Corn Pest Population Dynamics in Organic Systems Following Soybean: A Three-Year Study

How the productivity of crops in organic arable farming may be sustainably increased remains a key issue. We combined measurements of crop yield, total aboveground biomass (AGB) and light interception over a 4-year crop rotation cycle from 2015 to 2018 in a long-term experiment in Denmark with arable organic and conventional cropping systems. These cropping systems comprise one conventional (CGL) and two organic (OGL and OGC) crop rotations, where CGL and OGL had three spring cereal and one grain legume crop (faba bean) in the rotation, and the faba bean was in OGC replaced with grass-clover. All crop rotations were grown with and without the use of cover crops, and the organic systems were grown with and without the manure application. The light interception was calculated from measurements of spectral reflectance, and this allowed the AGB to be decomposed into accumulated intercepted PAR (AIPAR) and radiation use efficiency (RUE).The conventional cropping system (CGL) had significantly greater AGB, AIPAR and RUE compared with the corresponding organic, grain legume-based system (OGL). AIPAR of the organic grass-clover-based cropping system (OGC) was greater than CGL, although the contrary conclusion was found in AGB and RUE. Across crops, RUE was greatest for cereals and smallest for faba bean and grass-clover. AIPAR was consistently greatest for grass-clover, and both grass-clover and faba bean had smaller variability in AIPAR between years and treatments than the cereal crops. Cover crops significantly increased AGB and AIPAR in the organic cropping systems but not in CGL. RUE was not significantly affected by the inclusion of cover crops. The use of manure in the organic systems increased AGB, AIPAR and RUE. The results show that AIPAR can be higher in organic cropping systems compared with conventional cropping systems, but this is not translated into a greater yield of cereal crops. There is, therefore, a need for novel approaches to management and the use of biomass in organic cropping systems for increasing yields for feed and food, and which sustains soil fertility.

Transgenic crops expressing insecticidal toxins could soon provide safe, clean and effective means of pest control, but their usefulness will be short-lived if insects adapt to the toxins. Two planting strategies are among those that have been recommended to delay crop failure: susceptible insects could be conserved by planting either ‘refugia’, i.e. separate fields of toxic and toxin-free crop, or ‘seed mixtures’ of toxic and toxin-free plants in the same fields. However, we show that if insects can move from plant to plant, seed mixtures may actually hasten insect resistance compared with pure stands of toxic plants. Insect movement causes an increase in effective genetic dominance which can counteract reduced selection due to the mixture. This failure of seed mixtures is likely under just those conditions, low genetic dominance of resistance, which predict a good chance for resistance to the toxin to evolve slowly. Seed mixtures, unlike refugia, are therefore failure prone. This result also suggests potential problems with a third strategy, tissue-specific expression of toxins, which essentially provides a mixture of toxin-free and toxin-containing tissues on the same plant. However, better information and modelling are urgently required to evaluate alternative means of slowing insect adaptation to resistant crop plants. Legislation for toxinfree refugia may provide one of the best available means for conserving insect susceptibility.

Organic agriculture aims to build soil quality and provide long-term benefits to people and the environment; however, organic practices may reduce crop yields. This long-term study near Mead, NE was conducted to determine differences in soil fertility and crop yields among conventional and organic cropping systems between 1996 and 2007. The conventional system (CR) consisted of corn (Zea maysL.) or sorghum (Sorghum bicolor(L.) Moench)–soybean (Glycine max(L.) Merr.)–sorghum or corn–soybean, whereas the diversified conventional system (DIR) consisted of corn or sorghum–sorghum or corn–soybean–winter wheat (wheat,Triticum aestivumL.). The animal manure-based organic system (OAM) consisted of soybean–corn or sorghum–soybean–wheat, while the forage-based organic system (OFG) consisted of alfalfa (Medicago sativaL.)–alfalfa–corn or sorghum–wheat. Averaged across sampling years, soil organic matter content (OMC), P, pH, Ca, K, Mg and Zn in the top 15 cm of soil were greatest in the OAM system. However, by 2008 OMC was not different between the two organic systems despite almost two times greater carbon inputs in the OAM system. Corn, sorghum and soybean average annual yields were greatest in either of the two conventional systems (7.65, 6.36 and 2.60 Mg ha−1, respectively), whereas wheat yields were greatest in the OAM system (3.07 Mg ha−1). Relative to the mean of the conventional systems, corn yields were reduced by 13 and 33% in the OAM and OFG systems, respectively. Similarly, sorghum yields in the OAM and OFG systems were reduced by 16 and 27%, respectively. Soybean yields were 20% greater in the conventional systems compared with the OAM system. However, wheat yields were 10% greater in the OAM system compared with the conventional DIR system and 23% greater than yield in the OFG system. Alfalfa in the OFG system yielded an average of 7.41 Mg ha−1annually. Competitive yields of organic wheat and alfalfa along with the soil fertility benefits associated with animal manure and perennial forage suggest that aspects of the two organic systems be combined to maximize the productivity and sustainability of organic cropping systems.

