Nitrogen, Volume 4, Issue 4 (December 2023) – 6 articles

Nano-nitrogen fertilizers (NNFs) have emerged as a promising technology in the field of agriculture, offering potential solutions to improve nutrient uptake efficiency, enhance crop productivity, and reduce environmental impacts. NNFs showed superior characteristics and performance on crops and, therefore, became a potential alternative to conventional nitrogen (N) fertilizers. These fertilizers enhance plant uptake while simultaneously reducing environmental losses. For example, a hydroxy appetite-based urea NNF extended the N release for 112 days, which could cover the N demand of many perennial crops, thus reducing losses. The reported NNFs in this review increased the yield by 10–80% compared to conventional fertilizers. Additionally, their small particle size increases crop acclimation and decreases the application rate. With all these beneficial traits of NNFs, they potentially contribute to achieving Sustainable Development Goals (SDGs). This review article summarizes the materials used in NNF formulation, methods of preparing NNFs, and their crop responses. Also, it highlights the limitations identified in the research studies and provides research recommendations for the future. Further, it provides a critical assessment of the current state of NNFs and their prospects for revolutionizing modern agriculture to attain SDGs. Full article

Drought stress is one of the major abiotic stress factors affecting forage production; thus, it is essential to obtain a better understanding of how forage responds to drought. The main objective of this study was to evaluate how legume-grass mixed forage stands respond to drought stress when compared to grass monoculture. A greenhouse pot experiment was conducted using a red clover (Trifolium pratense L.)—timothy grass (Phleum pratense L.) mixed stand and a timothy monoculture stand, where plants were subjected to severe drought (20% field capacity—FC), moderate drought (40% FC), and well-watered (80% FC) conditions for four weeks and subsequently allowed to recover for another four weeks by adjusting moisture back to 80% FC. Both moderate and severe droughts significantly reduced the shoot biomass of the mixed stand, while no difference was exhibited in the timothy monoculture. The shoot biomass and nitrogen fixation capacity of red clover were reduced under drought stress. However, red clover plants subjected to moderate drought were able to recover shoot growth and nitrogen fixation capacity during the recovery phase, allowing more biologically fixed nitrogen and shoot nitrogen production similar to the plants growing under well-watered conditions. Overall, the results demonstrate that the inclusion of legumes in forage mixtures enhances resilience to moderate drought stress. Full article

Conservation agriculture (CA), which could contribute to sustainable agriculture, maintains or improves soil nitrogen fertility by eliminating tillage (no-tillage). Quantitative assessment of soil constituents is enhanced by stable isotope techniques such as ¹⁵N, which are used to better understand nitrogen dynamics. This study was therefore carried out to assess the impact of tillage type and fertilizer application on soil and plant nitrogen fractionation. The trial consisted of two tillage types: no-tillage (NT) and conventional tillage (CT). Three nitrogen doses (82, 115, and 149 kg ha⁻¹) were applied. The experimental design was a randomized complete block with three replications. The Louiza variety of durum wheat was used in this study. Soil nitrogen sequestration was assessed using the stable nitrogen isotope (¹⁵N) method. The statistical analysis (ANOVA) showed that, overall, there was no significant difference between tillage types and nitrogen doses for grain and straw yields and grain total nitrogen. In contrast, the effect of both factors and their interaction were significant for straw total nitrogen. There was no difference between tillage types for grain nitrogen use efficiency (NUE), even though NT was superior to CT by 3.5%, but nitrogen doses had a significant effect and a significant interaction with tillage type. When comparing nitrogen doses for each tillage type separately, results showed that the average NUE for grain was 20.5, 8.4, and 16.5%, respectively, for the three nitrogen doses for CT compared with 26.8, 19.0, and 30.6% for NT, indicating clearly the better performance of NT compared to CT. Regarding straw, the NUE is 3.2, 3.5, and 5.4% for CT compared with 3.4, 4.9, and 9.2% for NT. NUE in grain and straw under no-tillage was higher than under conventional tillage in all three nitrogen doses. These results show that soil conservation techniques such as no-tillage and the integrated application of nitrogen fertilizer can be good strategies for reducing soil nitrogen losses. Full article

