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Launched in 2006 with support from the National Science Foundation (NSF) and leveraged by the CAP LTER, the Carbon and Nitrogen deposition (CNdep) project sought to answer the fundamental question of whether elemental cycles in urban ecosystems are qualitatively different from those in non-urban ecosystems. Ecosystem scientists, atmospheric chemists, and biogeochemists tested the hypothesis that distinct biogeochemical pathways result from elevated inorganic nitrogen and organic carbon deposition from the atmosphere to the land. To test the hypothesis, scientists examined the responsiveness of Sonoran desert ecosystems to nutrient enrichment by capitalizing on a gradient of atmospheric deposition in and around the greater Phoenix metropolitan area. Fifteen desert study sites were established, with five locations each west and east of the urban core, and in the urban core in desert preserves. In addition to the gradient of atmospheric deposition in and around the urban core, select study plots at each of the fifteen desert locations receive amendments of nitrogen, phosphorus, or nitrogen + phosphorus fertilizer. Measured variables include soil properties, perennial and annual plant growth, and atmospheric deposition of nitrogen. At the close of the initial grant period, the CAP LTER assumed responsibility for the project, renamed the Desert Fertilization Experiment, which provides a remarkable platform to study the long-term effects of nutrient enrichment on desert ecosystem properties. 

The CAP LTER maintains two micrometeorological stations (10-m height) in the greater Phoenix metropolitan area, including at Lost Dutchman State Park and near the Desert Botanical Garden at Papago Park. The local terrain at both sites is flat or gently sloping Sonoran desert, and the vegetation canopy consists of patchy coverage of desert shrubs and trees. The dominant vegetation species include bursage (*Ambrosia deltoidea*) and creosote bush (*Larrea tridentata*), while minor species include palo verde (*Parkinsonia microphylla*) and saguaro cactus (*Carnegiea gigantea*). Wind speed and direction, incoming solar radiation, air temperature, relative humidity, and precipitation have been monitored nearly continuously since the fall of 2010. Each variable is measured every 5 seconds and the average (or total for precipitation and total solar radiation) saved to a data logger every 10 minutes. 

The Ecological Survey of Central Arizona (ESCA) is an extensive field survey and integrated inventory designed to capture key ecological indicators of the CAP LTER study area consisting of the urbanized, suburbanized, and agricultural areas of metropolitan Phoenix, and the surrounding Sonoran desert. The survey, formerly known as the survey 200 and renamed to ESCA in 2015, assesses conditions at approximately 200 sample plots (30m x 30m) that were located randomly using a tessellation-stratified dual-density sampling design. Beginning in 2000, the study is conducted every five years except the 2020 survey, which was conducted in 2023 owing to delays to due Covid. Study plots cover habitats throughout the CAP LTER study area ranging from native Sonoran desert sites to residential yards to an airport tarmac. Measurements include an inventory of all plants (identified to the lowest possible taxonomic unit, typically species), plant biovolume, soil coring for physicochemical properties, arthropod sweep-net sampling, photo documentation, and a visual survey of site and area characteristics. The objectives of the survey are to (1) characterize patches in terms of key biotic, physical, and chemical variables, and (2) examine relationships among land use, general plant diversity, native plant diversity, plant biovolume, soil nutrient status, and social-economic indices along an indirect urban gradient. A pilot survey was conducted in 1999, and the first full ESCA was conducted in 2000. The maiden survey in 2000 featured a suite of measurements that were not assessed in later surveys, including data from a portable weather station set up during the field survey at each location, organic matter decomposition, pollen, and mycorrhizae. In 2010, the survey was expanded to include an assessment of one of the residential parcels overlapping the survey plot at sites in residential areas. Many of the same variables that are measured in the 30m x 30m survey plot are measured in the parcel, including an inventory of perennial plants, and the biovolume of trees. In addition, a detailed assessment of characteristics of the parcel is performed. Investigators interested in the additional variables assessed in the 2000 ESCA, in parcel data collected in the 2010 and subsequent surveys, or in soil data collected during the 2000 ESCA (encapsulated in a separate data set owing to a different reporting format) should search for 'ecological survey of central arizona' (quoted!) in the Environmental Data Initiative (EDI) data catalog to locate those and other data related to the Ecological Survey of Central Arizona (ESCA). 

