RESUMEN
Nitrogen fertilizer plays a crucial role in keeping food production in pace with population growth. However, the exceeding application of nitrogen fertilizer causes environmental risks. Timely and accurate quantification of canopy nitrogen content in crops is important for the rational application of nitrogen fertilizer and reduction environmental risks. The current research aimed to remotely estimate canopy nitrogen content in winter wheat and summer maize. Experiments with different N rates for different cultivars of wheat and maize were conducted in southeast Germany and in the North China Plain from 2008 to 2011. The results showed that, compared with traditional red light based spectral parameters, optimized spectral parameters significantly improved the prediction capacity, overcoming saturation problem in deriving canopy nitrogen content of wheat and maize. Band combination of optimized parameters varied with the difference in species and canopy structure of crops. The optimized bands concentrated on 730~760 and 760~800 nm. The best performing spectral parameter was Rλ766/Rλ738-1 for maize, Rλ796/Rλ760-1 for wheat and Rλ876/Rλ730-1 for wheat and maize combination. The validation results further confirmed that the optimized spectral parameters had the lowest predictive error, indicating that optimized spectral indices could estimate canopy nitrogen content of crops. In conclusion, the band optimization of spectral parameters is a promising approach to derive canopy N content in wheat and maize. The findings from this study may be useful for designing improved nitrogen diagnosis systems and for enhancing the applications of satellite-based sensors.
RESUMEN
Although nitrogen (N) fertilizer application plays an essential role in improving crop productivity, an inappropriate management can result in negative impacts on environment and human health. To break this dilemma, a 12-year field experiment (2008-2019) with five N application rates was conducted on the North China Plain (NCP) to evaluate the integrated impacts of optimizing N management (Opt. N, 160 kg N ha-1 on average) on agronomic, environmental, health, and economic performances of summer maize production. Over the 12-year study, the Opt. N treatment achieved the maximal average grain yield (10.6 Mg ha-1) and grain protein yield (793 kg ha-1) among five N treatments. The life cycle assessment methodology was applied to determine the negative impacts on environmental and human health, and both of them increased with the N rate. Compared with the farmers' conventional N rate (250 kg N ha-1), the Opt. N treatment reduced acidification, eutrophication, global warming, and energy depletion potentials by 29%, 42%, 35%, and 18%, respectively, and reduced the health impact by 32% per Mg of grain yield or grain protein yield produced. Both the Opt. N and Opt. N*50-70% treatments resulted in high private profitability (2038 USD ha-1), ecosystem economic benefit (1811 USD ha-1), and integrated compensation benefit (17,548 USD ha-1). This study demonstrates the potential benefits of long-term optimizing of N management to maintain high maize yields and grain quality, to reduce various environmental impacts and health impacts, and to enhance economic benefits. These benefits can be further enhanced when Opt. N was combined with advanced agronomic management practices. The results also suggest that reducing the optimal N rate from 160 to 145 kg N ha-1 is achievable to further reduce the negative impacts while maintaining high crop productivity. In conclusion, optimizing the N management is essential to promote sustainable summer maize production on the NCP.
RESUMEN
The one-time application of blended urea (BU), combining controlled-release urea (CRU) and uncoated urea, has proven to be a promising nitrogen (N) management strategy. However, the long-term sustainability of blending urea remains largely unexplored. To assess whether a single application of blended urea could effectively replace split uncoated urea applications, a long-term field experiment was conducted in the North China Plain (NCP). The results indicated that, when compared to common urea (CU) at the optimal N rate (180 kg N ha-1), BU achieved comparable grain yields, N uptake and NUE (61% vs. 62). BU exhibited a 12% higher 0-20 cm soil organic nitrogen stock and a 9% higher soil organic carbon (C) stock. Additionally, BU reduced life-cycle reactive N (Nr) losses and the N footprint by 10%, and lowered greenhouse gas (GHG) emissions and the C footprint by 7%. From an economic analysis perspective, BU demonstrated comparable private profitability and a 3% greater ecosystem economic benefit. Therefore, BU under the optimal N rate has the potential to substitute split applications of common urea in the long-term and can be regarded as a sustainable N management strategy for wheat and maize production in the NCP.