Producing safe and nutritious food for consumers and ensuring profitability and sustainability of farming enterprises through environmentally friendly agronomic practices are some of the major challenges facing agriculture today. Field studies were conducted in 2001 and 2002 to evaluate the effect of conventional (chemical-intensive) monocropping, transitional (reduced-synthetic input), and an organic (non-synthetic input) multiple cropping systems on sweet potato (Ipomoea batatas (L.) Lam) yield and quality, as well as soil properties. The studies were conducted on a Dexter silt loam soil in northern Mississippi. In both years No. I sweetpotato yield was greatest for the transitional and organic cropping systems and lowest for the conventional cropping system. In 2001, cropping system did not affect plant survival. In 2002, plant survival was greatest for the conventional cropping system and lowest for the organic cropping system. Soil extractable nutrient levels prior to planting (preplant soil fertility) were very high for Mg, high for P and Ca, medium for S, and low for K. Final post-harvest soil levels after the 2nd year: the content of Mg was very high for the three cropping systems, and high for P, K and Ca. Sulfur was high for the organic cropping system, and medium for the conventional and transitional cropping systems. In 2001, sweetpotato P content was greatest for the conventional cropping system and lowest for the transitional cropping system. Both Ca and Mg were greatest for the conventional cropping system but were not different from the transitional cropping system. Potassium was greatest for the organic cropping system and lowest for the transitional cropping system. Both N and S were not affected by cropping systems. In 2002, N content in roots was greatest for the conventional and organic cropping systems and lowest for the transitional cropping system. The other nutrients were not affected by cropping system. Sweetpotato roots under the conventional cropping system had the greatest protein, fat and ash contents, whereas crude fiber was the greatest for roots under the transitional cropping system. Root dry matter was greatest for the organic cropping system and lowest for the conventional cropping system. Data suggest that Beauregard sweetpotato cultivar can be successfully grown on a Delta silt loam soil in northern Mississippi. Where the production of No. 1 marketable sweetpotato roots are desired, both the transitional and organic cropping systems are recommended over the conventional cropping system. While the conventional cropping system will enhance root protein, fat and ash contents more than the transitional and organic cropping systems, both cropping systems will, respectively, enhance crude fiber and dry matter more than the conventional cropping system.

Nematode-trapping fungi, nematodes, and microbial biomass were quantified in conventionally and organically managed field plots in the Sustainable Agriculture Farming Systems Project at the University of California at Davis. There were four replicate plots (0.135 ha per plot) for each management system, and plots were sampled three times each year for 2 years. The hypothesis that nematode-trapping fungi would be more abundant in organically managed plots was partially supported: the number of species of nematode-trapping fungi was slightly but significantly greater in organic than in conventional plots, two species (Arthrobotrys dactyloides and Nematoctonus leiosporus) were detected more frequently in organic plots, and the population densities of A. dactyloides and N. leiosporus were greater in organic than in conventional plots. Two other species (A. haptotyla and A. thaumasia), however, tended to be more numerous in conventional than in organic plots, and the total density of nematode-trapping fungi was similar in organic and conventional plots. Bacterivorous nematodes were more abundant and microbial biomass (substrate-induced respiration) was greater in organic than in conventional plots. Suppression of the root-knot nematode Meloidogyne javanica, as measured in a bioassay, was not related to management system or population density of nematode-trapping fungi but was positively related to microbial biomass.

Endophytic fungi dwell in the tissues of plants without causing disease symptoms. Coffee production can be performed using conventional or organic crop systems. Studies have been carried out to assess the endophytic fungal community in a conventional coffee crop system. However, little is known about them in organic conditions. Comparisons were made between an endophytic fungal community from leaves of Coffea arabica in organic and conventional crop systems. Mature and healthy leaves of C. arabica were collected from two crop systems during the wet and dry seasons, in the Northeast Brazil. A total of 432 fragments were analyzed and 336 specimens of endophytic fungi were isolated and distributed among 16 genera and 17 species. Colletotrichum gloeosporioides complex and Phyllosticta capitalensis were the most common fungi in conventional and organic crop systems, respectively. The largest number of fungal endophytes was observed during the wet season, although the diversity index and species richness were higher in the dry season. The endophytic fungal communities in conventional and organic crop systems exhibited 50.61% similarity, with six species occurring uniquely in organic and five in conventional coffee. Therefore, more research is needed to confirm that the species could be used as indicators of these management systems.

