The impact of different arable farming practices on soil erosion is only partly resolved, and the effect of conservation tillage practices in organic agriculture on sediment loss has rarely been tested in the field. This study investigated rainfall-induced interrill sediment loss in a long-term replicated arable farming system and tillage experiment (the FAST trial) with four different cropping systems: (1) organic farming with intensive tillage, (2) organic farming with reduced tillage, (3) conventional farming with intensive tillage, and (4) conventional farming with no tillage. Measurements were carried out under simulated heavy rainfall events with runoff plots in 2014 (fallow land after winter wheat) and 2017 (during maize growth). Organic farming decreased mean sediment delivery compared to conventional farming by 30% (0.54 t ha −1 h −1). This study demonstrated that reduced tillage in organic farming decreased sediment delivery (0.73 t ha −1 h −1) compared to intensively tilled organic plots (1.87 t ha −1 h −1) by 61%. Nevertheless, the combination of conventional farming and no tillage showed the lowest sediment delivery (0.24 t ha −1 h −1), whereas intensively tilled conventional plots revealed the highest delivery (3.46 t ha −1 h −1). Erosion rates were much higher in June during maize growth (2.92 t ha −1 h −1) compared to those of fallow land after winter wheat (0.23 t ha −1 h −1). Soil surface cover and soil organic matter were the best predictors for reduced sediment delivery, and living plant cover from weeds in reduced organic treatments appeared to protect soil surfaces better than plant residues in conventional, no-tillage plots. Soil erosion rates were significantly lower when soil cover was above 30%. In conclusion, this study demonstrates that both organic farming and conservation agriculture reduce soil losses and showed for the first time that reduced tillage practices are a major improvement in organic farming when it comes to soil erosion control.

Opencast mining causes severe impacts on natural environments, often resulting in permanent damage to soils and vegetation. In the present study we use a 14-year restoration chronosequence to investigate how resource input and spontaneous plant colonization promote the revegetation and reconstruction of mined soils in central Brazil. Using a multi-proxy approach, combining vegetation surveys with the analysis of plant and soil isotopic abundances (delta13C and delta15N) and chemical and physical fractionation of organic matter in soil profiles, we show that: (1) after several decades without vegetation cover, the input of nutrient-rich biosolids into exposed regoliths prompted the establishment of a diverse plant community (> 30 species); (2) the synergistic effect of resource input and plant colonization yielded unprecedented increases in soil carbon, accumulating as chemically stable compounds in occluded physical fractions and reaching much higher levels than observed in undisturbed ecosystems; and (3) invasive grasses progressively excluded native species, limiting nutrient availability, but contributing more than 65% of the total accumulated soil organic carbon. These results show that soil-plant feedbacks regulate the amount of available resources, determining successional trajectories and alternative stable equilibria in degraded areas undergoing restoration. External inputs promote plant colonization, soil formation, and carbon sequestration, at the cost of excluding native species. The introduction of native woody species would suppress invasive grasses and increase nutrient availability, bringing the system closer to its original state. However, it is difficult to predict whether soil carbon levels could be maintained without the exotic grass cover. We discuss theoretical and practical implications of these findings, describing how the combination of resource manipulation and management of invasive species could be used to optimize restoration strategies, counteracting soil degradation while maintaining species diversity.

Abstract. Further progress in understanding and mitigating N 2 O emissions from soil lies within transdisciplinary research that reaches across spatial scales and takes an ambitious look into the future.

