Determining nitrogen deficiencies for maize using various remote sensing indices

Determining a precise nitrogen fertilizer requirement for maize in a particular field and year has proven to be a challenge due to the complexity of the nitrogen inputs, transformations and outputs in the nitrogen cycle. Remote sensing of maize nitrogen deficiency may be one way to move nitrogen fertilizer applications closer to the specific nitrogen requirement. Six vegetation indices [normalized difference vegetation index (NDVI), green normalized difference vegetation index (GNDVI), red-edge normalized difference vegetation index (RENDVI), triangle greenness index (TGI), normalized area vegetation index (NAVI) and chlorophyll index-green (CIgreen)] were evaluated for their ability to detect nitrogen deficiency and predict grain maize grain yield. Strip trials were established at two locations in Arkansas, USA, with nitrogen rate as the primary treatment. Remote sensing data was collected weekly with an unmanned aerial system (UAS) equipped with a multispectral and thermal sensor. Relationships among index value, nitrogen fertilizer rate and maize growth stage were evaluated. Green NDVI, RENDVI and CIgreen had the strongest relationship with nitrogen fertilizer treatment. Chlorophyll Index-green and GNDVI were the best predictors of maize grain yield early in the growing season when the application of additional nitrogen was still agronomically feasible. However, the logistics of late season nitrogen application must be considered.

Spatial and Temporal Patterns in Carbon and Nitrogen Inputs by Net Precipitation in Atlantic Forest, Brazil

Understanding both carbon and nitrogen temporal and spatial inputs by rainfall in tropical forests is critical for proper forest conservation and management and might ultimately elucidate how climate change might affect nutrient dynamics in forest ecosystems. This study aimed to quantify the net precipitation contribution to the Atlantic Forest’s total carbon (C) and total nitrogen (N), identifying potential differences between these inputs regarding temporal (seasonal and monthly) and spatial scales. Rainfall samples were collected before and after interacting with the forest canopy from May 2018 to April 2019. The rainfall was enriched after crossing the forest canopy. Significant differences were found for gross rainfall and net precipitation between annual carbon (104.13 kg ha−1 and 193.18 kg ha−1) and nitrogen (16.81 kg ha−1 and 36.95 kg ha−1) inputs, respectively. Moreover, there was seasonal variability in the C and N inputs with 75% occurring in the wet season. Overall, the spatial patterns revealed that the same locations had the highest inputs regardless of the analyzed period. The forest-rainfall interactions provide constant C and N inputs, especially in the wet season, and are fundamental for the maintenance of ecological processes. Study Implications The hydrological and nutrient cycles are tied together. There was significant nutrient enrichment after rainfall interacts with the forest canopy. Rainfall seasonality and canopy deciduousness and heterogeneity drive the temporal and spatial variabilities of carbon and nitrogen. The wet season represented an average of 75% of the total annual carbon and nitrogen contribution, via net precipitation. Such findings enhance our understanding of nutrient deposition, leaching, and absorption processes by canopies and the importance of the tropical forest in the hydrological and nutrient cycle. This knowledge might serve as a guide to improve management practices and justify conservation initiatives.

Concentrations, Loads, and Associated Trends of Nutrients Entering the Sacramento–San Joaquin Delta, California

Statistical modeling of water-quality data collected at the Sacramento River at Freeport and San Joaquin River near Vernalis, California, USA, was used to examine trends in concentrations and loads of various forms of dissolved and particulate nitrogen and phosphorus that entered the Sacramento–San Joaquin River Delta (Delta) from upstream sources between 1970 and 2019. Ammonium concentrations and loads decreased at the Sacramento River site from the mid-1970s through 1990 because of the consolidation of wastewater treatment and continuously reduced from the mid-1970s to 2019 at the San Joaquin River site. Current ammonium concentrations are mostly below 4 µM (0.056 mg N L–1) at both sites, a concentration above which reductions in phytoplankton productivity or changes in algal species composition may occur. The Sacramento River at Freeport site is located upstream of the Sacramento Regional County Sanitation District’s treatment facility’s discharge point; nutrient water quality there is representative of upstream sources. Inorganic nitrogen (nitrate plus ammonium) concentrations and loading differed at both sites. At the Sacramento River location, concentrations decrease in the summer agricultural season, reducing the molar ratios of nitrogen to phosphorus. In contrast, inorganic nitrogen concentrations increase in the San Joaquin River during the agricultural season as a result of irrigation runoff, increasing the molar ratio of nitrogen to phosphorus. This increase suggests a possible nitrogen limitation in the northern Delta and a phosphorus limitation in the southern Delta, as indicated by the molar ratios of bioavailable nitrogen to bioavailable phosphorus. Planned upgrades to the Sacramento Regional Wastewater Treatment Plant (SRWTP) will reduce inorganic nitrogen inputs to the northern Delta. Consequently, the supply of bioavailable nitrogen throughout the upper estuary should diminish. Source modeling of nitrogen and phosphorus identifies agriculture, atmospheric deposition, and wastewater effluent as sources of total nitrogen in the Central Valley. In contrast, geologic sources, agriculture, and wastewater discharge are the primary sources of phosphorus.

