Assessing nitrate groundwater hotspots in Europe reveals an inadequate designation of Nitrate Vulnerable Zones

Monitoring networks show that the European Union Nitrates Directive (ND) has had mixed success in reducing nitrate concentrations in groundwater. By combining machine learning and monitored nitrate concentrations (1992-2019), we estimate the total area of nitrate hotspots in Europe to be 401,000 km2, with 47% occurring outside of Nitrate Vulnerable Zones (NVZs). We also found contrasting increasing or decreasing trends, varying per country and time periods. We estimate that only 5% of the 122,000 km2 of hotspots in 2019 will meet nitrate quality standards by 2040 and that these may be offset by the appearance of new hotspots. Our results reveal that the effectiveness of the ND is limited by both time-lags between the implementation of good practices and pollution reduction and an inadequate designation of NVZs. Substantial improvements in the designation and regulation of NVZs are necessary, as well as in the quality of monitoring stations in terms of spatial density and information available concerning sampling depth, if the objectives of EU legislation to protect groundwater are to be achieved.

Drought impact on cropland use monitored with AVIRIS imagery in Central Valley, California

During 2012-2016 California experienced the longest and most severe drought in the last centuries. This water scarcity led to an increase in non-cultivated croplands during this period. The objective of this study was to quantify agricultural trends in the Central Valley (California) at peak growth from 2013 to 2016 during the drought and in 2017-2018 post-drought. For this purpose, we analysed yearly official harvested area reported at county level for the main crops and compared them to visible-shortwave infrared (VSWIR) spectra acquired by the Airborne Visible/Infrared Imaging-Spectrometer (AVIRIS-classic) over 2334 km² of the Central Valley each year. Multiple Endmember Spectral Mixture Analysis (MESMA) was applied to AVIRIS data to estimate green vegetation (GV), non-photosynthetic vegetation (NPV) and soil fractions in crop fields each year. MESMA and crop reports (R² = 0.9) showed that soil (i.e.; non-cultivated areas) increased during the summers of the drought; with the smallest GV area in 2015, the second year classified with exceptional drought in this period. According to MESMA, 34 % of the cropland was covered by GV in 2015, and 69.5·10⁴ ha according to the crop reports. MESMA also registered the highest value of soil area in 2015 (48 %). The year with most cultivated area was 2017, the wettest year in the studied period, with 54 % of the croplands covered by GV and 75.2·10⁴ ha. This study verified that the non-cultivated areas increased in the Central Valley during the exceptional drought period and validated the use of AVIRIS imagery to monitor broad-scale cropland use changes in future climatic extreme events.

The cover crop determines the AMF community composition in soil and in roots of maize after a ten-year continuous crop rotation

Intensive agricultural practices are responsible for soil biological degradation. By stimulating indigenous arbuscular mycorrhizal fungi (AMF), cover cropping enhances soil health and promotes agroecosystem sustainability. Still, the legacy effects of cover crops (CCs) and the major factors driving the AM fungal community are not well known; neither is the influence of the specific CC. This work describes a field experiment established in Central Spain to test the effect of replacing winter fallow by barley (Hordeum vulgare L.) or vetch (Vicia sativa L.) during the intercropping of maize (Zea mays L.). We examined the community composition of the AMF in the roots and rhizosphere soil associated with the subsequent cash crop after 10 years of cover cropping, using Illumina technology. The multivariate analysis showed that the AMF communities under the barley treatment differed significantly from those under fallow, whereas no legacy effect of the vetch CC was detected. Soil organic carbon, electrical conductivity, pH, Ca and microbial biomass carbon were identified as major factors shaping soil AMF communities. Specific AMF taxa were found to play a role in plant uptake of P, Fe, Zn, Mn, and Cd, which may shed light on the functionality of these taxa. In our conditions, the use of barley as a winter CC appears to be an appropriate choice with respect to promotion of AMF populations and biological activity in agricultural soils with intercropping systems. However, more research on CC species and their legacy effect on the microbial community composition and functionality are needed to guide decisions in knowledge-based agriculture.

Do cover crops enhance N₂O, CO₂ or CH₄ emissions from soil in Mediterranean arable systems?

This study evaluates the effect of planting three cover crops (CCs) (barley, Hordeum vulgare L.; vetch, Vicia villosa L.; rape, Brassica napus L.) on the direct emission of N₂O, CO₂ and CH₄ in the intercrop period and the impact of incorporating these CCs on the emission of greenhouse gas (GHG) from the forthcoming irrigated maize (Zea mays L.) crop. Vetch and barley were the CCs with the highest N₂O and CO₂ losses (75 and 47% increase compared with the control, respectively) in the fallow period. In all cases, fluxes of N₂O were increased through N fertilization and the incorporation of barley and rape residues (40 and 17% increase, respectively). The combination of a high C:N ratio with the addition of an external source of mineral N increased the fluxes of N₂O compared with -Ba and -Rp. The direct emissions of N₂O were lower than expected for a fertilized crop (0.10% emission factor, EF) compared with other studies and the IPCC EF. These results are believed to be associated with a decreased NO₃(-) pool due to highly denitrifying conditions and increased drainage. The fluxes of CO₂ were in the range of other fertilized crops (i.e., 1118.71-1736.52 kg CO₂-Cha(-1)). The incorporation of CC residues enhanced soil respiration in the range of 21-28% for barley and rape although no significant differences between treatments were detected. Negative CH₄ fluxes were measured and displayed an overall sink effect for all incorporated CC (mean values of -0.12 and -0.10 kg CH₄-Cha(-1) for plots with and without incorporated CCs, respectively).

Risk of inadequate intakes of vitamins A, B1, B6, C, E, folate, iron and calcium in the Spanish population aged 4 to 18

A meta-analysis of the most representative Spanish nutrition studies was carried out to identify inadequate intakes of vitamins, A, B1, B6, C, E, folate, iron, and calcium in children aged 4 to 18. Information on vegetable, fruit and fruit juice/beverage intake was also solicited. Data drawn from the selected studies yielded a total of 6540 children and adolescents in eight geographical areas. The sample was stratified by age (children: 4 to 14 years old and adolescents: 13-18 years old) and sex. Inadequate intakes (below two-thirds of the recommended values) were notable in children for vitamin E, vitamin C, and vitamin A and in girls, iron. In adolescents, low intakes were especially marked for vitamin E and vitamin A, and in girls, calcium, folate, and iron. Adolescents consumed more vegetables, fruit juice, and fruit drinks whereas children had higher fruit intakes. Regional differences in consumption were also detected. Strategies for improving nutrient intake in these vulnerable populations are discussed.