Through meta-analysis, we synthesize results from field studies on the effect of biochar application on NO emissions and crop yield. We aimed to better constrain the effect of biochar on NO emissions under field conditions, identify significant predictor variables, assess potential synergies and tradeoffs between NO mitigation and yield, and discuss knowledge gaps. The response ratios for yield and NO emissions were weighted by one of two functions: (i) the inverse of the pooled variance or (ii) the inverse of number of observations per field site. Significant emission reductions were observed when weighting by the inverse of the pooled variance (-18.1 to -7.1%) but not when weighting by the number of observations per site (-17.1 to +0.8%), thus revealing a bias in the existing data by sites with more observations. Mean yield increased by 1.7 to 13.8%. Our study shows yield benefits but no robust evidence for NO emission reductions by biochar under field conditions. When weighted by the inverse of the number of observations per site, NO emission reductions were not significantly affected by cropping system, biochar properties of feedstock, pyrolysis temperature, surface area, pH, ash content, application rate, or site characteristics of N rate, N form, or soil pH. Uneven coverage in the range of these predictor variables likely underlies the failure to detect effects. We discuss the need for future biochar field studies to investigate effects of fertilizer N form, sustained and biologically relevant changes in soil moisture, multiple biochars per site, and time since biochar application.

Conventional tillage is a widespread soil management practice that controls weeds and promotes nutrient mineralization at the expense of a degraded soil structure and soil carbon (C) loss. Although C dynamics and soil structure are widely recognized as pivotal to essential environmental and crop-related agroecosystem processes such as belowground C storage and crop root establishment, there is still a need to evaluate cropping practices most favorable for soil structure. For example, the effects on soil structure by continuous intensive tillage after a ley period remains unclear. To address these issues, we measured mean weight diameter, total C and total nitrogen (N) in whole soil and water-stable aggregate fractions after a 4-year arable crop rotation on a Cambisol where organic and conventional management was combined with intensive tillage and different types of conservation tillage. Measurements were repeated following a 2-year grass-clover ley period. Results showed that 4 years of organic management (including the application of cattle manure slurry) combined with reduced tillage significantly improved soil structure through increasing the proportion of large macroaggregates and hence the aggregate mean weight diameter (MWD) in the 0-6 cm soil layer. Although an increase in MWD after ley was observed in organic intensive tillage and a marginal increase in conventional intensive tillage, a significant increase in total C was observed only for the organic cropping systems, which also showed a high C stratification between 0-6 cm and 6-20 cm depth. Thus, a ley period enhances soil structure after continuous cropping under intensive tillage and when organic management is combined with reduced tillage. In conclusion, soil structure is best maintained when combining organic management with reduced tillage due to additive effects.

Primary tropical forests generally exhibit large gaseous nitrogen (N) losses, occurring as nitric oxide (NO), nitrous oxide (N2O) or elemental nitrogen (N2). The release of N2O is of particular concern due to its high global warming potential and destruction of stratospheric ozone. Tropical forest soils are predicted to be among the largest natural sources of N2O; however, despite being the world’s second-largest rainforest, measurements of gaseous N-losses from forest soils of the Congo Basin are scarce. In addition, long-term studies investigating N2O fluxes from different forest ecosystem types (lowland and montane forests) are scarce. In this study we show that fluxes measured in the Congo Basin were lower than fluxes measured in the Neotropics, and in the tropical forests of Australia and South East Asia. In addition, we show that despite different climatic conditions, average annual N2O fluxes in the Congo Basin’s lowland forests (0.97 ± 0.53 kg N ha−1 year−1) were comparable to those in its montane forest (0.88 ± 0.97 kg N ha−1 year−1). Measurements of soil pore air N2O isotope data at multiple depths suggests that a microbial reduction of N2O to N2 within the soil may account for the observed low surface N2O fluxes and low soil pore N2O concentrations. The potential for microbial reduction is corroborated by a significant abundance and expression of the gene nosZ in soil samples from both study sites. Although isotopic and functional gene analyses indicate an enzymatic potential for complete denitrification, combined gaseous N-losses (N2O, N2) are unlikely to account for the missing N-sink in these forests. Other N-losses such as NO, N2 via Feammox or hydrological particulate organic nitrogen export could play an important role in soils of the Congo Basin and should be the focus of future research.

