查看更多>>摘要：? 2021 Elsevier B.V.Nitrate leaching from agricultural soils is a considerable environmental concern related to nitrogen (N) application, and in some countries N fertilizer application is regulated by legislation to reach environmental goals. Information about the change in nitrate leaching with changes in mineral N fertilizer rates is important under such conditions. The increase in nitrate leaching due to extra mineral N application near the economic optimal N application for crop production, called marginal nitrate leaching, depends on a number of factors like soil type, crop types, climatic conditions and N fertilization rates. In this study, we collected published experimental data from 44 site-years from Denmark and 31 site-years from other European countries (Germany, Sweden, UK) with measured nitrate leaching at increasing mineral N fertilizer rates. We focused on obtaining marginal nitrate leaching around optimal N rates based on available information from the different field experiments. The measured nitrate leaching varied from 3 to 92 kg N ha-1 in the Danish dataset. For the European data set, it varied from 1 to 124 kg N ha-1. The median and mean of the estimated marginal nitrate leaching at the optimal N rates were 17.0% and 20.5%, respectively, in the Danish dataset and 9.0% and 14.9%, respectively, in the European dataset. At the optimal N rate, a positive relationship was found between yearly nitrate leaching and marginal nitrate leaching. Both nitrate leaching and marginal nitrate leaching at the optimal N rate were positively correlated with precipitation during the hydrological year and winter periods, but not to any other environmental factors tested. There was no significant difference in either marginal nitrate leaching or nitrate leaching between growing spring cereals versus winter cereals. No significant effect of winter vegetation cover on marginal nitrate leaching was detected. Furthermore, the marginal nitrate leaching at the optimal N rate in the first year of the experiments with increasing N rates was significantly lower than the accumulated effect of two or more years with low or high N rates. Therefore, the long-term effects of N rates should be accounted for when estimating marginal nitrate leaching. The marginal nitrate leaching is highly variable between years and only a part of this variation was explained in this study. The positive correlation between marginal nitrate leaching and nitrate leaching at optimum N rates implies that cropping system and management factors reducing nitrate leaching also reduce the marginal nitrate leaching.
查看更多>>摘要：? 2021 Elsevier B.V.Multi-temporal analysis of land cover dynamics using remote sensing can enable the determination of the spatial extent and average rate of land cover change. With the application of an appropriate change analysis method, it is also possible to distinguish whether a land cover change has occurred by the effect of a random or a systematic process. In connection with this, characterizing rainfall variability and historical meteorological drought events can allow understanding of their effects on agro-ecosystems and vegetation cover dynamics. Therefore, this study has evaluated multi-temporal land cover change in response to the possible impacts of population pressure and rainfall variability on agro-ecosystem dynamics. This was conducted on a traditional agroforestry-dominated landscape in Southern Ethiopia. Using Landsat images acquired in 1985, 2000, and 2018, a post-classification land cover change analysis approach was employed to distinguish between a systematic and random process of inter-category transitions. Assessment of drought events and rainfall variability dynamics were performed using standardized precipitation index (SPI) and rainfall coefficient of variation (CV), respectively. Mann–Kendall test was also applied for the detection of a monotonic rainfall trend. A bias-corrected Climate Hazards group Infrared Precipitation with Stations (CHIRPS) over 1981–2017 was used to calculate the SPI, CV and Mann–Kendall trend test. The analysis showed that above 41% of the landscape has experienced land cover transitions between 1985 and 2018. This has primarily resulted by a systematic and rapid expansion of agriculture, urban areas, and eucalyptus plantations, at the expense of natural vegetation ecosystems. Consequently, over the last 33 years (1985–2018), natural forest, grassland, and wetland have declined by 74.8%, 83.3%, and 78.4%, respectively. Another major land cover change identified in this study was the replacement of open-field crops by agroforestry, mainly in the western part of the catchment. Such expansion of agroforestry has appeared to be spatially correlated with a lower amount of long-term average and more variable rainfall. Perhaps, this could indicate farmers’ response to rainfall variability by diversifying agricultural production options (i.e. agroforestry system), by replacing the more risk-prone mono-cropping culture. The observed persistence and further expansion of traditional agroforestry (a combination of perennial crops and scattered trees) have implications in terms of enhancing biodiversity conservation and environmental protection. Overall, the land cover transitions that occurred over the last three decades suggest future conservation priorities for improved landscape management, with more emphasis on the most exposed natural vegetation ecosystems.