Grazing and hay forage crops reduce erosion compared to annual crops, but few studies have compared soil and nutrient loss among grazing systems compared to a control. We evaluated runoff water quality and nutrient loss among three grazing systems and a hay crop production field with manure application (control) using a paired watershed design. Four edge-of-field sites at a research farm in central Wisconsin were managed as hay during calibration (2013–2018) followed by a grazing treatment phase (2018–2020). Grazing treatments of different stocking methods included continuous stocking (CS), primary paddock stocking (PPS), and adaptive multi-paddock stocking (AMPS). Runoff, sediment, nitrogen (N), and phosphorus (P) loads were monitored year-round. Grazing increased average runoff volume by as much as 1.7-fold depending on stocking method and tended to decrease event mean N and P concentrations. CS had larger mean sediment (2.0-fold), total N (1.9-fold), and total P loads (1.2-fold) compared to the control and had the lowest average pasture forage mass. AMPS had lower N and P loss as a percentage of that applied from manure application/livestock excretion (1.3 and 1.6%, respectively) compared to the control (2.5 and 2.1%), PPS (2.5 and 2.6%), and CS (3.2 and 3.0%). Stocking method had a marked impact on nutrient loss in runoff from these systems, suggesting water quality models should account for pasture management, but nutrient losses from all perennial forage systems were small relative to previous data from annual cropping systems. Full article

Maize (Zea mays) is a high-nitrogen (N)-demanding crop potentially contributing to nitrate contamination and emissions of nitrous oxide. The N fertilization is generally split between sowing time and the V6 stage. The right split N rate to apply at V6 and minimize environmental damage is challenging. Our objectives were to (1) predict maize response to added N at V6 using machine learning (ML) models; and (2) cross-check model outcomes by independent on-farm trials. We assembled 461 N trials conducted in Eastern Canada between 1992 and 2022. The dataset to predict grain yield comprised N dosage, weekly precipitations and corn heat units, seeding date, previous crop, tillage practice, soil series, soil texture, organic matter content, and pH. Random forest and XGBoost predicted grain yield accurately at the V6 stage (R² = 0.78–0.80; RSME and MAE = 1.22–1.29 and 0.96–0.98 Mg ha⁻¹, respectively). Model accuracy up to the V6 stage was comparable to that of the full-season prediction. The response patterns simulated by varying the N doses showed that grain yield started to plateau at 125–150 kg total N ha⁻¹ in eight out of ten on-farm trials conducted independently. There was great potential for economic and environmental gains from ML-assisted N fertilization. Full article

Abundance of soil microbial nitrogen (N) cycling genes responsible for nitrification, denitrification, and nitrous oxide reduction may vary with tree species and N inputs, and these variables may be used to predict or mediate nitrate (NO₃⁻) and nitrous oxide (N₂O) from soil. Nitrification and denitrification rates have also been linked to tree mycorrhizal associations, as soil beneath species associated with arbuscular mycorrhiza (AM) shows greater nitrification rates than species forming ectomycorrhizal (ECM) associations. In this study, we integrated N microbial functional gene abundance in the soil influenced by six tree species in two sub-catchments receiving either high or low N inputs. The soils beneath the two ECM-associated tree species and the four AM-associated tree species were analyzed for inorganic N content and potential N₂O flux and microbial gene abundance (nirK and nosZ) was quantified using qPCR techniques. Other parameters measured include soil pH, moisture, and organic matter. We determined that tree species influence NO₃⁻ and N₂O production in riparian soils, particularly under high N enrichment. The soil beneath black cherry had the lowest pH, NO₃⁻ concentration, potential N₂O production, and OM, though this result did not occur in the low N catchment. The strongest predictors of soil NO₃⁻ and N₂O across the study sites were N enrichment and pH, respectively. These results provide a framework for species selection in managed riparian zones to minimize NO₃⁻ and N₂O production and improve riparian function. Full article