perceived levels of concern among growers about glyphosate resistance in weeds and whether they believed they had experienced glyphosate resistance on their farms. Across the six states surveyed, producers reported 38, 97, and 96% of their corn, cotton, and soybean hectarage planted in a GR cultivar. The most widely adopted GR cropping system was a GR soybean/non-GR crop rotation system; second most common was a GR soybean/GR corn crop rotation system. The non-GR crop component varied widely, with the most common crops being non-GR corn or rice. A large range in farm size for the respondents was observed, with North Carolina having the smallest farms in all three crops. A large majority of corn and soybean growers reported using some type of crop rotation system, whereas very few cotton growers rotated out of cotton. Overall, rotations were much more common in Midwestern states than in Southern states. This is important information as weed scientists assist growers in developing and using best management practices to minimize the development of glyphosate resistance.

Dry pea improves corn yield and tolerance to weed interference compared with soybean, spring wheat, or canola as preceding crops. To understand this synergy between dry pea and corn, growth and nutrient concentration of corn were examined following dry pea or soybean in sequence. Each corn plot was split into weed-free and weed-infested subplots, with foxtail millet established at one density to provide uniform weed interference. Compared with soybean, dry pea improved corn grain yield 10% in weed-free conditions and corn tolerance to weed interference more than twofold. Dry pea synergy to corn in weed-free conditions was not related to differences in corn development, height, or nutrient status of corn seedlings. When foxtail millet was present, dry pea increased corn height and rate of development late in the growing season compared with soybean. Improved corn tolerance to weed interference was not related to seedling emergence or growth of foxtail millet, as these parameters did not vary with preceding crop. Other biological factors must be involved in dry pea synergy to corn.

Crop diversity may improve tolerance to weed interference and reduce the need for herbicides. This experiment measured weed interference in corn as affected by the preceding crop in two studies. The first study, based on interference of the resident weed community, compared dry pea, soybean, canola, and spring wheat for effect on corn tolerance to weeds. Prominent weeds were green and yellow foxtail. The second study examined corn tolerance to a uniform infestation of foxtail millet as affected by dry pea, soybean, spring wheat, and corn as preceding crops. Each plot was split into weed-free and weed-infested subplots in both studies. Corn was most tolerant to weed interference following dry pea; compared with soybean, dry pea improved corn tolerance more than twofold. Corn also yielded the highest in weed-free conditions following dry pea; compared across 4 yr, corn yielded 7 to 23% more following dry pea than following either soybean or spring wheat. Crop diversity has helped producers reduce herbicide inputs in the Great Plains and may provide an additional benefit of reducing weed impact on crop yield.

Although crop diversity has been identified as essential to enhance global food security and adapt to climate change, high loss of genetic resources is occurring due to agricultural industrialization and market requirements. Value chain development is an emerging market strategy that seeks to simultaneously achieve agrobiodiversity conservation and economic goals, though little empirical evidence exists regarding the extent to which value chains encourage biodiversity maintenance. This study considers the conservation of native potatoes among households in the highlands of Peru where value chain development is being pursued to create market niches for certain native potato varieties. Utilizing a mixed-methods case study approach, the findings of this study indicate that the conservers of native varieties are the households with more endowed resource bases as well as those that sell native varieties in value chains. However, the findings suggest that value chains themselves likely have only a marginal effect on conservation. Native potato conservation and potato production for value chains exist as two separate livelihood activities, and households with more resources are best positioned to engage in both. While value chains allow households to capitalize on the economic value of certain native varieties, the production of other native varieties allows households to fulfill cultural values. Based on these findings, this study concludes that value chain opportunities for native varieties should continue to be identified but they alone are not an adequate strategy to conserve agrobiodiversity. Therefore, in addition to value chain development, a full suite of conservation schemes should be implemented simultaneously.

Allotment food gardens represent important sources of food security for urban residents. Since urban gardeners rarely receive formal agricultural education and have extremely limited space, they may be relying on readily available gardening advice (e.g., seed packet instructions), inventing cultural strategies that consider inter-specific competitive dynamics, or making poor planting decisions. Knowledge of garden crop diversity and planting arrangements can aid in designing strategies for productive urban gardens and food systems. We surveyed 96 individual plots in 10 allotment gardens in the Toronto region, assessed crop diversity within gardens and recorded planting practices used by urban gardeners by measuring the proximity of individual plants relative to similar or different crop species. We also compared planting densities used by urban gardeners with those recommended by major seed distributers. Collectively, Toronto urban agriculture contributes substantially to urban plant diversity (108 crops), but each plot tends to be relatively depauperate. Carrots and lettuce were three to five times more likely to be planted in clusters than intermingled with other crops (P < 0.05); whereas gardeners did not appear to use consistent planting arrangements for tomatoes or zucchini. Gardeners tended to plant tomatoes and zucchini 56–62.5% more densely than recommended by seed distributers (P < 0.001), whereas they planted 147 times fewer carrots in a given area than recommended (P < 0.05). Furthermore, neither crop planting density nor crop diversity changed with plot size. The planting arrangements we have documented suggest gardeners using allotment plots attempt plant densely in extremely limited space, and are employing cultural strategies that intensify competitive dynamics within gardens. Future research should assess the absolute and relative effect of altered cultural practices on yield, such that any modifications can be prioritized by their impact on yield.

