Organic farming may contribute substantially to future agricultural production worldwide by improving soil quality and pest control, thereby reducing environmental impacts of conventional farming. We investigated in a comprehensive way soil chemical, as well as below and aboveground biological parameters of two organic and two conventional wheat farming systems that primarily differed in fertilization and weed management strategies. Contrast analyses identified management related differences between “herbicide-free” bioorganic (BIOORG) and biodynamic (BIODYN) systems and conventional systems with (CONFYM) or without manure (CONMIN) and herbicide application within a long-term agricultural experiment (DOK trial, Switzerland). Soil carbon content was significantly higher in systems receiving farmyard manure and concomitantly microbial biomass (fungi and bacteria) was increased. Microbial activity parameters, such as microbial basal respiration and nitrogen mineralization, showed an opposite pattern, suggesting that soil carbon in the conventional system (CONFYM) was more easily accessible to microorganisms than in organic systems. Bacterivorous nematodes and earthworms were most abundant in systems that received farmyard manure, which is in line with the responses of their potential food sources (microbes and organic matter). Mineral fertilizer application detrimentally affected enchytraeids and Diptera larvae, whereas aphids benefited. Spider abundance was favoured by organic management, most likely a response to increased prey availability from the belowground subsystem or increased weed coverage. In contrast to most soil-based, bottom-up controlled interactions, the twofold higher abundance of this generalist predator group in organic systems likely contributed to the significantly lower abundance of aboveground herbivore pests (aphids) in these systems. Long-term organic farming and the application of farmyard manure promoted soil quality, microbial biomass and fostered natural enemies and ecosystem engineers, suggesting enhanced nutrient cycling and pest control. Mineral fertilizers and herbicide application, in contrast, affected the potential for top-down control of aboveground pests negatively and reduced the organic carbon levels. Our study indicates that the use of synthetic fertilizers and herbicide application changes interactions within and between below and aboveground components, ultimately promoting negative environmental impacts of agriculture by reducing internal biological cycles and pest control. On the contrary, organic farming fosters microbial and faunal decomposers and this propagates into the aboveground system via generalist predators thereby increasing conservation biological control. However, grain and straw yields were 23% higher in systems receiving mineral fertilizers and herbicides reflecting the trade-off between productivity and environmental responsibility.

/pdf/long-term-organic-farming-fosters-below-and-aboveground-4glkyqeg5i.pdf

Long-term organic farming fosters below and aboveground biota: Implications for soil quality, biological control and productivity

Nutritional imbalances are of great interest in the ecological stoichiometry literature, in which researchers have focused almost exclusively on cases where nutrients are available in low amounts relative to energy (carbon), and animal growth is impaired due to insufficient nutrient intake. Little attention has been given to situations where food elemental content is higher than the level that satisfies animal requirements. However, most animals are strongly homeostatic with respect to the elemental composition of their body; hence they must excrete the excess of elements that are not in short supply. To date, stoichiometric theory has assumed that excretion of superfluous elements does not come with a cost and, thus, that consumption of food with surplus nutrients does not impair performance. Here we challenge this assumption, based on a compilation of several examples involving food phosphorus content that show that the performance of a wide variety of animals decreases when supplied with food containing high concentrations of (potentially) limiting nutrients. We discuss possible mechanisms for this phenomenon, and suggest that animals most vulnerable to effects of high food nutrient content are those that normally feed on low- quality (low-nutrient: C) food, and have a relatively low body nutrient content themselves, such as herbivores and detritivores.

Too much of a good thing: on stoichiometrically balanced diets and maximal growth.