We investigated the effect of biochar type on plant performance and soil nitrogen (N) transformations in mesocosms representing an organic lettuce (Lactuca sativa) production system. Five biochar materials were added to a silt loam soil: Douglas fir wood pyrolyzed at 410 °C (W410), Douglas fir wood pyrolyzed at 510 °C (W510), pine chip pyrolyzed at 550 °C (PC), hogwaste wood pyrolyzed between 600 and 700 °C (SWC), and walnut shell gasified at 900 °C (WS). Soil pH and cation exchange capacity were significantly increased by WS biochar only. Gross mineralization increased in response to biochar materials with high H/C ratio (i.e., W410, W510, and SWC), which can be favorable for organic farming systems challenged by insufficient N mineralization during plant growth. Net nitrification was increased by W510, PC, and WS without correlating with the abundance of ammonia oxidizing gene (amoA). Increases in N transformation rates did not translate into increases in plant productivity or leaf N content. WS biochar increased the abundance of amoA and nitrite reductase gene (nirK), while SWC biochar decreased the abundance of amoA and nitrous oxide gene (nosZ). Decreases in N 2 O emissions were only observed in soil amended with W510 for 3 days out of the 42-day growing season without affecting total cumulative N 2 O fluxes. This suggests that effects of biochar on decreasing N 2 O emissions may be transient, which compromise biochar's potential to be used as a N 2 O mitigation strategy in organic systems. Overall, our results confirm that different biochar materials can distinctively affect soil properties and N turnover.

RESUMO O armazenamento adequado dos tubérculos é muito importante para manter o equilíbrio da oferta de batata no mercado e para a obtenção de tubérculos-semente em adequado estádio fisiológico no momento do plantio. O objetivo deste trabalho foi determinar o efeito de diferentes temperaturas de armazenagem no envelhecimento fisiológico de tubérculos de três clones de batata produzidos durante o outono e a primavera. O experimento foi desenvolvido em um fatorial de três clones (Asterix, SMIJ461-1 e SMINIA793101-3) por quatro temperaturas de armazenamento (4, 8, 12 e 25 ºC) e duas épocas de plantio (outono e primavera) no delineamento experimental inteiramente casualizado, com quatro repetições. As avaliações foram em intervalos de 30 dias, do início até os 180 dias de armazenamento. O armazenamento refrigerado prolongou a dormência dos tubérculos, reduzindo o número de brotos e evitando o apodrecimento; as temperaturas de 4 e 8 o C impediram a brotação dos tubérculos produzidos no outono. A perda de massa fresca e a respiração dos tubérculos aumentaram com o tempo e a temperatura de armazenamento. A época de plantio altera o comportamento fisiológico dos tubérculos durante o armazenamento. O armazenamento à baixa temperatura (4 e 8 ºC) é eficaz para retardar o envelhecimento fisiológico.Palavras-chave: Solanum tuberosum L., temperatura de armazenamento, perdas pós-colheita, respiração, batata-semente. ABSTRACT PHYSIOLOGICAL AGING OF POTATO TUBERS PRODUCED DURING FALL AND SPRING GROWING SEASONS AND STORED UNDER DIFFERENT TEMPERATURESAdequate tuber storage is necessary to maintain a good availability of potato tubers in the market and to get seeds with adequate physiological age at planting. The objective of this work was to determine the effect of different storage temperatures on tuber physiological aging of three potato clones produced during fall and spring growing seasons. The experiment was carried out as factorial of three clones (Asterix, SMIJ461-1 and SMINIA793101-3) by four storage temperatures (4, 8, 12 and 25 ºC) and two growing seasons (fall and spring) in a random design with four replications. At 30-day intervals, tubers were evaluated from the beginning to 180 days of storage. Cold storage increased dormancy period, reduced sprout number and kept health tubers. Tubers produced during fall season did not sprout at the storage temperatures of 4 and 8 o C. Tuber fresh weight loss and respiration increased with storage period and temperature. Crop growing season changes tuber physiological aging during storage. Storage in low temperature (4 and 8 ºC) conditions is efficient to slow down tuber aging.