Patrick W. Inglett

In Florida, many agricultural soils contain up to 600 mg/kg of Mehlich-3 extractable phosphorus (P), yet potato growers continue to apply P fertilizers, indicating complex P dynamics that remain underexplored. Previous studies have mainly focused on P fertilizer trials, overlooking crucial factors like phosphatase activity and P sorption isotherms in high-legacy P systems. This study aimed to address this gap by examining acid phosphatase activity (AcPA) and P sorption dynamics in a potato field in northeastern Florida. Utilizing a split-block design, 24 plots were subjected to two P application rates (0 and 49 kg/ha) and three management treatments: a multispecies cover crop (MSCC), MSCC with Telone-C35 (a nematicide), and an untreated control. Significant increases in AcPA were observed during the tuber bulking stage, suggesting that applied P was insufficient for plant needs. P sorption isotherms indicated that the soil had reached maximum P sorption capacity, with applied P primarily fixed through chemical processes. These findings underscore the need for revised P fertilizer strategies in high-legacy P soils and highlight the importance of monitoring AcPA and sorption phases for effective nutrient management.

Introduction: Successful management and mitigation of harmful algal blooms (HABs) requires an in-depth understanding of the physiology and nutrient utilization of the organisms responsible. We explored the preference of various nitrogen (N) and phosphorus (P) substrates by two novel groups of HAB-forming phytoplankton originating from the Indian River Lagoon (IRL), Florida: 1) a consortium of picocyanobacteria (Crocosphaera sp. and ‘Synechococcus’ sp.) and 2) ananochlorophyte (Picochlorum sp.).Methods: Short-term kinetic uptake experiments tested algal use and affinity for inorganic and organic N substrates (ammonium (NH₄⁺), nitrate (NO₃^-), urea, and an amino acid (AA) mixture) through ¹⁵N and ¹³C isotope tracing into biomass.Results: Picocyanobacteria exhibited Michaelis-Menten type uptake for the AA mixture only, while nanochlorophytes reached saturation for NH₄⁺, the AA mixture, and urea at or below 25 µM-N. Both picocyanobacteria and nanochlorophyte cultures had highest affinity (V_max/K_s) for NH₄⁺ followed by the AA mixture and urea. Neither culture showed significant uptake of isotopically-labeled nitrate. Disappearance of glucose-6-phosphate (G6P) added to culture medium suggesting use of organic P by both cultures was confirmed by detection of alkaline phosphatase activity and the tracing of ¹³C-G6P into biomass.Discussion: Together, our results suggest that these HAB-forming phytoplankton groups are able to use a variety of N and P sources including organic forms, and prefer reduced forms of N. These traits are likely favorable under conditions found in the IRL during periods of significant competition for low concentrations of inorganic nutrients. Bloom-forming phytoplankton are therefore able to subsist on organic or recycled forms of N and P that typically dominate the IRL nutrient pools.

Biological soil crusts (biocrusts) are widespread in dryland ecosystems worldwide and were only recently discovered in agroecosystems. As agroecosystem biocrusts complete biological nitrogen (N) fixation, this research investigated if biocrust N could be released to biocrust subsoil and assimilated by a perennial tree crop. Biocrust was pulse labeled with ¹⁵NH₄Cl (¹⁵N) in the greenhouse for eight weeks prior to application in a citrus (Citrus spp.) orchard in Southwest Florida, USA. Patches of labeled biocrust were applied to twelve citrus trees in September, with twelve trees in the same orchard not receiving biocrust (controls). The ¹⁵N in the biocrust, subsoil, crop fibrous roots, and crop leaves was quantified at seven dates leading up to fruit harvest 158 days after application. Sampling dates overlapped with citrus root (September–October) and shoot (March) flush periods. Isotopically labeled biocrust N was present in subsoil and crop roots one day after biocrust application and in leaves after three days. Results revealed that N was released from biocrust at a rate of 0.63% ¹⁵N released per day leading up to fruit harvest when 91.7% of ¹⁵N had been released. The amount of biocrust ¹⁵N in the fibrous roots increased during a root flush period (September–October) until 28 days after biocrust application and then decreased leading up to a leaf flush period and fruit harvest. Approximately 23.8% of total biocrust ¹⁵N was in the crop tissue at fruit harvest. Overall, these results indicate agroecosystem biocrusts have the potential to support tree crop growth during N demanding growth stages.

The recognition that texture is a “master soil property” points toward the need for actual quantification of particle size in organic soil material. Using a multi‐wave particle size analyzer, fibric and sapric soil samples were circulated in deionized water through a closed aqueous loop at 9.6 L min ⁻¹ , and the following methodological parameters were investigated: pre‐treatment, circulation time, and refractive index. Our results show that pre‐treatment for organic soil samples is dependent upon the degree of decomposition; the intact and dispersed PSDs for fibrous samples were similiar, whereas the PSDs for sapric samples showed a shift from 500–2000 (intact) μm to 5–100 (dispersed) μm. Circulation time was investigated using mean particle diameter and specific surface area. We demonstrated that as circulation time increased, the mean particle diameter decreased and the specific surface area increased out to 30 min as mechanical dispersion and/or fragmentation of organic particles occurred. However, circulation time after 5 min is not significantly different in terms of mean particle diameter. To investigate refractive index, 12 optical models were created. When determined across all intact samples, uncertainty was low within individual bins, with a maximum value of 0.07 ± 0.04% v/v. For dispersed samples, uncertainty increased within the silt sized region and had a maximum value of 0.17 ± 0.07% v/v. This study demonstrates that the particle diameter of organic soil material can be measured by LD with comparable certainty as that of mineral soil material using the methodological approach used in this study.

