The Fate of Nitrogen from Soil to Plants: Influence of Agricultural Practices in Modern Agriculture

Nitrogen is an element present on Earth in different forms, such as gaseous in the air, dissolved in water, immobilized in the soil, as well as biologically bound in all living organisms. The transition from one form to another constitutes the nitrogen cycle. Current agricultural systems rely on nitrogen fertilizers, which represent the reactive or biologically available nitrogen in soil. The excessive presence of reactive nitrogen in the environment has become a threat to soil, water, and air. The increasing demands for food in the world are associated with significant increase in nitrogen fertilizers inputs which threatens the environment and living organisms. The quantities of nitrogen used per capita in developed countries exceed those in developing countries. However, developed countries are regulated by restrictions of fertilizers inputs in agriculture, whereas such regulations do not exist in most of the developing countries. The need to resort to alternative and eco-sustainable strategies to mitigate the pollution related to human activities, is increasingly evident. This review aims to highlight the fate of nitrogen through the main agricultural practices in modern agriculture. Special attention was given to rocket (Eruca sativa) which is considered a nitrate hyper-accumulator and was used as a case study in the present review. Finally, some eco-sustainable solutions, useful for mitigating or preventing the excessive release of harmful forms of nitrogen into the environment, were also discussed.

Distribution Coefficients of Nitrogen Pollutants Between Water-Sediment And Their Environmental Risks In Lingang Hybrid Constructed Wetland Fed By Industrial Tailwater, Tianjin, China

Exploring the fate of nitrogen pollutants in constructed wetlands (CWs) fed by industrial tailwater is significant to strengthen its pollution control and promoting the development of CWs in the field of micro-polluted water treatment. In this study, the distribution coefficients and the environmental risks of nitrogen pollutants between water-sediment of the hybrid CW in Tianjin were systematically investigated. From a spatial perspective, the nitrogen pollutants could be removed in this hybrid CW, and subsurface flow wetland played a key role in nitrogen pollutant removal. From a temporal perspective, the consistence of nitrogen pollutants was largely affected by the dissolved oxygen (DO) and temperature. The distribution coefficient of nitrogen pollutants between water-sediment was further clarified, suggesting that NH4+-N was more likely to be enriched in sediments due to microbial process. The overall level of pollution in hybrid CW was moderate according to the nutritional pollution index (NPI) analysis. The risks assessment indicated that timely dredging control measures should be considered to maintain the performance of hybrid CW.

Fate of Nitrogen from Artichoke (Cynara cardunculus L. var. scolymus (L.)) Crop Residues: A Review and Lysimeter Study

The goal of the European Nitrate Directive 91/676/CEE is to mitigate or prevent water pollution associated with the nitrogen (N) cascade. Vegetable crops have a high risk of nitrate leaching during autumn and winter. Information about the fate of N from artichoke (Cynara cardunculus L. var. scolymus (L.)) residues is reviewed and then supplemented with a three-year study with 15N-labelled residues in an artichoke-cauliflower (Brassica oleracea L. cv. botrytis) rotation in six lysimeters. After three years, 6% of N in artichoke residues was leached, 8% was exported by crops, while 86% remained in the lysimeter. Summed over the rotation, 16% of artichoke-residue N was absorbed by artichoke and 14% by cauliflower. Total aboveground N uptake by all crops during the entire rotation ranged from 370 to 534 kg N ha−1, of which 207–311 kg N ha−1 returned to the soil as residues. Increasing N-recycling efficiency and reducing the risk of N leaching while conserving crop productivity requires capturing N mineralized from soil organic N. Cauliflower performs this capture effectively during the drainage period. A break crop should be introduced after the first and second harvests of artichoke to further synchronize N mineralization and uptake and reduce leaching risk during the rotation.