Spatio-temporal microbial regulation of aggregate-associated priming effects under contrasting tillage practices

Tillage intensity significantly influences the heterogeneous distribution and dynamic changes of soil microorganisms, consequently shaping spatio-temporal patterns of SOC decomposition. However, little is known about the microbial mechanisms by which tillage intensity regulates the priming effect (PE) dynamics in heterogeneous spatial environments such as aggregates. Herein, a microcosm experiment was established by adding 13C-labeled straw residue to three distinct aggregate-size classes (i.e., mega-, macro-, and micro-aggregates) from two long-term contrasting tillage histories (no-till [NT] and conventional plow tillage [CT]) for 160 days to observe the spatio-temporal variations in PE. Metagenomic sequencing and Fourier transform mid-infrared techniques were used to assess the relative importance of C-degrading functional genes, microbial community succession, and SOC chemical composition in the aggregate-associated PE dynamics during straw decomposition. Spatially, straw addition induced a positive PE for all aggregates, with stronger PE occurring in larger aggregates, especially in CT soil compared to NT soil. Larger aggregates have more unique microbial communities enriched in genes for simple C degradation (e.g., E5.1.3.6, E2.4.1.7, pmm-pgm, and KduD in Nitrosospeera and Burkholderia), contributing to the higher short-term PE; however, CT soils harbored more genes for complex C degradation (e.g., TSTA3, fcl, pmm-pgm, and K06871 in Gammaproteobacteria and Phycicoccus), supporting a stronger long-term PE. Temporally, soil aggregates played a significant role in the early-stage PEs (i.e., < 59 days after residue addition) through co-metabolism and nitrogen (N) mining, as evidenced by the increased microbial biomass C and dissolved organic C (DOC) and reduced inorganic N with increasing aggregate-size class. At a later stage, however, the legacy effect of tillage histories controlled the PEs via microbial stoichiometry decomposition, as suggested by the higher DOC-to-inorganic N and DOC-to-available P stoichiometries in CT than NT. Our study underscores the importance of incorporating both spatial and temporal microbial dynamics for a comprehensive understanding of the mechanisms underlying SOC priming, especially in the context of long-term contrasting tillage practices.

Modelling pesticide degradation and leaching in conservation agriculture: Effect of no-till and mulching

No-till and mulching are typical management operations in conservation agriculture (CA). To model pesticide degradation and leaching under a CA scenario, as compared to a conventional-tillage scenario (CT), the mulch module of the agro-hydrological model Daisy was extended. A Daisy soil column was parameterized with measurements of topsoil, mulch, and a realistic subsoil, and tested against published experimental data of pesticide fate in laboratory soil columns covered by mulch. Uncertainty and sensitivity analyses of the new Daisy version were conducted for a series of weather, soil, pesticide, and mulch parameters, using 4939 Monte Carlo simulations under each scenario. Results showed that there was no systematic difference in pesticide leaching from the topsoil (to the subsoil and directly to drains via drain-connected biopores) between CA and CT, but pesticide degradation and sorption were significantly different; degradation in the mulch and uppermost soil surface layer (0-3.5 cm) was larger in CA while degradation was larger in CT when considering the whole topsoil (0-30 cm). This difference for the whole topsoil could be explained by pesticide interception in CA in the part of the mulch not in direct contact with the soil where degradation is assumed not to occur. The sensitivity analysis highlighted non-influential parameters and seven parameters out of twenty-five to be better estimated to improve the accuracy of the predictions.