The Presence of Denitrifiers In Bacterial Communities of Urban Stormwater Best Management Practices (BMPs)

Stormwater best management practices (BMPs) are engineered structures that attempt to mitigate the impacts of stormwater, which can include nitrogen inputs from the surrounding drainage area. The goal of this study was to assess bacterial community composition in different types of stormwater BMP soils to establish whether a particular BMP type harbors more denitrification potential. Soil sampling took place over the summer of 2015 following precipitation events. Soils were sampled from four bioretention facilities, four dry ponds, four surface sand filters, and one dry swale. 16S rRNA gene analysis of extracted DNA and RNA amplicons indicated high bacterial diversity in the soils of all BMP types sampled. An abundance of denitrifiers was also indicated in the extracted DNA using presence/absence of nirS, nirK, and nosZ denitrification genes. BMP soil bacterial communities were impacted by the surrounding soil physiochemistry. Based on the identification of a metabolically-active community of denitrifiers, this study has indicated that denitrification could potentially occur under appropriate conditions in all types of BMP sampled, including surface sand filters that are often viewed as providing low potential for denitrification. The carbon content of incoming stormwater could be providing bacterial communities with denitrification conditions. The findings of this study are especially relevant for land managers in watersheds with legacy nitrogen from former agricultural land use.

Inter-phylum negative interactions affect soil bacterial community dynamics and functions during soybean development under long-term nitrogen fertilization

Understanding interspecies interactions is essential to predict the response of microbial communities to exogenous perturbation. Herein, rhizospheric and bulk soils were collected from five developmental stages of soybean, which grew in soils receiving 16-year nitrogen inputs. Bacterial communities and functional profiles were examined using high-throughput sequencing and quantitative PCR, respectively. The objective of this study was to identify the key bacterial interactions that influenced community dynamics and functions. We found that the stages of soybean development outcompeted nitrogen fertilization management in shaping bacterial community structure, while fertilization treatments significantly shaped the abundance distribution of nitrogen functional genes. Temporal variations in bacterial abundances increased in bulk soils, especially at the stage of soybean branching, which helps to infer underlying negative interspecies interactions. Members of Cyanobacteria and Actinobacteria actively engaged in inter-phylum negative interactions in bulk soils and soybean rhizosphere, respectively. Furthermore, the negative interactions between nitrogen-fixing functional groups and the reduction of nifH gene abundance were coupled during soybean development, which may help to explain the linkages between population dynamics and functions. Overall, these findings highlight the importance of inter-phylum negative interactions in shaping the correlation patterns of bacterial communities and in determining soil functional potential.

Developing a System Dynamics Model for the Nizhniy Kaban and Sredniy Kaban Lakes, Kazan, Russia, Assessing the Impacts of Phosphorus and Nitrogen Inputs on Lake Ecology

The Kaban Lakes Integrated Assessment Model (KLIAM) was developed for the lake hydrology, chemistry, and plankton dynamics of the Nizhniy Kaban and Sredniy Kaban lakes, Kazan, Russia. KLIAM is able to describe the variations seen in the Kaban lakes chemical and biological states as far seen through measurements available at the moment. KLIAM is able to reconstruct the lake history as it is approximately known from the data and written narratives. KLIAM was used to assess the measures to return the lakes to their original pre-urban status as alkaline and semi-oligotrophic lakes. The Kaban Lakes periodically goes through plankton blooms, as seen in the lake in the last decades since before World War II, which are caused by plankton growth promoted by phosphorus and nitrogen coming to the lakes as pollution from the human environment. In the new plans for development of the area surrounding the Nizhniy Kaban and Sredniy Kaban lakes, we suggest that attention is paid to reducing phosphorus and nitrogen flows to the lakes, as the best way to improve their ecological status. This is based on simulations with KLIAM. We recommend that the monitoring of lake chemistry and lake ecology is improved with reoccurring analysis of samples from the Kaban Lakes.

Oat Cover Crop and No-tillage Can Provide Weed Suppression and Alter Weed Community Dynamics in Sweet Corn

Along with the many known benefits of cover crops, they may be an effective ecological weed management strategy in low-input agriculture. This research aimed to determine the effect of cover crops, combined with reduced-tillage and nitrogen inputs on sweet corn (Zea mays) yield and weed communities. During the 2-year study, the impact of the cover crop on yield varied. Yield within the no-till conventional treatment plots was not significantly different from the conventional treatment [6844 and 7721 lb/acre (P = 0.592)] in year 1 but differed in year 2 (P = 0.003). Weed density and experimental area covered by weeds were not significantly different between conventional and no-till conventional treatments. Multivariate analyses showed associations between specific weed species and management practices. Weeds were greatest in no-till organic treatments, and they had significantly lower yields, suggesting additional weed control beyond cover crops may be necessary for organic vegetable systems under reduced tillage.