Relations between nitrogen leaching and food productivity in organic and conventional cropping systems in a long-term field study

SummaryHigh weed abundance in organic crops is thought to be a key factor contributing to the greater yield loss in organic as compared with conventional cropping systems. However, even with greater weed densities than conventional systems, some organic systems have yields comparable to conventional systems, suggesting that cropping systems might differ in yield loss due to weed competition. The diversity in soil nutrient resources due to diversity in crop rotations and variable inputs might enhance crop tolerance to weed competition. We assessed the long‐term effects of contrasting levels of crop rotations (low, medium and high diversity) on weed density, weed biomass and wheat yield loss in organic and no‐till conventional cropping systems using a microplot study within a long‐term cropping systems trial at Scott, Saskatchewan, Canada. Weed density and biomass were found to be four times higher in the organic systems than in the conventional systems. Under standard weed management practices, organic had 44% lower yield than the conventional system. Lower yields in organic, even without weed competition, suggest that the lower yields are due to low soil productivity rather than weed competition. No differences in yield loss were observed among the organic and conventional systems or among the diverse crop rotations. We conclude that the organic management practices and/or increased crop rotation diversity did not enhance yield or reduce yield loss due to weed competition, due to the factors associated with lower soil fertility.

SummaryExperiments comparing conventional and organic systems often report similar yields despite substantially higher weed abundance in the organic systems. A potential explanation for this observation is that weed–crop competition relationships differ between the two types of systems. We analysed weed and crop yield data from the Rodale Institute Farming Systems Trial (FST), which provides a unique 27‐year dataset of a conventional (CNV) and two organic [manure (MNR) and legume (LEG)] soyabean (Glycine max (L.) Merr.) and maize (Zea mays L.) cropping systems. Average soyabean yields were similar between the MNR and CNV systems and only slightly reduced in the LEG system, whereas average maize yields did not differ among systems despite the two organic systems having more than four and six times greater weed biomass in soyabean and maize respectively. Plot‐level weed biomass–crop yield relationships indicated that weed–crop competition differed between the two organic and CNV systems in maize, and was strongest in the CNV system, intermediate in the LEG system and weakest in the MNR system. These results suggest that organic cropping systems may be able to tolerate a greater abundance of weeds compared to conventional systems and that fertility management within organic systems may influence weed–crop competition.

Despite the recent interest in organic agriculture, little research has been carried out in this area. Thus, the objective of this study was to compare, in a dystrophic Ultisol, the effects of organic and conventional agricultures on soil organism populations, for the tomato (Lycopersicum esculentum) and corn (Zea mays) crops. In general, it was found that fungus, bacterium and actinomycet populations counted by the number of colonies in the media, were similar for the two cropping systems. CO2 evolution during the cropping season was higher, up to the double for the organic agriculture system as compared to the conventional. The number of earthworms was about ten times higher in the organic system. There was no difference in the decomposition rate of organic matter of the two systems. In general, the number of microartropods was always higher in the organic plots in relation to the conventional ones, reflectining on the Shannon index diversity. The higher insect population belonged to the Collembola order, and in the case of mites, to the superfamily Oribatuloidea. Individuals of the groups Aranae, Chilopoda, Dyplopoda, Pauropoda, Protura and Symphyla were occasionally collected in similar number in both cropping systems.

Bacterial community dynamics and functional profiling of soils from conventional and organic cropping systems

<p>Projections of crop-pest dynamics under climate change (CC) impact negatively throughout the 21<sup>st</sup> century, suggesting increased pest pressure over central Europe. Variability in environmental conditions significantly affects the spread, abundance, and management of maize pests, such as Western corn rootworm (WCR), European corn borer (ECB) and wireworms, as indicated from the past monitoring data and quantitative pest models. Regional climate change and landscape factors are modifying the development of these thermophile insects and their impact on crops. Several conceptual modelling works related to pest population dynamics, phenology models, spread and risk mapping have been proposed. The challenges become complex for WCR and wireworms due to their soil-dwelling nature, eventually bringing significant site-specific spatial uncertainties to simulate the soil-crop-pest ecosystem. Most of the approaches have been quantitatively standardised, leaving out qualitative factors prioritizing farmer’s behaviour towards pest control measures. In our study we investigate statistical-empirical and process based models and integrated modelling frameworks for future simulation of soil-crop-pest phenology under the CC impact. We identified gaps in the improvements of pest modelling approaches and site-specific agrometeorological indices for four agro-climatic zones. In conclusion we propose a mechanistic physiological based demographic model, including improved population models under defined landscape extent and agrometeorological drivers. For example, temperature, photoperiod, precipitation changes, and topography are the significant drivers for ECB, whereas in addition, WCR and wireworms include soil type, crop rotation, and farmer’s management options. We derive crop damage factors from the quantitative surveys influencing maize grain yield, root damage and pest control measures, including weather conditions, insecticide distribution, pest pressures, and synchrony between pest and crop growth cycle. Agro-climatic zones of central Europe will experience northward shifts in temperature zones, growing season length, by further accelerating climate change. Hence, it is exposed to more vulnerabilities and demands improved alert services and control measures. The improved pest modelling approach integrated with crop models under CC impact provides a reasonable basis for advanced crop protection strategies with reduced pesticide use in maize production. It is used to formulate a regional risk assessment for specific pests to inform an integrated approach of cultivation, biological and chemical measures.</p>