The business case for carbon farming in the USA

U.S. agricultural producers are increasingly able to participate in private voluntary carbon initiatives that compensate their efforts to sequester CO2, reduce GHG emissions, and provide ecosystem services through eligible conservation practices. This study examines the potential effects of alternative private payment regimes (per practice vs. per output), prices paid to farmers relative to out-of-pocket costs (low vs. high), and the availability of information on CO2 sequestration (limited vs. full), on the adoption of cover crops and no-till in the United States, the resulting CO2 sequestration, and changes in farmers' net returns. The analysis relies on a highly stylized model of heterogeneous farms calibrated with county-level agronomic data, and simulated for current estimates of GHG impacts of cover crop planting and no-till under different scenarios. Our results indicate that agricultural carbon markets can be profitable for U.S. farmers, although with substantial geographic variability, and that annual carbon sequestration could range between 17 and 75 million mtCO2e. Payments per output would incentivize higher carbon sequestration than payments per practice, but the former regime would be less favored by farmers as a unified group than the latter (due to lower aggregate net returns). However, if operators of farms with high carbon sequestration potential could decide the payment regime to be implemented, they would choose the payment per output regime (due to higher net returns per enrolled hectare). Total projected net changes in GHGs under payments per practice, based solely on county-average net GHG effects of cover crops and no-till, over-estimate actual total GHG sequestration (based on the entire distribution of net effects by county) by 2.1 and 14.2 million mtCO2e, or 18% and 21%, respectively.

Circular agriculture increases food production and can reduce N fertilizer use of commercial farms for tropical environments

World food production must increase in the coming years with minimal environmental impact for food and nutrition security. Circular Agriculture has emerged as an approach to minimize non-renewable resource depletion and encourage by-product reuse. The goal of this study was to evaluate Circular Agriculture as a tool to increase food production and N recovery. The assessment was conducted for two Brazilian farms (Farm 1; Farm 2) with Oxisols under no-till and a diversified cropping system, including five species of grain, three cover crop species, and sweet potato. Both farms implemented an annual two-crop rotation and an integrated crop-livestock system with beef cattle confined for 2-years. Grain and forage from the fields, leftovers from silos, and crop residues were used as cattle feed. Grain yield was 4.8 and 4.5 t ha^-1 for soybean, 12.5 and 12.1 t ha^-1 for maize, and 2.6 and 2.4 t ha^-1 for common bean, for Farm 1 and Farm 2, respectively, which is higher than the national average. The animals gained 1.2 kg day^-1 of live weight. Farm 1 exported 246 kg ha^-1 year^-1 of N in grains, tubers, and animals, while 216 kg ha^-1 year^-1 was added as fertilizer and N to cattle. Farm 2 exported 224 kg ha^-1 year^-1 in grain and animals, while 215 kg ha^-1 year^-1 was added as fertilizer and N to cattle. Circular practices, i.e., no-till, crop rotation, year-round soil covered, maize intercropped with brachiaria ruziziensis, biological N fixation, and crop-livestock integration, increased crop yield and decreased N application by 14.7 % (Farm 1) and 4.3 % (Farm 2). 85 % of the N consumed by the confined animals was excreted and converted into organic compost. Overall, circular practices associated with adequate crop management allowed recovering high rate of applied N, reducing environmental impacts, and increasing food production with lower production costs.

Soil physicochemical and biological properties in soybean areas under no-till Systems in the Brazilian Cerrado

No-till (NT) as a conservation practice aims to minimize soil disturbance and enhance soil sustainability. However, how NT practice affects soil physicochemical and biological properties in soybean areas remains unclear. This study selected 65 high-yielding soybean farms under a long-term NT system in the Brazilian Cerrado and collected soil samples at 0.0-0.10 m (L1), 0.10-0.20 m (L2) and 0.20-0.40 m (L3) depths. The effect of NT on soil properties and interactions with soybean productivities were assessed. Results showed that the average soybean yield of the study areas in the last three years was 4.13 Mg ha^-1, with 26 areas presenting yields over 4.20 Mg ha^-1. Most studied soil properties showed a depth stratification and were strongly concentrated in L1, except for S, Al³⁺ and aluminum saturation, which displayed lower surface and higher subsurface concentrations. Moreover, a high proportion of SOM is composed of light SOM fraction in areas of high soybean yield, with the average SOM values of 39.9, 27.8 and 19.6 g kg^-1 in L1, L2 and L3, respectively. Soils under long-term NT present moderate values of enzyme activity compared with the relatively low values under conventional tillage system, especially 94 % of the plots have moderate values of activity of arylsulfatase enzymes. The data presented support the conclusion that NT system can enhance soil fertility and biological quality in soybean cultivation. Our results suggest that it is necessary to adopt NT practice because it allows increasing soybean productivity in Brazil without the need to increase the sown area, in addition to increasing productivity associated with an improvement in the agroecosystem quality, thus moving toward a more sustainable agriculture.