查看更多>>摘要：? 2021 Elsevier B.V.With fast development of industry and agriculture in last two decades, land use changed greatly on specific soil types of intrinsic low quality with C loss potential and necessitates avoiding. Although researchers studied the effect of land-use changes on soil carbon storage, that on some soil types had rarely been reported, which led to relatively more C loss. We explored the impact of land-use changes and soil types on soil organic carbon (SOC) sequestration in the top 30 cm in the Tarim River Basin (the second largest inland river in the world) from 2000 to 2020. The land-use images with a one-kilometer spatial resolution and soil data from the Harmonized World Soil Database were analysed. The groundwater levels were monitored by 11 wells along the river from 2012 to 2017. Land-use changes were dominated by increases in the areas of cultivated land (1843–4099 km2) and woodland (5055–5433 km2) and decreases in grassland area ( 19076–12634 km2). The increase in cultivated land area was acquired from grassland (54%), woodland (32%) and unused land (14%), which was dominated by Phaeozems, Solonchaks and Fluvisols (84%). The converted land use to woodland was dominated by Fluvisols, Phaeozems, Arenosols and Solonchaks (98%). The converted land use from grassland to other land-use types was dominated by Arenosols, Fluvisols and Phaeozems (85%). The SOC was reduced by 9.83 Tg (+8.04 in cultivated land, +0.06 in woodland, ?17.93 in grassland). The SOC stock change efficiency (SOCE kg C m?2) was SOC change divided by area change. The increase in SOC (Tg) of cultivated land was 5.04 from grassland (SOCE 3.76) and 2.9 from woodland (SOCE 3.68). The SOC of woodland increased by 8.66 Tg at cost of losing grassland (SOCE 3.35). Moreover, land-use changes affected local ecological environment. The cultivated land along the river increased 298 km2, and the desertification advanced towards oasis by decreasing 950 km2 of grassland in transition zone. The average groundwater table increased in the upstream (?3.12 to ?2.33 m) and midstream regions (?1.84 to ?1.71 m) monthly from 2012 to 2017 and in the downstream region (?7 to ?2.84 m) annually from 2009 to 2017. This was attributed to expanded cultivated land and salt-washing cultivation on Solonchaks. In conclusion, the land-use conversion from grassland to woodland and cultivated land, mainly for Fluvisols, Phaeozems and Solonchaks, caused negative SOC storage, especially in riverbanks and oasis-desert transition zones facing climate change.
查看更多>>摘要：? 2021 Elsevier B.V.Faba bean is a globally produced agricultural crop due to the high protein content in seeds. However, yields strongly vary depending on biotic and abiotic factors. Here, we evaluated the combined effect of faba bean varieties and climate on crop productivity, seed quality and Bruchus spp. infestation to identify most promising faba bean varieties for use in the food industry as local protein source. Varietal and year related factors were studied during two cropping years to explain variation of field yield, seed protein/ash/lipid content, protein production, and infestation rates. Fourteen varieties including nine winter varieties and five spring varieties were compared, from which one variety presented stable and promising yield, seed composition and low infestation rates. Annual effects significantly impacted field yield and protein production in contrast with the varietal effect that significantly impacted seeds protein content and infestation rates. Principal components analysis showed that infestation rate and yield were not correlated; thus, these two parameters could be optimized independently. The spring variety Fanfare exhibited the best and most stable results over the two study periods. Winter varieties had higher yields, whereas spring varieties had higher seed protein content. The main parameters impacting bruchid infestations were variety, indicating the need to select certain varieties that reduce the impact of pests on seed quality. During 2020, a drought during growing season significantly impacted faba bean production, demonstrating the importance of developing drought-resistant varieties. Thus, fourteen faba bean varieties were characterized considering together key parameters for food uses, and were ranked to identify most interesting ones. We also highlighted most impacting parameters that should be taken into account for the future improvement of varietal resilience in European countries.
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