Tracing nitrogen transformations during spring development of winter wheat induced by 15N labeled cattle slurry applied with different techniques

Effect of mineral and organic fertilizer on N dynamics upon erosion-induced topsoil dilution

Erosion-induced topsoil dilution strongly affects cropland biogeochemistry and is associated with a negative effect on soil health and crop productivity. While its impact on soil C cycling has been widely recognized, there is little information about its impact on soil N cycling and N fertilizer dynamics. Here, we studied three factors potentially influencing N cycling and N fertilizer dynamics in cropping systems, namely: 1.) soil type, 2.) erosion-induced topsoil dilution and 3.) N fertilizer form, in a full-factorial pot experiment using canola plants. We studied three erosion affected soil types (Luvisol, eroded Luvisol, calcaric Regosol) and performed topsoil dilution in all three soils by admixing 20 % of the respective subsoil into its topsoil. N fertilizer dynamics were investigated using either mineral (calcium ammonium nitrate) or organic (biogas digestate) fertilizer, labeled with 15N. The fertilizer 15N recovery and the distribution of the fertilizer N in different soil fractions was quantified after plant maturity. Fertilizer N dynamics and utilization were influenced by all three factors investigated. 15N recovery in the plant-soil system was higher and fertilizer N utilization was lower in the treatments with diluted topsoil than in the non-diluted controls. Similarly, plants of the organic fertilizer N treatments took up significantly less fertilizer N in comparison to mineral fertilizer treatments. Both topsoil dilution and organic fertilizer application promoted 15N recovery and N accumulation in the soil fractions, with strong differences between soil types. Our study reveals an innovative insight: topsoil dilution due to soil erosion has a negligible impact on N cycling and dynamics in the plant-soil system. The crucial factors influencing these processes are found to be the choice of fertilizer form and the specific soil type. Recognizing these aspects is essential for a precise and comprehensive assessment of the environmental continuum, emphasizing the novelty of our findings.

Nitrogen fertilization regulates crosstalk between marandu palisadegrass and Herbaspirillum seropedicae: An investigation based on 15N isotopic analysis and root morphology

Strategies seeking to increase the use efficiency of nitrogen (N) fertilizers and that benefit plant growth through multiple mechanisms can reduce production costs and contribute to more sustainable agriculture free of polluting residues. Under controlled conditions, we investigated the compatibility between foliar inoculation with an endophytic diazotrophic bacterium (Herbaspirillum seropedicae HRC54) at control and low, medium and high N fertilization levels (0, 25, 50 and 100 mg of N kg-1 as urea, respectively) in Marandu palisadegrass. Common procedures in our research field (biometric and nutritional assessments) were combined with isotopic techniques (natural abundance - δ15N‰ and 15N isotope dilution) and root scanning to determine the contribution of fixed N and recovery of N fertilizer by the grass. Overall, the combined use of 15N isotopic techniques revealed that inoculation not only improved the recovery of applied N-urea from the soil but also provided fixed nitrogen to Marandu palisade grass, resulting in an increase in the total accumulated N. When inoculated plants grew at control and low levels of N, a positive cascade effect encompassing root growth stimulation (nodes of smaller diameter roots), better soil and fertilizer resource exploitation and increased forage production was observed. In contrast, increasing N reduced the contributions of N fixed by H. seropedicae from 21.5% at the control level to 8.6% at the high N level. Given the minimal to no observed growth promotion, this condition was deemed inhibitory to the positive effects of H. seropedicae. We discuss how to make better use of H. seropedicae inoculation in Marandu palisadegrass, albeit on a small scale, thus contributing to a more rational and efficient use of N fertilizers. Finally, we pose questions for future investigations based on 15N isotopic techniques under field conditions, which have great applicability potential.

Fates of slurry-nitrogen applied to mountain grasslands: the importance of dinitrogen emissions versus plant N uptake

Intensive fertilization of grasslands with cattle slurry can cause high environmental nitrogen (N) losses in form of ammonia (NH3), nitrous oxide (N2O), and nitrate (NO3 -) leaching. Still, knowledge on short-term fertilizer N partitioning between plants and dinitrogen (N2) emissions is lacking. Therefore, we applied highly 15N-enriched cattle slurry (97 kg N ha-1) to pre-alpine grassland field mesocosms. We traced the slurry 15N in the plant-soil system and to denitrification losses (N2, N2O) over 29 days in high temporal resolution. Gaseous ammonia (NH3), N2 as well N2O losses at about 20 kg N ha-1 were observed only within the first 3 days after fertilization and were dominated by NH3. Nitrous oxide emissions (0.1 kg N ha-1) were negligible, while N2 emissions accounted for 3 kg of fertilizer N ha-1. The relatively low denitrification losses can be explained by the rapid plant uptake of fertilizer N, particularly from 0-4 cm depth, with plant N uptake exceeding denitrification N losses by an order of magnitude already after 3 days. After 17 days, total aboveground plant N uptake reached 100 kg N ha-1, with 33% of N derived from the applied N fertilizer. Half of the fertilizer N was found in above and belowground biomass, while at about 25% was recovered in the soil and 25% was lost, mainly in form of gaseous emissions, with minor N leaching. Overall, this study shows that plant N uptake plays a dominant role in controlling denitrification losses at high N application rates in pre-alpine grassland soils.

Supplementary information

The online version contains supplementary material available at 10.1007/s00374-024-01826-9.

Balancing grain yield and environmental performance by optimizing planting patterns of rice-wheat cropping systems

To alleviate the adverse consequences of conventional planting of the rice-wheat cropping system and achieve long-term sustainability, a 3-cycle experiment (2019-2022) was conducted to investigate the effects of six planting patterns (PPs) on the grain yield and environmental performance. PP1 entailed annual rotary tillage (RT) without straw returning but without fertilization for rice and wheat seasons. PP2 was the same as PP1 but involved fertilization. PP3 was the same as PP2 but included straw return. PP4 entailed rice planting the same as in PP3, but with innovative zero-tillage (ZT) seeding technology for wheat planting. PP5 entailed wheat planting the same as in PP4, but with rice planting involving direct paddy seeding under RT. PP6 entailed wheat planting the same as in PP4, but rice planting followed dry direct seeding under ZT. The results showed that the average total yield under PP2, PP3, PP4, PP5, and PP6 was 64 %, 54 %, 69 %, 51 %, and 54 % higher than that under PP1, respectively. The highest methane and nitrous oxide emissions occurred under PP4 and PP6, respectively. When soil organic carbon changes were included in the calculations, the carbon footprint per unit area (CFA) was sharply reduced under PP4 and PP6, and the highest CFA was achieved under PP1, followed by PP2. Implementing annual RT promoted soil mineral nitrogen accumulation under PP2 and PP3 after wheat harvest, increasing the risk of mineral nitrogen leaching and the nitrogen footprint per unit area than that under the other PPs. PP4 exhibited the highest ammonia volatilization, which was offset by reduced mineral nitrogen leaching. Overall, PP4 exhibited a yearly increase in the comprehensive scores obtained via Z-score analysis and yielded the highest score in the last year due to the highest annual grain yield, steady SOC increase, and lower nitrogen loss.