No-till practices have improved crop yields in the semiarid Great Plains. However, a recent assessment of research studies across the globe indicated that crop yields are often reduced by no-till. To understand this contrast, we examined corn yields across time in a no-till cropping system of one producer in central South Dakota to identify factors associated with increased yield. The producer started no-till in 1990; by 2013, corn yield increased 116%. In comparison, corn increased only 32% during this interval with a conventional, tillage-based system in a neighboring county. With no-till, corn yields increased in increments due to changes in management. For example, corn yield increased 52% when crop diversity in the rotation was expanded from 2 to 5 crops. A further 18% gain in yield occurred when dry pea was grown before corn in sequence. Nitrogen (N) requirement for corn is 25% lower in no-till compared with a tillage-based rotation. Furthermore, phosphorus (P) fertilizer input also has been reduced 30% after 20 yr of no-till, even with higher yields. Our case study shows that integrating no-till with crop diversity and soil microbial changes improves corn yield considerably. This integration also reduces need for inputs such as water, N and P.

A study was conducted on the spatial dimension of crop diversity in Jutpani Village Development Committee (VDC) in central Nepal. Many crop diversity studies focus only on home gardens, but this study aimed to investigate the crop diversity among different production systems, and the factors affecting variations in the crop diversity on a household level. A survey of inter-household variation in cultivated crop diversity in different land-use types among 134 households indicates that 96 different types of annual crops, perennial crops and fruit trees are cultivated. Individual farms cultivated an average of 26 different crops, with this number ranging from 11 to 45. Crops were used as food by the households and, based on their adaptive characters, they were grown either in home gardens or in upland, Tandikhet and lowland. Research showed that home gardens have the highest crop diversity (a total of 78 different crops grown) compared to upland, Tandikhet and lowland. Statistical analysis to understand the factors affecting the variation in crop diversity in the household level showed that the total number of crops grown (crop diversity) on a farm is significantly higher (P<0.001) in the Indo-Aryan ethnic group compared to the Tibeto-Burman group. Farmers with three different production domains maintained higher (P<0.001) crop diversity compared to having only one or two production domains. Poor farmers with small land holdings were associated with higher crop diversity (P<0.001) compared to rich farmers with large land holdings. Therefore, planning for agrobiodiversity management should focus on the production systems, and social and economic settings within the farming community.

Synergy between dry pea and corn can reduce the density of corn needed for optimum yield. Lower crop density may accrue an additional benefit, as after-harvest residues of corn lying on the soil surface can reduce yield of crops planted the next year. This study evaluated impact of corn residue levels on growth and yield of three cool-season crops in no-till. Corn was grown at two densities, 52,000 and 73,000 plants ha−1, leading to after-harvest residue levels designated as low and high residue. Residue quantity on the soil surface differed by 21%. Controls were included for each residue level by burying residue with tillage. Spring wheat, dry pea and red clover were planted the following year. Grain yield of spring wheat and dry pea and forage yield of red clover were reduced 13–33% by residue on the soil surface. However, yield of cool-season crops were 10–18% higher in the low-residue treatment compared with high residue. Furthermore, yield loss because of weed interference in spring wheat and red clover was greater with high residue. Of the three crops, spring wheat was the least affected by corn residue on the soil surface. One contributing factor to lower yield with high residue was reduced crop seedling establishment. Producers may be able to reduce the negative impact of corn residue on following crops in no-till systems by using synergistic crop sequences in the rotation.

The loss of variation in crops due to the modernization of agriculture has been described as genetic erosion. The current paper discusses the different views that exist on the concept of genetic erosion in crops. Genetic erosion of cultivated diversity is reflected in a modernization bottleneck in the diversity levels that occurred during the history of the crop. Two stages in this bottleneck are recognized: the initial replacement of landraces by modern cultivars; and further trends in diversity as a consequence of modern breeding practices. Genetic erosion may occur at three levels of integration: crop, variety and allele. The different approaches in the recent literature to measure genetic erosion in crops are reviewed. Genetic erosion as reflected in a reduction of allelic evenness and richness appears to be the most useful definition, but has to be viewed in conjunction with events at variety level. According to the reviewed literature, the most likely scenario of diversity trends during modernization is the following: a reduction in diversity due to the replacement of landraces by modern cultivars, but no further reduction after this replacement has been completed.

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.