Liza Garcia

Accurate spatial quantification of soil organic carbon (SOC) stocks and their associated uncertainties is vital for climate mitigation and sustainable grazing management. However, regional SOC mapping remains challenging due to complex soil–landscape interactions, dynamic environmental processes, and sparse and non-representative field observations. This study advances regional SOC mapping by developing a parsimonious, uncertainty-aware digital soil mapping framework to estimate topsoil (0–20 cm) SOC stocks across Florida’s grazing lands at 30 m resolution. Grounded in the STEP–AWBH soil-forming framework, the approach explicitly operationalizes time-invariant and dynamic controls through spatiotemporal feature construction. SOC stocks were modeled using Quantile Regression Forests to generate point estimates and 90% prediction intervals, validated via spatial cross-validation. While a baseline model using contemporary data achieved modest results (R2 = 0.38; RMSE = 9.52 t ha-1), cross-temporal spiking with legacy samples significantly enhanced predictive accuracy and uncertainty calibration (R2 = 0.57; RMSE = 7.93 t ha-1). In contrast, unconstrained spiking across heterogeneous land uses degraded model performance, underscoring the importance of domain-specific data integration. SHAP-based interpretation revealed that SOC variability reflects the influence of pedological properties (e.g., available water capacity), grazing intensity, and temporal signatures—persistence, variability, and long-term trends—of hydroclimate, soil moisture, and vegetation phenology. Total topsoil SOC storage for Florida’s grazing lands was estimated at 36.11 Tg, with a mean stock of 20.3 t ha-1. The resulting high-resolution SOC stock and uncertainty maps are hosted on an open-access interactive GIS platform, providing a robust baseline for monitoring and managing soil carbon in subtropical grazing systems.

Nutrient cycling via livestock excreta is an important grassland ecosystem service. This study was conducted in 2016 and 2017 and determined nutrient excretion from cattle grazing three systems: (a) N‐fertilized bahiagrass (Paspalum notatum Flüggé) overseeded with rye (Secale cereale L.) and oat (Avena sativa L.) during winter (Grass+N), (b) unfertilized bahiagrass overseeded with rye–oat–clover (Trifolium sp.) mixture (Grass+clover), and (c) rhizoma peanut (Arachis glabrata Benth.)–bahiagrass mixture overseeded with a rye–oat–clover mixture (Grass+CL+RP). Urinary volume excreted in the warm season ranged from 122 to 182 L ha⁻¹d⁻¹, more than double that in the cool season (56–70 L ha⁻¹ d⁻¹). Urinary N concentration during the warm season was greater in Grass+CL+RP compared with Grass+N (4.4 vs. 3.1 g kg⁻¹, respectively). In addition, fecal dry matter and organic matter output was greater for Grass+N than for steers grazing Grass+CL+RP during the warm season (3.8 and 3.2 vs. 2.8 and 2.2 kg hd⁻¹ d⁻¹, respectively). Total annual feces excretion concentrations of P, K, Mg, and N were greater in the Grass+N than in Grass+CL+RP system. The introduction of legumes increased the proportion of N returning via urine. However, when summed across seasons, total N excretion (feces and urine) was greater in Grass+N than in Grass+CL+RP (89 vs. 71 kg ha⁻¹ yr⁻¹), mainly due to the greater stocking rate in the former. Grass–legume systems receiving 34 kg N ha⁻¹ yr⁻¹ recycled 80% of the N recycled in the grass system receiving 224 kg N ha⁻¹ yr⁻¹, indicating the potential of forage legumes to add N to grasslands.