The effect of resource-saving tillage technologies on the mobility, distribution and migration of trace elements in soil

The influence of agricultural tillage technologies on the accumulation and distribution of trace elements in the soil is poorly studied. At the same time, intensive agriculture requires large amounts of fertilizers, growth stimulators, pesticides, and other substances, which can effect the ecological safety of the plant products and soil. This paper represents studying the effect of various agricultural techniques (including resource-saving technologies) on the mobility and profile distribution of Pb, Zn, and Cu in Haplic Chernozem. No significant influence of resource-saving tillage technologies was found on the total Pb content. Contrary, the resource-saving tillage technologies was observed to promote the growth of the total Zn and Cu content depending on the cultivation method (by 26% Zn, 34% Cu at minimal tillage, and 28% for both elements using No-till in Ap horizon). Amongst different applied agrotechnologies, there was no influence found on the profile distribution of total elements content. Only two horizons showed the total Pb content accumulation: biogenic (Ap-A) and carbonate (BC-C) horizon. In contrast, the only biogenic accumulation for Zn was determined. Copper characterizes by even distribution over the soil profile. The use of resource-saving agricultural technologies increases exchangeable fraction of Zn, Pb and Cu in soil almost by 1.5-2.0 times in the Ap horizon compared to moldboard ploughing. Despite the increase in the exchangeable fraction of Zn and Cu, this amount of micronutrients is not enough for adequate plant nutrition. The use of various agricultural technologies at Haplic Chernozem led to changes in the distribution of studied elements' exchangeable fraction over the soil profile. The study results suggested a need to increase the amount of Cu and Zn fertilizers applied to the soil with resource-saving cultivation technologies.

Sieving soil before incubation experiments overestimates carbon mineralization but underestimates temperature sensitivity

The sensitivity of soil organic carbon (SOC) mineralization to temperature could affect the future atmospheric CO₂ levels under global warming. Sieved soils are widely used to assess SOC mineralization and its temperature sensitivity (Q₁₀) via laboratory incubation. However, sieved soils cause a temporary increase in mineralization due to the destruction of soil structure, which can affect estimates of SOC mineralization, especially in soils managed with no-till (NT). To identify the effects of soil sieving on SOC mineralization and Q₁₀, soil was collected from an 11-year field experiment under a wheat-maize cropping system managed with a combination of tillage [NT and plow tillage (PT)] and residue [residue returning (RR) and residue removal (R0)]. Soil was either sieved or left in an undisturbed state and incubated at 15 °C and 25 °C. SOC mineralization in sieved soils at 25 °C was 47.28 g C kg^-1 SOC, 160.1% higher than SOC mineralization in undisturbed soils (P < 0.05). Interestingly, Q₁₀ values in sieved soils were 1.29, 77.6% lower than Q₁₀ in undisturbed soils (P < 0.05). Highly significant correlations (P < 0.01) were observed between sieved and undisturbed soils for SOC mineralization (r = 0.85-0.98) and Q₁₀ (r = 0.78-0.87). Soil macro-aggregates had lower SOC mineralization by 6.1-21.9%, but higher Q₁₀ values by 4.7-6.5% compared with micro-aggregates, contributing to lower mineralization and higher Q₁₀ under NT and RR. Furthermore, structure equation and random forest modelling showed that increased SOC contents in NT and RR could not only reduce SOC mineralization, but also constrained the improvement of Q₁₀ in NT and RR. Overall, these results indicated that although sieved soils overestimated SOC mineralization and underestimated Q₁₀ due to the destruction of macro-aggregates, the patterns between treatments were similar and sieving soil for incubation is considered as a suitable approach to evaluate the relative impacts of NT and RR on SOC mineralization and Q₁₀.