Historical repository of UF/IFAS Extension numbered publications made available on the EDIS website. UF/IFAS Extension is a federal, state, and county partnership dedicated to developing knowledge in agriculture, human and natural resources, and the life sciences and to making that knowledge accessible to sustain and enhance the quality of human life.

Biological soil crusts (biocrusts) are widespread in dryland ecosystems worldwide and were only recently discovered in agroecosystems. Agroecosystem biocrusts complete biological nitrogen (N) fixation, therefore, this research investigated if biocrust N could be released to biocrust subsoil and assimilated by a perennial tree crop. Biocrust was pulse labeled with 15NH4Cl (15N) in the greenhouse for eight weeks prior to application in a citrus (Citrus spp.) orchard in Southwest Florida, USA. Patches of labeled biocrust were applied to twelve citrus trees in September, with twelve trees in the same orchard not receiving biocrust (controls). The 15N in the biocrust, subsoil, crop fibrous roots, and crop leaves was quantified at seven dates leading up to fruit harvest 158 days after application. Sampling dates overlapped with citrus root (September-October) and shoot (March) flush periods. Isotopically labeled biocrust N was present in subsoil and crop roots one day after biocrust application and in leaves after three days. Results revealed that N was released from biocrust at a rate of 0.63% 15N released per day leading up to fruit harvest when 91.7% of 15N had been released. The amount of biocrust 15N in the fibrous roots increased during a root flush period (September-October) until 28 days after biocrust application and then decreased leading up to a leaf flush period and fruit harvest. Approximately 23.8% of total biocrust 15N was in the crop tissue at fruit harvest. Overall, these results indicate agroecosystem biocrusts have the potential to support tree crop growth during N demanding growth stages.

Biocrusts are communities of microorganisms within the top centimeter of soil, often dominated by phototrophic dinitrogen-fixing (N₂-fixing) organisms. They are common globally in arid ecosystems and have recently been identified in agroecosystems. However, unlike natural ecosystem biocrusts, agroecosystem biocrusts receive regular fertilizer and irrigation inputs. These inputs could influence seasonal biocrust N₂-fixation and their relationship with soil nutrients in perennial agroecosystems, which is of particular interest given crop management requirements. In this study, biocrust and adjacent bare soil N₂-fixation activity was measured in the field during the summer, fall, spring, and winter seasons in a Florida citrus orchard and vineyard using both acetylene reduction assays and ¹⁵N₂ incubations. Samples were analyzed for microbial and extractable carbon (MBC, EC), nitrogen (MBN, EN), and phosphorus (MBP, EP). In both agroecosystems, biocrusts had greater microbial biomass and extractable nutrients compared to bare soil. The citrus and grape biocrusts were both actively fixing N₂, despite crop fertilization, with rates similar to those found in natural arid and mesic systems, from 0.1 to 142 nmol of C₂H₄ g^–1 of biocrust dry weight h^–1 (equivalent to 1–401 μmol m^–2h^–1). Lower soil temperatures and higher EC:EN ratios were associated with higher N₂-fixation rates in citrus biocrusts, while higher soil moisture and higher EP were associated with higher N₂-fixation rates in grape biocrusts. The N₂-fixation activity of these agroecosystem biocrusts indicates the possibility of biocrusts to enhance N cycling in perennial agroecosystems, with potential benefits for crop production.

Stormwater infiltration basins (SIBs) are vegetated depressions that collect stormwater and allow it to infiltrate to underlying groundwater. Their pollutant removal efficiency is affected by the properties of the soils in which they are constructed. We assessed the soil nitrogen (N) cycle processes that produce and remove inorganic N in two urban SIBs, with the goal of further understanding the mechanisms that control N removal efficiency. We measured net N mineralization, nitrification, and potential denitrification in wet and dry seasons along a sedimentation gradient in two SIBs in the subtropical Tampa, Florida urban area. Net N mineralization was higher in the wet season than in the dry season; however, nitrification was higher in the dry season, providing a pool of highly mobile nitrate that would be susceptible to leaching during periodic dry season storms or with the onset of the following wet season. Denitrification decreased along the sediment gradient from the runoff inlet zone (up to 5.2 μg N/g h) to the outermost zone (up to 3.5 μg N/g h), providing significant spatial variation in inorganic N removal for the SIBs. Sediment accumulating around the inflow areas likely provided a carbon source, as well as maintained stable anaerobic conditions, which would enhance N removal.