In 2014, Khan et al. presented evidence that soil exchangeable K (Exch-K) increases over time without addition of potassium (K) to the soil despite the removal of K in crops on a soil rich in montmorillonite and illite. The authors term this behavior ‘The potassium paradox’. From their review of the literature, the authors also report a lack of crop response to potassium chloride (KCl) fertilization. Close evaluation of these findings reveals that their observations can be interpreted and predicted using current knowledge of K in soil chemistry and its uptake by plants, and there is no paradox in K behavior in the soil–plant system. There is also no evidence of a detrimental effect of KCl on crop yield or quality. Their conclusion that the widely used Exch-K soil test is inadequate for managing K fertilization is discussed and some possible modifications to improve its performance are included. We believe that measurement of Exch-K is an essential and valuable tool and its use should be continued, along with improvements in recommending K fertilizer application.

For many years, crop potassium (K) availability has been estimated by soil testing the plow layer for exchangeable K, in conjunction with potassium chloride fertilization widely promoted as an essential prerequisite for ensuring crop yield and quality. As rigorously documented in our paper, both components of chemical-based K management are seriously flawed by the lack of a scientific basis. Under the pretext of providing economic benefit for the producer and a healthy food supply for the public at large, the real purpose is to generate revenue for the fertilizer industry.

Pollinator declines and dependence on insect pollination, particularly in fruit and vegetable crops, creates a pressing need to understand growers' interactions with pollinators and factors affecting pollination strategies. At present, many growers are dependent on commercial honey bees (Apis mellifera), but diversified strategies may be necessary to secure adequate crop pollination in the future. As of yet, little social science research exists on pollination practices. This article presents the results of a survey of lowbush blueberry growers in Maine. The survey was part of a five-year pollination security study focusing on four fruit and vegetables crops in the Northeast US. The survey assesses grower perceptions of native pollinators' effectiveness and their perceptions of native pollinators' contribution to fruit set. Results indicate a widespread perception among growers of native pollinators' importance. While native pollinators are not effective enough to replace rented honey bees for three-quarters of the industry, they are broadly seen as an important form of insurance in poor weather when honey bees' effectiveness is reduced. The main obstacle to greater utilization of native pollinators found in this study was uncertainty over native pollinators' contribution to yield and the associated difficulty monitoring native pollinators' population size. Scientists and extension experts must work to reduce these obstacles before more widespread use of native pollinators will occur.

Conventional soil management systems (SMS) use synthetic inputs to maximize crop productivity, which leads to environmental degradation. Organic SMS is an alternative that is claimed to prevent or mitigate such negative environmental impacts. Vegetable production systems rely on frequent tillage to prepare beds and manage weeds, and are also characterized by little crop residue input. The use of crop residues and organic fertilizers may counteract the negative impacts of intensive vegetable production. To test this hypothesis, we evaluated the effect of sweet corn (Zea mays L. var. rugosa) residue incorporation in a corn–cabbage (Brassica oleracea L.) rotation on crop yields, nutrient uptake, weed biomass and soil nutrients for organic and conventional SMS in two contrasting soil types (a Chromosol and a Vertosol). Yields of corn and cabbage under the organic SMS were not lower than the conventional SMS, possibly due to the equivalent N, P and K nutrients applied. Macro-nutrient uptake between the organic and conventional SMS did not differ for cabbage heads. Corn residue incorporation reduced the average in-crop weed biomass in cabbage crops by 22% in 2010 and by 47% in 2011. Corn residue-induced inhibitions on weed biomass may be exploited as a supplementary tool to mechanical weed control for the organic SMS, potentially reducing the negative impacts of cultivation on soil organic carbon. Residue incorporation and the organic SMS increased the average total soil N by 7 and 4% compared with the treatments without residue and the conventional SMS, respectively, indicating the longer-term fertility gains of these treatments. Exchangeable K, but not Colwell P, in the soil was significantly increased by residue incorporation. The clayey Vertosol conserved higher levels of nutrients than the sandy Chromosol. Yields under organic SMS can match that of conventional SMS. Residue incorporation in soil improved soil nutrients and reduced weed biomass.