Crop yields between 1982 and 1988 are reported here as a part of a cropping system experiment carried out at Suitia, Southern Finland. The soil was silty clay. There were four conventional and four organic systems: conventional cropping systems for barley monoculture, cereal production, diverse plant production, or a cattle farm, and organic cropping systems either for plant production with or without composting, or for cattle farms with or without composting. The crop sequences were fixed by six-year rotations, carried out in two phases. There were great differences in yields between the years, and the organic cropping systems were more negatively affected by poor growing conditions than the conventional ones. In the organic systems, the barley yields in 1985 and in 1988 were 25 % of the yields obtained from conventional stands, when the latter yielded about 3 t/ha. In better years, barley in the organic plant production yielded 50 % of the yield obtained in conventional barley monoculture (6 t/ha). It was not possible to differentiate between the effects of two different causes the preceeding crop and annual variation. The yields obtained with ’organic’ winter wheat and oats (+ Vicia faba) were 40 % of those from the respective conventional pure stands. The clover-grass leys of the organic systems yielded as much as the conventional grass leys until they were destroyed by water and the resulting ice cover during winter. Compared to those of ‘conventional’ system, the ‘organic’ system gave annual mean yields of potato varying from 37 % of the 16 t/ha obtained conventionally to 48% of the 21 t/ha obtained conventionally. Barley variety was found to interact with cropping system in 1988, a year characterised by draught stress. In 1989, in a separate trial carried out on the same field, an interaction between soil wetness (location) and cropping system was observed. Wetness of soil in winter seemed to interfere more severely in the organic system than in the conventional one. Because the uncontrolled variation of the field itself as to topography and drainage makes the comparisons between the organic and the conventional systems somewhat biased and unreliable, these results should not be generalised to cover the overall question of yield level in organic cropping.

The effect of increased energy prices on the viability of organic agricultural systems on arable farms in the U.K.

Soil-bound intensive greenhouse production has been scrutinized for its sustainability due to contamination of ground water by over-fertilization resulting in leaching of nutrients. As environmental guidelines are becoming more restrictive worldwide, and especially in Europe, many greenhouse growers have converted to more sustainable production systems including rockwool culture with recycled water and organic cropping systems in soil. The increase in popularity of organic production systems has amplified the debate whether organically grown produce is healthier than conventional produce. So far, little is known about the variations in fruit quality associated with production systems for greenhouse grown tomatoes. Thus, two organic (organic fertilization with and without straw amendment) and three conventional tomato cropping systems (regular and increased nutrient solution in rockwool and regular fertilization in soil) were compared in order to evaluate differences in nutrient availability and effects on fruit quality over a three-year period. Three modern medium-sized round tomato cultivars and one old cultivar were compared. There were no significant interactions between cropping systems and cultivars, so that main effects of systems and cultivars could be evaluated. Fruit yields in the organic systems were similar to those obtained in the conventional soil-bound system, but 15% lower than in the regular rockwool system, even though nitrogen concentrations in soil were not limiting in any of the production systems. Frequent organic amendments resulted in higher soil $\rm NO_{3}^{2-}$ contents in the organic system without straw than in the other soil-bound systems, indicating that the organic systems were not yet stable in terms of nutrient availability after three years. A fruit quality index, based on the contents of compounds such as lycopene, β-carotene and vitamin C, was similar in all cropping systems. The old cultivar had a significantly higher quality index, but a lower yield than the other cultivars. According to this study, high quality tomatoes can be obtained through proper adjustment of the quantity and the source of nitrogen fertilizers in organic and conventional cropping systems and the use of selected cultivars with a high nutrient use efficiency for organic systems.