Systemic acropedal influence of endophyte seed treatment on Acyrthosiphon pisum and Aphis fabae offspring development and reproductive fitness

Information that describes soybean aphid (Aphis glycines Matsumura) feeding injury effects on soybean [Glycine max (L.) Merr.] yield and seed composition is needed to develop better management practices for this invasive pest. This 2-yr controlled-infestation field study measured aphid populations and the effects of those populations on soybean seed yield, yield components (shoot biomass, pods plant -1 , seeds pod -1 , and 100 seed weight), and seed composition (oil and protein concentrations) when infested at the vegetative (V5) or reproductive (R2) development stages. In 2003, initial infestation rates of 10, 50, or 100 aphids plant -1 applied at V5 resulted in population peaks of 21,000, 18,000, and 12,000 aphids plant -1 and maximum cumulative aphid-days of 381,000, 327,000, and 242,000, respectively. In 2004, initial infestation rates of 1, 3, 10, 50, or 100 aphids plant -1 applied at V5 resulted in population peaks of 4,600, 9,400, 14,000, 22,000, and 21,000 aphids plant -1 and maximum cumulative aphid-days of 101,000, 229,000, 355,000, 514,000, and 537,000. In both years, the same infestation rates applied at R2 resulted in population peaks and cumulative aphid-day values that were about 42 to 88% lower than the V5 infestation dates. Seed yield, yield components, and seed oil concentration declined linearly as peak aphid numbers plant -1 and maximum cumulative aphid-days plant -1 increased. In contrast, seed protein concentration increased linearly with increasing peak aphid numbers plant -1 . Relating these aphid population parameters at the plant growth stages studied enables producers to make informed decisions about the need for and timing of pest management treatments.

Soybean Aphid Feeding Injury and Soybean Yield, Yield Components, and Seed Composition

Transgenerational phenotypic changes, whereby offspring have an altered trait or a distinct alternate phenotype, frequently occur in response to increased maternal predation risk. The cotton aphid, Aphis gossypii (Glover), is unique, however, as offspring consist of four distinct phenotypes (“normal” light green apterae, “normal” dark green apterae, “dwarf” yellow apterae, and alatae), all with divergent life history patterns and resulting population dynamics. Here, we show that increased predation risk induces transgenerational phenotypic changes in cotton aphids. When exposed to search tracks from larval or adult convergent ladybird beetles, Hippodamia convergens Guerin-Meneville, cotton aphids produced greater numbers of winged offspring. In a subsequent experiment, apterous and alate individuals on clean plants were found to have primarily normal and dwarf offspring, respectively. We suggest that elevated predation risk may cause phenotypic changes in aphids over multiple generations, resulting in a more precipitous decline in herbivore populations than could be explained solely by increased predation rates.

/pdf/predator-induced-transgenerational-phenotypic-plasticity-in-47w6c35igl.pdf

Predator-induced transgenerational phenotypic plasticity in the cotton aphid

The effect of nitrogen fertilization on Aphis gossypii Glover color and size, fertility, and intrinsic rate of increase (rm) was studied on cotton plants. Nitrogen fertilization treatments consisted of 0, 50, 100, and 150% of the agronomic recommended level. Adult and nymph densities, as well as rm, were positively correlated with nitrogen fertilization. Aphid body length, head width, and darkness of color were recorded in populations on cotton plants fertilized with 100% nitrogen or with no nitrogen fertilization. Aphids on nitrogen-fertilized plants were significantly bigger and darker. All body size and darkness of color measurements were positively correlated with aphid fecundity. It was also found that the nutritional quality of the host plant on which the parent generation feeds has a stronger effect on the aphids than that of the quality of their own food plants. This phenomenon may dampen the effect short-term fluctuations in host plant quality have on aphid performance. Results are discussed in the context of aphid population biology, aphid–plant interactions and aphid population management.

https://bioone.org/journals/journal-of-economic-entomology/volume-94/issue-1/0022-0493-94.1.27/Effect-of-Nitrogen-Fertilization-on-Aphis-gossypii-Homoptera--Aphididae/10.1603/0022-0493-94.1.27.pdf

Effect of Nitrogen Fertilization on Aphis gossypii (Homoptera: Aphididae): Variation in Size, Color, and Reproduction

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Effect of Nitrogen Fertilization on Aphis gossypii (Homoptera: Aphididae): Variation in Size, Color, and Reproduction