Commercial farmers have been using polyethylene plastic mulch since the 1950s. Despite the affordability and effectiveness of polyethylene mulch, the disposal process is financially and environmentally costly. Biodegradable plastic mulches, an ecologically sustainable alternative to polyethylene mulch films, were introduced in the 1980s. Biodegradable plastic mulches can be tilled into the soil or composted at the end of the season, reducing the labor and environmental costs associated with plastic removal and disposal. However, research results are mixed as to the effectiveness, degradability and ease-of-use of biodegradable plastic mulches. In 2008–2012, researchers, funded by a USDA Specialty Crop Research Initiative grant, conducted surveys and focus groups in three different agricultural regions of the USA to better understand the barriers and bridges to the adoption of biodegradable plastic mulches for specialty crop production systems. Data on the experiences and views of specialty crop growers, agricultural extension agents, agricultural input suppliers, mulch manufacturers and other stakeholders showed that the major adoption barriers were insufficient knowledge, high cost and unpredictable breakdown. The major bridges to adoption were reduced waste, environmental benefits and interest in further learning. These findings are discussed with reference to the classic innovation diffusion model, specifically work on the innovation–decision process and the attributes of innovations. The study results can be used to guide the activities of those involved in the design, development and promotion of biodegradable plastic mulches for US specialty crop production systems.

We analyzed the productivity levels of smallholder farms in northern Thailand practicing different ‘clean and safe’ vegetable farming systems or conventional vegetable (CV) production. ‘Clean and safe’ farmers are categorized into three groups based on their use of synthetic chemicals: organic, pesticide-free and safe-use. Farm-level data on vegetable production were collected from random samples of farms operating these farming systems. A standard stochastic production frontier model and a metafrontier model were estimated for each system to obtain estimates of technical efficiency (TE) with respect to their cohorts, metatechnology ratios (MTRs, showing the extent of technology gaps between farming systems) and overall productivity measures. Productivity levels were found to vary moderately between farming systems. ‘Clean and safe’ farms achieved a higher mean TE score than conventional farms, indicating a more efficient use of inputs in producing a certain level of output within their system. However, their MTRs were significantly lower than those of conventional farmers, indicating greater production technology constraints because of the need to conform to strict guidelines. All four farming systems had at least one farmer who could overcome the technological constraints to achieve the highest possible output regardless of the technology used. Effective assistance providers were found to be crucial for farmers to achieve high productivity in the organic farming system. Improvements are needed to raise low productivity levels through technology transfer, value chain improvement and farmer capacity in production and marketing. The required improvement strategies differ among farming systems.

Cocoa-based small-scale agriculture is the most important source of income for most farming families in the region of Alto Beni in the sub-humid foothills of the Andes. Cocoa is grown in cultivation systems of varying ecological complexity. The plantations are highly susceptible to climate change impacts. Local cocoa producers mention heat waves, droughts, floods and plant diseases as the main impacts affecting plants and working conditions, and they associate these impacts with global climate change. From a sustainable regional development point of view, cocoa farms need to become more resilient in order to cope with the climate change related effects that are putting cocoa-based livelihoods at risk. This study assesses agroecosystem resilience under three different cocoa cultivation systems (successional agroforestry, simple agroforestry and common practice monocultures). In a first step, farmers’ perceptions of climate change impacts were assessed and eight indicators of agroecological resilience were derived in a transdisciplinary process (focus groups and workshop) based on farmers’ and scientists’ knowledge. These indicators (soil organic matter, depth of Ah horizon, soil bulk density, tree species diversity, crop varieties diversity, ant species diversity, cocoa yields and infestation of cocoa trees with Moniliophthora perniciosa) were then surveyed on 15 cocoa farms and compared for the three different cultivation systems. Parts of the socio-economic aspects of resilience were covered by evaluating the role of cocoa cooperatives and organic certification in transitioning to more resilient cocoa farms (interviews with 15 cocoa farmers combined with five expert interviews). Agroecosystem resilience was higher under the two agroforestry systems than under common practice monoculture, especially under successional agroforestry. Both agroforestry systems achieved higher cocoa yields than common practice monoculture due to agroforestry farmers’ enhanced knowledge regarding cocoa cultivation. Knowledge sharing was promoted by local organizations facilitating organic certification. These organizations were thus found to enhance the social process of farmers’ integration into cooperatives and their reorientation toward organic principles and diversified agroforestry.

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.

A participatory plant breeding (PPB) program involving the French farmers' association ‘Réseau Semences Paysannes’ and the French National Agricultural Research Institute (INRA) at Le Moulon was initiated in 2005. In the process of designing the breeding scheme, we evaluated the impact of farmer selection at an early stage (F2) on bread wheat cross progeny populations. The objectives were to characterize the effect of farmer selection, to evaluate the impact of farmer selection on intra-varietal diversity, to provide farmers with relevant information that they can use to improve their selection practices. Early selection was found efficient for some traits and for some of the 35 F2-derived F3 families. For traits of interest such as thousand kernel weight or grain weight per spike, when the response was significant, it was always positive. For most of the traits studied, the among-family genetic variance increased after selection while the average within-family genetic variance decreased. This study provides the first quantitative results for this PPB program and information that will help optimize it in the future.

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.