Soil nutrients and plant uptake parameters as related to greenhouse gas emissions.

Fertilizer and water management practices have short- and long-term effects on soil chemical and physical properties and, in turn, greenhouse gas (GHG) emissions. The goal of this 4-yr field study was to establish the relationships between soil properties, agronomic practices, and GHG (CO2 and N2 O) emissions under different fertilizer and water table management practices. There were two fertilizer treatments: inorganic fertilizer (IF) and a mix of solid cattle manure and inorganic fertilizer (SCM), combined with tile drainage(DR) and controlled drainage with subirrigation(CDS). The cropping system was a maize (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation. Nitrogen in biomass (BMN) and N in grain (GRN) were measured and used to calculate other plant N parameters. Nitrous oxide and CO2 fluxes were collected weekly, and their respective cumulative emissions were calculated. The results show that soil organic matter (OM), soil total carbon (C), and soil total nitrogen (N) were greater in SCM than IF by 23.7, 35.2, and 24.4%, respectively. Water table management did not significantly affect soil N and C. Increased CO2 emissions were witnessed under higher soil OM, soil total C, and total N. Plant N uptake parameters were negatively correlated with N2 O and CO2 emissions. Higher plant N uptake can reduce environmental pollution by limiting N2 O and CO2 emissions.

Phosphorus characteristics of Canada-wide animal manures and implications for sustainable manure management with a cleaner environment.

Animal manure can be a serious environmental concern if improperly managed, particularly with regard to phosphorus (P). A good understanding on manure P chemistry is required for improving manure management in an environmentally sustainable manner. In the study, 102 representative manure samples collected from farms of major intensive livestock areas of Canada were sequentially fractionated with H2O, 0.5 M NaHCO3, 0.1 M NaOH, and 1.0 M HCl, respectively, for measuring inorganic (Pi) and organic P (Po). Across the manures, total P (TP) ranged from 3.71 to 17.3 g kg-1, with total Pi and available P (i.e., the sum of H2O-Pi and NaHCO3-Pi) accounting for 67.0-92.4 % and 35.6-67.3 % of TP, respectively. Composting reduced the percentages of available P and Po in TP, and meanwhile increased the percentages of moderately stable HCl-Pi. Compared to other P fractions, manure available P increased more rapidly with increases in TP; once manure TP reached 7.8-9.6 g kg-1, further TP increase enhanced transformation to more recalcitrant P (i.e., NaOH-Pi and HCl-Pi). Under Canadian conditions, manure application to meet the demand of crops for N would lead to P buildup in the soil at rates of 6.1-41.6 kg P ha-1 yr-1, increasing runoff P loss risk. Manure compost and poultry manure tend to cause rapid P buildup in the soil after land application and become a long-term P source for runoff losses. The results help to develop scientifically-sound manure-specific P management technologies which would enable farmers to achieve sustainable crop production with improved environment.

Modeling of phosphorus loss from field to watershed: A review.

Phosphorus (P) losses from nonpoint sources into surface water resources through surface runoff and tile drainage play a significant role in eutrophication. Accordingly, the number of studies involving the modeling of agricultural P losses, the uncertainties of such models, and the best management practices (BMPs) supported by the modeling of hypothetical P loss reduction scenarios has increased significantly around the world. Many improvements have been made to these models: separate manure P pools, variable source areas allowing the determination of critical source areas of P loss, analyses of modeling uncertainties, and understanding of legacy P. However, several elements are still missing or have yet to be sufficiently addressed: the incorporation of preferential flow into models, the modification of P sorption-desorption processes considering recent research data (e.g., pedotransfer functions for labile, active, or stable P, along with P sorption coefficients), BMP parameterization, and scale-up issues, as well as stakeholder-scientist and experimentalist-modeler interactions. The accuracy of P loss modeling can be improved by (a) incorporating dynamic P sorption-desorption processes and new P subroutines for direct P loss from manure, fertilizer, and dung, (b) modeling preferential flow, connectivity between field and adjacent water bodies, and P in-stream processes, (c) including an assessment of model uncertainty, (d) integrating field and watershed models for BMP calibration and scaling field results up to larger areas, and (e) building a holistic interaction between stakeholders, experimentalists, and modelers.

Modeling and Mitigating Phosphorus Losses from a Tile-Drained and Manured Field Using RZWQM2-P.

Prediction of P losses from manured agricultural fields through surface runoff and tile drainage is necessary to mitigate widespread eutrophication in water bodies. However, present water quality models are weak in predicting P losses, particularly in tile-drained and manure-applied cropland. We developed a field-scale P management model, the Root Zone Water Quality Model version 2-Phosphorus (RZWQM2-P), whose accuracy in simulating P losses from manure applied agricultural field is yet to be tested. The objectives of this study were (i) to assess the accuracy of this new model in simulating dissolved reactive phosphorus (DRP) and particulate phosphorus (PP) losses in surface runoff and tile drainage from a manure amended field, and (ii) to identify best management practices to mitigate manure P losses including water table control, manure application timing, and spreading methods by the use of model simulation. The model was evaluated against data collected from a liquid cattle manure applied field with maize ( L.)-soybean [ (L.) Merr.] rotation in Ontario, Canada. The results revealed that the RZWQM2-P model satisfactorily simulated DRP and PP losses through both surface runoff and tile drainage (Nash-Sutcliffe efficiency > 0.50, percentage bias within ±25%, and index of agreement > 0.75). Compared with conventional management practices, manure injection reduced the P losses by 18%, whereas controlled drainage and winter manure application increased P losses by 13 and 23%, respectively. The RZWQM2-P is a promising tool for P management in manured and subsurface drained agricultural field. The injection of manure rather than controlled drainage is an effective management practice to mitigate P losses from a subsurface-drained field.