Eric O. Young

Phosphorus concentrations in soil and subsurface water: a field study among cropland and riparian buffers.

Riparian buffers can be effective at removing phosphorus (P) in overland flow, but their influence on subsurface P loading is not well known. Phosphorus concentrations in the soil, soil solution, and shallow ground water of 16 paired cropland-buffer plots were characterized during 2004 and 2005. The sites were located at two private dairy farms in Central New York on silt and gravelly silt loams (Aeric Endoaqualfs, Fluvaquentic Endoaquepts, Fluvaquentic Eutrudepts, Glossaquic Hapludalfs, and Glossic Hapludalfs). It was hypothesized that P availability (sodium acetate extractable-P) and soil-landscape variability would affect P release to the soil solution and shallow ground water. Results showed that P availability tended to be greater in crop fields relative to paired buffer plots. Soil P was a good indicator of soil solution dissolved (<0.45 microm) molybdate-reactive P (DRP) concentrations among plots, but was not independently effective at predicting ground water DRP concentrations. Mean ground water DRP in corn fields ranged from < or =20 to 80 microg L(-1), with lower concentrations in hay and buffer plots. More imperfectly drained crop fields and buffers tended to have greater average DRP, particulate (> or =0.45 microm) reactive P (PRP), and dissolved unreactive P (DUP) concentrations in ground water. Soil organic matter and 50-cm depth soil solution DRP in buffers jointly explained 75% of the average buffer ground water DRP variability. Results suggest that buffers were relatively effective at reducing soil solution and shallow ground water DRP concentrations, but their impact on particulate and organic P in ground water was less clear.

Dynamic Model Improves Agronomic and Environmental Outcomes for Maize Nitrogen Management over Static Approach

Large temporal and spatial variability in soil nitrogen (N) availability leads many farmers across the United States to over-apply N fertilizers in maize ( L.) production environments, often resulting in large environmental N losses. Static Stanford-type N recommendation tools are typically promoted in the United States, but new dynamic model-based decision tools allow for highly adaptive N recommendations that account for specific production environments and conditions. This study compares the Corn N Calculator (CNC), a static N recommendation tool for New York, to Adapt-N, a dynamic simulation tool that combines soil, crop, and management information with real-time weather data to estimate optimum N application rates for maize. The efficiency of the two tools in predicting the Economically Optimum N Rate (EONR) is compared using field data from 14 multiple N-rate trials conducted in New York during the years 2011 through 2015. The CNC tool was used with both realistic grower-estimated potential yields and those extracted from the CNC default database, which were found to be unrealistically low when compared with field data. By accounting for weather and site-specific conditions, the Adapt-N tool was found to increase the farmer profits and significantly improve the prediction of the EONR (RMSE = 34 kg ha). Furthermore, using a dynamic instead of a static approach led to reduced N application rates, which in turn resulted in substantially lower simulated environmental N losses. This study shows that better N management through a dynamic decision tool such as Adapt-N can help reduce environmental impacts while sustaining farm economic viability.

Total and Labile Phosphorus Concentrations as Influenced by Riparian Buffer Soil Properties.

Riparian buffers can act as a phosphorus (P) source under active stream bank erosion. Using soil and landscape variables (soil series, drainage class, organic matter, and pH) to index P concentrations could improve P loss risk tools for buffers. The objectives of this study were (i) to determine if soil properties could predict total and labile P concentrations within a 10-ha riparian buffer and (ii) to quantify the degree of spatial dependence of P and related properties. Soil samples were taken in 15-cm increments to a depth of 60 cm using a grid ( = 71) from an established riparian buffer along the Rock River in Vermont. Total soil P (TP), plant-available P determined by Modified Morgan extraction (MM-P), pH, soil organic matter (SOM), soil texture, and select cations were measured. We found that TP (152-1536 mg P kg) and MM-P (0.4-14.6 mg kg) ranged widely, with distinct differences between soil series. Mean TP and MM-P were greater in alluvial and glaciolacustrine soils compared with glacial till. Across all samples, MM-P was weakly related to soil properties; however, total labile P (orthophosphate + organic P measured by ICP) and unreactive labile P (ICP-P - colorimetric-P) could both be predicted by SOM ( = 0.59 and 0.73, respectively). Strong spatial dependence was found for P and related properties as revealed by geospatial analyses. Results show that P availability in the buffer was strongly related to soil genesis and support site-specific approaches for P loss risk evaluation in buffers.

