Development of a Model-based Phosphorus Management Tool for Manure Applications in Subsurface Drained Field

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A by-product of the livestock industry, manure is a valuable source of crop nutrients (e.g., phosphorus, nitrogen, and organic matter). The three major clusters of manure production and disposal on subsurface drained cropland in Canada are south-western Ontario, south-eastern Quebec, and southern Ontario. However, agricultural soils and the nutrients applied thereon, in the form of either inorganic fertilizers or manures, are the major non-point source pollutants of standing water bodies. Eutrophication of such water bodies has been linked to phosphorus (P) and nitrogen (N) enrichment by subsurface drainage. Field studies have shown that the majority of P leached to these water bodies followed subsurface drainage flow. *A number of field experiments have been conducted to investigate the fate and transport of P under manure application in subsurface-drained croplands. In combination with field experiments, model-based tools can help to understand the science of P and N cycles in soil-plant systems and facilitate the management of nutrients to protect aquatic environments while maintaining crop yield. However, P routines in most models have seen little updating since the mid 1980s; therefore, the need arises to improve the simulation of P transport. In particular, a number of these models assume applied manure to be immediately mixed with top soil. This simplification was made because in most cases the models had not defined a sufficient number of different organic matter pools and only a very limited number of field management practices were simulated. In most cases, the SCS (Soil Conservation Service, USA) curve method was used to compute surface runoff and the Revised Universal Soil Loss Equation was employed to estimate sediment loss. Furthermore, the majority of such models have neither a subsurface drainage component, nor any ability to speciate applied manure. *The objective of the present program is to develop a P management tool based on the Root Zone Water Quality Model (RZWQM2) and use it to simulate the fate and transformations of P at the field scale. This new model-based tool, RZWQM2-P, will be used in Canada as a decision-support tool for P management under manure applications. The new features of this P and nitrogen model will include: (i) the use of the Green-Ampt model and variable source area to predict runoff, (ii) simulation of sediment detachment, deposition, and transport processes using a mechanical subroutine adopted from WEPP (Water Erosion Prediction Project), (iii) partitioning of P in manure into soil residue and soil humus pools depending on the application method (surface applied or injected) ,(iv) adsorption/desorption of P will be computed by a NICA (non-ideal competitive adsorption) model which uses Fe/Al/Ca content to predict dissolved P adsorption/desorption; transport of particulate P attached to soil nanoparticles from the soil surface to tile drains will be simulated considering preferential flow, and (v) a crop P uptake and stress subroutine will be adopted from the DSSAT (Decision Support System for Agrotechnology Transfer) model. *The new model-based P management tool, RZWQM2-P, will be tested against P levels measured on subsurface-drained crop field in Canada. P in surface runoff and subsurface drainage has been measured in several areas and can be used to calibrate and validate the new management tool. Data from an on-going lysimeter study on P movement under poultry and cattle manure, conducted by my team at the Macdonald Farm of McGill University, can serve in parameterizing the new P model. This new management model can be used as a decision-support tool for water quality and crop yield management under manure applications.