Bahiagrass (Paspalum notatum Flüggé) is the most utilized forage in Florida and requires N fertilization to optimize production. Integrating legumes into bahiagrass pastures may reduce N fertilizer inputs and improve forage nutritive value. This 2‐yr, 2‐location, on‐farm study established two legumes, alfalfa (Medicago sativa L.) or rhizoma peanut (RP; Arachis glabrata Benth.), in mixtures with bahiagrass. We compared bahiagrass–legume mixtures + 45 kg N ha⁻¹ harvest⁻¹ with their non‐N fertilized monocultures and with bahiagrass + 90 kg N ha⁻¹ harvest⁻¹ (N‐fertilized bahiagrass). Treatments were bahiagrass, N‐fertilized bahiagrass, bahiagrass–alfalfa, bahiagrass–RP, alfalfa, and RP. Variables analyzed included herbage accumulation (HA), botanical composition, forage N concentration, forage total N aboveground (TNAG), and N agronomic efficiency. Mixtures and N‐fertilized bahiagrass resulted in similar cumulative HA (10,400 kg dry matter [DM] ha⁻¹ yr⁻¹, on average) and they were greater than all other treatments (4,190 kg DM ha⁻¹ yr⁻¹, on average). Alfalfa and RP represented low proportions of the mixed swards, with alfalfa proportion being as high as 16.1% and as low as 1.6%. Rhizoma peanut greatest proportion was 2.1% and the lowest was 0.5%. Mixtures and N‐fertilized bahiagrass maintained similar N concentrations, but they were consistently lower than legume monocultures. The N‐fertilized bahiagrass and mixture treatments resulted in the greatest TNAG in four out of the six sampling dates. The AE_N of mixtures was typically greater than N‐fertilized bahiagrass. Since legumes had low proportion in mixtures, 45 kg N ha⁻¹ harvest⁻¹ was the upper limit for reaching maximum HA in bahiagrass.

Nitrogen (N) is one of the major off-farm inputs in livestock systems, either in the form of N fertilizer or purchased feed. Fortunately, you can reduce those expenses by growing your own nitrogen using forage legumes. Rhizoma perennial peanut (RPP) is a legume adapted to the Florida environment that grows well in mixtures with bahiagrass. This 4-page fact sheet discusses varieties, establishment, weed management, grazing management, and the cost-share program. Written by Jose Dubeux, Lynn Sollenberger, Joao Vendramini, Marcelo Wallau, Ann Blount, Liza Garcia-Jimenez, Erick Santos, and David Jaramillo, and published by the UF/IFAS Agronomy Department, July 2018. http://edis.ifas.ufl.edu/ag421

Fertilization of perennial grass pastures is a major expense in beef cattle operations, and grass pastures may degrade in the absence of N fertilization. Grass–legume mixtures can reduce the demand for N fertilizer use while increasing productivity of the system. Arachis spp. have shown potential for use in association with grasses in the southeastern United States. During 2014, 2015, and 2016, we evaluated one annual peanut species (Arachis hypogaea L. TUFRunner ‘727’) and two perennial peanut species, pintoi peanut (A. pintoi Krap. & W.C. Greg ‘Amarillo’) and rhizoma peanut (A. glabrata Benth. ‘Florigraze’ and germplasm Ecoturf), when planted into previously established ‘Pensacola’ bahiagrass (Paspalum notatum Flügge) sod. Responses measured included herbage accumulation (HA), botanical composition, nutritive value, biological N₂ fixation, and belowground root‐rhizome responses. TUFRunner 727 showed reseeding ability, illustrating potential for use as a short‐term forage, but by 2016, its contribution was negligible. In 2016, Ecoturf–bahiagrass had greater HA than unfertilized bahiagrass (4160 and 2710 kg ha⁻¹, respectively), and the Ecoturf contribution to HA was ∼30% in 2016. Average N concentrations for Ecoturf and Florigraze were 25 and 22 g kg⁻¹, respectively, and in vitro digestible organic matter concentration was 700 g kg⁻¹ for both. Pintoi peanut contributed little to mixture HA in the first 2 yr, but it persisted and increased in proportion with time. Over the course of 3 yr, Ecoturf rhizoma peanut performed better than all other entries, exhibiting increasing participation in mixtures each year and the greatest total HA in 2016.