Degradation of transgenic Bacillus thuringiensis proteins in corn tissue in response to post-harvest management practices

Knowledge of the persistence of Cry proteins in transgenic corn residue after harvest is necessary to assess the ecological risk to nontarget organisms. The amount of protein remaining in crop residue declines over time by a combination of microbial decomposition and leaching, both influenced by temperature, precipitation, and the amount of residue-soil contact. Here, we investigated how long biologically active Cry proteins persist in SmartStax corn residue expressing Cry1A.105, Cry1F, Cry2Ab2, Cry3Bb1, and Cry34/35Ab1, when subjected to four post-harvest practices (chisel plow tillage, flail mowing, cover crop planting, and undisturbed residue). Protein activity in residue samples collected up to 25 weeks after harvest was measured by Ostrinia nubilalis feeding bioassays and cross validated with detection frequencies determined by ELISA. All corn residue remained above ground in the flail-mowed and undisturbed treatments, while the cover crop and chisel plow treatments left 88.3 and 39.6% of the residue remaining above ground, respectively. Cry proteins retained biological activity for as long as 24 weeks after harvest when residue was left above ground with less soil contact, typical of no-till corn systems. ELISA detections were positively correlated with results of the feeding bioassays, which revealed the presence of active proteins beyond the point of ELISA detection.

[Effect of winter cover crops on the soil microbiome: a systematic literature review]

The inclusion of winter cover crops (WCC) in no-till (NT) systems in replacement of bare fallow is a promising alternative to improve soil health and consequently, contribute to environmental sustainability of agricultural systems. This review provides a comprehensive evaluation of the effects of the use of WCC in rotation with summer cash crops under NT systems on the soil microbiome versus bare fallows. A systematic literature search was conducted to evaluate the impact of WCC on microbial parameters indicative of abundance, activity and diversity. Twenty-two papers were selected based on seven combined criteria. The results of this review show that enzyme activities in soil are enhanced with the inclusion of WCC in the rotation, particularly those that include legumes and mix of species. In general, more than half of the analyzed papers report higher microbial biomass in soils with WCC than in bare fallow. Interestingly, the effects of WCC on microbial parameters are independent of the duration of the experiments. However, more basic research is necessary to reduce the heterogeneity of the studies and to better understand the complexity of the interactions between WCC and the soil microbiome.

A comprehensive modeling framework to evaluate soil erosion by water and tillage

Soil erosion is significantly increased and accelerated by unsustainable agricultural activities, resulting in one of the major threats to soil health and water quality worldwide. Quantifying soil erosion under different conservation practices is important for watershed management and a framework that can capture the spatio-temporal dynamics of soil erosion by water is required. In this paper, a modeling framework that coupled physically based models, Water Erosion Prediction Project (WEPP) and MIKE SHE/MIKE 11, was presented. Daily soil loss at a grid-scale resolution was determined using WEPP and the transport processes were simulated using a generic advection dispersion equation in MIKE SHE/MIKE 11 models. The framework facilitated the physical simulation of sediment production at the field scale and transport processes across the watershed. The coupled model was tested using an intensively managed agricultural watershed in Illinois. The impacts of no-till practice on both sediment production and sediment yield were evaluated using scenario-based simulations with different fractions of no-till and conventional tillage combinations. The results showed that if no-till were implemented for all fields throughout the watershed, 76% and 72% reductions in total soil loss and sediment yield, respectively, can be achieved. In addition, if no-till practice were implemented in the most vulnerable areas to sediment production across the watershed, a 40% no-till implementation can achieve almost the same reduction as 100% no-till implementation. Based on the simulation results, the impacts of no-till practice are more prominent if implemented where it is most needed.