The Ecological Survey of Central Arizona (ESCA) is an extensive field survey and integrated inventory designed to capture key ecological indicators of the CAP LTER study area consisting of the urbanized, suburbanized, and agricultural areas of metropolitan Phoenix, and the surrounding Sonoran desert. The survey, formerly known as the survey 200 and renamed to ESCA in 2015, assesses conditions at approximately 200 sample plots (30m x 30m) that were located randomly using a tessellation-stratified dual-density sampling design. Beginning in 2000, the study is conducted every five years except the 2020 survey, which was conducted in 2023 owing to delays to due Covid. Study plots cover habitats throughout the CAP LTER study area ranging from native Sonoran desert sites to residential yards to an airport tarmac. Measurements include an inventory of all plants (identified to the lowest possible taxonomic unit, typically species), plant biovolume, soil coring for physicochemical properties, arthropod sweep-net sampling, photo documentation, and a visual survey of site and area characteristics. The objectives of the survey are to (1) characterize patches in terms of key biotic, physical, and chemical variables, and (2) examine relationships among land use, general plant diversity, native plant diversity, plant biovolume, soil nutrient status, and social-economic indices along an indirect urban gradient. A pilot survey was conducted in 1999, and the first full ESCA was conducted in 2000. The maiden survey in 2000 featured a suite of measurements that were not assessed in later surveys, including data from a portable weather station set up during the field survey at each location, organic matter decomposition, pollen, and mycorrhizae. In 2010, the survey was expanded to include an assessment of one of the residential parcels overlapping the survey plot at sites in residential areas. Many of the same variables that are measured in the 30m x 30m survey plot are measured in the parcel, including an inventory of perennial plants, and the biovolume of trees. In addition, a detailed assessment of characteristics of the parcel is performed. Investigators interested in the additional variables assessed in the 2000 ESCA, in parcel data collected in the 2010 and subsequent surveys, or in soil data collected during the 2000 ESCA (encapsulated in a separate data set owing to a different reporting format) should search for 'ecological survey of central arizona' (quoted!) in the Environmental Data Initiative (EDI) data catalog to locate those and other data related to the Ecological Survey of Central Arizona (ESCA). 

Abstract Crop N decision support tools are typically based on either empirical relationships that lack mechanistic underpinnings or simulation models that are too complex to use on farms with limited input data. We developed an N mineralization model for corn that lies between these endpoints; it includes a mechanistic model structure reflecting microbial and texture controls on N mineralization but requires just a few simple inputs: soil texture soil C and N concentration and cover crop N content and carbon to nitgrogen ratio (C/N). We evaluated a previous version of the model with an independent dataset to determine the accuracy in predictions of unfertilized corn (Zea maysL.) yield across a wider range of soil texture, cover crop, and growing season precipitation conditions. We tested three assumptions used in the original model: (1) soil C/N is equal to 10, (2) yield does not need to be adjusted for growing season precipitation, and (3) sand content controls humification efficiency (ε). The best new model used measured values for soil C/N, had a summertime precipitation adjustment, and included both sand and clay content as predictors ofε(root mean square error [RMSE] = 1.43 Mg ha⁻¹;r² = 0.69). In the new model, clay has a stronger influence than sand onε, corresponding to lower predicted mineralization rates on fine‐textured soils. The new model had a reasonable validation fit (RMSE = 1.71 Mg ha⁻¹;r² = 0.56) using an independent dataset. Our results indicate the new model is an improvement over the previous version because it predicts unfertilized corn yield for a wider range of conditions. 

Abstract Agricultural fields in drylands are challenged globally by limited freshwater resources for irrigation and also by elevated soil salinity and sodicity. It is well known that pedogenic carbonate is less soluble than evaporate salts and commonly forms in natural drylands. However, few studies have evaluated how irrigation loads dissolved calcium and bicarbonate to agricultural fields, accelerating formation rates of secondary calcite and simultaneously releasing abiotic CO 2 to the atmosphere. This study reports one of the first geochemical and isotopic studies of such “anthropogenic” pedogenic carbonates and CO 2 from irrigated drylands of southwestern United States. A pecan orchard and an alfalfa field, where flood-irrigation using the Rio Grande river is a common practice, were compared to a nearby natural dryland site. Strontium and carbon isotope ratios show that bulk pedogenic carbonates in irrigated soils at the pecan orchard primarily formed due to flood-irrigation, and that approximately 20–50% of soil CO 2 in these irrigated soils is calcite-derived abiotic CO 2 instead of soil-respired or atmospheric origins. Multiple variables that control the salt buildup in this region are identified and impact the crop production and soil sustainability regionally and globally. Irrigation intensity and water chemistry (irrigation water quantity and quality) dictate salt loading, and soil texture governs water infiltration and salt leaching. In the study area, agricultural soils have accumulated up to 10 wt% of calcite after just about 100 years of cultivation. These rates will likely increase in the future due to the combined effects of climate variability (reduced rainfall and more intense evaporation), use of more brackish groundwater for irrigation, and reduced porosity in soils. The enhanced accumulation rates of pedogenic carbonate are accompanied by release of large amounts of abiotic CO 2 from irrigated drylands to atmosphere. Extensive field studies and modelling approaches are needed to further quantify these effluxes at local, regional and global scales.