Influence of Controlled Drainage and Liquid Dairy Manure Application on Phosphorus Leaching from Intact Soil Cores

Controlled drainage can reduce nitrate export from tile drainage flow, but its impact on phosphorus (P) loss is largely unknown. We compared P leaching from soil cores treated as free drainage (FD) or controlled drainage (CD) before and after manure application. In August 2012, 16 intact cores (45 cm long, 15 cm diameter) were collected from a grass forage field () located in Chazy, NY, and modified for drainage control and sampling. In Experiment 1 (no manure), initial leachate was defined as FD, and leachate collected 21 d later (valves closed) was considered CD. In Experiment 2, seven cores were randomly assigned to CD or FD. Liquid dairy manure was applied at 1.2 × 10 L ha, followed by simulated rainfall 2 h later. Leachate was sampled on Day 7, 14, and 21. Deionized water was applied at 3.4 cm h over 1 h to mimic a 10-yr rainfall event. Total P (TP), soluble reactive P (SRP), dissolved oxygen, iron (Fe), and pH were measured. Results showed that TP ( = 0.03) and SRP ( = 0.35) were lower for CD prior to manure application. Manure application caused 36- and 42-fold increases in TP and SRP; however, TP was lower for CD at 7 ( = 0.06), 14 ( = 0.003), and 21 d ( = 0.002) of water retention. Mean SRP for CD was nearly 40-fold lower than FD by Day 7 ( = 0.02) and remained low, suggesting CD in the field may reduce P export risk to tile drain flow after manure applications.

Phosphorus in Morgan Soil Test Extracts Measured By Molybdate Colorimetric and Inductively Coupled Plasma Spectroscopy Methods

ABSTRACT Colorimetric P determination mainly reflects inorganic P, whereas inductively coupled plasma spectroscopy (ICP) measures all P in solution. We compared Morgan extractable P for ICP (MP-ICP) and colorimetry (MP-Color) using dairy farm field samples (0 to 20 cm) across northern New York (n = 250) and hayfield transect samples (0–15, 15–30, 45–50 cm; n = 164). Soil organic matter, pH, and extractable cations were also measured. Mean ratio of MP-ICP: MP-Color was 1.46 and differed significantly among Morgan P categories, ranging from 1.89 for low to 1.06 for very high. The numeric difference between MP-ICP and MP-Color ranged from 0 to 12.9 mg kg−1. Organic matter, Al, and pH jointly accounted for 55% of the variability between methods across samples. Fertilizer P recommendations differed based on the two methods, suggesting results from both methods should be reported, particularly in the responsive range.

Phosphorus Mobilization in Flooded Riparian Soils From the Lake Champlain Basin, VT, USA

Riparian soils and sediments have the potential to release bioavailable phosphorus, contributing to water quality degradation. Here, we measured phosphorus (P) release to soil porewater (PW) and overlying floodwater (FW) in 12 riparian buffer and 2 agricultural floodplain soils from northwestern Vermont, USA to evaluate P mobilization risk and determine relationships with soil properties (total P, labile P concentrations, pH, organic matter). Duplicate samples (field-moist) were flooded with distilled water in polyethylene beakers modified for PW sampling. Soluble reactive P (SRP) (PW and FW) and PW ferrous iron (Fe2+) concentrations were measured over a 75-day period in the laboratory. Soluble unreactive P (SUP) in PW was also measured twice. Two samples were also flooded after air-drying soil to determine the influence on SRP release. Results showed that PW-SRP tended to increase over time, whereas FW-SRP tended to decrease. The ratio of PW-SRP on day-75 to initial concentrations ranged from 0.21 to 8.4 (mean = 3.2 ± 2.7), while the ratio for FW-SRP was 0.19 to 1.3 (mean = 0.63 ± 0.39). Mean PW- and FW-SRP ranged from 0.03 to 2.2 mg/L and 0.01 to 0.33 mg/L, respectively. Biochemical reduction occurred in 13/14 soils as indicated by PW-Fe2+, while FW remained oxidized (mean dissolved oxygen on day 75 = 6.8 ± 0.3 mg/L). Soil pH was positively related to mean PW- (R2 = 0.48, P = 0.006) and FW-SRP (R2 = 0.47, P = 0.007), whereas mean PW-SUP was inversely related to pH (R2 = 0.44, P = 0.01). Mean ratio of PW-SRP:FW-SRP was 3.5 ± 1.9 and increased with soil pH (R2 = 0.59, P = 0.001). Modified Morgan extractable P was the best predictor of FW and PW-SRP release. Flooding dry soil decreased FW dissolved oxygen concentrations while increasing PW-Fe2+, PW-SRP, and SRP mobilization to FW relative to a field-moist state. Results indicate that SRP release could pose water quality concerns, however mobilization to overlying water was limited by re-adsorption of released P. Our results highlight the importance of integrating measures of labile soil P with hydrologic flow pathways in models to better predict P transport in riparian landscapes.