Agro-ecological options for fall armyworm (Spodoptera frugiperda JE Smith) management: Providing low-cost, smallholder friendly solutions to an invasive pest

Fall armyworm (FAW), a voracious agricultural pest native to North and South America, was first detected on the African continent in 2016 and has subsequently spread throughout the continent and across Asia. It has been predicted that FAW could cause up to $US13 billion per annum in crop losses throughout sub-Saharan Africa, thereby threatening the livelihoods of millions of poor farmers. In their haste to respond to FAW governments may promote indiscriminate use of chemical pesticides which, aside from human health and environmental risks, could undermine smallholder pest management strategies that depend to a large degree on natural enemies. Agro-ecological approaches offer culturally appropriate low-cost pest control strategies that can be readily integrated into existing efforts to improve smallholder incomes and resilience through sustainable intensification. Such approaches should therefore be promoted as a core component of integrated pest management (IPM) programmes for FAW in combination with crop breeding for pest resistance, classical biological control and selective use of safe pesticides. Nonetheless, the suitability of agro-ecological measures for reducing FAW densities and impact need to be carefully assessed across varied environmental and socio-economic conditions before they can be proposed for wide-scale implementation. To support this process, we review evidence for the efficacy of potential agro-ecological measures for controlling FAW and other pests, consider the associated risks, and draw attention to critical knowledge gaps. The evidence indicates that several measures can be adopted immediately. These include (i) sustainable soil fertility management, especially measures that maintain or restore soil organic carbon; (ii) intercropping with appropriately selected companion plants; and (iii) diversifying the farm environment through management of (semi)natural habitats at multiple spatial scales. Nevertheless, we recommend embedding trials into upscaling programmes so that the costs and benefits of these interventions may be determined across the diverse biophysical and socio-economic contexts that are found in the invaded range.

A mixed-methods approach to determine how conservation management programs and techniques have affected herbicide use and distribution in the environment over time

No-till agriculture has the ability to reduce fuel consumption, increase soil moisture, reduce soil erosion and increase organic matter. However, it remains unclear whether it increases herbicide use overall in the long term for communities that use no-till as their primary source of conservation agriculture. The preponderance of literature suggests that no-till has increased herbicide use, but it is difficult to quantify how much herbicide has increased in a given location and to directly correlate changes in herbicide use to changes in soil and water quality. This paper provides several methods to determine how herbicide use has changed over time in an agricultural community in Oregon that switched over to no-till in the late 1990s and early 2000s. These methods include: spatial analysis of remote sensing satellite imagery of vegetation health along streams; use of a drone fitted with an agricultural camera to detect vegetation health; and soil, sediment, and water sampling for the most commonly used herbicides in the study area. By using these methods, this study shows where stream vegetation health continues to be an issue in the agricultural community, and where concentrations of a commonly used herbicide in the community may be impacting human and ecological health. This study has important implications for impacts to soil and water quality over time in agricultural communities, as many researchers have noted the need to determine the long term effects of conversion to no-till and other forms of conservation agriculture. By providing these methods, communities heavily engaged in multiple forms of conservation agriculture may be able to track herbicide use changes in real time and on shorter decadal time spans in places where conservation agriculture is practiced.

Glyphosate decreases mycorrhizal colonization and affects plant-soil feedback

Our aim was to study the effects of glyphosate, tilling practice and cultivation history on mycorrhizal colonization and growth of target (weeds) and non-target (crops) plants. Glyphosate, the world's most widely used pesticide, inhibits an enzyme found in plants but also in microbes. We examined the effects of glyphosate treatment applied in the preceding fall on growth of a perennial weed, Elymus repens (target plant) and a forage grass, Festuca pratensis (non-target plant) and their arbuscular mycorrhizal fungal (AMF) root colonization in a field pot experiment. Non-target plants were sown in the following spring. Furthermore, we tested if glyphosate effects depend on tillage or soil properties modulated by long cultivation history of endophyte symbiotic grass (E+ grass). AMF root colonization, plant establishment and growth, glyphosate residues in plants, and soil chemistry were measured. Glyphosate reduced the mycorrhizal colonization and growth of both target and non-target grasses. The magnitude of reduction depended on tillage and soil properties due to cultivation history of E+ grass. We detected glyphosate residues in weeds and crop plants in the growing season following the glyphosate treatment. Residues were higher in plants growing in no-till pots compared to conspecifics in tilled pots. These results demonstrate negative effects of glyphosate on non-target organisms in agricultural environments and grassland ecosystems.

Can conservation tillage reduce N2O emissions on cropland transitioning to organic vegetable production?

Nitrous oxide (N₂O) is an important greenhouse gas and a catalyst of stratospheric ozone decay. Agricultural soils are the source of 75% of anthropogenic N₂O emissions globally. Recently, significant attention has been directed at examining effects of conservation tillage on carbon sequestration in agricultural systems. However, limited knowledge is available regarding how these practices impact N₂O emissions, especially for organic vegetable production systems. In this context, a three-year study was conducted in a well-drained sandy loam field transitioning to organic vegetable production in the Mid-Atlantic coastal plain of USA to investigate impacts of conservation tillage [strip till (ST) and no-till (NT)] and conventional tillage (CT) [with black plastic mulch (CT-BP) and bare-ground (CT-BG)] on N₂O emissions. Each year, a winter cover crop mixture (forage radish: Raphanus sativus var. longipinnatus, crimson clover: Trifolium incarnatum L., and rye: Secale cereale L.) was grown and flail-mowed in the spring. Nearly 80% of annual N₂O-nitrogen (N) emissions occurred during the vegetable growing season for all treatments. Annual N₂O-N emissions were greater in CT-BP than in ST and NT, and greater in CT-BG than in NT, but not different between CT-BG and CT-BP, ST and NT, or CT-BG and ST. Conventional tillage promoted N mineralization and plastic mulch increased soil temperature, which contributed to greater N₂O-N fluxes. Though water filled porosity in NT was higher and correlated well with N₂O-N fluxes, annual N₂O-N emissions were lowest in NT suggesting a lack of substrates for nitrification and denitrification processes. Crop yield was lowest in NT in Year 1 and CT-BP in Year 3 but yield-scaled N₂O-N emissions were consistently greatest in CT-BP and lowest in NT each year. Our results suggest that for coarse-textured soils in the coastal plain with winter cover crops, conservation tillage practices may reduce N₂O emissions in organic vegetable production systems.

Farm-level economics of innovative tillage technologies: the case of no-till in the Altai Krai in Russian Siberia

In the agricultural Altai Krai in Russian Siberia, soil degradation problems are prevalent. Agronomists recommend "reduced tillage systems," especially no-till, as a sustainable way to cultivate land that is threatened by soil degradation. In the Altai Krai, less is known about the technologies in practice. In this paper, we provide information on plant cultivation technologies used in the Altai Krai and on selected factors preventing farm managers in this region from adopting no-till technology based on our own quantitative survey conducted across 107 farms in 2015 and 2016. The results of the quantitative survey show that farm managers have high uncertainty regarding the use of no-till technology including its economics. To close this gap, we provide systematic analysis of factors influencing the economy of the plant production systems by using a farm optimization model (linear programming) for a real farm, together with expert estimations. The farm-specific results of the optimization model show that under optimal management and climatic conditions, the expert Modern Canadian no-till technology outperforms the farm min-till technology, but this is not the case for suboptimal conditions with lower yields.